The preservation of the Developmental Biology Film Series was made possible by generous contributions from Publisher of “The Biggest Picture” Producer of the documentary, “Symbiotic Earth” [Music]
The preservation of the Developmental Biology Film Series was made possible by generous contributions from Publisher of “The Biggest Picture” Producer of the documentary, “Symbiotic Earth” [Music]
Topic: Pneumonia. What causes pneumonia? The letter P.
No. Pneumonia is a lung infection caused by microorganisms which generally leads to difficulty in breathing. Normally, we inhale oxygen rich air which
reaches our alveoli. Alveoli are surrounded by blood capillaries. Here, the oxygen through the walls of alveoli diffuses into our blood. However, sometimes we also inhale harmful microorganisms. Mostly, the cilia and mucous in our respiratory tract trap these microorganisms, which are then expelled while coughing. But sometimes the microorganisms don’t get trapped and reach the alveoli. There they start to multiply, causing lung
infection, that is, pneumonia. No. Now what to do? Now, to protect ourselves, the immune cells start attacking the microorganisms, causing inflammation and accumulation of fluid in the alveoli. As a result, the inhaled oxygen cannot get
easily diffused into blood, thus causing difficulty in breathing.
Stanford University. Let us get started here. So picking up from the other
day, where have we gotten? Not very far. Behavior– full
range variability of sexual behaviors,
fixed action patterns. Is this kind of dark here? No. Seeing in some ways
what’s interesting is the conservative nature of
sexual behavior across species, other ways the sheer
variety, trying to make sense of what aspects
of human behavior are unique, all of that. Then beginning to march
backwards– what goes on in the nervous system one second
before sexual behavior occurs? And marching through the
relevant limbic structures, some of which have
strong sex differences, some of which don’t. Seeing some ways in
which neurotransmitters in the whole world of dopamine
complicates things enormously, marching through there. Where we had then gotten
to was asking, OK, so what sort of bits of information
in the environment, what sort of ethological
releasing stimuli can trigger the nervous
system to do its thing? And you’ve got the drill by now. So what we had done
was look at a couple of different sensory
systems, and we had just started to wallow in
the world of pheromones, of pheromonal communication. What we ended with was number
one, the hormone dependency of generating sexually
meaningful pheromones, that business being
that males have to have sufficient testosterone. Females have to have
ovaries on board to be producing pheromones
that carry sexual meaning. What is the reason for that? The fact that a whole lot
of the actual chemicals that constitute sexually meaningful
pheromones are made out of some sex hormone
breakdown products and the sheer bizarrity but
eventual wonderful clarity of what’s up with perfumes. Then transitioning
at the very end to the business about how your
endocrine status has a lot to do with your perception of
pheromones from the other sex, that women who are
ovariectomized to low estrogen levels have trouble being
able to differentiate the smell of males and
females, men and women. And estrogen replacement
takes care of that. The exact same thing when you
take away testosterone for men, and what we were just about to
get to before we had to stop was one additional
thing, which is one’s opinion about
the pheromones that you were smelling. And this goes back
to a literature, a really interesting
one showing that not only are women
better at differentiating between the smell
of men and women– gonadally intact men and women. Not only are they
better at doing that around the
point of ovulation, but their preference
for the smell of males gets more dramatic around
the time of ovulation. Meanwhile, over at the
male end of things, something rather
similar in terms of what you make of the pheromones. And this was a famous classic
study in which women volunteers had their armpits swabbed
at different points in their menstrual cycle and
put into little sealed jars, and all sorts of male
volunteers sniffing them and rating their pleasantness. And what you found
was on the average, the odorants were rated in
the unpleasant direction, but they were rated as least
unpleasant around the time that women are ovulating. And I think once we get
past the world of armpit smells in little
glass jars, one can get into the more ethologically
relevant world of men prefer pheromones derived from
women around the time when women are ovulating. Once again, a
testosterone-dependent phenomenon. What we now begin
to look at are some of the physiological effects of
sexual pheromones between sexes within sexes. One example you heard about
in the very first lecture, which is that whole business,
that Wellesley effect the ability of females of all
sorts of different species, including college
freshman human females, to synchronize each
other’s cycles, this being done with pheromones,
intersexual perception of pheromones, so
the Wellesley effect. What’s also shown in a
number of rodent species is the pheromones, the
smell of an adult female, will delay the onset of
puberty of younger females. And how might one frame that? That is utterly a gene
competition sort of strategy there. This is reproductive
competition. If you arrest the development
of the other females around you, you are going to leave
more copies, et cetera. Meanwhile, a
literature of intramale physiological
effects– what happens to the physiology of
males in various species when smelling the
pheromones of other males? What you see, first
off, is it depends on who the other guy you’re
smelling, the dominance rank. In lots of rodent species and
some primate species as well, males are able to
differentiate between smells of very high ranking males
and very low ranking ones, and what do you know? They’re not all that upset
about the low ranking ones. What do you see in terms of
the physiological effects in the number of
species when males are smelling the pheromones
of big, healthy, strapping, androgenic other males? In some cases, it drives down
their testosterone levels. They’re totally
physiologically intimidated, this being some great
competitive strategy for males who could pump
out just the right kind of suppressive pheromones. In other species,
though, what you see is a sudden burst
of sperm production, and what’s that about? Another version of
the same logic– this is a counter-strategy. If males have come up, evolved
the means in various rodent species to generate pheromones
that will drive down testosterone levels in
opponents, what males also want to have evolve with some
mechanism of when smelling those sorts of pheromones
to try to counter that by increasing sperm production. What we have here is a
co-evolutionary arms race. Terms of interactions of
pheromones between the sexes, and what I’ve been
doing here is describing all this without
making use of this, so what you see
is physiologically when the female is
the pheromone donor, and the other recipient is
a female in terms of, say, puberty, decreasing
puberty onset, and what we just saw with
male is donor versus male is in some ways suppressing
some endpoint’s testosterone, in some ways increasing
sperm production. What you see in lots
of rodent species, when you’re looking at
between genders, when males are the source of
pheromones among rodents, it accelerates puberty
onset in the females. And when you’ve got
females as the donors, it increases testosterone
level and sperm production in the males of lots
of different species. So all this makes
wonderful, wonderful, sort of sociobiological sense in
terms of how this should work. Elaborations on this, of course. What you also see is
not only puberty onset and being regulated. You also see in all
sorts of species where you can induce
ovulation by sensory stimuli. What you see is the
smell of a female will decrease the likelihood
of induced ovulation. Female– the smell of
a male will increase the likelihood of ovulation. All sorts of species
that do not have automatic rhythms of
ovulation cycles of that way, but rather they are induced. And one classic example
of that are pigs. Pigs are inducible ovulators,
if you’ve always wondered whether that’s the case or not. And you can go and
recreationally buy a variant of pig pheromone. This is known as Boar
Mate, and no doubt, that’s not only patent
pended, but somewhere out in the Midwest,
there’s all sorts of TV jingles about Boar Mate. And Boar Mate is an ovulation
inducer in female boars and involving a same
male-derived pheromone, which are found in truffles,
truffles which somehow have stumbled on the means to
induce female pigs to ovulate. And no doubt, that’s explaining
some very interesting interspecies interactions,
so that being another realm. Inducible all
physiological changes– in this case, one classic
demonstration of it. In this case,
probably pheromones of female causing an indirect
measure of testosterone levels in a male. This is a classic
paper, and you will note that I didn’t
say females and males. Saying a female and a male. This was a classic paper in
nature some 30 years ago or so, which was written by the very
famous and well-known doctor Anonymous. The author’s name was
not published there. And this was a researcher
who did research in an unspecified hemisphere
with an unspecified species, but involved long stretches of
being at a research facility completely on his own in
isolation from other humans, and all sorts of people in
the business for decades afterward have been speculating
on who the author is. And it’s generally understood. And what this person noted
was every now and then, he would pick up and
go to the city that was a three-hour
seaplane flight away or some such thing,
where among other things, he had a highly significant
other with a great deal of physical intimacy
and all that stuff from kind of the right
side of the chart. And what he noticed
was what he perceived to be an extraordinary
difference in what he was subjectively interpreting
as testosterone-driven mood and level of energy and all of
that depending on where he was. Not quite being the
type of field ethologist that took blood from
himself, what he did instead was take an indirect assay
building on the well-known fact that testosterone
has something to do with the rate of beard growth. And what he wound up
doing was very soon, having a razor there
every day, shaving, and getting the little bits
of stubble, and weighing it. Weighing it is an indirect
assay of testosterone levels, and what was shown was
sit out there by himself with whatever ungulates
he was obsessing over, and this sort of rate
of beard growth– go back to the rest of the
world, and it does this. And this square wave
going on like that, this as a very– and OK, what
are all the confounds here? It’s not clear if
it was pheromones. Maybe it was actually
being in proximity to the newspaper
in the town that he returned to now and then. Maybe there was a
confound of whatever aftershave he was using
that was doing something rather to his testes. Nonetheless,
generally interpreted as this being a really
interesting, indirect, and equal– was one
example of induction of physiological
changes in human males by pheromones from females. So if you ever meet Dr.
Anonymous, who interestingly, has been publishing
papers for about 300 years or so every now and then,
congratulate that individual on the research. So pheromonal stuff–
now elaborations of it, which you should be able
to derive all on your own from some of our
principles by now, which is, what if for example,
you are a female donor and female recipient,
and the whole logic here being decrease the
likelihood of ovulation? Delay the onset of puberty. What if these are siblings,
if these are two sisters? And you were off and
running with that one. It will not work as effectively. Easy kin selection argument. So all sorts of
aspects of relatedness, you will not have your
testosterone levels driven up if you are a hamster, and you
were smelling your sister, all that sort of thing that
makes perfect sense by now. Now switching over– one last
piece of business, though. In terms of the pheromonal
attractiveness stuff, a handful of studies showing
that among homosexual men, what you have is it’s the smell of
men who are preferred to women, and it’s when men have
higher testosterone levels that they are preferred. And what we’ve got there
is an exact same physiology in a somewhat going in the
opposite direction, flipping of things that sure argues for
some interesting biological underpinnings. One final thing– women not only
prefer the smell of men when around the time that
they are ovulating. Their noses selectively
become more sensitive to such smells, and estrogen has
all sorts of receptors on olfactory neurons. So that makes sense. Leaping over to other
sensory systems– gustatory stimuli–
this is not one of the more exciting outposts,
unless you are something like a giraffe, in which case
you take part in what is called flehmening, a good old Germanic
ethological term, which is you want all sorts of interesting
reproductive information on somebody else,
and you just don’t have the time to sniff
the air for pheromones. So what you do is you go over
and lick the individual’s private parts, and suddenly,
you know oh so much about their personal lives. In this case, gustatory
information being passed. We’ve already heard
about examples of auditory priming,
inducible ovulation in various moose-like species
in the wilds of Minnesota, where what the stags have
these roaring fixed action patterns, which will induce all
sorts of ovulatory responses in females around. So this is another domain. Remember also that
interesting factoid when this was
mentioned previously that in human
females, voices get a little bit higher around
the time of ovulation and in a way that is detectable. Something important in terms
of all this pheromonal stuff in humans, what
has been shown over and over and over again is these
are all subliminal processes as in the humans are not
consciously aware of wow, this one smells more like my
gonadally intact second cousin who was adopted away to Bolivia
for awhile when I was a kid. There is not the consciousness,
but nonetheless, you force people to
make these choices, and implicitly, you get
insight into these same sort of influences. But, of course, by the
time you get to humans, and you talk about sensory
releasers and all of that, you get, of course, the point
endlessly emphasized by Cosmo and God knows where else that
ultimately, the most erogenous organ in humans is the
brain, thought as a releaser, thought as a more powerful
humans are not a particularly olfactory species. We are not a particularly
great auditory one, et cetera, et cetera. An awful lot of these
sexual priming in humans coming by way of
thought bypassing this whole ethological world. More environmental factors,
acute environmental factors that can affect all of
this, and what you’ve got is a very reliable
way to drive down libido is to make an
organism terrified. Fear as suppressive of
reproductive behavior. What you also have is
extreme rage doing the same. Stress in general–
stress is interesting, because what you get is
a dichotomous outcome, chronic stress. So now we’re not talking
about an acute stressor, but all the way
back, chronic stress is extremely suppressive
of reproductive physiology and behavior, which
you will be finding out when you read the relevant
chapter in the zebra’s book. But what you see as short term,
there’s a lot more variability, particularly among males. What you see is a
lot of variability as to whether short term stress
stimulates arousal or inhibits it. And people have
pointed out all sorts of horrific bits
of evidence showing in circumstances of
extreme arousal and stress, say, during warfare, where
that produces all sorts of violent sexual behavior. No shortage of horrible
historical precedents for those. So a difference between
chronic stress versus acute stress– more
effects around here. One final interesting bit of
releasing stimulus, stimuli, whatever a bit of a
stimulus is, and one that transcends a
particular sensory system is something called
the Coolidge effect. And the Coolidge effect
probably accounts for like 49% of the
misery encapsulated in human literature and
movies and all of that. What is the Coolidge
effect in species after species after species? You take an individual,
who is sexually sated, which is to say that,
for example, you’ve got some male rodent who’s been
mating with the female rodent there, and has gotten to the
point where he has had enough, enough on some
physiological level or some deeply emotional
what matters to me in my life rodential sort of level. But in any case,
the male is sated, has stopped having
sex with a female. And what the Coolidge
effect is about is he put in a different
female, and things start all over again. Variety as wildly stimulating
of sexual arousal, and the Coolidge effect sure
works in humans and accounts for all sorts of misery. Coolidge, by the way,
was not the scientist who first described
it, but Coolidge refers to Calvin Coolidge,
and as far as I know, this is the only
anecdote ever to occur about the guy, something
where he and his wife were being shown
some chicken farm, and there were
breeding roosters. And when they would get sick
of breeding with this pen, they would stick a new one in. And Mrs. Coolidge made
some sarcastic remark, and he made one back,
and before you knew it, it was the Great Depression. So I actually have no
memory of what they said, but in terms of
wittiness, you get what you can when you
have Calvin Coolidge, so. OK. We hurtle on. We hurtle on here, now beginning
to look at an entire missing category here in my rush. Now we have what’s
going on with hormones, longer term hormonal stuff? Not the hormone levels
that you have influenced as a result of sexual behavior,
not the hormone levels just right around the time
of all this neurobiology happening, but now beginning
to talk about hormone levels like over the last 28
days or so in a female. And what one
immediately barrels into is this issue of how much
is sexual behavior in women a function of where
you are in your cycle? What’s the reason
even to suspect that the entire world of other
species that will have females coming into estrus,
coming into heat, having elevated
estrogen levels only at very demarcated times of
the year, and what you see is in lots of species,
a large number of them, in fact– what you see is you
only get reproductive behavior, you only get sexual behavior
in females around the time that they are ovulating. You only get active female
proceptive seeking of sex around those times. By the time you get
to non-human primates, it depends on the species
you’re looking at. But in general, it’s not quite
as tight of a relationship. So if you had some
rodent across a year, this was all the
points of ovulation. Your pattern of sexual
behavior of a female would look like this. Likelihood of mating
with a male by the time you get to non-human
primates in most species, it looks more like that. It’s not quite as dramatic, and
thus, of course, the question becomes, where do
humans fit in on this? And a classic study, extremely
influential in the early ’70s was the first to look at this,
which was females, humans, women reporting their
levels of sexual activity, as well as the
likelihood of orgasm per sexual bout, if
that’s the right word, and where they
were in the cycle. So this is what you
wound up seeing, and this by any measure,
likelihood of having sex, whatever, the curve looked
something like this. And what they reported
was a big increase around the time of day 14 and
a secondary increase around day 28. Not as large of
one, and when you looked at the
likelihood of orgasm, it was basically doing
the same exact thing. Day 14– that’s just a somewhat
less restricted version of the exact same phenomenon. Never down to zero,
but nonetheless, this is another version of
this exact same phenomenon– libido sexual proceptivity
increasing in women, in human females around
the time of ovulation. But no other species shows
this one going on here, so what’s up with that? Any speculation why you
have the secondary increase around day 28? Come on. Somebody’s got to–
yes, you’re right. That’s exactly what they found. That’s exactly what they
found, and good for you feeling comfortable
speaking up in class all in unison like that. OK. What that tends to be
is that women are more relaxed about fear of
pregnancy around the time of their period, and, thus,
sexual behavior increases somewhat around that point. But the thing that everybody
most importantly came away with was just like every
other mammal out there that has regular cycling
or only seasonal ones, high estrogen is when you
get the most sexual behavior. Instead of high estrogen
is the only time you get sexual behavior. Instead, you simply get
the most around then. In the years since,
lots of people have done versions
on this study, and it is frequently difficult
to replicate this phenomenon in terms of a change in
levels of sexual activity in women around the
time of ovulation. What has remained very
clear in the literature though is that sexual arousal
increases around the time of ovulation in women. Very reliable effect. And what that is
interpreted as is behavior here may not be
telling you anywhere near as much as motivation,
arousal, proceptivity at that time, and that’s
a more pure measure of what’s going on
physiologically there or what’s going
on in the brains. Fitting with that is a
very interesting literature suggesting that women act
a little bit differently in terms of proceptive
sexual signaling around the time of ovulation. Studies showing, for example,
that women as assessed by both women and men,
women on the average wear more provocative
clothing around the time that they are ovulating. Yes, people would go and study
things like this for a living. These were not big effects,
but the all-time bizarre study I’ve ever heard
of in this domain was actually published with
a straight face by this guy, and he’s an evolutionary
psychologist, University of New Mexico, a guy
named Jeffrey Miller, who reported the following. And you know what he
was spending his time doing, which he
reported was that around the time of ovulation,
lap dancers get larger tips. OK. That has since been
replicated in E. coli and in various yeast
species, and you know, I’m not going to try to unpack
that one in any sort of way. But nonetheless,
this was reported and shows you just how wonderful
it could be to be a scientist. Can you imagine
that money was being spent on that– your
research dollars– instead of strafing people in Kandahar
province or something? So we have a peak there,
this general issue of what does hormonal
cyclicity, in a time scale of weeks to months. What does that do to sexual
behavior in various species? What does that do to sexual
arousal proceptivity? What are some of the
building blocks of that? Estrogen– as
estrogen levels go up, estrogen increases
the expression of receptors for progesterone. So you can immediately
begin to piece that apart in at least two different
ways, first one being estrogen, thus increasing the
sensitivity in the brain. This is a brain effect. Sensitivity to
progesterone, which has something to do with the
rewarding aspects of sex. You can also translate that
into molecular biology. Estrogen, being a
steroid hormone, is going to bind to its receptor
and do the whole transcription factor, translocation
sort of thing, telling you that
upstream of the gene for the progesterone
receptor is a promoter that’s responsive to estrogen
and estrogen receptors. You know how this
one works by now. More pieces of it–
estrogen when rising here, also increases the
synthesis of oxytocin. Back to all that
social bonding stuff, and what that suggests– I don’t
know if it has been studied, but that women will feel
more affiliative with someone they’ve had sex with if
around the time of ovulation than at other points. That is certainly
the case with a vole, but that is certainly
the case, because they don’t mate the rest of the time,
and because male voles suddenly are expressive around there
in terms of their feelings. OK So more building
blocks of it. Estrogen is not only having
effects in the brain, but it’s also having
effects throughout the body at those times in terms
of lowering the threshold of certain tactile receptors. What does that mean? That means around
the time that women are ovulating,
thanks to estrogen, they are more
sensitive to touch. And I’m sure this has been
studied in consenting hamsters, but my bet is that more
sensitive to tactile stimulation in some parts
of the body over others. What estrogen also is
doing, as we just heard, is working on the
olfactory system and lowering thresholds for
detecting the smell of males. So we’ve got all sorts
of ways within the brain and in the periphery to
bias towards more arousal at that time. Wonderful evolutionary biology. No problem at all. One additional piece
of the female story, which is the effects over the
course of this kind of time span– weeks to months to
years or so– the effects of those androgens,
those male sex hormones that females are releasing. And what you see
there is that plays a role in proceptivity,
increasing sexual arousal, sexual motivation. Meanwhile, on the other side
of the road, we’ve got males, and what does testosterone–
testosterone over this time span– what
does it have to do with sexual behavior in males? Well, on first pass,
it sure looks like it has a lot to do with it. What sort of evidence? Initially, correlative evidence. Well, the time of year
in various species where males do their
mating is the time of year when testosterone
levels are elevated. Over the life span,
testosterone levels go up around puberty
and from about age 30 on, very gently cascade
down into alarming senescence, and what you see there is
a similar profile in terms of sexual behavior. That does not tell us much. These are correlations. Furthermore, correlative
studies in humans, a handful, showing more sexually
active men tend to have higher
testosterone levels, and for what it’s worth,
a number of studies have documented a dramatic
drop in testosterone levels in men right around the time
that they become fathers. OK. So figure that one out. Also an increase in vasopressin
levels at that time. You know how to interpret
this one by now. So we’ve got testosterone
and higher levels of male sexual behavior
going hand in hand. Are we looking at
any causality here? First off, we already know
about one piece of causality, which was the other day, sexual
behavior in men, in males, increases testosterone levels. So that’s one reason why
they may go hand in hand. In that scenario,
testosterone has nothing to do with increasing
the likelihood of the behavior. So does testosterone
actually have a causal role in
increasing the likelihood of male sexual behavior? And the answer is yes. And how do you show it? With the most simple classic
way of doing something in an endocrine study,
which is get rid of the guy’s testosterone. And you castrate the
male, your rodent male, your non-human
primate male, and what you see is there is a big drop
in levels of sexual behavior. And this could range from male
lever pressing to get access to a female to
courtship displays to extent of pomading
of hair or something in the right neighborhoods,
and whatever the measure is, this is when normal testosterone
levels are on board. And this is after castration,
a very, very dramatic drop. Now to fulfill the second
ironclad requirement in endocrinology, the last
thing you need to do now is after the
subtraction experiment, to do a replacement one. Artificially give
back the normal levels to the castrated individual,
and levels of sexual behavior go back to there. Whoa. OK. That proves that we have a
causal relationship here. Not so fast. First thing to note, which
is 0% testosterone and sexual behavior goes way, way down. It doesn’t go to zero. In every species
looked at, starting with the embarrassing sexual
behavior of everyone’s pet dogs when they were six years old,
even after being neutered, what you see is there’s a level
of residual sexual behavior– rodents, dogs, primates,
including humans. This is a critical point. How much residual
sexual behavior is there after castration? The more sexual experience
before castration, the more there is going
to be retained afterward. In other words, on a certain
like totally artificial level, this amount of
sexual behavior is being driven by testosterone. This amount, which
persists here, is being driven by
social experience. It’s got nothing to
do with the hormones. Yes, this is ridiculous
dichotomizing into this, but the fact
that it doesn’t go to zero, and the fact that the
more sexual experience pre-castration, the more
residual behavior, this is a vote for just
how much of a role social experience, social
conditioning plays. Next thing that takes
away from the yes, it’s all caused
by testosterone– now you do an
elaboration on the study. You castrate a male,
and now instead of replacing with
100% of normal levels, you give 10% of
normal levels, or you give 200% of normal levels. And what do you wind up seeing? If testosterone plays a
strictly causative role, even in this range, you are
going to get something– this is going to
be lower than 100%, and this is going to be higher. That’s not what you see. Instead, it is
something like that. You get roughly the
same reinstatement of sexual behavior when you
return testosterone levels over anything
roughly approximating the normal physiological range. What does that tell you? The brain circuits we learned
about the other day involved in sexual motivation– it
requires testosterone around to work fully, not
entirely, but to work fully. But those brain
regions are not really all that concerned with the
exact level of testosterone. Rough approximation of normal,
rough approximation of normal has the exact same effect. If you were seeing
a tight relationship in a male between the
amount of sexual behavior and testosterone
levels, it’s not because every little smidgen
bit of more testosterone is going to drive
more sexual behavior. It’s because every little
additional smidgen of behavior is going to drive higher
testosterone levels. So we’ve got this really
important observation. Yes, testosterone is needed
in species after species, including humans, for the
normal range of sexual behavior. Just as importantly, castration
never drops it down to zero. The more social experience,
that whole song and dance, and very importantly
as well, the system is not sensitive to
little differences in testosterone levels. Stating that a different
way, if some guy has one and 1/2 percent
more testosterone on board than the guy
sitting next to him or than he had last week,
is that going to mean he is going to be more sexually
motivated, more aroused? No, not at all. Within the normal range, the
system doesn’t distinguish it. The relevant brain regions
are sensitive to testosterone and require it, but do not care
a whole lot about the levels. One exception, which is
if you instead of, say, 200%, push testosterone
levels like 1000%, tenfold higher than normal,
this is supraphysiological, which means it’s out of
the normal range, which means no bodies normally
generate those sorts of levels. Put it up in that range,
and you will get an increase in sexual behavior
and sexual arousal. When do you see this? The idiots who go and
abuse anabolic steroids for their weight lifting or
whatever, people doing that are not pushing up their
testosterone levels into the higher range of what
human bodies can generate. They are pushing it way
above the normal range. In that range, you
do see an increase in sexual proceptivity. In a week or so, what we will
see is the exact same story. It will be the exact
same chart here when asking the question,
what does testosterone have to do with aggression? And what you’ll see is the
exact same conclusions. What are we beginning
to see here? That testosterone is not playing
a strictly causative role. It is playing one
of the words that should be becoming repetitive
here and clearly really important. Testosterone is playing
a modulatory role. What testosterone
does is sensitize you towards stimuli that are
evocative of sexual arousal. It lowers the
threshold, and that could be shown in
all sorts of studies, but where it’s most clear
cut is in this case. Does testosterone cause
this sexual behavior? No, but when it is on
board, it facilitates it. It modulates it. Theme again and again and again. And that, obviously, has tons to
do with individual differences. One last hormone to mention in
this realm of hormone levels over the last couple of
weeks, months, seasons, or so– the hormone melatonin. And I think that’s the
only time melatonin is going to be mentioned in class. Melatonin has something to do
with telling the body what time of year it is. It is responsive to the amount
of light you are exposed to. What is melatonin about? It is one of the driving
forces on seasonal mating. Those species where you
suddenly get on one afternoon each year, all the wildebeests
ovulate the same afternoon kind of thing– it
is almost certainly a whole pathway in the brain
sensitive to the amount of light and the amount of
light per day over recent weeks, which by way of
melatonin, triggers the onset of the mating season. Do humans have a
seasonal mating pattern? There’s a smidgen
of evidence for it. If we’ve got it, it is
a very, very weak echo of what you see in
some other species. Now we shift over to getting
really way back then. Instead of over
your last 28 days or over the last three
seasons, now beginning to look at perinatal factors. Perinatal– before birth. Prenatal– after birth. Postnatal– very
early development. First off, focusing
on early environment, environmental factors
having something to do with adult
sexual behavior. What we can translate
that into is ways in which early environment
affects every single one of these subsequent ones. What does early
environment childhood have to do with shaping
of sexual behavior? A theme that’s also going
to come out in every topic we’re going to hear of
after this, buzz words that should be beginning to be
keeping you awake at night– modulatory, contingent,
if then, all that stuff. Here is another one. Here’s another concept
that comes through. The evidence shows that there
is very little about early life experience, which
influences the quality, the way in which an organism
goes about having sex. What’s another
way of stating it? This is a pretty set in stone
bunch of fixed action patterns. Early experience is not about
learning how to be sexual. Early experience
is about learning the appropriate social
contexts for being so. And that is shown in
species after species. That is what
experience is about. Not how to do it,
but when to do it and who you should
not in your right mind try to do something proceptive
to and things of that sort. This is what early
experience is about. And what we’re going
to see in a week is the exact same
boring paragraph. Early experience does not teach
organisms how to be aggressive. It teaches organisms
the appropriate context for being aggressive. So what’s the sort of evidence
for these early effects? One example, the
whole literature that emerged that is covered
somewhat in the zebra book in another domain, but this
whole literature that emerged in the 1950s, work looking
at captive primates, what are the consequences
of growing up in a certain degree
of social isolation? What happens to behavior–
and eventually, people studying behavior
and physiology– what happens to behavior in adulthood
if you are a young rhesus monkey, who grows up only
with peers and no mother, or grows up only with
a mother and no peers, or grows up with
Mother being present only intermittently, or at
the most extremes, growing up with neither mother nor
peers or any other member of your species around? You will see in the
book a whole discussion of the ethics of these
studies, but what does your early
social environment have to do with things
like sexual behavior? And what you see
coming out the end is when you looked at
these adult primates, since replicated
over and over, they go about the sexual behavior
the plain old way that everybody else does, but they do
it in totally socially inappropriate context. And thus, you have
these males who were raised in some degree
of isolation early on, growing up and carrying
out perfectly normal sexual fixed action patterns
on the towel in the room, on the bowl of food, on the
who knows what wrong context. You have trying to do things
with animals you should not go anywhere near in
terms of social dominance and such in appropriate context. Early experience shaping
not how but when, what the if-then clauses are. More issues of early experience
shaping adult sexual behavior, arousal, proceptivity,
et cetera– we already heard one example
of this with humans. That’s the whole
kibbutz literature. That was that whole
business that if you spend lots of intimate time
with somebody before age six, what you will do is in some
subliminal imprinting way, decide forever after
this individual does not feel like a potential mate. This individual
feels like a sibling. That was the example in the
recognizing relative lecture of showing that
hooray, we are such a cognitively
sophisticated species. We can figure out who’s
somebody’s fourth cousin three steps removed by
thinking, and that’s how we make our mating
decisions, showing instead in those studies, there is
this non-conscious level. One of the rules that humans
have is lots of exposure intimately to somebody
early on in life, and you are not going
to be very likely to get that proceptive behavior
stuff going on later, part of turning them
into a pseudo kin because of that early exposure. One additional domain
I will touch on here in terms of early
experience, which is, what does early
experience have to do with sexual orientation? And depending on which decade
you are asking this question, the answer would
range from everything to virtually nothing. Going back to the virtually
everything time, which was dominating sort of the first
half of the 20th century, how people thought about the
subject, what you had were two broad models for what
sort of early environments increase the likelihood of
boys becoming gay as adults. And these were the two models. The first one was the absence
of a father figure model, and this was one
straight out of monkeys learning who they should
try to pelvic thrust with or some such thing. This was the argument that
what do father figures provide? Training for appropriate context
for proceptive sexual behavior, growing up absent a
father, father figure, increasing the
likelihood of being gay. The other model was having
this totally pain in the neck neurotic screwed up
mother, who, as basically said between the lines, makes
you crazy when you grow up, and thus you have circa 1950,
psychiatrically certifiable disorder of having a
different sexual orientation. Obviously, where I’m
going to head right now is there has not been a
slightest shred of evidence over the years either for
the missing father figure model of sexual orientation or
the neurotic mothering style model. Complete nonsense. Nonetheless, dominating thinking
about what was going on there. OK. So what we are now
ready to shift to is what’s going on with hormones
around this time period. Let’s take our five-minute
break, and then we’ll resume. Looking at what perinatal
hormone levels have to do with adult
sexual behavior, and you already know the answer. You know it in
your hearts by now, which is, well, it depends on
what species you’re looking at. And what we will see is a
very similar thing to the rule there, which is in
lots of species, rodent species, prenatal or
perinatal hormonal environment has everything to do with
adult sexual behavior. And by the time
we get to humans, what we’ll see is maybe kind of
sort of more research needed. What we begin with
here, implicit in that, is a dichotomy that runs
through all of endocrinology when thinking about behavior. The effects of hormones
back when you were little, jargon in the field, an
organizational effect of the hormone. And what that is
about is explicitly is what are hormones
doing at a time in terms of organizing what kind of
brain you’re developing there. Effects of hormones,
instead, in this range or so, what you are talking about is
an activational hormonal effect. So this is a very sort
of consistent dichotomy that people in the business
use, early, early hormonal environments having
organizational effects on the nervous system,
hormones forever after having
activational effects. So what you see is
in rodent species that perinatal
hormone exposure has massive organizational
effects that dramatically influence sexual behavior. What you also see is it’s not
so dramatic and clear cut. A whole literature
initially suggesting that, for example, male
rodents, if they are not exposed to testosterone,
perinatally, will have a different male
rodent sexual orientation later on, a dichotomous outcome. What a huge literature
now shows is something that is evident to
every sort of human sexologist for centuries, which is it’s
not a dichotomous function. It is on a continuum in
terms of sexual orientation, and 300 different species
have been documented by now to have both heterosexual
and homosexual behavior at different times in
naturalistic settings. So perinatal hormones
having organizing effects on adult sexual
orientation– what you see is these are not all or
none properties at all. What else? OK. What you see specifically
in non-human primates is perinatal period. Expose a female monkey fetus
to high testosterone levels, and what you will do is
masculinize the brain. Masculinize the brain, having,
thus, an organizational effect. What does masculinization
then manifest itself as in adulthood? If nothing else is different,
it has no effects at all. On the other hand, if you
inject a female monkey who is masculinized perinatally, if
you inject her with androgens, with testosterone, you get a
wild burst of male fixed action patterns. In other words, you’ve
got an if-then clause. If and only if there was
prenatal masculinization, then testosterone will have
an acute activational effect on sexual behavior. Translating this. OK. So in the absence in a
normal female monkey, in the absence of prenatal
androgens or adult androgen levels, this is the amount
of male fixed action pattern sexual behavior. Now prenatal androgenization–
normal low action levels in adulthood. Same low levels. Now no prenatal androgenization,
and exposure to androgens in adulthood– same low levels. Prenatal exposure and
acute activational effects, and suddenly, you get high rates
of male typical fixed action patterns. So what we’ve got here is
a contingent organizational effect. Yet again, one of our
if-then clauses, this one not being an if this
physiology is going on only in this social environment, then
if this early life endocrine environment occurs coupled with
this acute adult one, then. Yeah, question. [INAUDIBLE]? That is a great question,
and as you’re about to see, the answer is so
insanely complicated, you are going to regret having
asked that question for days. But you are going to
find out about it anyway. Apropos of that, I just
forgot a great question during the break, which
is, OK, when you’ve got those weightlifter
folks, they’re abusing their steroids,
their anabolic steroids, their testosterone-derived
drugs, when you push things up into the
supraphysiological range, higher than the body
normally ever comes up with, do you see a phenomenon
from last Wednesday? Does the body down
regulate the number of testosterone receptors? And you see exactly the case,
but you could never down regulate them low
enough to compensate for the huge screaming
testosterone signal. It is a partially successful
compensatory response. What have you got
in terms of humans, in terms of perinatal
androgenization of females? And people used to know
exactly the answer to it. First off, when do you get
human females as fetuses and as predominately in
humans prenatal, rather than postnatal effects? It depends on how fast,
how much of development occurs before birth,
but in humans, when are circumstances
where female fetuses will get heavily androgenized? Historically, two circumstances. One is in the case
of a disease where there is something wrong
with the adrenal glands, and they pump out
tons of testosterone. You remember, if I
actually did say this, and if I didn’t, I hope
you’re not remembering it hallucinatorily,
but you’ll remember that the adrenal glands make a
certain amount of testosterone, and in females, it
pumps out maybe 5% the levels that males do. When you have this disease of
an overactive adrenal system, you pump out way too high
of levels of testosterone, a disease called congenital
adrenal hyperplasia. Hyperplasia, the
number of cells– OK, come up with a limerick
about that one. I dare you. Is it possible to
come up with a haiku? How many syllables are there in
congenital adrenal hyperplasia? Well, it depends if we’re
talking about rodents or not. So congenital
adrenal hyperplasia, a genetic and inborn error
of metabolism in the adrenal glands, and you pump out
huge amounts of androgen. So suddenly, there is a world
of the occasional girl, who was born suffering from
this disorder or the mother suffering from it during
pregnancy, who has been prenatally androgenized. The other population,
thanks to a drug that was very popular in the
1950s, a drug that decreased the likelihood of miscarriage
that was very heavily used at points around then, a drug
called diethylstilbestrol, DES. And in a subset of
women, their biochemistry was such that a lot of the DES
was converted to androgens. So you had kids, who were
prenatally androgenized, girls, either because of this
congenital adrenal hyperplasia or because of DES exposure. So then the question
immediately becomes, OK, so what are they like afterward? And this prompted the
great, large, massive set of studies on the CAH, the
congenital adrenal hyperplasia, on the CAH girls
as they grow up, and you knew exactly what
the expectation was straight out of primates here,
non-human primates, which was this was going to
have masculinizing effects on their behavior. And what was shown
was in adulthood, there were all sorts
of differences. No, not just in adulthood. Starting around
adolescence, there were all sorts of differences
in the behaviors of these girls, and as we’ll see next week,
a whole cluster of them were thought to fall into the
realm of aggressive behavior. But what we’re seeing
here was eventually, a higher likelihood
of becoming a lesbian in terms of sexual orientation. Whoa. What we’ve just shown
is prenatal androgens, and you produce a
lesbian later on. That’s just– there’s a little
problem with these studies, a slight confound,
and one that’s going to be very
pertinent next week as well when talking about
the aggression stuff. The confound being if you
were prenatally androgenized, you would get born with
kind of weirdo genitals, and you would have sort
of intersexual genitals in all sorts of ways. And all of these
girls typically had to have gone through
a dozen rounds of reconstructive
plastic surgery over the first
decade of your life. These were not girls where the
only thing different about them was what sort of hormones
their brains were marinating in back when they were fetuses. These are girls who grow up with
this really interesting part of the body that
all sorts of people seem kind of creeped out about,
but doctors are endlessly examining, and all sorts
of painful surgeries. And this literature
was completely confounded by the
fact that there was all this masculinization
of genitalia and a whole world of surgeries, often confusion
about gender assignment early on in life. Things were not merely a
change in the hormone levels. So it remains
relatively unclear. There is by now, at this
point, weak evidence of prenatal
androgenization increasing the likelihood of a woman
being gay as an adult. I’m seeing here in my notes
I have the words Indonesia, tomboy, and Hobson Jobson. And I haven’t a clue
what that’s about. So we will just skip over that. OK. What we begin to see
here is another feature of early experience. What does– where were we–
prenatal endocrine environment have to do with
sexual identification? Which is different than who
you are sexually attracted, but rather what sex you
feel yourself to be. And what we heard the other day
with the transsexualism example is you could have gender being
dictated by your chromosomes and which organ, which
types of gonads you have and hormones and all of
that, but that is not enough to determine that there
are clearly other things that can happen that could produce
a very, very different gender identity. What also was seen from that
literature of individuals who were born intersexual where
they have sexually ambiguous, gender ambiguous genitalia
is it is far from clear which decision to
make, whether that was made circa
1950s by the surgeon with no consultation
with the parents, or, fortunately, these days,
a very different scenario in terms of how successful
the assignment is by the individuals
in the outside world. What’s going on in terms
of sexual identity inside? Now what this begins to bring
up is the most miserable, irritating, confusing
thing about the effects of steroid hormones
in the brain, which is where your question came from. And this is where you’re all
going to start to regret this, but it actually is necessary
in terms of an important point. So you’ve got testosterone,
and what does testosterone do? We know already it binds
to testosterone receptors, testosterone receptor, and
does its steroid hormone transcription factor deal. Throughout the 1970s, there
was an astonishing amount of confusing irritative research
done showing the two following things. In some parts of the
body, testosterone has its effect as testosterone. It binds to the
testosterone receptor. In some parts of the body,
there is biochemical conversion of testosterone to something
called dihydrotestosterone. OK. It’s not testosterone. It’s a little bit
different chemically. It binds to the same
testosterone receptors. It works a little
bit differently. OK, we can live with that. The thing that had people
jumping off buildings was the discovery at
the time that some of testosterone’s actions are
due to it being biochemically converted to estrogen,
which then binds to estrogen receptors and
causes male typical behaviors. OK. It’s at this point that about
half the people in the field quit and went to
business school, because this was so confusing
and impossible and all of that. This consumed years
of labor of people trying to sort this one out. It goes as follows. Once testosterone
enters a target cell, if this is the scenario
that’s going to happen, it’s inside the cell. The testosterone is turned
to estrogen. In other words, this weirdo phenomenon has
no effect on circulating testosterone levels. It’s only in target cells
that have the enzyme that could do that conversion. OK. So it’s an intracellular
phenomenon. If this is leaving you
totally in the dust, don’t worry about it, except for
a small point coming in awhile. But if you want to devote
the rest of your life to figuring this
out in more detail, there is something
wrong with you. But what you’ve
got here is normal circulating levels,
but different effects throughout the body. In general, what is found is
the effects of testosterone in the brain involve this
turning into estrogen, as symbolized meaninglessly
by that asterisk. Throughout the genitals
or throughout the body, and secondary sexual
areas of skin and such, testosterone exerts its
effects by being turned into dihydrotestosterone. And whatever parts are
left over at that point, testosterone just does
its regular old thing. So this is incredibly
confusing how this can be. Immediately, or not so
immediately, two things should come to mind. OK, so prenatal
testosterone levels are going about
their normal prenatal organizational masculinization
effects, and part of it is on how the brain organizes. So what we just saw was prenatal
neurobiological masculinization requires testosterone
to be working like estrogen in the brain. Why don’t all the female
fetuses then get androgenized? Since they’re not generating
estrogen right on site there within the cell, but
they’re getting estrogen through some other route
as their fetal ovaries start to work. Why isn’t mom and her
estrogen androgenizing every single fetus out there? How is it possible
to ever get a female? And the answer to
that is there is a protein, which occurs
during pregnancy, that occurs in the circulation. And what it does is
it binds estrogen, and it takes it out of action. It leads to estrogen
being degraded. In other words, estrogen in
the bloodstream of a fetus never has an effect on
any cells in the body. Estrogen, whether derived from
the female fetus beginning to get her ovaries going there,
or from mom’s circulation, the estrogen has no effect. And in other words,
the only fetuses that ever have estrogen
inside their neurons are fetuses that are male,
where the estrogen came from testosterone. So you have to
have this protein, and it’s something
called alpha fetoprotein. It only occurs in fetal life. This winds up
being the solution. What is implicit
in that, you do not get the organizational
feminizing effects of hormones prenatally because of
estrogen, because you’ve just guaranteed that doesn’t happen. You’re getting androgenizing
effects that way. You don’t get prenatal
feminizing effects from estrogen. Where does the
brain feminization come from? The irritating
answer back when was this was always– sort
of the same phrase was always used that the female
brain is a default brain. You have to actively in a
muscular excited chopping down the trees and clearing
the prairie sort of way, you have to actively
do something hormonal to masculinize a brain. And in the absence of that,
you just kind of wind up with one of them female brains. What’s clear now is this default
model was not really the case. It’s other hormones that
are doing that there. OK. So this totally confusing,
irritating thing that everybody had to assimilate
at the time of testosterone having different effects,
having been converted to different messengers in
different parts of the body, and that having to produce this
whole complex Rube Goldberg sort of solution as to
how to ever get a female. Now one additional
interesting implication– back to, you remember the other
week, remember– actually, did I talk about it, or
was it two years ago? Jeez. OK. I think I mentioned
testicular feminized males. Yes. Good. OK. Thank you for the grounding. You remember when
those folks were about. This was someone who was
phenotypically a girl and would not hit
puberty, would not start menstruating until
every other kid in her grade had, and it still
hasn’t happened, still hasn’t happened. And you take her to the
doctor, and what is discovered is that she is not female. She is a testicular
feminized male, and we went through
exactly what the building blocks were of that. The individual is
chromosomally male, has testes, undescended
testes, is producing tons and tons of testosterone. What was the problem there? We knew already it
was the mutation in the testosterone receptor. So if testosterone
is not able to send a signal through the
testosterone receptor, you don’t get a male
phenotype, and you get an individual whose
sexual identity is female, because these are
people who are girls and grow up to
become women, women who simply can’t reproduce. But otherwise, the sexual
identification is female. This should be
really puzzling now, because what we’ve
just seen is if you have this mutation in the
testosterone receptor, you’re not going to get
any signaling mediated by testosterone. You’re not going to get
any signaling mediated by dihydrotestosterone. But you’re going to
get perfectly normal masculinization of
the brain by way of estrogen. In
other words, people who were testicular
feminized males, who in terms of their
sex identification, have been female from
day one and will be for their entire lives,
nonetheless, prenatally they had masculinization
organizational effects on the brain. What does that tell you? All of this great hormone
stuff, in some cases, doesn’t hold a candle to social
sex identity assignment, which is when you have
somebody growing up with a certain gender’s
genitals, and all of you treat that individual as a girl. It turns out virtually
100% of the time, it doesn’t matter that you
still had this pathway working prenatally. All the social cueing produces
a female sexual identity. So we’ve just gotten a big,
big vote here for this. It’s doing all sorts of
exciting endocrine stuff there, which nonetheless,
may not hold a candle to some social environmental
factors at this end. OK. What else do we have here? Something I don’t
want to talk about. OK. So hurtling on, now we are ready
to move back another box here, which is genetics. What does the genetic makeup
up of an individual, not of a population or
species, what do genes have to do with sexual behavior? And the answer is lots of
things, starting with the fact that genes determine which
gonads you make as a fetus. And thus, that determines
which sex hormones you were secreting,
and thus, that determines what sort of
genitals you wind up with and secondary sexual stuff, and
off you go running with that. And we’ve seen that nonetheless,
that can be blunted by, depending on the environment,
the testicular feminized male pathway here showing that. So genes play a role in terms
of just sheer sex determination. What is known about genes
and sexual orientation? This has been studied
a lot, because this is one of those
irresistible subjects that, ooh, people just
can’t get enough of. What’s up with that? What does the literature show? A certain degree of heritability
of sexual orientation, and you should be able to leap up right
now and say exactly what that means and doesn’t mean. Here’s the sort of evidence. Twin studies, twin
studies– when you look at monozygotic
twins, identical twins, there’s approximately
50% concordance of sexual orientation. Translated into the terms
that people are usually focusing on in those
studies, which is to say, if somebody is gay,
their identical twins has a 50% chance of being gay. Dizygotic twins, non-identical
twins– what is the number? Instead it’s 22% covariance. What’s the number
with other siblings? 9% covariance. So what do we see here? We see a suggestion
that the more genes you have in common with somebody,
but also the more prenatal environment you had with
your non-identical twin, all of that stuff, the greater
the likelihood of sharing a trait of sexual orientation. And you can be off and running
right now about the limitations of that interpretation,
because obviously, this suggests genetic
effects, and it also suggests the whole world of
identical twins being treated differently than
non-identical ones. One additional piece
in that story, and this was another one of those front
page stories in Time, Newsweek, et cetera, and this
came a couple of years after Simon Levey’s finding of
that sexually dimorphic nucleus in the brain, that
whole deal there. And this was the reporting
of the first genetic markers for sexual orientation. And this was reported
by a geneticist at National Institute
of Health, a guy named Dean Hamer, who was a
very well-respected geneticist. And what he reported was that
he was finding genetic markers for sexual orientation. In other words, certain
gene locations that were more likely to be shared
between gay siblings, where both were gay, than
between partially gay siblings or non-gay siblings
or however that one runs. You know that one by now. Beginning to find genetic
markers going with this. This was really interesting,
and no surprise– what the newspapers were
screaming about within days was scientists
announced today they have discovered the gay gene. Great. Maybe we shouldn’t let people
learn any science out there. So scientists have
discovered the gay gene. It goes to all the newspapers
and Reader’s Digest, and if I recall at the
time, Ronald Reagan as well, but he was completely
demented at that point, so I won’t hold it against him. But the people at Newsweek
should have known better. So we have cover stories
about the gay gene. Obviously, you can rip
this to shreds right now. Number one, this was not a gene. This was a genetic marker. You remember the other
week, the difference there. Number two, there was
no consistency in this. What do I mean by this? This pair of
identical twins would tend to share a certain genetic
marker, which was predictive of sexual orientation. And the next pair over, it
wasn’t the same area of genes that showed that covariance. It would be a completely
different area that they had in common. In another pair, a
completely different area, you got this genetic covariance
in various twin pairs, but it wasn’t the same gene
marker in all those cases. All of them were
different, which makes zero sense in
terms of the genetics. The biggest problem with it
is that since then, all sorts of people have tried to
replicate the finding, and it has never
been replicated. Nonetheless, Hamer became
quite famous for this. He is gay, and he used this
sort of politically some of the same ways that Simon
Levey did with his study, which is, don’t tell me about choice. Don’t tell me about my
neurotic mother anymore. We are looking at a very hard
wired biological trait– what sexual orientation you have. Levey’s finding I have
found quite convincing in terms of replications. Hamer’s– nobody else has
replicated any actual genetics that he reported. Makes no sense at all. So great limitations in
what you could make of this. OK. This allows us to make our
great final leap to the left with this thing,
this logic that’s going to run through
everything we talk about, which is the second you’re
talking about genes, you are implicitly talking
about the evolutionary history that brought about the
existence of those genes. And that you’re also talking
about the proteins made by those genes and early
environment changing the epigenetic state of
transcribing those genes. Yes, yes, that whole
song and dance now. So now we have to transition to,
what does evolutionary biology tell us about sexual behavior? So the first thing that it tells
us is absolutely obvious, which is organisms have sex for
the good of the species. So that one’s out of the way. So now we go to what is
much more logically in terms of contemporary, evolutionary
thinking– contemporary starting circa 1965 or
so– the whole notion of maximizing the number of
copies of your own genes, all of that translated into
sort of the economic terms of [INAUDIBLE] copies of genes. What that basically
states is sexual behavior is about reproduction. And people who would
study phenomena like these in various
rodent species or wildebeest ovulating the
same afternoon, all of that, would say, yes, indeed, you
only have sexual behavior when it’s around the time when
females are ovulating and yes. Reproductive behavior
is about reproduction. It’s about passing
on copies of genes. What soon began to fall apart
was not only making sense of us with our having non-reproductive
sex all sorts of times, was the discovery that we’re
not the only species that does that. And far and away
the flagship species as a sort of emblem of
that are bonobo chimps, who are, according to almost
all primatologists out there, the coolest primate
species there is. OK. Bonobo chimps– they
were historically known as pygmy chimps, which is
to say that when people first discovered them in
terms of scientists, they were viewed as,
well, these are chimps, but they’re just kind of
weirdo atrophied chimps, which I don’t quite know
how you come up with a pygmy atrophied
chimp, but that was the view. And not very interesting–
what eventually became clear is they are a separate
species of chimp, and bonobo chimps
are utterly different from your standard issue
Jane Goodall chimps. Again, Jane Goodall chimps,
we have a tournament species with extreme high levels
of male aggression. As we will hear
about next week, you have chimps who are
building weapons. You have chimps
that form something resembling organized
warfare, and meanwhile, over, as it turned out, on
the other side of the Congo, which is where the
main division occurs, you only find bonobos in
one area of the Congo basin, and they clearly have been
reproductively isolated from all the rest of
the chimps heading there east all the way to the Indian
Ocean by way of the Congo. There, go on the other
side of the river. You’ve got the bonobos, and
bonobos are totally different. Bonobos, unlike chimps, have
virtually no sexual dimorphism, so you’re off and
running with that one. We know exactly what that means. Bonobo chimps have female
dominance rather than male. All bonobo chimps play the
guitar and sing soulfully. What else? And we have astonishing
amounts of sex. Wait a second. We just went off the rails here. A species with low degrees
of aggression, because they have virtually no aggression
whatsoever, species with low degree of aggression
and with no sexual dimorphism in body size– what
we’re looking at is a pair bonding species,
a monogamous species. Bonobos are not a
monogamous species. Bonobos make– I don’t know
who– look like a pair bonding species by comparison. Bonobos are the most sexually
promiscuous species on Earth. Bonobos have astonishing
amounts of sex with every other type of
bonobo they could run into. They have sex in
order to reproduce. They have sex in order
to decrease tensions. They have sex in
order to celebrate having decreased tensions. They have sex, because it’s an
even numbered day of the month, because this is odd. Every variety, and
the vast majority of it being non-reproductive,
non-reproductive because it’s not at a time
when anybody’s ovulating, or because it’s with
someone of the same sex, or it involves sexual behavior,
which traditionally does not result in eggs getting
fertilized and all sorts of variants that
people only dream about from buying books
and trying to get lessons and this sort of thing. And you have, perhaps,
having something to do with that astonishingly
limber spinal columns, but what you’ve got is a
totally different picture. Wait a second. They are very low
aggression, and they have no sexual dimorphism,
but they’re as far from pair bonding
as you can get. And instead, you have a highly
promiscuous social system, female-dominated,
and they’re all just so cool and wonderful
you can’t believe it. And every time people go
to primatology meetings, if you study some dumb old
stupid species like a baboon, you spend the whole
time basically feeling like you’re some sort
of immature jerk, because you’re not
hanging out with bonobos. They are the kings of
primatologists these days, the people who study bonobos. As the soundbite goes,
chimpanzees are from Mars. Bonobos are from Venus. OK. So that’s what the t-shirts
say from the bonobo people at the conferences there. Totally different system. So what we already see is
violating our simple rules of what predicts a
tournament species and what predicts
a pair bonding one. What’s most striking
here is [INAUDIBLE] reproductive behavior
is reproduction for passing on
copies of the genes, not for the good of the species. But we know individual
selection could [INAUDIBLE]. And here’s these guys having
sex with 14 other bonobos while they’re all upside
down or who knows what, and it’s not just for passing
on numbers of copies of genes. Huge, huge exception there. And huge exception in
lots of other species. And the ecologist
Joan Roughgarden here in the biology
department has made an argument there is far
more non-reproductive sex that goes on in lots of
different species, weakening the classic
Darwinian concept from three, four weeks ago of
sexual selection being a very important
driving force. What sex is very heavily
about is one gender choosing who are going to mate
with the other one, and it’s all driven by
that of seeing instead if the world of
bonobos, there’s not a whole lot of evolutionary
drive being built around sex equals reproduction. So bonobos are
really interesting. What’s the sex there about? One of the common themes
that comes through is it’s about promoting
group cohesion, and one of the things that
people emphasize or focus on with bonobos is you look at all
sorts of other primate species, and what do they do when
they’re upset about something? They groom each other. What do they do
when they’re happy? They groom. What do they do–
social grooming, as termed the social glue, the
social lubricant of a society. You get a troop of
baboons that have just gotten a bad scare from
a lion, and as soon as the coast is clear,
everybody comes down and spends the next 30
minutes grooming each other. And sexual behavior
in bonobos appears to be serving a
very similar role– all about social cohesion
as well as decreasing individual tensions,
reconciliation, things of that sort. Now this flies on the face of a
dominant theory that was around in the last century,
the first part of it, and this was due to one
of the grand poobahs in this field, a guy, this
Brit named Solly Zuckerman. Solly Zuckerman, who eventually
became Sir Solly Zuckerman, which probably didn’t
help him in society at all still despite that,
but old Zuckerman there was, for his time, the
embarrassed Wynne Edwards. He was the Lamarck
of the earliest part of the 20th century. The people who will
only be remembered for coming up with
Lamarckianism, old Lamarck or coming up with something
as idiotic as group selection. What Zuckerman came
up with was the notion that sexual behavior is purely
for promoting group cohesion and for decreasing violence. And all you need to do is go
to half the movies out there or study half the
species on Earth, and what you will see is
sexual behavior or inability of or unrequited or
whatever vanquished is the cause of the majority
of aggression in organisms out there in various
mammals, and that argues very strongly against it. So what you see in most species
that have been studied– it’s a strong argument
against the Zuckerman stance. Nonetheless, you see in
some species like bonobos and Roughgarden’s
argument, lots more species than people traditionally
would think, where instead you see sexual
behavior often serving a non-reproductive group
cohesion sort of role. What else does evolution have to
tell us about sexual behavior? One critical issue and
one that was touched on the first couple of
lectures is, what does it cost you to reproduce? And there we get the
hugely important asymmetry, which is sperm don’t cost
a whole lot, whereas eggs and pregnancy and postnatal
care and all of that is hugely expensive. What is that the
driving force on according to all the
sociobiological thinking? The fact that in species
after species after species, females are more
selective about who they will mate with than
males, and it’s usually the case the males are not
selective in the slightest. And what you’ve
got instead is just a couple of sperm that accost
you, and that’s not a big deal. Increased female selectivity,
higher levels of it than males, argument being that it is
all about the differential costs of pregnancy. What we also saw was
not of pregnancy, but of reproduction
and raising of kids. What we saw was the
interesting realm where you got the
exception to that, which were the pair bonding species. The marmosets, for example,
and what we saw back when was the male does as
much child care as the female does, and the
females always twin. So around the time
that the kids are born, the female has put in far
more of the investment. She’s gone through
the pregnancy in terms of caloric expenditure. The males do, if anything,
more of the child rearing in terms of carrying the
kid around when foraging, all sorts of costly stuff
like that, and eventually, what you see is the
curves don’t do that. But at some point,
the cumulative amount of calories that the
male has expended is greater than the female. That’s when you see
that cuckoldry business. That’s where females
will potentially pick up and abandon, and because
the male has made the greater investment at that point, that
is seen very frequently in bird species with pair bonding. So we’ve got here an
exception to the argument that the cost of reproduction
and child raising is always greater for females
and, thus, will always produce greater female
pickiness for mates than you find in males. Nonetheless, you see
that an awful lot. What else do you see? A whole world not only
of female pickiness, but a whole world
of male attempts to control female
reproductive behavior. And this found in species
after species after species an obvious interpretation
there in terms of male-male
competition decreasing the ability of females to
mate with someone else. And that ranges
from primates who are in consortships, where
the male will do what is often termed mate guarding,
which is he tries to keep the female from
going near any other guy to all sorts of
other stuff as well. And you certainly see
this in the human realm. What are two cultural inventions
humans have come up with to decrease the likelihood–
by men– to decrease the likelihood of women
being sexually active outside that relationship? The first one is
clitoridectomies, and something else that serves
a very similar function, which is inventions of things
like chastity belts. What’s up with that? What you find are
cultural inventions like those in groups that tend
to have occupations where males disappear for long periods. For example, nomadic
pastoralists, where depending on
the time of year, you pick up with your camels
or your cows or whatever, and you, the guy, are going
to spend the next three weeks at the grazing area
that’s a good five miles west of there. And what this is about–
the argument culturally for the clitoridectomies is
it decreases female pleasure, decreases the likelihood of
her having sex with someone else when you were elsewhere. What were chastity
belts about when the guy picked up and decided to
spend the next six years trying to liberate Jerusalem
from the Ottomans or whatever off in the Crusades? And just so you don’t have any
ideas over the next half decade while I go die from the plague
somewhere in Eastern Europe, that’s when those were,
again, a model of cultures where there were
extended periods of men being away from women. You have very often
elaborate cultural inventions for men trying to control the
reproductive access of women. What that also winds
up doing is explaining what was thought to
be the dominant models of reproductive success
and reproductive choice in all sorts of other species. And seen, for
example, in something like baboons, what you had
was termed the linear access model of reproduction. It goes as follows. You have a social
group– for example, a baboon social
group– and there is only one female who is in
estrus, only one female who is ovulating. Who winds up mating with her? The alpha male in the troop. Now instead, there’s two
females who were ovulating. Who gets the two females? Numbers one and two
in the hierarchy. Three females– numbers one,
two, and three get the female. And implicit in that is the
activeness implied in the word “get,” the passive
lack of choice at the female end of things. This was the linear access
model in which male dominance rank was entirely predictive
of male reproductive success. So that’s what people
thought lots about then. That was the original thinking
about the relationship between male dominance rank
and reproductive success. As we will see shortly,
it’s not quite so clear. Lots of other species, where
you see males attempting in the evolutionary
sense, attempting to limit female access
to other males– this is the whole world
of copulatory plugs. Lots of dog canine related
species, where a semen plug is left there in the vagina
of the female, which soon hardens into a
plug like nothing else is happening there. You see that. There are other cases. There are fly species where
the males penis is barbed, and ooh, I heard a–
I’m not drawing that. What are you thinking? Where it’s barbed and
where the barbs, in fact, go in the opposite direction,
point back at the male. Once you get the penis in there,
and it’s not coming out again. It’s like one of
those– you put your– [LAUGHTER] Well, it’s actually
not like one of those, but you get the point. And what’s that about? The male leaves
his penis in there, which he manages to
do without afterward, because they can make new ones. And this is a very different
world you’ve got here. Then you’ve got the whole world
we’ve already heard about about sperm competition, of sperm from
one male in various fly species containing toxins that will
kill the sperm of another male. Then there’s a whole
interesting world that goes on, which is when
males mate with a female, they do something
biochemically, which decreases the sexual
attractiveness of the female
subsequent to that. In a number of fly
species, males with mating release a chemical, which
decreases mating pheromone production in the female. And suddenly, nobody else
is interested in her, or there are other
flies species where males release a chemical, which
decreases sexual proceptivity in the female. Viciously clever ways
for males to control female reproductive
behavior after they’ve left. Male-male competitive
strategies. So what do you see at
the female end of things? No surprise, you see
female counterstrategies. One brilliant one
that evolved in humans is this relatively unique human
phenomenon of hidden ovulation. Yes, all that pheromone
stuff and smelling people’s armpits and things that don’t
happen much in the real world, but what you see for the most
part is that humans are not terribly aware of where
somebody is in their cycle. Humans have invented
hidden ovulation. What’s that meant to do? Decrease paternity certainty. And one argument is
that’s a good mechanism for decreasing the likelihood
of competitive infanticide. The other is it
decreases male attempt to control female
sexual behavior, because it’s less clear when
you need to be doing that. So counterstrategies. More examples– this is argued
that in some species that have non-reproductive sex
throughout the cycle, that is a female counterstrategy
to, again, fool the male when ovulation is actually occurring,
increasing the likelihood that at such times, she can
get somebody else’s genes. Other strategies– we’ve already
heard about one– [INAUDIBLE] in the competitive
infanticide one, which is that whole world of females
that can fake being in estrus, that go through pseudo
estrus, all of this meant to be ways of keeping
males a little bit less certain of when they should be trying
to control female sexual access, and thus, she has more
choice in the matter. What that brings
us to is thus– oh, that’s something
interesting that I left out. Eh, it’s not that interesting. OK. So back to male-male
competition. This was first looking at
male in lots of species, male attempts to regulate
female sexual behavior, female counterstrategies. What’s up with
male-male competition in terms of evolution
and sexual behavior? Most obvious one being
is male-male competition for reproductive access
and the standard old models being that linear access model–
one female winds up with number one male, two, and so on. What that thus
begins to explain is when you look at all
social species out there, the leading cause of aggression
is male-male aggression built around female access. And as we’ll see
by next week, that is the case as well for every
human culture ever looked at. You also see, of course,
the sperm competition. And once again, we have
one of those issues with humans, which is where do
we fit on the spectrum there? If you have a
monogamous species, males tend to produce only
small amounts of sperm and tend to have small testes. When you have
polygamous species, males want to pump out
insane amounts of sperm to increase the likelihood of
outcompeting some other guy’s sperm if it shows
up on the scene or for making a sperm plug, and
what you wind up getting there in those species
are large testes. So you look at the
various primates, and chimps have gigantic
testicles per body size. Gorillas do not. Gorillas that have a
very different world of male-male com–
what about humans? Once again, the
same exact thing. We are about halfway in between. When compared to
other primates, we are intermediate between a
tournament species and a pair bonding species in
yet another domain. We’ve been hearing about
this again and again. Something really
interesting that has been shown in humans, which is–
no, I’m not going to tell that. That’s too hard to explain. But it was great. You would really wish– so
now what we have is also looking at evolutionary aspects
of female choice in there, and in what cases do you get
female-female competition? First off, the answer
was obvious in terms of looking at traditional
tournament species, which is that females have no choice
who they are mating with. It’s linear access models. One female winds up with
the alpha male, two females and so on, and this
was the dominant model in all of primatology
starting in the ’60s. And then by around
1980 or so, it was recognized that,
in fact, there’s virtually no evidence
for strict linear access models of the main determinant
of who a female mates with is who’s the winner of male-male
competitive interactions. People discovered at the
time that, in fact, there was this strange, strange
violation of all these models, because it turned out the models
were not based on behavior. And this generally was
discovered around that time, because that was around
the time that the majority of primatologists on
earth suddenly became female and started looking
at the female end of things and discovered that this
linear access stuff is not, in fact, what occurs. And out of that came a
completely shocking concept that ran through primatology
like a bolt of lightning– the notion that there was–
this is the technical term– some degree of female choice. Oh, whoa. That’s kind of bizarre,
where females have something to do with who they mate with. And there’s been a whole
world of primatology studies since then showing what
female choice is about. First off, how
does female choice occur in a typical
tournament species? You’ve got this problem. With primates, for example,
you wind up with a pair bond, with a consortship between a
male and an ovulating female, and because it’s a
tournament species, the male is twice
the size or has big huge canines or whatever
stuff he’s got there. He is physically able
to dominate the female quite readily. You do not see female choice
in those cases being exerted by the female
beating up on the guy and her getting to go mate
with who she’s interested in. What you see is much
more clever behavior on the part of the female. She will, for example,
exhaust the guy. Every time he sits down
to feed, the female gets up and starts walking. And he has to jump up and
pile together the picnic and go running after her. Every time he tries to take
a nap, she goes walking. Or what you find with baboons
is the most clever thing that females do is they go
walk and leave the male right in front of his
worst rival, or then they’ll do it again
and again and again and get the guy totally
harried out and crazed, and at some point, those
two males will have a fight. And what then happens is
she runs off to the bushes and has what is
technically called a stolen copulation with the guy
she’s actually interested in. Maybe it’s not so bad
to be a female baboon. So now what this
brings us to insofar as this alternative female
strategy is available, we now come to this
absolutely critical question, one that is run through
the ages, which is, what do female baboons want? Who do they want to mate with? And people are not
positive, but there is some suggestion in the data. It needs to be replicated more. There is this trend, but
there’s this suggestion that female baboons like to
mate with male baboons, who are nice to them. No, are they sure? Are they certain? Have they done their
statistics right? They go, and they mate with
guys who groom them a lot, guys who play with
their infants, guys who, when they’re in a
bad mood, don’t beat up on them but beat up on somebody else. This counts as a prince
of the male baboon. This is someone you
take home to meet mom. When he’s in a bad mood, he
pummels someone else, not me. This is someone you
want to mate with. And in the mid 1980s, excellent
primatologist Barbara Smuts of University of
Michigan came up with the very jargony
scientific term that all sorts of
non-human primates have intersexual friendships. And that’s not an
anthropomorphic term. What it was though
was people sort of snickering at it in
that the initial notion was that these were just friends. These were platonic
monkey relationships. They were not
about reproduction, and it was not until people
got good enough and enough data to start picking up on all
those stolen copulations to see that the
females were picking up and mating with their nice
guy– oh, we’re just friends. I could never see him–
whoa, and they’re suddenly in the bushes with him. And it suddenly turned from the,
yeah, nice guys finish last. OK, they do lots of grooming,
but let’s count the number of copies of genes,
to becoming apparent that the being a nice guy was a
viable alternative reproductive strategy as long as there was
this thing of female choice. And what the paternity
studies began to show was that was a very viable
alternative strategy, in part, because you’re not
mating anywhere near as much if you were a low
ranking affiliative male. With a female, you’re not
mating anywhere near as much as the high ranking males,
but you’re not burning out. You’re not getting injured. You’re not having the
male-male fighting. You live a lot longer,
and this keeps happening. There’s a problem,
though, which is suppose you are a
female baboon, and you want to mate with
this nice guy, and one of the things that
he’s nice about is he’s nice to
your kid, who’s now about three or four years old. And there’s a very
good chance that where that affiliative
relationship started with him got jump started was
the fact that he was the most likely father of that kid
and has developed somewhat of an affiliative
relationship with the kid and hangs out with them
and hangs out with you. And so you’ve
established this is a nice guy I want to mate with. But there’s a problem,
which was if he was the likely
father of your now three, four-year-old
offspring, the odds are that three,
four years ago, he was a pretty high ranking male. And what that means now
three, four years later is he’s likely to be some
aging guy over the hill, whose rank has been dropping. In other words,
not someone who is going to be very effective
at male-male competition, and you get this
horrible sort of tension there going on between the
male-male competitive world generates some Arnold
Schwarzenegger jerk, who’s the one who’s supposed
to be where she wants to mate with Alan Alda or whoever. And what you have
then is he’s not up to the male-male
competitive stuff, because he’s some aging guy. And you instead have the
world of stolen copulations. So isn’t that great? Isn’t that heartwarming? A whole world of what are now
called alternative strategies. If you’re some scheming
male baboon wanting to pass on as many
copies of your genes, you may decide the
really manipulative thing to do is to be
nice to some female and groom her more
than she grooms you, which is a very rare
thing for a male baboon to do. So great alternative
strategies, very heartwarming. Not so heartwarming,
because there are other alternative strategies
available in some species, alternatives where male
sexual behavior is not the outcome of explicit
male-male competition, but instead takes an
alternative strategy. And you see one example
of this in orangutans. Orangutans, great
apes, and they’ve got a very interesting bizarre
social system, but what you have is your basic,
nonetheless, sort of familiar picture of male-male competition
with a large percentage of orangutan male
aggressions built around the reproductive
access to females, and you’ve got a whole
world of very peripheralized low ranking males
who never mate. And there’s an
interesting physiology that goes along with it. That was the picture that
everybody used to have, and then in the 1970s, pioneer
researcher in this, Birute Galdikas, who has studied
orangs for decades out there in Indonesia,
she noted something really disturbing,
which is low ranking, non-reproductive male orangs
have an alternative mating strategy. What do they do? They rape females, and this
was the first introduction of that term into
zoology, and that is not an anthropomorphism. If defined as a violent
process of mating with a female against
her will, this is what goes on in orangutans. A certain percentage
of reproduction is low ranking guys who
have no direct access to females as a result of
male-male interactions. This is not the nice
guy alternative, so there is precedent
for this also. And this is by now very
well-documented behavior among orangutans. Then if you want to
call it with something very subtle and clever,
there’s apparently this whole world
of fish species, where low ranking males
can pretend to be a female and take on female coloration
and pretend to be just friends and someone they
can pour their heart out to, and then suddenly one
day they have a penis, and where’d that come from? And everything
suddenly changes there. OK. So we have the very
strict boring models. Females invest more
calories than males, and, thus, they are
much more picky. Males mate with females
entirely as a function of male-male competition,
and thus, evolution is driven by male
aggression and all of that. Let me just see as
people are clearly about to run out the door. For more, please visit
us at stanford.edu.
Hi, I’m Cynthia Kenyon and I’m going to be talking about genes that control aging. So, you all know what aging is. There’s an example of it in the slide. And for many years, people thought that aging was just something that happened. You just wear out like an old car. But I guess in the early 1990s or so, in the late 1980s, I started to think more and more that aging was going to turn out to be subject to active control by the genes. And the reason I thought that is because everything else that people think just sort of happens in a haphazard way in biology turns out to be regulated in a very elaborate way by the genes. For example, if you look in nature what you see is that different animals can have really different lifespans. A mouse lives only two years, but a canary lives 15 years, and a bat can live 50 years. So, these animals have extremely different lifespans in spite of the fact that they’re about the same size, and, even if they’re living in the same place, they have very different lifespans. And the reason they have different lifespans is because they have different genes. So that says right off the bat that there’s something about these genes that’s influencing their lifespan. So the idea that I had was, look, if there are genes that actually control aging, then if we change these genes we ought to be able to produce an animal that lives longer. And then if we study the genes in more detail, we’ll be able to understand how aging is controlled. So we didn’t study this problem in people. Instead, we studied it in my favorite little animal, C. elegans, which is shown here for you that this is an old individual. Now, what C. elegans is, is a very tiny little round worm that lives in the soil. It’s about the size of a comma at the end of sentence. Very tiny. And they’re really good for studying things like aging because they grow old and die in just about two weeks. And we wondered, “Could C. elegans teach us anything about aging in humans?” Because obviously, we like our worms, but we don’t really only want to learn about the worms. We really want to learn about people and higher animals, mammals. So the question of course is: could studying aging in one of these little round worms teach us any thing about humans? And I thought that the chances were pretty good that it could because the idea that I had was that aging was actually going to be controlled by genes- a set of genes that would be controlling aging in all animals. And the reason I thought that is that many biological mechanisms that control other aspects of biology, like how a muscle cell differentiates or how an egg is fertilized, or how a cell divides happen in the very same way in all animals. And, in fact, lots of genes that are important for people were first discovered in these little C. elegans. OK, now, we were very optimistic starting out that we would be able to find genes that extend lifespan. And the reason was that there already was an animal that had an altered gene that lived longer. And this was a mutant that had been identified by Michael Klass and studied by Tom Johnson for a long time. These worms lived about 30-50% longer than normal. So we set out to look for long lived mutants and amazingly, we found that mutations that damage one single gene in the worm, a gene whose name is DAF-2, doubled the lifespan of the worm. So here you see a diagram of the lifespans of these worms. So what we did is we took a whole population of worms and we just let them age and asked how long they live. So these here in black are normal worms here. And you can see that by day 30, the end of a month, they’re all dead. So the fraction alive, what you see is over here, is now 0. Whereas at the same time, our mutant worms, the worms that have only one gene change, all the other genes are the same, are almost all still alive. And it’s not until about twice as long, until 70 days, when they’re all dead. So, it’s incredible really. We just changed one gene, all the other genes are the same, and the whole animal lives twice as long as normal. And the really magical thing about these worms is that it’s not that they, you know, get old and just hang on. They actually age more slowly than normal. So here you see a normal C. elegans worm, quite beautiful, crawling along on its bacteria. So this is a movie of these worms. What you’re going to see first are the normal worms. Here it is. A normal worm when it’s about the age of a college student. It’s three days old, so it’s a young adult. And you can see that they’re very healthy. Now what you see here is the mutant worm, the one that’s going to live twice as long, when it’s also a young adult. And what you see is that it’s very healthy. That’s important. It’s not sick when it’s young. Now here, prepare yourself because this is a little bit sad, is the normal worm in just 2 weeks. You see? Now the head here is moving. See the head? See it move? There. But otherwise, it’s just lying there. It’s in the nursing home basically, the old folks’ home. You’re going to see some more worms in just a second. This worm is dead. And again, this one, you see its head is moving but otherwise it’s just lying there. So these are what worms look like when they’re old which is just when they’re 2 weeks old. And here is our long lived mutant. One gene change, that’s all. And look at it! See? It looks healthy. It’s moving around actively. They look much younger than the worms… and this is like actually looking at someone who’s 90 and thinking that they’re 45. That’s what it’s like. So it’s like a miracle, but it isn’t a miracle. It’s science. OK, so we want to know everything we possibly can about how changing one gene can produce this miraculous appearance-a worm that doesn’t get old on time. The gene was cloned in the lab of Gary Ruvkun at Harvard. And Gary’s lab showed that the DAF-2 gene encodes a hormone receptor. So here I’ve drawn for you a cell. This circle here’s a cell. And here we have the DAF-2 receptor, which is situated in the membrane of the cell with one part out in the environment and the other part inside the cell. And here are hormones that it’s receiving here in green. OK, so, what we have found was that the normal function of this hormone receptor is to speed up aging. That’s what this arrow means. It means it promotes the aging process because when we damage the gene with a mutation, the animals live long. So the normal function is to speed up aging. So, together our finding, along with the Ruvkun lab’s findings, demonstrate that aging is controlled and it’s controlled by hormones. Specifically, there are hormones in the worm that are speeding up the aging process. They’re making the worm get old faster. Now, the really cool thing about this hormone receptor is that it’s similar to two hormone receptors in humans, the receptors for insulin and IGF-1. These are two very well known hormones. They’re known to do the following. Insulin is known to promote the uptake of nutrients into the tissues after a meal and IGF-1, the IGF-1 receptor, is known to promote growth. And so what our findings suggested in these little worms was that maybe these hormones had another function that nobody knew about, which is to speed up aging. Remember I told you that a lot of processes that happen in these little worms happen the same way in higher animals. OK, so the idea was that if these hormones are speeding up aging in worms maybe they would be speeding up aging in other animals as well. And that actually turns out to be the case as shown here in this slide. First, over here we have the worm. This is the situation in C. elegans. So we have the insulin and IGF-1 hormone activating (that’s what this arrow means) the receptor. And when the receptor’s active it blocks longevity. That what this little cross bar is. It means “blocks” longevity. So people who work on fruit flies, the Tater and Partridge labs made the same kind of change in the gene that encodes the fly hormone receptor for insulin and IGF-1. And what they showed was that the flies lived longer. That was true if you changed the insulin/IGF-1 receptor or genes that act downstream of the pathway, down here. And in mice, there are separate genes for the insulin receptor and the IGF-1 receptor. There’s one gene that encodes the insulin receptor and another one for the IGF-1 receptor. And it turns out, amazingly enough, that if you change either one of these genes mice can live longer. So first of all, the Halzenberger lab showed that if you make a mutation in the IGF-1 receptor, in other words what you really do is… A normal mouse has two copies of the gene, one from its mother and one from its father. But if you make a mouse that has only one copy, so it’s a heterozygous mouse, it has half as much receptor. And what they found was that these mice live long, about 20% longer than normal. They’re very healthy. They were completely fertile, and they had a normal metabolic rate. The Kohn lab showed that if you remove the insulin receptor specifically from the fat tissue the whole mouse lived longer and these mice were very lucky. If you fed them a high fat diet, they didn’t get fat. OK, so it’s really quite amazing because what this tells you is that the insulin/IGF-1 hormone system is controlling aging in all three of these very different kinds of animals which suggests that it was actually controlling aging during evolution in a common ancestor of these three animals. And that common ancestor also gave rise to humans. So, it suggests the possibility that maybe these genes also control aging in us. So what about higher organisms? Do we know anything? Well, very recently we learned something about dogs. Now, dogs as you know come in different sizes. Here’s a Great Dane and here’s a little Chihuahua here. And it turns out that small dogs live a lot longer than large dogs. So large dogs like a Great Dane live only 5-7 years, whereas these little small guys can live up to twenty years. So it’s very different. And what was shown very recently was that the reason that these small dogs are small is because they have a mutation in the gene that encodes IGF-1, which is the hormone that we’ve been talking about. So that makes them small and as I say, small dogs are long lived, so it makes them long-lived as well. So, this is really interesting for lots of reasons. First of all, these small dogs, they’re real animals. I mean the mutants are real animals, but they’re laboratory animals. But these small dogs are fully functional, happy, little, intelligent, little creatures. So, that’s one thing. You can have this low level of IGF-1 and they have much lower levels of the IGF-1 hormone and be very healthy. But it also raises a question. The question is: Would they have to be small to be long-lived? So in other words, the IGF-1 gene is promoting two things, growth to be a big dog number one and number two, long life. So can they be separated from one another? Or would be you have to small to be long lived if you’re a dog? Well, I think the answer is you would not have to be small, and I’ll tell you why I think that. First of all, if you go back to this chart, the worms that we study are not small. The fruit flies, if you make mutations in this gene here, in the insulin/IGF-1 receptor the flies are small and long lived, but if you just perturb the pathway slightly just a little bit not too much, then you get flies that are still long lived, but they’re not small. They’re big and long-lived. Same with these mice. These mice here are not small. They don’t get fat, but they’re not particularly small. And these mice here, the IGF-1 receptor mice, the heterozygous mice are almost completely the normal size. They’re just a tiny bit smaller, almost completely normal. And yet the mice live long. OK, so in all these animals it’s possible to uncouple the two of them. And the second thing is if you think about it when would the hormone be needed in the life of the animal to make it large? Of course it would be needed during childhood, when it’s developing into an adult. When would the gene be needed for aging? Well, maybe not until it’s an adult. So, we did this experiment. We asked, “When is the gene needed to control aging in our little worms?” OK, this was done by Andrew Dillin when he was a post-doc in the lab. So the question is: When does the DAF-2 receptor gene affect lifespan? So what we did was to turn the activity of the gene down in different times in the animal’s life. And the way we did this was to subject the animals to something called RNAi. Now if you don’t know what it is, don’t worry to much about it. Basically, all you have to know is that it’s a way of inhibiting the function of any gene that you want. This is how it works. If you feed a worm. Well, let me start over. If you introduce double stranded RNA for a worm’s gene or any gene into an animal or into a cell, the double stranded RNA will initiate a process that leads to the destruction of all of the mRNA messengers in the cell (or lots of them anyway) for that particular gene. And with worms, what’s really cool is that you can have bacteria express a worm gene in the form of double stranded RNA and then you can feed the bacteria to the worms. The bacteria go into the worms. They eat bacteria. They go into the worms and then somehow the double stranded RNA gets out of the bacteria and into the worm’s cells and it catalyzes this break down of messenger RNA inside the worm which essentially does the same thing as making a mutation in the gene. It knocks down the activity of the gene. So we did our timing experiments in the following way, where we just took our worms and we grew them on bacteria, normal bacteria until we wanted to turn the gene down and then we took the worms off that bacteria and put them on bacteria expressing double stranded RNAi sorry, double stranded RNA for the gene and let them eat that bacteria. So here’s what we found. We found that if we turned the activity of that gene down throughout life, that is if we put the worms on these RNAi bacteria from the time of hatching, they had a long lifespan. So now, here, the control are normal worms that have the DAF-2 gene completely active. And here is what happens if you subject the animals to this RNAi from the time of hatching. And sure enough…so they have the gene down when they’re growing up and when they’re aging and they live long. So what happens if we just turn it down only during adulthood? Look, they live just as long. You see? So that tells us that the DAF-2 gene acts during adulthood to affect lifespan because if you don’t have it on when the animal’s an adult, if you turn it down when it’s an adult, if you don’t have it on it doesn’t…live correctly, it lives too long. OK, and we did other experiments where we turned the gene down during development and then we turned it back up when it was an adult, and those experiments told us that DAF-2 acts exclusively during adulthood to affect lifespan, OK? So this gene is acting during development, you know, to do what ever it has to do. For example, promote growth in these dogs. But then, at least in worms it’s acting in the adult to control aging. And there are hints that it’s also acting in mice to control aging in the adult as well. OK, so basically, it would be really interesting to take a tiny little dog like a Chihuahua that’s going to live, say, 15 or 20 years and give it IGF-1 when it’s a puppy and let it become a big dog and lower the IGF-1 levels when it’s a adult and see if it lives long, and I bet it would based on these experiments. OK, so this is all very good for our pets, but what about people? Could this little worm, C. elegans actually lead us to the fountain of youth? And I don’t have the answer for you, but I can tell you that there are some interesting unpublished data floating around so keep your eyes open. OK, so now, how do these hormones ultimately affect the rate of aging? How does a hormone coursing around through the circulation affect the aging of an animal? Wrinkles, grey hair, the nursing home, the whole shebang? Well, our first clue came when we discovered that another gene, a gene called DAF-16, is required for these daf-2 mutations to extend lifespan. So, here in this graph you can see what happens if we take away the DAF-16 gene in a daf-2 mutant. So in red here you see the long lifespan of the daf-2 mutant and what you see in green here is the mutant that…it still has the daf-2 mutation so it should live twice as long but we took away the daf-16 gene and now you see it doesn’t live long anymore. So, DAF-16 is like a fountain of youth gene. It’s a gene whose normal function let’s you live long. In fact, we call it “sweet 16” for youthfulness. OK, so what is DAF-16? Well, we cloned the gene, and it was also cloned in the Ruvkun lab, and it encodes a transcription factor. That is, it makes a protein that goes in the nucleus and binds DNA and switches genes on and off. So, if there ever were a regulatory protein, that’s it. In other words, there’s no question that aging is subject to regulation or to control because in order for these animals to live long, they have to be expressing genes at different levels. OK, so there’s definitely a control system for aging. OK, so what is it that the DAF-16 transcription factor is controlling that lets the animals live long? First of all, before I go into that let me just tell you a little bit more about the DAF-2 pathway. So basically, I showed you before the DAF-2 receptor. And what I’m showing you here in this slide is a summary of information that was gathered from a lot of different laboratories, primarily the laboratory of Gary Ruvkun but with important contributions from the Riddle lab, the Thomas lab, our lab and Johnson’s lab. So what you see if that the way the hormones affect gene expression is that they activate a highly conserved phosphorylation cascade or a kinase cascade which ends up phosphorylating..these little yellow circles here are phosphate groups attached to the DAF-16 transcription factor. And when this happens the DAF-16 transcription factor is not able to accumulate in the nucleus. But, if you make mutations in DAF-2 or any of these downstream genes here then the transcription factor no longer gets phosphorylated, and it does accumulate in the nucleus where it regulates genes that affect lifespan. So, we needed to know: What are those genes? What are the genes that affect lifespan? So nowadays there are really very good ways of asking what genes in the animal are changed under a certain condition. So worms have about 20,000 genes and you can actually profile all these 20,000 genes using a technique called microarray analysis to find out which genes are expressed at a higher level or more active or which genes are less active in the long lived mutants. So Colleen Murphy, a post-doc in the lab did that. She subjected these worms to microarray analysis. What she found is that DAF-2 controls the expression of many different downstream genes. OK, so here what this slide shows is the DAF-2 receptor when it’s turned down by a mutation let’s say. The DAF-16 transcription factor becomes more active so that up arrow means more active and as a consequence the expression of a lot of different genes changes. Some go up, some go down. OK, so that’s interesting. Now, just because a gene is more or less active doesn’t mean it has anything to do with lifespan. It could just be more or less active and not doing anything. So we had to test that. So the way we tested this idea that these genes that were changing were doing something to lifespan was again we used this RNAi technique. So we took…we just made a list of all our genes and at the top of the list we had the genes whose expression changed the most in the long lived animal and at the bottom we had the ones that changed the least. And we just started marching down the list, testing the activity of each individual gene with RNAi. So we went to the refrigerator, opened it up, got the bacteria out of it that were…or the freezer I guess, got the bacteria out that expressed each one of these genes whose expression changed in the long lived animal and then we fed the long lived mutants those bacteria and we asked, “OK, if you knock down like, this particular gene here, if you knock it down, if it can’t go up anymore, can that worm still live long? And what about this one and what about this one?” And that’s what we did. And what we found was that lots of different genes affected lifespan. So this shows you that inhibiting the activity of many of the genes that are turned up in the long-lived daf-2 mutants shortens their lifespan. OK, what you see here in black is the long lifespan of the daf-2 mutant, and here as a control in this line you see what happens if we subject these animals to RNAi for DAF-16, the transcription factor. So, now we don’t have the transcription factor so they can’t live long. But here what you see in color here are the lifespan curves of lots of different populations of worms that have been subjected to RNAi for any one of a number of those genes that were more active in the long lived mutant. And you can see that now they don’t live as long. So, all of these genes here and more are needed for the long lifespan of the daf-2 mutant. And there were some genes that were turned down in the long-lived mutants. So we asked, “OK, are those genes preventing long lifespan? If so, what would happen if you turned them down in the normal worm?” So, we did that and what we found is that many genes that were turned down in the daf-2 mutants also affect lifespan. And what we did here is we turned them down in normal animals. So, here we have a control. It has a normal lifespan, OK? And each one of these lines here corresponds to a set of normal worms with a good DAF-2 gene, in which all we’ve done is to turn down one of these many genes that are less active in the long-lived mutant and you can see that they’re living longer. So, it’s really interesting. Both the genes that are turned up and the genes that are turned down in the long-lived mutants make a difference. OK, so what are these genes? Well, it turns out they do many different things. Some encode antioxidant proteins. Some of these had already been shown to be more active in the long lived mutants by the lab of Gordon Lithgow and others, and we discovered some new ones. But all together they include genes like superoxide dismutase, metallothionine, glutathione S-transferases, catalases, a whole variety of anti-oxidant proteins and as I say inhibiting the function of these genes shortened the lifespan of the long lived mutant. There were also genes that encode proteins called chaperones. Now, what’s a chaperone? A chaperone is a protein that just like the name suggests takes care of other proteins. A chaperone protein will bind to another protein physically and it will help it assume the right shape, or if the protein is damaged it will actually escort it to the cell’s garbage can so the cell can get rid of it and make a new protein. So, these genes encoding chaperones were more active in the long lived animals and that made a difference because when we turn the activity of these genes back down with RNAi, the worms didn’t live as long. We also found a set of genes that are part of the worms innate immunity system, genes whose protein products kill microorganisms. These genes were much more active in the long-lived mutants. And that’s very interesting because we showed… before that we had shown that if you feed worms bacteria that can’t divide, that can’t proliferate, the worms live longer suggesting that they’re actually dying from infections and sure enough these long lived animals, the daf-2 mutants, actually have more active anti-bacterial genes. And actually the Ausubel and Ruvkun labs showed that these long lived animals are resistant to pathogenic bacteria. And then there were metabolic genes whose activities were changed. So, for example, there are some genes that whose normal function is to make proteins that transport fat around the animal from place to place and these genes were less active in the long lived animals. And when we made the genes less active in normal worms, they live longer. And that’s interesting because genes that transport fat or whose protein products transport fat around the animal have been implicated in the ability of people to live to be a hundred. People who live to be a hundred are called centenarians and it turns out that a lot of centenarians seem to have mutations in genes whose function is to transport fat around the body. And the mutations cause the genes to be less active just like these long-lived worms. So there may be a link between this part of the worm pathway and centenarians. And that was discovered by Nir Barzilai and other people. OK, other labs, also, using different techniques identified individual genes that are controlled by DAF-2 and DAF-16. And again, they found that when they inhibited their activities in many cases they affected the lifespan of the animal. OK, so now let’s look at the big picture here. What we’ve seen is that these two genes, DAF-2 and DAF-16 together control a wide variety of subordinate genes, lots of them. See, all these genes here, not just one but many. OK? So, it’s pretty neat. It’s actually kind of like a regulatory circuit or a little cassette in which, you know, these control genes up here say, you know, “Dance!” and all these genes down here say “OK, I will.” So it’s kind of like an orchestra where here we have the flutes and the violins and the cellos and the French horns and so forth. Each doing something different, but all doing…everybody doing it at the same time. And actually, I should point out…I didn’t really emphasize this, but it’s important, when you change any one of these genes you get an affect on lifespan that is not as big as the effect that you get when you change daf-16 or daf-2 suggesting that they act in a cumulative or additive way to produce these huge effects on lifespan. I just wanted to point out that DAF-16/FOXO, the transcription factor, is actually a really important regulator of lifespan. You can get C. elegans to live long as I said by changing the DAF-2 pathway, the insulin/IGF-1 hormone pathway, but you can also get them to live long by changing other genes. You can get them to live long if you over-express the gene encoding a protein called Heat Shock Factor which is a stress response protein that protects worms from heat, worms and other animals from heat. Another stress response protein called Jun kinase or a histone deacetylase protein called SIR-2. Over-expressing any of these proteins in the worm extends lifespan. And interestingly, in each case the lifespan extension requires DAF-16/FOXO. OK, so while the drawing that I just showed you has, you know, DAF-16 and DAF-2 up at the top and then it branches down at the bottom, maybe it’s more like a network where you have lots of inputs- one from DAF-2, one from SIR-2, one from Jun kinases and so forth into DAF-16 which is like a node in a regulatory circuit in a way and then you have another bifurcation where you regulate all the downstream genes. OK, so DAF-16 is a key regulator. So, what does it all mean? Why should insulin and IGF-1, which are essential hormones, why should inhibiting them extend lifespan? Insulin and IGF-1 are very important, and they’re very good for you. If you don’t have them you die. If you’re a worm, if you’re a mouse, if you’re a dog, or a person, anybody–everybody dies. So, they’re very important because they promote growth and food storage. So, again, why would inhibiting their activities extend lifespan? Well, I think this is the way to think about it. I think that what happens is that when you lower the level of insulin or IGF-1 you actually shift the metabolism of the animal from one that favors growth and storage of food, and things like that, to one that favors maintenance. So, low insulin/IGF-1 signaling or high heat shock factor or high Jun kinase or high SIR-2 activity promotes cell maintenance and kind of resistance to stress. And actually these long lived animals are very resistant to lots of environmental stresses. This was shown by Tom Johnson’s lab, first by Pam Larson’s lab actually a long time ago and more recently also to other stresses by Gordon Lithgow’s lab. But basically, they’re resistant to heat, to UV, to hydrogen peroxide, to paraquat, to all sorts of things. And it may be that the same proteins that make them resistant to these environmental insults also allow them to be resistant to the toxic products that build up say from reactive oxygen species generated by the mitochondria during normal lifespan. So there may be a connection between the resistance that an animal has to environmental stress and its ability to live long. And, like I said, some of those downstream genes that I told you about do both. They make the animals resistance to environmental stress and to aging. OK, so the way to think about it is that you can shift the physiology from one that favors growth to one that favors stress resistance and maintenance. OK, and then there are lots of different ways I think to accomplish this shift-by lowering insulin/IGF-1 levels, by activating SIR-2, heat shock factor, lots of ways. OK. ` So what are the implications for this? Well, the implication again, as I said, is that a longevity regulatory module exists. So, this is a regulatory module for lifespan. This is a little set of gene interactions that’s built into the cell that allows the animal to live longer. We didn’t have to introduce something from Mars to get these animals to live longer. We just briefly perturbed genes that they already have. And because they are connected to one another in this way functionally we get the this big affect on lifespan. So this actually brings up an interesting question, which is how could this regulatory module evolve? How could it have come around in evolution? Well, it could be that there’s an advantage for the worms to get old. So they have, you know, genes that allow them to get old. For example, maybe it prevents an older animal from competing with its progeny which in the case of the worm has the exact same genes because C. elegans is a hermaphrodite so it reproduces by self-fertilization. So that’s one possibility. But there’s another possibility and in order for me to explain this other possibility to you I have to tell you a little more about the lifespan, or, sorry… I have to tell you a little more about the lifecycle of C. elegans. And I’ll do that here in this slide. Now, what you see up here is the egg. This is…C. elegans hatches from an egg and then it grows up to be an adult. And it goes through these four different stages called L1, L2, L3 and L4 and then it becomes an adult. Now, that’s what it does if there’s a lot of food. But, if you take a C. elegans egg and you put it in an environment where there’s not a lot of food and where the animals are all crowded together, what happens is the animals don’t grow up. Instead of becoming normal L2d’s here they actually, oh sorry, normal L2 animals here. They become L2d animals here. And then they enter a state called dauer. Now, what’s a dauer? Dauer is a German word that means “enduring.” And this is a kind of…it’s like a hibernation kind of state except it’s not really hibernation, it’s also sort of like a bacterial spore. Anyway, these animals can move around, but they don’t eat, and they don’t grow, and they don’t reproduce. They’re arrested. They’re sort of suspended in time. And if you then give them food again, they exit from this dauer stage and then they grow up and become L4s. OK, so I should also tell you the only time an animal can become a dauer is before puberty. Puberty is when the reproductive system matures and that happens at this time. So, if you take an adult animal and you restrict its food, it doesn’t become a dauer-only at this time right here. OK, so what does this have to do with the evolution of aging? Well, let me just tell you this, if you turned the DAF-2 gene off instead of just down (we turned it down when we got these animals that live long) but if you turn it off what happens is the worms hatch… well, if you turn it completely off it’s likely that they die, but if you turn it down really far what happens is that they hatch from an egg here and then they grow up to become dauers. They don’t grow up, they become dauers. OK. And then they just stay there. They never grow up. So that means that you need the normal function of the DAF-2 gene to grow to be an adult. Now remember I told you that we found out from doing timing experiments that DAF-2 acts during the adult to affect aging. Of course, it acts during development to affect the dauer because it has to. It has to be on at this time in order for the animal not to become a dauer. That is, to be able to grow up to become an adult you have to have the gene on at this time. And then we show, like I told you, that you have to have it on again in the adult to age normally. OK, what the DAF-2 gene is doing is two things: during development, it’s preventing the animal from becoming a dauer, and during the adult it’s preventing the animal from living longer than it would otherwise live. OK, so we know already that a lot of the same genes that are…whose expression is changed in the long-lived adults that allows the worm to live long, that those same genes have a different expression in the dauer. They’re turned either up or down, same as the adult in the dauer. And dauers also are resistant to all sorts of stresses. Like, if you take a dauer and you heat it up, it doesn’t die. If you put hydrogen peroxide or paraquat on it, it doesn’t die. If you shine UV on it, it doesn’t die. So they’re very stress resistant just like the long-lived adults. OK, so it’s possible that this lifespan module that I’ve been telling you about didn’t evolve to control the lifespan of the adult. Maybe instead it evolved along with other dauer specific functions to allow the dauer to live for a long time. So think about this. If…what this means…the fact that the animal can go into dauer is very beneficial for it. Because it means that if food is limiting it doesn’t have children that will all die. It just stops and waits for conditions to improve and then it grows up and has children. So, it’s obviously very advantageous for a worm to be able to become a dauer. You can see that there’s great survival benefit and that would be selected for during evolution. But, once you have the regulatory system up and running, so that it can extend lifespan of the dauer (dauers can live a very long time) well, there it is. It exists. So, it seems like it’s possible then to elicit at least part of this program in the adult so the animals can live long. Now, I should say, the long-lived adults-they’re not dauers. They’re very active. They eat, unlike a dauer. They can be completely fertile, unlike a dauer. So, they’re not completely dauers. Just like little dogs aren’t dauers, they’re normal little animals. OK. but I think that the same…like I said the same regulatory module that can allow the animal to become.. to live long can also be used to protect it. In fact, it would be interesting to study mammals when they’re hibernating to see if they have low levels of insulin/IGF-1 activity or high levels of DAF-16 activity. That would be very interesting. OK, so it could have evolved to permit survival in response to environmental conditions of the dauer. But, once it’s already up and running the same system is there so it will automatically influence aging in the adult. And this also leads me to suggest that changes in either the regulators, like DAF-16 or DAF-2 or SIR-2 or heat shock factor, these other regulators or in the downstream genes like the chaperones and other genes may be responsible for increasing lifespan during evolution. So, in other words maybe the bat lives a lot longer than the mouse because bats have either lower, less active regulators or more active regulators or less or more active downstream genes. OK, the next question I want to ask is a very interesting one having to do with hormones. The question is: Could some kind of environmental signal affect the activity of this DAF-2 pathway? Now, one thing about hormones is that…the cool thing about them is that they don’t have to be there all the time. They can be…a hormone can be present under some circumstances but not others. So, for example, the hormone testosterone is present in a developing XY human embryo. And that’s why the XY embryo develops into a male, but is not present in the XX embryo. So that’s an example of a hormone being present under some conditions but not others. So, is it possible that there are some kind of environmental conditions that affect the activity of this DAF-2 pathway so that you could slow down aging? I should just note that all the changes that we’ve made so far are changes where we actually reach in and change the gene itself. We make a mutation in the gene. But, what I’m trying to suggest here is that maybe it would be possible to change the activity of the pathway by changing something in the environment. OK, so the first obvious idea is caloric restriction. So, this is a rat, a picture of a rat. And if you…a normal rat lives about three years here. But if you calorically restrict a rat, that is if you give it less food than it wants to eat it will live a lot longer. And not only that, it stays disease resistant, they don’t get cancer or a lot of other age related diseases. It’s kind of magical. It’s really neat. And…so you would think that the insulin/IGF-1 pathway would mediate the response to caloric restriction because when you eat food your insulin levels rise. And so, I just told you that if you keep the insulin level down, and IGF-1 levels down, you live longer, at least in these animals. So, it’s a nice model to think that if you…when you don’t eat enough you lower the level of these hormone pathways, the activity of these pathways and as a consequence you live longer. It’s a very pleasing idea and it seems like it’s probably right. It’s not really clear actually yet whether it’s true in the worm. It may be and it may not be. There’s some conflict there. Or it may be in some conditions but not others. But it is pretty clear that caloric restriction…that the response to caloric restriction is mediated at least in part by the insulin/IGF-1 pathway in yeast. Yeast actually also have a little insulin/IGF-1 pathway. They don’t have the actual hormones, but they have some of the genes that are downstream of the receptor, one called AKT, here. And if you change this gene, the yeast actually are small. They’re tiny little yeast and they live long. And it turns out that that pathway, the group of Brian Kennedy and others showed that pathway is required for the response to caloric restriction. In fruit flies the Partridge lab showed that the same thing is probably true. And in mice there’s some really cool experiments recently from the Bartke lab. Now, I didn’t tell you this already, but the hormone IGF-1 is produced under the control of another hormone, growth hormone. So growth hormone, which is made by the pituitary gland, stimulates the release of IGF-1. And mice that lack the receptor for growth hormone are also long lived. And what Andre Bartke showed was really interesting. He showed that if you took these long lived mice that don’t have growth hormone receptor and you calorically restrict them, they don’t live any longer. And it’s pretty cool. You take a normal mouse and a long lived growth hormone receptor mutant mouse. One is already living long-the growth hormone receptor mutant mouse and that mouse, its tissues are very sensitive to insulin already. When you calorically restrict this mouse, the mutant mouse, it doesn’t live any longer and it doesn’t become any more insulin sensitive. But when you calorically restrict the normal mouse, it becomes just as insulin sensitive as the mutant mouse, and it lives just as long as the mutant mouse. OK, so it kind of turns into that mutant mouse in that physiologically sense. Although, it’s not a mutant, it’s just a hungry mouse. The cool thing is both lose weight. In fact, these growth hormone receptor mice are just a little bit on the chubby side to begin with. But they lose weight. So, it looks as though these growth hormone receptor mutants are actually reaping the benefits or caloric restriction without going hungry. So, OK, now I get to the most important part of my talk which is to acknowledge the people that did the work that I talked about. Now, this list of names, these are people that did the work in both part one and part two of my lecture series. But the work I just talked about was done by…first it was started by Ramon Tabtiong. Ramon was a rotation student who came to my lab and discovered that daf-2 mutants were long lived. And I was so happy, because it was extremely hard to get anyone at the time to come and studying aging. People generally thought that aging was something that just happened and there was nothing to study. So, I was very, very lucky that he came to the lab. Colleen Murphy did the work on the lifespan regulatory module that I talked about. She did the microarray analysis. And she showed that some genes were turned up in the long lived mutants and others down. And that that made a big difference. Andy Dillin did the timing experiments I talked about showing that the DAF-2 gene and DAF-16 also act exclusively in the adult to affect aging. And Kui Lin over here, Kui cloned the DAF-16 gene and showed that the protein that is encoded by the DAF-16 gene is a transcription factor that regulates gene expression. OK, see you in part 2.
In the “The Martian,” astronaut Mark Watney
uses a slightly…smelly source of fertilizer to grow food on Mars, mixing Martian dirt
with feces to create soil for his potatoes. But the idea of using human by-products on
a deep-space exploration mission isn’t so far-fetched. In fact, it’s probably essential if we want
to make the months-long trip to the red planet for realsies. Human waste is inevitable, but rather than
thinking of our bathroom leavings as a dead end, space researchers see them as an appealing
resource. Astronauts on the International Space Station
already drink their own urine. Ever since 2009, filtration systems on the
station have been able to convert water from sweat, showers, and yes, pee into drinking
water. In a multi-step process, the water is carefully
filtered by vacuum distillation. Then it’s treated with iodine to kill any
bacteria and comes out squeaky clean. It does in the US-built part of the station,
anyway. The Russian-built water reclamation system
doesn’t use urine. Which means whenever the astronauts get a
chance, they haul bags of pee from the Russian side and feed it into the American reclamation
system. No point in letting that water go to waste. Water isn’t the only thing in urine. It’s packed with carbon and nitrogen, locked
up in a molecule called urea. It’s a good bet that if a molecule has carbon
and nitrogen in it, then there’s a microorganism that can eat it. Which is how researchers from Clemson University
plan to convert astronauts’ urine into plastics and nutrients using some mighty microbes. Specifically, yeast. Yeast are super great. They give us beer, bread, and in the future,
maybe brain food. This little superhero is called Yarrowia lipolytica. To grow it in space, astronauts would feed
it algae grown from the recycled carbon in their breath. But it would also need nitrogen. Fortunately, it thinks pee is delicious. With all that tasty good stuff from breath
and pee, this space yeast could become a living recycling plant. That’s because they are carbon master craftsmen. They’re great at making oils and fats, stringing
carbon together in long chains to produce a huge variety of energy-packed products. A little genetic tampering by humans can shape
what products they make, and how much of them. One thing the researchers want the yeast to
make is omega-3 fatty acids. You may have heard of these as the healthy
fats abundant in fish. They’re needed for proper brain function
and may improve heart health. Inconveniently, our bodies can’t make omega-3s. We have to get them in our diet. And as supplements, omega-3s have too short
of a shelf life to last through your joyride to Mars. So these yeast are being engineered to become
supplement powerhouses, producing omega-3s that astronauts can harvest from some of the
growing yeasties and eat. Which means the yeast will be making plenty
of brain food so our astronauts can continue scienceing. But that’s not all the researchers want
to harness this handy little yeast for. Future space missions will rely on 3D printers
to make tools and other things that astronauts will need on the fly. That 3D printer still needs plastic to make
things from, though. Enter our hero yeast once more. The fats and oils this yeast produces are
made mostly of carbon and hydrogen. But those same organic raw materials are also
what you need to make plastic. The yeast can actually be genetically engineered
to spit out PHAs, which are a kind of polyester — the same kind of plastic fiber that pops
up in your clothes. Which means this space-faring, pee-swilling
yeast could make not just nutritional supplements, but raw material for plastic tools that astronauts
can use. Just don’t think too hard about where that
wrench came from. The yeast makes plastic as a way of storing
food for itself to eat later. Yum, plastic. I love soda bottles, don’t you? That means it can be hard to get the PHAs
out of the yeast, which is holding on to its precious food supply. There could be a way to engineer the yeast
to feed right into the printer, but the researchers aren’t sure yet, and they might end up using
a more traditional extraction method. Basically, space researchers are thinking
hard about how to recycle everything astronauts touch–again and again and again–on an atomic
level. The yeast is just one way to tackle some of
these problems, and we’ll probably need lots of creative engineering to get astronauts
to Mars in one piece–and eventually, to bring Matt Damon home. Again. Seriously, why do we always have to keep saving
that dude!? Could you swallow supplements knowing they
were grown from last week’s pee? Let us know in the comments, and give the
thumbs up and subscribe buttons some love while you’re there. And hey, thanks for watching!
Hello friends Welcome to surjeet’s biology tricks biology made easier Today we will talk about fungal diseases Occuring in humans as well as animals, asked in NEET, AIIMS and other competitive exams, So, let’s play
Hello and welcome to Biology Professor. Today, we will be talking about one way that you can distinguish most types of bacteria. Most bacteria fall into one of two categories. Gram-Positive or Gram-Negative So first, let’s talk about the Gram-Positive type of bacteria. The way they are distinguished is between differences in their cell walls. With the Gram-Positive cell wall, Tte two most important features are a thick layer of peptidoglycan and one membrane. Let’s look at this in a little bit more depth. This thick layer of peptidoglycan is important for structure of the cell and for helping the bacteria cell maintain its shape. Then you have this inner wall zone that is between the thick peptidoglycan layer and the single membrane. Within this plasma membrane, you have two main components. These are the lipids which are shown here, a lipid bilayer, and also several different types of proteins. I’ll mark these with an asterisk (*) each. So these are all proteins that serve different functions within that plasma membrane. Finally there is one other distinguishing characteristic that you see in Gram-Positive cell walls and this is what I have indicated here with these blue lines. These are called lipoteichoic acids and these anchor through the peptidoglycan layer onto lipids in this lipid bilayer. So these are lipoteichoic acids. And now if we look these are some common examples of Gram-Positive bacteria. That I am sure you have heard of Staphylococcus aureus can actually be part of the normal human bacterial flora. Actually, a majority of humans have staph in their nose and on the skin. But it can also cause disease. Specifically some strains of Staph. aureus can cause food poisoning and they can also cause infections of the skin and of the respiratory tract. There is also Bacillus anthracis which causes Anthrax. Clostridium tetani which is responsible for Tetanus. and Streptococcus mutans this is usually associated with cavities in the mouth.
So, this is the structure of a Gram-Positive cell wall. So now we are going to continue our conversation about the difference between Gram-Positive and Gram-Negative cell walls. This time looking at Gram-Negative cell wall. We still see some of the same components. There is still a plasma membrane. It’s still composed of a lipid bilayer and it still contains proteins. That I will label here with an asterisk (x). There is still a layer of peptidoglycan, but you can see that compared to Gram-Positive peptidoglycan layer, in Gram-Negative cells, this peptidoglycan layer is much, much thinner. and also unique to Gram-Negative cell walls, this peptidoglycan layer is anchored to an outer membrane, so a second lipid bilayer, with additional proteins. Now in the outer membrane there are some proteins that are called porins. These porins allow for passive diffusion of things from the outside into the space between the two membranes, which is called the periplasmic space. These porins allow most things to diffuse through as long as the can fit. There is nothing specific about that. The actual selective permeability of the cell is still controlled by this inner plasma membrane. Now another very important feature of Gram-Negative cell walls is what is on the very outside of the this outer membrane. LPS, or lipopolysaccharides, this a component that is only found on the outside of Gram-Negative cell walls. and that has very important consequences when you have infections of Gram-Negative bacteria in the blood. This LPS, you will also hear it referred to as endotoxin. for exactly that reason. Now lets look at some examples of Gram-Negative bacteria. You have probably heard of a lot of these. E. coli is one that we hear about a lot as a pathogen because it can cause food poisoning. But it is actually a normal commensal part of the human flora. So it is not always pathogenic. There is also Helicobacter pylori, which causes ulcers and stomach cancer. Vibrio cholerae, which causes cholera. Yersinia pestis, which causes plague. This is the bacteria that is responsible for the historically famous Black Death. Also, Salmonella enterica, which is another common cause of food poisoning. So that concludes our explanation of the differences between Gram-Positive cell walls and Gram-Negative cell walls. If you are interested in more information about how these two types of bacteria are distinguish between when diagnosing illnesses or when studying them in the laboratory, please see my video on the Gram stain procedure and also thank you for watching.
Captions are on! Click CC at bottom right to turn off. When I was a little kid, my parents would
let me take my favorite set of dinosaurs into the tub…probably to persuade me into taking
a bath. I remember my dinosaurs well! In fact, I used to know all of my dinosaurs. I had epic dinosaur battles. Sometimes my sister would play with them,
too…just…a little differently. Anyway, I remember that one day, unfortunately,
my favorite stegosaurus lost his head. I mean, literally, it just popped off. And while I was determined to get my parents
to fix it, we discovered that there was stuff growing in the toy. Now, I realize what was actually large enough
to be visible was likely mold, but at the time, my mother told me that Sergeant Stegosaurus
would have to retire from the bathtub, and I’d have to get a new one because bacteria
had taken over. It led to two misconceptions I developed about
bacteria: (1) that bacteria were only found on or in things that had gotten contaminated
somehow and (2) that bacteria are always bad and that is why Sergeant Stegosaurus required
replacing. Those are both not correct. First of all, there probably were bacteria
in the dinosaur along with the mold. But that shouldn’t be surprising, because
bacteria are everywhere. Bacteria are found in our houses- yes, even
very clean houses- and they are found outside. Bacteria colonize our skin and our digestive
system. That addresses the first misconception that
you only find bacteria on contaminated or “dirty” surfaces. And as for the second misconception, well,
bacteria sure do get a bad reputation. Now I’m not disagreeing that the toy should
have been thrown out. That was a good decision. There was probably mold that was in that toy
dinosaur- a fungus – but there was likely plenty of bacteria growing there with it. A growing community of mold and bacteria…not
ideal for a bath toy. But we do want to mention that many times,
all bacteria are lumped together as a bad thing- which shouldn’t happen, because not
all bacteria are bad. In fact, many types of bacteria are helpful
for organisms and ecosystems. We’ll give you some examples. Some of the bacteria that colonize your skin
are beneficial and actually help keep harmful strains and other types of pathogens from
growing. Bacteria in your digestive system actually
help break down food and some can produce certain vitamins. Some types of bacteria are used in producing
some foods that we eat. In ecosystems, bacteria have a very important
role as decomposers. Bacteria also have major roles in the nitrogen
cycle to fix nitrogen that plants need. These are just a few examples of helpful,
beneficial bacteria. Now that’s not to say bacteria can’t be
pathogens. Bacteria are the cause of strep throat, tetanus,
tooth decay, some forms of pneumonia, diphtheria, salmonella, cholera…I could go on. Antibiotics can be used to combat some of
these. And while antibiotics are very important for
destroying bacterial infections, we shouldn’t leave out saying that some broad spectrum
antibiotics can harm some of the “good” bacteria as well. Also, we should mention that antibiotics do
not work on viruses. Viruses are pathogens that are not made of
cells at all; you can check out our video on them. Additionally, there are vaccines which can
prevent many types of both bacterial and viral infections. Ok, so what are bacteria exactly? In the three domains of life, bacteria encompass
one of them. They come in different types of shapes as
you can see here. Some of them are heterotrophs—meaning they
consume or feed on some organic matter. But some are autotrophs—they can make their
own food. Plants aren’t the only one that can be autotrophs. Let’s take a look at a bacterium here—bacterium
is just singular word while bacteria is plural. A bacterium is a prokaryotic cell, which are
generally much smaller than eukaryotic cells like ours. If you recall from our prokaryotic vs. eukaryotic
cells video, that means bacteria do not have a nucleus or other membrane-bound organelles. But you will find ribosomes, cytoplasm, a
cell membrane, and nearly all bacteria have a cell wall. Like all living organisms, bacteria have DNA. Bacterial DNA, while still double stranded,
is arranged in a circular shape. Depending on the species, bacteria can also
have a flagellum to help with movement, a capsule which can help give them extra protection
or attachment abilities, or pili which can help with attaching to surfaces…including
each other. Oh, and many bacterial species have a plasmid. Which is basically like…extra DNA. More about that later. Bacteria have some intriguing abilities that
are different from our human cells that we’d like to mention. Unlike our own body cells which perform mitosis
and cytokinesis to divide, bacteria generally multiply even faster in a process called binary
fission. This is a type of asexual reproduction when
the bacteria can easily divide to make a copy of themselves. Since it is asexual reproduction, the daughter
cells would be expected to be identical to the parent cells unless there is a mutation. Some types of bacteria do have the ability
to share genetic material with each other. Remember how we mentioned that bacteria can
have a plasmid—an extra copy of DNA with usually just a few genes on it? Bacteria can share these plasmids with each
other in a process known as conjugation. The pili can be used to share this genetic
information with each other. If the plasmid happens to have a gene that
gives some degree of resistance to an antibiotic, this may allow the bacterium that received
the plasmid to survive exposure to that antibiotic. Which could be very problematic. You can learn more about how antibiotic resistance
can develop over time in bacteria in our natural selection video. Bacteria can also pick up plasmids from their
environment. Often when this happens it is during a time
of stress for the bacteria. In a process known as bacterial transformation,
scientists can use a type of stimulus—such as a heat shock—to induce bacteria in a
lab setting to pick up genetic material. There are all kinds of these uses for these
genetically engineered bacteria that you can explore. Some types of bacteria can form endospores. Endospores allow bacteria to be survivors
in all kinds of hostile environments: lack of nutrients, freezing temperatures, drought…just
some examples. This is a reason why hospitals have to be
very good at sterilization processes. We won’t go through the process of endosporulation—or
how bacteria reactivate after forming endospores—but this is definitely something interesting to
explore Finally, some types of bacteria (along with
other types of prokaryotes called Archaea), can be extremophiles. Unlike our own cells, extremophiles can live
in extreme environments where there may be excessive heat, chemicals that our cells would
find toxic, or even radiation. Overall, we share this planet with so many
kinds of bacteria that scientists continue to learn more about them every day. And if this kind of topic interests you, you
may want to look into the study of microbiology. So many careers- from agriculture to the medical
field to environmental work- rest heavily on the study of microbiology. Well, that’s it for the Amoeba Sisters,
and we remind you to stay curious.
>>Ladies and gentlemen welcome to the
2013 Royal Society GlaxoSmithKline Prize Lecture.
I’m Jean Thomas, I’m the Biological Secretary and I have the housekeeping
duties of asking you to turn off your mobile phones, please, because the lecture
is being recorded and webcast. And also, to tell you in the that
actually, I hope, unlikely event that there’s a fire, you don’t go out through
the usual doors but you, because of the snow and whatever, you go out through
these doors instead. So, 2013 is the Royal Society Year of
Science and Industry. This is the year when the society will
showcase excellence in UK industrial science and strengthen links between the
society industry and academia. The Royal Society recognizes that world
class research and development in the UK industry is essential for transforming
innovative ideas into commercially successful products into its economic
growth and securing the science space. And it will be proactive in anticipating,
understanding, and responding to the needs of industry’s scientists.
Symposia and meetings with high industry interests have been added already to the
society’s calender which already includes longstanding initiatives in scientific
excellence, such as the Royal Society Industry Fellowship and the Brian Mercer
Awards for Innovation and Feasibility. So, the year of science, science and
industry will bring a renewed focus on engaging with the industrial sector to
develop cogent arguments that high level investment in the UK science space is
essential for international competitiveness.
Something we would all, I’m sure, sign up to.
Now, to the prize and the lecturer, the Royal Society GlaxoSmithKline Prize and
Lecture is awarded biannually for original contributions to medical and veterinary
sciences published within 10 years of the date of the award.
The prize consists of a very nice gold medal, an even nicer check for 2,500
pounds, and the recipient is called upon to deliver an evening lecture at the Royal
Society which is why we’re all here this evening.
And this is really a, a capacity audience, and the reason we’re a few minutes late
starting is that there is an overflow room, and I don’t remember that in the
last, certainly, in the last four years of chairing these evening lectures.
So, Adrian has really put in a big crowd tonight.
So, no pressure there, Adrian, at all. It was, the award was initially
established following a donation from the Wellcome Foundation.
First award was made in 1980 the centenary of the work and foundation and since 2002,
it is being supported by GlaxoSmithKline Limited.
So, this year’s recipient of the prize is Adrian Bird an old friend and colleague,
I’m delighted that he’s received this award.
Adrian has held the Buchanan Chair of Genetics at the University of Edinburgh
since 1990. And he’s a member of the Wellcome Trust
Center for Cell Biology in Edinburgh. His research focuses on the basic biology
and biomedical significance of DNA methylation and other epigenetic
processes. His laboratory identified CpG islands as
gene markers in the vertebrate genome. And he discovered proteins that read the
DNA methylation signal to influence chromatin structure.
Mutations in one of these proteins, MECP2, and I’m sure we’ll hear a lot more about
this, this evening, causes the severe neurological disorder Rett Syndrome, which
is the commonest genetic cause of mental retardation in females.
Adrian was made a Fellow of the Royal Society back in 1989.
He’s received several awards, numerous awards for his work, including notably the
Louis-Jeantet Prize for Medicine, the Charles-Leopold Mayer Prize of the French
Academy, and the Gatineau Prize. This evening, it’s the turn of GSK and the
Royal Society to give him this special GS Royal Society, GSK prize.
And has to give his lecture in order to earn that.
His lecture is entitled, as you can see, Genetics, Epigenetics, and Disease.
So, Adrian, over to you.>>Thank you very much, Jean.
Thank you very much for this award. It’s a great honor to, to be asked to give
this lecture. And thank you very much for braving the
elements to come and listen. I think, probably the title of Genetics,
Epigenetics, and Disease is broad enough that it sounds like it’s going to change
all our lives in this next 45 minutes. But in fact, I’m going to focus on a
relatively small part of it ultimately. But I’m going to start off reasonably
broad. There’s one deliberate mistake on the, the
first slide. I hope it’s the last one.
It’s the year. So let’s go back in time to the draft
sequence of the human genome because this was a, heralded as a, a time when biology
really became a, a hard science. If you like, it was seen as the, the
beginning of the end. We now knew the entire code for all, we
knew the sequence of all the genes required to make a human being.
But it’s pretty clear that it was actually the end of the beginning.
And the somewhat apocalyptic predictions that now one simply had to automate, the
discovery of all the medical innovations that would result from the genome sequence
was premature. In fact, it’s likely in my opinion that
there’s still another century of biology to be done and this will be an exciting
century of discovery converting the promise of the genome into the reality of
biomedical applications. And that, one of the issues I think that,
that, that we would really love to be able to solve, a big, a big question if you
like, is where DNA, despite being the thread of life, you can put it in a tube
and gaze, gaze at it for as long as you want and it remains utterly dead.
So the question is really what does it take to make it alive?
When Craig Venter synthesized a bacterial genome an important synthetic biology
milestone, it had to be put into a living cell before it became alive.
How can one bypass that? As the chemists say, you only really
understand something if you can make it. We can’t actually make life but it would
be good to know some of the rules required to do that.
So, some key unanswered questions about the genome that, that remain and this is
only a selection. First of all a basic fact, genes make
proteins, here is the chromosome, here is the sequence of the genes, there is the
RNA. It encodes the sequence of the amino acids
that lead to the protein that folds up to then do all the lifelike things that are
required. But how are only the right genes expressed
in a cell type? This has been a question, a long standing
question. Do we know the answer to it?
Why globin is expressed in blood cells and keratin is expressed in skin cells,
etcetera. We, we approximate knowledge about it, but
actually, there’s an enormous amount to find out.
Most of the genome is actually inaccessible.
This is this gray, it’s rather difficult to look at this picture I think because
the DNA is gray and looks although it should be in the background but this is a
nucleusome, the repeating unit of the, of the chromosome, if you like.
The fundamental repeating unit. And the DNA clings to the outside of it.
And proteins that want to make genes active, can’t actually get at the DNA
properly. So, how does the gene activation machinery
gain and how does it keep access? Again, we have some beginning answers to
this, but we don’t, by any means, have a full picture.
Protein-coding DNA sequences are only 1% of our genome.
So, if you look at a piece of the human genome, you see these vertical stripes
correspond to the bits of this gene that are separated from each other.
In fact genes are fragmented and they are a tiny minority of all the DNA.
What is the rest of it for? There is an enormous, there’s a vast
majority that is, that we can’t explain. This isn’t the case with all organisms.
This, for example, is yeast, and you can see now the genes are packed together.
It’s difficult, it used to be said casually that the rest of this DNA was
just junk. But now, it’s sort of almost politically
incorrect to call it junk. It’s particularly after the encode project
which found lots of potential regulatory sequences throughout here.
So, this other DNA is doing stuff. And perhaps, it’s doing stuff that makes
for example, humans and other mammals far more complex than yeast.
So finally, there are questions almost sociological questions.
Does the environment have any impact on gene expression?
And this is a, a question I’ll allude to in a moment.
But it’s not one that is the main subject to this, this talk.
So, I put in the title Epigenetics because I’m quite mine, our work is quite often
described as epigenetics. It literally means above or in addition to
genetics. But the definition has been controversial
and I’m just going to skim somewhat lightheartedly over some of this because
it’s, it’s at meetings to do with Epigenetics.
One can see various opinions expressed with varying degree, this one I believe
was in Barcelona with great vehemence. So, let me just try to sort of consolidate
this. The original epigenetics definition comes
from Conrad Waddington, who was actually my predecessor as Buchanan Chair, Chair,
Chair of Genetics in Edinburgh. And what he meant was in contrast to
pre-formationism, but the development proceeded by the gradual unfolding of the
information in the genes, to produce the whole organism.
So, for him, how information of the genes is read during embryo, during embryonic
development to give the whole organism was the essence of what epigenetics was about.
We would now call this developmental biology.
How the genotype gives rise to the phenotype.
But it’s acquired, or a sort of, a special status in epigenetics, really, because of
this iconic picture, the epigenetic landscape.
I’m not going to dwell on this either. Because quite honestly, having had it
explained to me several times, I’m never totally sure, exactly how this helps.
It’s a picture of a bull rolling down a hill.
The number of options for the bull get progressively less.
But I don’t feel that this encapsulates anything very useful.
This, however, is a fundamentally important question that remains on our
agenda. Second definition of epigenetics which is
rather different has actually different origins epistemological origins.
How characteristics are inherited across cells or organism generations without
changes in the DNA, its sequence, itself. An example of this is this cat, the
so-called tortoise shell cat, or calico cat, in, in, in the US, which has these
patches of fur. It has two x chromosomes.
One of them has a gene that gives black fur, the other one has a gene that gives
orange fur, and cells early in development, inactivate one or the other
of those chromosomes for, for reasons we don’t, which I will, I will come back to
actually, a little bit later. And you get a patch of skin because the
cell that originally inactivated the orange fur gene gave rise when it divided
to cells that did exactly the same thing. So, that was inherited.
All the gene or the, the DNA is still there in these cells, in, in the orange
ones, and the black ones, but there is difference that is inherited and that’s
epigenetic according to this definition. So, heritable traits of this kind might be
influenced by the environment. And this is sort of revitalized that an
ancient argument about nature versus nurture, where nature is genetics, the
idea that we’re, our genes are, are in control and nurture is the opposite, the
idea that our environment determines who we are.
Of course, it’s a mixture of both but epigenetics has given a, a, a new lease of
life to the nurture argument. And so, one can see articles such as this
and there are many examples I could have chosen why your DNA isn’t your destiny,
the new science of epigenetics reveals how choices you make can change your genes and
those of your kids. Now, I’m not an expert on some of the
epidemiology behind this, but the, the molecular biology, in my opinion, is far
less convincing than it is for other aspects of epigenetics.
It is, however, an extremely interesting idea, that the environment can give rise
to changes that get passed on, but it is systematically overstated in a lot of
places one finds it described. So, one has to be circumspect about the,
this kind of argument in my opinion. There are couple of excellent examples in
plants, in worms where immune, immunity is involved, but some of the more
sociological aspects, in my opinion, require further evidence.
So, I’m sticking with this as my example of heritable epigenetics.
It’s closer to the molecular biology we actually understand.
So, Epigenetics 3, biological significance of the epigenome.
Another definition, it’s risen pragmatically.
What is the epigenome? Well, here is a genome of a, of a cell.
It’s, it’s the chromosomes that were obviously designed for an experiment
because there are fluorescent pinpoints here.
Ignore those, that’s a human chromosome compliment.
If you explode those chromosomes, you see beads on a string and this is that
repeating unit I referred to earlier, the nucleosome with the DNA going round the
outside. It looks like beads on a string.
So, the epigeno, epigenome refers to markings of those beads, of that string of
beads in such a way that the region, it is regionally, regionally adapted to its
function. So, for example, there can be a region
where gene is stably ON, and there is a whole plethora of marks that appear that
reinforce that decision. And similarly stably here, a gene OFF,
such as the black-coat gene in our orange patch of fur.
And again, you get adaptation, and this is the epigenome, and the study of what the
epigenome means, is another definition of epigenetics.
So, you have DNA methylation here where these methyl groups are added to the DNA.
You can’t do much to DNA without changing its propterties, its important properties.
Almost, the only thing it seems you can do is put these methyl groups on and even
that is bad in a way. I don’t have time to go into, it causes an
increase in the frequency of mutations. But the, by far, the most elaborate way of
marking the chromosomes, is via these beads which, invisibly on any of the
structures I’ve shown you before previously, have tails.
And these tails are basically ticketing entities that you can add chemical
information to. That the cells can write information in
the form of chemical alterations. And so, you add this and, that says,
stably ON or stably OFF. Again, we have the broad outlines.
We can correlate quite a lot of these with activity and silence.
But if you were to ask exactly what each of these modifications does, we have,
still have a lot to learn. So, if you like, it’s the, epigenetics is
the structural adaptation of chromosomal regions so as to register signal, or
perpetual, perpetuate altered activity states.
And importantly, proteins that read these marks, write the marks, or erase the
marks, remove the marks are implicated in human disease and quite a lot of
excitement in pharma including GSK is devoted to finding out what these drugs
might be good for in terms of human disease.
So, epigenetics then embraces key unsolved problems in Biology, how, how the genotype
give rise to phenotype, that’s the Waddington one, how traits are inherited
across cell or organism generations without changes in the DNA sequence and
how structural adaptation of the genome facilitates gene activity programs.
As far as I’m concerned, this is not a word one needs to dwell on with sort of
almost a theological interest about what it means.
Everything it possibly means is interesting.
So, let’s get on with studying it. And I, I like to think of it as how the
genome is organized and managed to make DNA if you like, come alive.
So CG is one such signal it’s one of those marks and you’ll notice CG is not actually
a, a mark, it’s actually a sequence, it’s a 2 based pair sequence.
Dna sequences that recognize proteins are usually longer than that because they’re
rarer. If you have a sequence of one base, every
few bases you come across it, and it doesn’t have much information.
Two bases is not much better, but nevertheless, as you will see, CG is used
as a genetic signal and also as an epigenetic signal.
So, here’s a piece of DNA, flattened out so it’s no longer helical.
Those two strands are anti-parallel and CG is paired with itself.
So, CG pairs with CG. This TA is paired with itself, but it’s
nearly so interesting. And one of the things we’ll talk about
that can happen to CG is that the C can get, gets methylated.
And that, since there are two of them, that can be a symmetrical event.
And it looks like this, they sit in the major grooves.
I’ve already shown you a different picture, though with less vulgar coloring
that shows the two methyl groups sitting in the major groove and they influence
interactions between proteins and DNA. So, what are the features that adapt CG
for a genome signalling function? The first is that, as I’ve mentioned, you
can get it in, in three different chemical forms, actually there are more than three,
there are another two but that, it’s not yet clear whether these are biologically
important or just by-products, at least it’s not clear to me.
You have CG unadorned, you have CG methylated, and you have CG where the
methyl group has had an oxygen added to it, and it becomes hydroxy methylated.
So, it exists in different forms. Specific proteins are attracted or
repelled by different modified forms and we’re going to talk more about that.
Highly variable in frequency, so then, the frequency of CG despite the fact that it’s
just a two base per sequence is dramatically different going along the
genome. In the bulk of the genome, 99%, it’s quite
far apart. These lollipops represent CGs.
The lollipops that are solid represent methylated ones and the open ones
represent unmethylated ones. So, 99% of the genome has not many CGs and
most of them are methylated. But then, there are these clusters where
the density is about 10 times higher and these are the so-called CG islands.
They are interesting because they sit right on top of the control regions for
genes. So, here’s a gene, it’s red in this
direction and then these blue bits are spliced together to make the messenger
RNA. And sitting right on top of the promoter
is this CG island, and this amounts to about 1% of the genome.
There’s another one there. And here’s a biological consequence of the
methylation. If you look at this CG island, it can,
under certain circumstances, this happens on the inactive x, this happens at
imprinted genes. It happens at germline genes in the soma,
it happens in cancer, abberantly. It gets methylated.
And when that happens, you shut down transcription of the gene.
And because methylation is something I haven’t gone into, is relatively stable,
it can be transmitted from one generation to another, if you like, copied.
When cells divide one cell generation to another, it’s this is quite a
stable[UNKNOWN]. So, one of the things DNA methylation
does, is it shuts down the expression of genes.
So, we’re gonna talk about specific proteins that are attracted or repelled by
modified forms of, of CG. And I’m gonna start just with a protein
that recognizes unmodified CG so it cant recognize this or this.
So, Cfp1, sorry about the acronyms, it’s a, it’s a protein that recognized, it was
discovered, in fact, by David Skalnik it binds to non-methylated CG.
I don’t know why I’ve drawn the DNA at this jaunty angle, but it, it just meant
to show that it’s interacting with it. And it also interacts with a complex of
proteins. An enormous complex, well, relatively big
complex, called set 1. And this complex does something to the
nucleusome. We’ve seen this before, this is the bead
on the string, the DNA going round the outside.
Haven’t, in, in, when you look, determine the structure of something like this, you
don’t find the tails, the things that you write on.
And so, I’ve drawn them freehand, nobody actually knows where they are because
they’re so floppy, they don’t come up in the x-ray structure.
But, amino acid lysine number 4 gets methylated and this is done by this
complex. So, we have a protein that binds to
non-methylated CG that recruits a complex that methylates this.
Now, why is that interesting? This is a mark of active genes, so if we
look where CG island are, CpG island as they’re more often called, in fact, here
are the CpG islands, I’m not going to tell you how we know they’re there.
But you’ll notice these, this gene is going this way, there’s a CpG island at
the start of it. This gene is going this way, actually
bidirectionally, there’s one going this way, one going this way, there’s the CpG
island. So, they’re all the CpG islands, there’s
the RNA polymerase, the protein, the machine that makes that starts to be
converted, copied into to messenger RNA. And it’s just at the beginning of them
because this is the, a particular form of RNA polymerase that is only at the
beginning of genes. And here is this mark, H3K4me3, which
means this purple blob on this tail, which is put on here.
So, we have the non-methylated CG cluster here and we have the mark, and this mark
is involved in gene expression. So could it be that the, the proteins
attracted by the CG brings in this and that’s what causes this mark?
If you look as, as we did where the protein is, it coincides with the CpG
islands. So, it’s in the right place.
If you take it away, the k4 trimethylation, this, these peaks here go
down and that’s consistent with the idea that this is reading the CpG island signal
but the key experiment is really the Pete Skene and John Thomson did is to insert a
piece of CpG-rich, CG-rich junk into the genome, real junk in fact, it’s not
actually quite junk, it’s the jelly fish gene that’s been optimized for expression
in humans lacking any control sequences, just inserted into the genome, so you make
a CG island like sequence with a cluster of CGs.
Now, are you creating a new H3K4 trimethylation peak?
So, here’s a, here’s a map of all the CGs. The vertical lines show where they are and
this is what we’ve inserted. And you can see the density of CGs has
gone up. And now, you can plot that density.
Now, where’s Cfp1, the protein that binds CG.
There it is. We’ve now got a new peak of it.
And what about H3K4 trimethylation? It’s there, too.
And you notice, where there’s most CG, there’s most, more, most of that
modification. Is there, have we just made a gene?
In other words, all the stuff that does geney things is there.
No. Because there’s no RNA polymerase there.
So, this is just the DNA sequence, talking to the chromatin.
And, and as one can do this with other sequences and verify that it’s the case.
So, a CG-rich piece of DNA creates a new region of H3K4 trimethylation, this active
promoter mark, even when there is no active promoter there.
So, the presence influences of the CGs influences the chromatin structure via
this link between the DNA binding proteins and the set enzyme complex and other CG
binding proteins also recruit, rcruit modifying enzymes.
In fact, for a long time, we were used to the fact that CG islands existed, but we
didn’t really know what they were for. And, and actually, one almost forgot to
ask, well, they’re always there, what are they for?
In fact, it now seems very likely that they are platforms to set up appropriate
genome structures at gene promoters. Very important function.
And there are other proteins that bind CG, that recruit other things to them, and
this is a very, a rapidly growing area. So, suddenly, we find that the CG island
is a, is a, is a, a structure of biological importance, and we’re starting
to disentangle how. So here is a CXXC protein which has its
domain. Cxxc is the name of the protein domain
that binds CG. It comes in wearing this ludicrous wig.
And creates a sunny promoter gene, gene activity friendly region of the genome.
If there was a methyl CG,it comes in and it is goes away.
It can’t bind. So now, I’m going to turn to for the rest
of my talk proteins that bind to the methyl CG mark, the one with the purple
blobs on. The purple blobs that were on the DNA, not
the purple blobs that was on, was on the histone tail.
So, what binds this form of CG? Well, a protein that we found a long time
ago is MECP2, and this binds, specifically, and I’m going to show you
some of the prehistory of this protein. First of all, a picture from the paper and
you could either take from this how prescient he was, to be able in 1992, to
find this protein that turns out to be so interesting.
Or you can think, he’s been working on that protein for 21 years and he’s still
not quite sure where it does. Let’s you can shoot, take your pic at the
end of, of the talk. So this shows how we first found it.
We run the proteins that are in a nucleus on a gel.
And then, we probe them with a piece of DNA that’s labeled and methylated.
And then, the same sequence of DNA with no methylation.
And clearly, there’s a protein that bind one that’s methylated and at about 84
kilodalton and doesn’t bind when it’s not. And we now know a structure for this in,
in an atomic detail. Here are the two methyl groups sitting in
the major group. And this is the domain of this protein
that interacts with them. So, we were happily studying this for
blue, blue skies reasons to, to try to find out a protein that read DNA
methylation and therefore a reader of DNA methylation, and find out what it did.
When Huda Zoghbi showed that the gene that causes Rett Syndrome, an autism spectrum
disorder, is almost exclusively, more than 90% MECP2.
So, this is the gene that is mutated in Rett Syndrome.
So, what is Rett Syndrome? This is a, a, a film just taken from
YouTube, not somebody I have ever met but you can see the characteristic features of
Rett Syndrome which involve this repeated hand clasping and a period of apparently
normal development saw 6-18 months, and then regression, progressive
encephalopathy, repetitive hand movements, breathing a, a, arrythmia, a, a profound
problem. But nevertheless, a life expectancy of
about 40 years on average. So, there is no effective treatment and
24-hour nursing is required. So, this was all caused not by a brain
gene, that was what was being looked for by everybody.
And those were in the days where you thought the gene would have something to
do with the, the, the tissue that was affected, but a basic housekeeping protein
that reads DNA methylation that’s expressed in every cell type.
So, why does this disorder only affect girls?
Well, you probably guessed it’s because it’s on the x chromosome.
Males are always more affected by mutations in genes on the x chromosome
than females because they only have one x and females have another one which can
compensate and males die. There is no male Rett Syndrome simply
because males don’t survive. So then you have a new mutation.
Nearly always as it happens like many of these things, paternally derived.
And then proceeds x chromosome inactivation.
I remember so, in order that females have only the same number of functional x
chromosomes as males, they shut one off. And this happens in random cells and I’ve
shown you the example of the cat and I’ll show you the cat again.
X, this gene, this cell inactive[UNKNOWN], this progeny of this cell inactivates this
x chromosome this one inactivates the other one and this then is inherited so
this is the epigenetic inheritance phenomenon it’s passed on.
And the end result is, there’s the wretched cat again but with his different
things, I will show you a different example of that in a moment.
But the, this, well, the point to be made here is that the brain and, in fact, the
other tissues of a Rett patient consist of a mosaic of a salt and pepper mixture of
cells that are functionally normal with respect to MECP2 and cells that are
functionally without normal, I mean, without MECP2.
So here, for example, if the phenomenon a new mutation arises, sometimes, that
mutation is the only MECP2 in the cell, and the other time, it’s invisible.
And you just get the wildtype express. So, this is the mosaicism.
Now, the equivalent of the cat picture in the brain, though, is rather different.
This shows the dentate gyrus of, which is a region of the hippocampus, which is part
of the brain in, in from a mouse, I haven’t talked about the mouse yet in any
detail but just to show you that you can see patches.
It’s probably better to see it here in the merge, this is MECP2 and it’s in blobs and
there are gaps. But actually, there aren’t gaps in the
nuclei staining and so there are patches of cells here that are inactivated the
functional MECP2 gene, and there are other patches here that function that
inactivated the non-functional MECP2 gene. And you see these patches, the point I’m
making here is the patches in a cat are gigantic and involves millions and
millions and millions of cells. The patches in the brain are, for reasons
we don’t quite understand, tiny and so you get a bigger mixture of functional and
nonfunctional cells in this tissue. So, the first thing we did when we found
this out was to make a mouse. We were gonna make a mouse anyway for our
blue skies reasons but now we were energized, I would say, and that
energizing has continued to the present day by the fact that we were working on a
human disorder and we’re actually in touch with a community of people who are
affected by it. So if you take a normal mouse, it lives in
this green state for a long time. But the MECP2 minus mouse, the male, the,
the equivalent of the human male that doesn’t survive, doesn’t survive.
And these colors are meant to indicate that they get symptoms, get worse and
worse, and eventually die. The female and this, this shows a, a sign
of neurological symptoms in a mouse. It does this hind limb clasping and it
does that at this blue stage here. Initially, there is no observable
phenotype. But later on, they become ill and
subsequently die. The females and these are really the true
model of Rett Syndrome because they’re heterozygous as, as geneticists say for
these mismutations. They’re fine, and that’s how you keep the
line going. They breed for several months and a mouse
at six months of age is quite an old mouse.
It’s had quite a few liters. But then, they suddenly hit a, a, a wall
and they become immobile and they develop all the other sorts of symptoms including
hind limb clasping, arrhythmic breathing lack of mobility that, that characterize
the Rett-like phenotype. And there’s a dramatic change in their
behavior but it’s stable, just as it is with humans.
So if you like though, the MECP2 deficient mouse is actually quite a good model.
Not all, not all models are, are particularly persuasive.
But it’s quite easy to persuade skeptics that this is a good model of this disorder
because a lot of the things that MECP2 seems to do in humans it also does in
mice. So, we’ve got, we’re armed with this
model. Now, how are we going to find out what
MECP2 actually does, and how that’s connected to the function of the brain?
Because that’s what’s gone wrong in Rett syndrome.
Well, the big resource you always have is in, in genetic disorders, is the mutations
that give rise to the disorder. Particularly, if, like Rett Syndrome,
they’re all new mutations. This does not run in families, the males
don’t survive and the females don’t reproduce either.
So, it doesn’t run in families everything is a new mutation.
And so, this is the sort of picture you get.
Everywhere, absolutely all over the place. But I will point out to you that these
frame shifts, these grey ones, the longest bars, everything downstream of that is
disrupted. Because the, the protein goes out of frame
when you start making junk afterwards. So, they don’t mark the spot where there’s
an important bit of this protein. They only tell you that this the boundary
between and everything downstream gets lost.
The other ones, the nonsense mutations, also stop the protein.
That’s, that’s why you put x here. They just terminate the protein.
The ones that are most informative are the missed sense mutations.
Because what’s happened there is, you’ve put an alien amino acid.
One single subunit of the protein in the wrong is wrong.
Everything before it, is fine. Everything after it is, fine.
Just that one amino acid is wrong. And so this is telling you the really
important bits. And if you’ll notice, the blue ones, which
are the missense are not randomly distributed.
So, we went into the database. Now, of course, for a lot of disorders
that look like they might be related to MECP2, and there’s more than Rett
Syndrome. I, I don’t have time to go into that.
People look at the database. And they start, sorry, they, they
sequence. And so, there’s an awful lot of
polymorphisms, a lot of, lot of changes that are not associated with disease.
The one way of being sure it’s associated with disease, is to look for mutations
that are not found in the parents. They’re only found in the offspring.
Cuz then, the probability that, that is, is a, is a function-less genetic variant
is, is vanishingly low. When you see very specific domains here,
interestingly and, I don’t have time to go into this, there are now more and more
xsomes sequences. People are sequencing genes of normal
individuals or for people who have other things.
And so, you can find all the missense mutations where there’s no obvious effect.
And what you notice is that this cluster here, for example, doesn’t have any genes
with no obviously effect. This cluster here the same.
So, you can use the, the normal polymorphisms as a way of seeing the
inverse of what you see with the mutations.
So, now we have two domains. What’s this domain?
Well, I’ve labeled it MBD. Actually, what that stands for is
methylated DNA binding domain. I showed you the x-ray structure of that
bound to methylated DNA. That’s the bit that contacts DNA and
brings this in, and many of these mutations prevent that.
So, we’re pretty clear what’s going on, I’m just going to tell you a couple of
things about that domain. The first thing that emerged when we
studied it was people, you tend to think when you find a DNA binding protein that
it goes to specific targets and then, it does stuff there and those targets are its
main function. But actually, it turns out, it turns out
that MECP2 is incredibly abundant in, specifically in neurons.
And in fact, there are 17 million molecules per nucleus in a cell.
And this is a lot it’s one every four hundred base pairs, it means there’s
enough to coat the genome and then that’s actually what it does.
Dna methylation goes up and down along a chromosome so this a very low resolution
picture and the MECP2 goes up and down in exactly the same way.
So, it’s, it’s not in special places, it’s all over the place, with somewhat
different densities and it’s very, very abundant.
It doesn’t behave like a transcription factor which goes to specific target
genes, it binds globally. So, that’s that domain, let’s now talk
about this domain and this is more interesting to us.
What’s more interesting to us, because we had no idea what it might be.
So, hypothesis was that this region binds to DNA.
And then, this region binds to some sort of partner that it brings in, and that’s
its job. And you can’t mutate that because it fails
to do that. And Matt Lyst really led this aspect of
the project. What he, we did, was we made a mouse with
a green fluorescent protein tag on the MECP2 and then we pull down that tag from
the brain, an extract of the brain of the mice that had it.
And then, we ask what came down with it, those of the partners?
And by mass spectrometry, we found these, these proteins.
This is the list of the top 8. Interestingly well, MECP2 came down.
That’s a relief. You expect, if it didn’t, you’d have a
real problem. Then two proteins that transport it into
the nucleus. But then these 5 subunits and more
acronyms, I’m afraid, of a complex that’s well-known.
This is a huge complex, more than a million daltons complex, which contains
which contains a histone deacetylase 3. So, what a histone deacetylases do is,
they remove a mark on one of the tails, that mark is associated with activity.
If you remove that mark, you work against gene activity.
In fact, you silence gene expression. So, this is a complex that reinforces the
silence of gene expression. Shuts the genes down by removing this
methyl group. So, here it is, there’s the methyl group,
PowerPoint extravaganza goes. So this, it’s well-known to buying nuclear
receptors. And it also, now we find that it binds to
MECP2. Now, where does it bind to MECP2?
Well, it binds it, you won’t be surprised to hear, exactly in this second domain.
And all of those mutations that cause Rett Syndrome in this second domain, abolish
the interaction with this, this complex. So, this mutant protein can’t bind DNA.
This mutant protein can’t bind NCoR SMRT. This what, which is the unfortunate name
for this complex. And also, you lose the ability to shut
down transcription. So we, we now have this fairly persuasive
model I think that MECP2 is a bridge. It’s a bridge between DNA, there’s a
methyl group MECP2 is attached to it. It’s brought in this complex which is a
gene silencing complex and if you have mutations in the DNA binding domain and it
can’t bring it in and if you have mutations in the complex interaction, you
can’t quite bring it in either. So, MECP2 then and other proteins that
bind metal CG, and there are others about which we know something.
They come in, bind. And instead of creating the sunny
atmosphere, they create a foggy trans, transcription-hostile environment.
I was going to say like, Edinburgh in January but it’s not really
transcription-hostile in Edinburgh. We express our genes perfectly well.
So then, the big question is, have we got any further now?
We know that, it’s likely to be a repressor.
And to you, it see, it probably seems likely that was always going to be the
case. Dna methylation represses transcription,
this binds DNA methylation, what more natural than it represses.
Actually, it’s a very controversial area, as to whether or not it does repress
transcription. And my feel is, is, is that the important
advance. So the question is what transcription does
it repress because it’s not obvious. When you look in the brains of the mice,
histone acetylation is up, histone H1 is up.
The epigenome is disorganized, expression of some genes is up, other genes is down,
other genes are down. Or and some are unchanged and these
effects aren’t very big. So, very, very briefly, I’m going to say
you could be controlling the activity of specific genes, you could be controlling
transcription in response to neuronal activity only when neurons fire, something
happens, this protein actually gets phosphate groups added to it, maybe that’s
something to do with it or dampening of transcriptional noise.
And this is a, a boring sounding possibility, it just kind of sits on the
genome and keeps everything down. But there’s some evidence for that, we
know that the transposons, which are selfish elements in the genome that like
to jump around when there is, normally, they jump around, represented by these
yellow dots, a very small amount. When you don’t have MECP2, they jump
around an awful lot more and so, in other words, MECP2 is preventing the expression
of the RNA that allows these things to move, and this is no function for the
organism. It’s actually something it would prefer to
keep quiet. So, that’s noise dampening, so this
question is unresolved. So now, in the last part of my talk, I, I,
I left you there with, that’s as far as we got with the Molecular Biology I’m afraid.
But I think we’re now making progress. Now, we know we have this bridge model.
Let’s now talk about the pathology and the trying to get all the way from the
Molecular Biology up to the patients, and our, surrogate for the patients which is
the mouse model. So what we really want to do is have a
molecular description of the legion in MECP2 and the count for all steps to, the
brain of the patient, so that we can understand.
And this requires we know an awful lot more than we do now, for example, how
brains work. So we’re trying to bridge this gap.
Now our involvement in this is really to do with one specific question and that is
this one. Can the symptoms be reversed?
In the pathology, as observed in post mortem brains and as seen in the mouse, is
that neurons are slightly simpler. So, if you put a, a bulls-eye over the
center of a neuron then its arms are more complex and branchy in a normal animal
compared to what they are in an animal that doesn’t have MECP2.
That’s about it for pathology. There’s no cell death so it’s not a
neurodegenerative disorder. It’s not like Parkinson’s or Alzheimer’s
or Huntington’s, where nerve cells die. It’s just a kind of shrinkage they become
underpowered neurons. So, the question then arises, if their not
dead, if we put MECP2 back, can it be reversed?
And I’m gonna tell you about that and then our attempts to do some therapy based on
that. So how do you, how do you have the, how do
you do this experiment? Well, what you do, is you take the MECP2
gene, you put a stop in it, which is just a chunk of DNA that is poisonous for
transcription and then you flank it with sequences that mean, that when you want to
you, and so that then causes transcription to stop.
You’re let the animal grow up, it has no MECP2 and it becomes ill as a result and
then, at your chosen moment, you remove that stop and start transcription again
and you can do that in ways that I, that have been published and I can tell you
about if, if you want to know afterwards but this works and that’s the first
surprise that actually works. And the reason why it works is because
Jacky Guy, who’s an unbelievably talented person in the lab is took charge of these
experiments. So, I’ve shown you the mouse that’s
wildtype, the mouse that’s male. What we’re going to do now, is look at a
mouse where it’s male, it’s on the, it’s in the death zone, if you like.
It’s and we interject it with tamoxifen, which is the way we trigger the deletion
of the stop cassette. Does it work?
Well, this is the, this is MECP2 in a normal mouse brain.
This is in a stop mouse brain. So, the stop works.
This, this looks like it’s cell that haven’t been stopped.
But actually, it’s blood cells that autofluoresce .
And then, you treat with tamoxifen and back comes the MECP2.
So, that works. And then, he is a mouse on, on the day we
started the experiment. So, it is grown up with no MECP2.
It have the classic symptoms of the MECP2 null mouse it has this tremor, it has
arrhythmic breathing which you may be able to see in the flanks.
They breathe and then it stops. They breathes and stops.
And it doesn’t move. And the film is much longer than this and
it still doesn’t move. And then when you humanely suspend it by
the tail, it, it does this hind limb clasping.
So, then, then the question is what does tamoxifen do for that?
And then, this is the same mouse a month later.
Under our animal license, this mouse would not be able to survive for more than a
week or two at the most. And here, it is a month later, remarkably
healthy. And it went on to live I wouldn’t say, a
natural life, but you know, a quite a long life.
So this is an unexpected finding, we didn’t expect it and it turns out nobody
else did either. And, and for that reason it was, it, it,
it’s turned out to be quite important in the field there.
This somewhat unedifying image of a mouse I will leave you and go, go on to the, the
females. Because, you know, those mice are young.
They’re only 6 or 8 weeks old, and so, it could be that they’re young and plastic,
and, and reversal therefore, works better at that age.
Also, they’re not real model of Rett Syndrome.
This is the real model of Rett Syndrome, and these animals are no longer young and
plastic. So, we want to do this experiment.
Inject with tamoxifen when the animals are 6 months old or so.
And then this just shows that this also works.
That’s a reversed animal, that’s a, a wild type animal, a normal animal and you can
see they’re indistinguishable. And this is an animal that was unable to
respond to tamoxifen for the, for the, because we genetically made it that way.
So, it’s still is obese, which is a characteristic of the females on this
genetic background. Immobile, and it does the hind limb
clasping and breathing arrhythmia and all that sort of stuff.
So, you can this, this mouse looked like that mouse when the treatment started.
So, the implications of this reversibility is that, obviously, Rett Syndrome is
potentially a curable condition. You have to use the potentially word there
because these are mice, not humans. But nevertheless, it’s encouraging.
It also means, Rett Syndrome, like most of the autism diseases, have been called
neurodevelopmental disorders. And the implication is that something goes
wrong during development in terms and that you can never recover from that.
And, and I, I think that when one thinks of brain diseases, brain disorders one
tends to think of them as irrevocable. And in, in actually, there’s no, the
experimental evidence to support that is, is not strong.
And this questions that, and there’s work with fragile X Syndrome as well, and other
so-called neurodevelopment diseases disorders that suggest that actually
they’re not neurodevelopmental at all. And, in fact, if you take away MECP2 in
adults, adults die. Certainly, not only required during
development, and so this reversibility may be more widespread and true than was
previously thought, and that can only be good in terms of exploring therapeutic
options. Everything we’ve done suggests that
actually what MECP2 does is sustain neuronal function.
These are cells that are never going to divide.
They take ages deciding who they’re going to be connected to.
And in an elaborate dance of synaptogenesis and culling of excess
neurons and then they never get to refresh themselves and so maintenance is probably
a vitally important function and I think MECP2 may be one of the proteins that does
that. So, that’s just a hypothesis at this
point. So, prospects for therapy, you could do
all sorts of things. And for time reasons, I’m not going to go
through this. I’m just going to talk about our attempts
to do gene therapy. The dose of this protein is critical.
So, gene therapy doesn’t sound very promising.
But I’m just going to show you some results.
Because I think gene therapy or more likely, gene editing, is the logical end
point of the genomics revolution. Having found all these genetic variability
associated with disease what better than to be able to fix it.
And I feel that where, this is what’s going to take awhile of basically
engineering to find out exactly how we should do that.
So, this by comparison with that aspiration, is very primitive.
This is a Adeno-associated virus. And the experiments here were done in
collaboration with Gail Mandel of Howard Hughes Medical Institute in Oregon and her
laboratory and[UNKNOWN] Helene Cheval did the experiments as well.
So we take this, this MECP2 promoter. We drive a, a truncated MECP2 gene, not
much fits into these viruses, and they don’t replicate.
You then, in put them in and there are 2 ways.
And you can go directly into the brain through 6 bore holes in the brain which is
very laborious. And this doesn’t actually work very well.
But what Gail Mandel’s lab did was to use this virus in an unexpected way, namely,
to put it in the systemic circulation system.
So, put it in through the facial vein or through the tail vein and then, in females
that are 7 to 12 months old. So, this is the real rats model and ask
what happens and their, their improvements are quite dramatic.
This is rotter rod, it’s a wheel you put a mouse on, turn it round slowly and they
fall off. But it takes them a while to fall off.
And actually, the first day they fall off more quickly than the second day when
they’ve learned a bit, and then the third day, they’re a bit better.
The animals, without MECP2 we’ve stopped MECP2 acquired sorry, without MECP2
acquired bad at this. But then, if you put in this virus, you’re
getting a significant improvement. This is the so-called inverted grid test,
which is simply taking the lid off the cage, and turning it upside down.
So, that’s rather a fancy name for that. And you see how long before they fall off.
And you see that the red the red bar is the way they are when you without MECP2.
And these, these are the rescued mice, they’ve improved a lot.
And the third test, and there are other tests I could show you, is the nesting
test. You weigh a certain amount of nesting
materials, you plonk it in the cage and then the next day you come back and see
how much of it they’ve used to make a nest.
So it gives you a number. And the not much of it is gone with the
mutant mice. A lot is gone with the normal mice, and
the rescued mice are vastly better. So I’ll finish up by showing you as the
final thing, a couple of mice. This is not as good as an experiment that
I showed you before. There, I showed you one mouse before and
after. This is, for obvious reasons a mouse
that’s had the virus, treated with an empty virus so it has the virus but it
didn’t have anything in it. And this is the, this is the way, it, the
symptoms looked in a females, that almost you can imagine the high, the, the, the,
the limb clasping very immobile and clearly not that healthy.
And then, this is an example of a mouse that whirls like that.
But now as, as a result, it’s a different mouse as a result of receiving the virus,
it’s vastly improved. This is the data of Saurabh Garg in the
Mandel Laboratory with whom we are collaborating.
So this, I would hesitate to say that this is a therapy that necessarily can be
adapted to humans rapidly because the viral load would be colossal.
The amount that gets into the brain is relatively small and 10% of humans have
antibodies against these viruses anyway. But it’s a basis.
So, research into the causes of Rett Syndrome is currently a hot area in
biomedical science. Epigenetics, yes, the epigenomes disturbed
in these mice and brain autism, these are fascinating areas that are combined in
this in this field. Findings over the past decades, actually
changed our perception of this disorder and by implication of others.
And by that, I mean, reversibility, because it was thought to be impossible.
The search for potential therapies is going on a pace.
I showed you what we’re doing. We are far from a learn, there’s lots
going on, and no approach is yet proven to work clinically.
There is a way to go yet, unfortunately, it’s frustrating that one feels one is
quite close if only one could engineer something that would do it.
And the goal remains to discover robust treatments that either reduce or even
eliminate the burden of Rett Syndrome. So, just to summarize then the whole
thing, we’ve ranged over quite a lot. Epigenetics is more or less how the genome
of living things is organized and managed. It’s a high level word.
There’s no worry about exactly what it means.
Every definition is, encompasses fascinating biology.
Cg is a genome signaling module, module. It’s very short, it sounds too short to be
useful but I hope you’re persuaded that actually it is used as a way of, say,
adapting regions, adapting regions of the genome to their function.
Proteins that read different chemical forms of CG, unmethylated, methylated,
lead to contrasting biological outcomes. And mismanaged, disorganized epigenomes
are involved in disease. And the extent to which they are involved
in disease, is actually profoundly unknown.
And, for that reason, epigenome manipulation, for example,
pharmacologically, may have therapeutic value in diversed human disorders.
Epigenetic drugs, so-called, are already in the clinic, the histone deacetylase is
its inhibitors, etc. And there are far more in the pipeline.
I would say that we don’t really know what they’re gonna be good for.
Because there could be all sorts of disorders where global epigenome mech,
manipulation has a consequence. And so, I think we’re in for exciting
times. This is my lab.
I, this is not my whole lab. This is just, it’s people who were in my
lab, whose data I’ve shown. People who are in my lab, whose, some of
whose data I’ve shown. Gail Mandel, who I’m grateful to for
allowing me to use our the, her data the data that was generated in her lab on the
gene therapy. Brian Kaspar, who made the viruses for her
and, and us. And Stuart Cobb and colleagues from
Glasgow University who are our nearest, tell us about neuroscience of which we’re
ignorant. And finally, all this plethora of funding
agencies from the very small to the very large who have made our work possible over
the years. And this is my lab.
I wanted to go to north of Scotland for our retreat.
They wanted to go somewhere hot and they won.
So, this is Barcelona again. Thank you very much.
>>Thank you, Adrian for a splendid lecture, and, and Adrian will now take
questions for ten minutes or so. There’s one over there.
If you if you have a question, if you’d like to ask one, put your hand up in
advance, there are two roving mics so we can send one near you so that we can keep
the questions coming.>>Hi there you recently published an
article in The New Scientist, about epigenetics I wonder if you’ve got time
just to mention a little bit about the post mortem suicide data that you came
across. You weren’t able to talk about it at
length in your article, but I wondered if you could briefly mention a point about
that?>>It’s not my data, it’s, it’s a report
that people who had committed suicide claiming to have been abused as children
were, had a different degree of methylation of a stress hormone receptor
promoter in their brains. And I don’t feel, and I’m not sure the
authors would feel despite their elevated status of the publication, that they have
achieved statistical significance with just 12 and also leaving out, as it says
in the method section, outliers, that presumably didn’t fall within their
average. So, I feel if you know, the way you treat
your children becomes hardwired in, into their lives at, through this epigenomic
mechanism I feel before one announces that to the world, one has to be pretty sure.
And I don’t feel, in this case, they could be.
>>At the back.>>If there’s a guard, guardian of the
genome, is there a guardian of the epigenome?
>>Sorry, I missed the very first phrase.>>If there’s a guardian of a genome, is
there a guardian of the epigenome?>>A guard, is there a guardian of the
epigenome, I don’t know, this is a phrase and people, I mean, guardians of the
genome are proteins like P53 that takes steps when the genome is damaged.
It’s not really clear if damaging the epigenome.
The epigenome is quite in a state of flux. There is no one epigenome.
Now, that’s really the problem with epigenome analysis, epigenomic analysis.
Every cell type will have a different one and actually, do , so it depends on your
stance, some people believe that the epigenome is somewhat fixed and the genes
operate within this rather inflexible set of rules.
I, from what I have seen, find the epigenome does what its told by the genes
and their transcription factors. In a way, the epigenome adapts the genome
to its function as determined by other proteins.
Now, that’s, there’s a question of degree between those 2 extremes.
But I don’t see the epigenome as something that gets fixed, and then is transmitted
forever, and you can’t do anything about it and even your grandchildren can’t do
anything about it, two generations later. That, there may be some of that going on.
But I feel it’s likely to be far less than is sometimes suggested.
It’s dried up the questions.>>Another one, 4 rows from the back.
Oh, there’s one here. Okay.
Speaker:[cough] Why does it take so long for clinical symptoms to become manifest,
both in the mice and in the humans?>>Let, that’s a very good question.
We actually haven’t the faintest idea, I mean, you could argue so in the case of
humans, the time when they get it, 18 months of age is a time of great activity
in the brain. And so, you, that sort of fuels the idea
that this is a neurodevelopmental disorder and you only really start getting the
problems when the brain is going through particular types of dance of the neurons
in particular synaptogenesis . But actually, in the, in the mouse, if one
looks at that, these mice are 6 months old, they’re, they’re not going through
any developmental processes at all as far as we know, they’re, they’re just
gradually aging like, like the rest of us. So in that case, it doesn’t quite fit.
And I think that the alternative hypothesis is, that without MECP2, the
functional half life of your neurons, not their lives but their functional half life
is reduced. And they, you, you’ve crossed some
threshold at which the brain stops to, stops working properly.
But actually, I don’t have a satisfactory answer for your question.
So, it’s, it’s one of the key questions.>>Hi, my questions is about gene therapy
and one of the limitations of this is that you can’t cause large enough change
throughout the entire tissue to correct the fault.
And I was wondering whether or not you thought that gene therapy had greater
therapeutic impications for epigenetic disease rather than genetic disease.
>>Well, I’m not quite sure about the link between the first bit of your, I mean, I
agree with the, the, the reservation that you have to hit a high, a high percentage
of cells. Actually, these adeno-associated viruses
do that. They’ve selected stereotypes.
They’re all naturally occurring, none of them have been engineered in any way and
so there’s scope to improve them. But they spread throughout the brain so
the systematic injection if you look in the brain, it’s everywhere.
So, it, it does get everywhere and if you do the injection into the brain, and these
are, there are clinical trials now for[UNKNOWN] disease, lysosomal storage
disease where there are 6 bore holes and they’re putting it in and they’re getting
a big spread through the brain of the, this virus.
They don’t, they don’t divide, and they keep churning out the protein for a very
long time. So, I think that sort of thing can be
solved. I wouldn’t say that gene therapy, I mean,
gene therapy, this is a blunder buster approach.
You’ve got, you’re shoving in an uncontrolled number of genomes into cells
different numbers into different cells. It’s, it’s the primitive end of what
hopefully ultimately will be a rather sophisticated therapy.
But I wouldn’t say it’s for epigenetic, rather than genetic.
I haven’t seen anything that suggests to me that it prefers one or the other.
>>Well, I, I was also going to ask, whether or not it was the case of being
the opposite when you said that the, the epigenome was constantly in flux.
So, does that mean using gene therapy to try and to correct the epigenome is
actually more difficult than gene therapy?>>What you’ve got to remember is that
Rett Syndrome is a genetic disorder. It’s, it’s it affects the epigenome.
There, there aren’t epigenetic disorders and genetic disorders necessarily.
This, the, the, the, the mutation is a standard mutation in a gene, and it’s
inherited in a Mandelian manner if you, you know, in those very rare families
where it’s transmitted. So it’s a genetic disorder that effects
the epigenome. It’s not an epigenetic or genetic
disorder.>>So, so, Adrian, do, do the virus
treated mice, do they stay cured?>>Well.
>>Or do they get well again when they get older?
>>That’s a good question and we don’t know because actually those pictures were
only taken within the last 4 weeks. They’ve lived for four weeks beyond that.
>>One at the very back.>>But actually, the model experiments say
that these things are expressed for a very long time.
They don’t ever get integrated, and for that reason, it seems they don’t seem so
susceptible to being shut down by the epigenetic mechanisms that are scouting
for strange things in the genome.>>Hello.
What’s your feeling about the big psychiatric disorders like schizophrenia
and bipolar affective disorder and so on? Do you think your research in these
epigenomatic processes, approaches are going to be important for those?
>>I don’t know, there’s a, you know people argue about autism.
As to whether or not it’s more environmental than genetic.
And there’s now really quite strong evidence that it’s genetic.
But it’s not one genetic disorder. It’s hundreds of genetic disorders,
actually, literally. There are very many genes that are
contributing to autism. That’s why it’s been so difficult to pin
down genetically. So, I would say autism, this work is
related to you know, relevant to, it’s difficult to know psychiatric disorders.
You know, they tend to, autism, despite being caused by large numbers of different
genes, where almost no two patients have the same set of genetic lesions,
nevertheless have common presentations, features that are in common among them.
So, it’s almost as though when there are problems with the brain, it gravitates
towards certain types of behavior. So, either it doesn’t work at all, in
which case, survival is, is in question or it gravitates toward certain types of
presentation. So, in other words, it says more about the
way in which the brain can cope than about the function of the proteins.
Now, I, I would say schizophrenia is a very interesting question.
They’re having meetings about schizophrenia and bipolar, always been
groups that go off and talk about the possibility that’s it’s pure, called
what’s purely by epigenetics and the environment.
But I think, increasingly, as more and more sequencing gets done, my bias would
be that they will find, we will find genetic causes for these disorders, and
then all of the[UNKNOWN] of ways of dealing with genetic disorders will be
drawn upon to try and fix that. To me, one surprising thing of that, if I
may,[UNKNOWN], the brain, you would have thought, is the most inaccessible place to
ever do stuff like gene therapy. But actually, it’s quite a good place
because the cells don’t divide, there’s not there is immune response in there but
it’s nowhere near as virulent as it is in other places, so you can do more stuff in
the brain and things will spread through the brain, so maybe that will apply to the
disorders you are talking about, but it’s really a long way away, I think.
>>Is anyone working on Friedreich’s ataxia?
That’s where they.>>Lots of people are working on, on
Friedreich’s ataxia but you’re not talking to the right person to ask about it
unfortunately. I mean, I, I, I would need a quick
reminder about exactly what the lesion is, is it DNA repair?
I can’t remember, can anyone remember? Dna repair, yes, that would be very
different if it’s, if the lesions due to DNA damage then, then that’s not really
quite in the league of epigenetics as we’ve been discussing it.
But rest assured, Friedreich’s ataxia is a very active area of research.
>>Okay. There’s one there.
Then, one in the green cardigan and then, one against the wall and we might have to
wrap it up that, that point.>>Yeah.
Fantastic talk, Adrian. It’s interesting that you observed obesity
in the, the mice. Were any aspects of feeding or weights
changed with the adeno virus treatment?>>Well, unfortunately, we’ve never really
investigated that. I think they don’t eat more, I think it’s
probably but, but we don’t really know. All I can tell you when you do the
reversal, it’s the nicest thing to watch, you just simply watch them come down over
a period of three weeks, their weight goes from being obese to being normal.
So, but on the other hand, we’re, we’re activating MECP2 in every cell in the
body. And that actually is an area we’re
interested in now because are there also peripheral, neuroscientists call
everything that isn’t the brain, the periphery, for some reason but are there
peripheral phenotypes that we’ve been missing, perhaps.
>>Okay, I hope these are two quick questions.
>>Hello, I was just, just to ask about that.
So you, can you see more[UNKNOWN] cells in other organisms, or organs, and does they
have>>We’ve never looked.>>And some genotype.
And, and, another more thing, so if it’s not like that, it means that in some
cases, some cells will be dying because they don’t express it, and so they are
kind of selected and because in the brain they cannot.
>>No, but that’s, that doesn’t happen, you see.
>>Okay.>>You, you, you can, the cells without it
don’t die. That’s why reversal is such an interesting
possibility, and in fact, with respect to[UNKNOWN] and other tissues, there are
so, there’s quite a variation in the severity of Rett Syndrome.
And quite often, it’s due to skewed x chromosome inactivation in the population.
There’s quite a variation, it isn’t always 50-50, half of the paternal, half of the
maternal. Quite often, it’s very skewed, like one in
10, one in 20 one in one and two in 10, it’s very skewed.
When the skewing is against the mutated version, the symptoms are much milder and
so you get what’s called a speech preserved version where, you know, there,
there is a spectrum to normality. Now, you did measure that by looking at
the blood. So, presume, whatever you find in the
blood looks as though, quite often, it reflects what’s going on in the brain.
>>Okay, thanks. Is there one last one?
>>Thank you. Do all animals have epigenomes?
Or is it just a characteristic of the higher animals?
>>Even, even yeast has marks on its genome.
Actually, yeast doesn’t have DNA methylation.
C elegans, this worm, doesn’t have DNA methylation.
Drosophila melanogaster has virtually no DNA methylation.
So, the models that are quite often worked on, don’t.
That’s chosen actually quite often because they’re, they have a small genome rapid
generation time. But those animals, nevertheless, have what
one would call an epigenome, because they have histone tails covered in marks.
So, these are quite conserved to, throughout all, all organisms that one
would call eukaryotes. That’s animals, plants, fungi.
>>Okay on that affinitive note, the I think we could have kept on going for much
longer with the questions but Adrian has another rest of his program to get
through, so I was asked to bring this to a halt the floor, the floor now actually.
I think you’ve done rather well out of it. As expected, Adrian has given us a
wonderful lecture, wide ranging, quite challenging and he has covered a, a very
large area so thank you very much for that.
And now, I want, going to ask Patrick Vallance, who is the President for
Pharmaceutical R&D at GSK to come and present Adrian with his medal.
Patrick joined GSK as Head of Drug Discovery, I think in 2000?
2000 and 2006. And he’s now President of R&D
Pharmaceuticals. What’s that?
Oh, yes he’s the man with the monies. He’s the one actually giving the check.
>>Yeah, I’m the man with the check. And you’re giving the medal.
Adrian, thank you very much, it was absolutely terrific, and it’s a real
privilege, for GSK to be able to fund this lecture and prize.
And it’s been a privilege for GSK, or its precursor companies, for 32 years, as Jean
said, that we started with the Wellcome Foundation in 1980, and then,
GlaxoWellcome, and now, GSK. And some things have stayed constant over
those times and some things have changed. The company is much, much bigger.
The company is totally global. And, of course, the whole nature of drug
discovery and development has changed. But some things have stayed constant.
And one of the things that stayed constant is our base in the UK and our commitment
to the UK and just about 50% of our R&D activity is in the UK.
And one of the reasons that we’re here is excellence of the science base and I think
that’s been admirably demonstrated today, Adrian, by what you’ve said and, of
course, is embedded in the values in of this institution.
The second thing that stay constant, perhaps not constant, but in a way,
started at the beginning, and is very, very important to us now, is a very close
working relationship with academics. I think it was absolutely the hallmark of
the Wellcome Foundation. And I think it’s absolutely the hallmark
of what we’re doing now. And it’s perhaps no surprise, that I think
it was 5 or 6 years ago when we decided that we needed to understand what the
opportunities were in epigenetics for drug discovery.
We reached out to the very leading academics in this field to find out what
we should be thinking about. And Adrian, it was you that came in to
talk to some of our team to help us to get started on that.
So, it’s terrific to hear this today. Unbelievably impressive and Jean gives the
lasting thing, which is the medal and I give the transient thing, which is the
money. But I hope it brings some pleasure and
thank you very much indeed.>>Thank you very much.
Thank you very much, thank you.
Thanks to Squarespace for sponsoring this
video. One summer afternoon when Doctor Martin Blaser
was still a medical student, he went to see an eleven-year-old boy who had suddenly become
ill and was hospitalized. He was perfectly fine until two days earlier when he suddenly
developed a fever and an upset stomach. The next day the fever worsened, and on the third
day, the boy developed small purplish dots on his body. The emergency room doctors quickly
realized the boy had Rocky Mountain spotted fever, something caused by a bite from a tick
infected with a type of bacteria called rickettsia. This bacterium multiplies within cells lining
blood vessels, invoking an aggressive immune response. Since this involves the brain’s
blood vessels, it caused a form of encephalitis, a swelling of the brain provoking a massive
headache. When Blaser accompanied doctors to see the
boy, the room was darkened as the light hurt his eyes, his body was covered with purple
spots, and he was thrashing around in his bed covered in sweat. He was yelling incoherently
as loud as he could while hallucinating. As Dr. Blaser explains in his book “Missing
Microbes,” the boy was started on an antibiotic called tetracycline and after just five days,
he was discharged from the hospital. Especially considering the Gut Microbiome
is the big topic in health and science recently, you may know that not all microbes are bad.
While there are pathogenic microbes like these just mentioned, at all times there are 500
to 1000 different species of bacteria in the human body. And the importance of their function
is becoming more apparent as we learn new things about them. However, it’s hard to picture how tiny microbes
in our gut contribute to our day to day cognition and brain function. In the case of rocky mountain
spotted fever it may not be surprising that the introduction of a deadly pathogen could
induce drastic changes in a person’s mental state. However, the relationship between the
microbes normally residing in the gut and how our brain operates becomes apparent when
we take them out. Scientists observing microbe-free mice living
in sterile bubbles quickly noticed that these mice have a personality that is distinct from
mice with gut microbes. Microbe-free mice were found to be more prone to taking risks
and they freely explore their environment. Risk taking might be good if you’re a young
entrepreneur, but the kind of risk these mice engage in is wandering further out in an open
field. For a mouse, this is an excellent strategy for quickly getting killed by a predator.
Not only are the mice unusually reckless, scientists also noticed that these microbe-free
mice have memory-related defects. The book “The Good Gut” by Erica and Justin
Sonnenburg describes how a group of researchers put normal and microbe free mice through some
memory tests. First, the mice were given five minutes to explore two new objects, a small
smooth ring and a large checkered ring. Then the objects were removed for twenty minutes.
After that, the large checkered ring and a new object, a star-shaped cookie cutter, were
put in the cages. Predictably, the mice with the normal microbiota checked out the cookie
cutter and paid less attention to the checkered ring because they already knew what it was.
The microbiota free mice, explored the new cookie cutter, but spent just as much time
checking out the old object – the checkered ring. It seemed that these mice had completely
forgotten an object they had just seen twenty minutes earlier. The forgetfulness in these mice may be explained
by the fact that the microbe free mice have lower levels of BDNF. BDNF, brain-derived
neurotrophic factor is a powerful protein important for learning and memory. It stimulates
the production of new brain cells and strengthens existing ones. Low levels of BDNF are linked
to depression and anxiety. Since making microbe-free humans would be
quite unethical, such experiments haven’t been repeated in humans, but… you may have
heard of the woman who, after receiving a fecal microbiota transplant, became obese.
The fecal microbiota transplant or FMT is just as it sounds, it’s taking the poop
from one healthy person and putting it into another person, in order to share the healthy
microbiota of the donor. FMT is not a common practice, but it’s the most effective treatment
for a Clostridium difficile infection, which causes diarrhea and abdominal pain for weeks.
In this case, the woman’s donor was her 16 year old overweight but otherwise healthy
daughter. The transplant went smoothly and successfully cured the woman’s issues. But,
over a period 16 months, the woman gained 34 pounds. And this happened despite persistent
diet and exercise efforts. She even went on a medically supervised liquid protein diet
and still could not get the weight off. On the flipside of this, it’s been found
that putting the microbiota of lean mice into other mice protects them from gaining weight.
So it looks like a microbiota transplant can transplant body types, but what about personality? In 2011, a research group at McMaster University
did an experiment with two different types of lab mice. One type had a personality that
was the mouse equivalent of anxious and the other type was sociable and extroverted. To
set a metric for how nervous the mice were, they put them on an elevated platform and
recorded how long it took for them to step down. The mice with the anxious personality spent
an average of four and a half minutes slowly and carefully making their way off the platform.
The “extroverted” mice jumped down in seconds. Then, the scientists switched the
microbiota of the two types of mice and did the platform test again. The mice with the
extroverted personality, after receiving the microbes of the anxious mice, now took over
a minute to get off the platform. On the other hand, after getting the microbes from the
extroverted mice, the “anxious” mice got off of the platform a whole minute quicker.
What this group showed was that in these mice, behavior and levels of anxiety were dependent
on which microbes were living in their gut. One other thing: remember BDNF, the protein
that we should like to have more of for better brain function? Well, the microbiota switch
that made the “anxious” mice more “confident” also increased their levels of BDNF. The change
in microbiota not only made observable changes in behavior, but in brain chemistry as well. In fact, there’s all kinds of chemistry
going on in the gut that can affect the brain. There’s even research identifying which
specific microbes produce which neurotransmitters. For example it’s estimated that 90% of our
serotonin is produced in the gut, and it’s been found that some of this serotonin is
produced by these four microbes. These two microbes produce gamma-Aminobutyric
acid or “GABA” – our chief inhibitory neurotransmitter which has relaxing and anti-anxiety
effects. And these two (Bacillus and Serratia) produce
our motivation neurotransmitter, dopamine. [R] So we basically have this huge mass of little
drug factories sitting in our gut pumping out different substances that affect our brain.
In fact the gut and its microbes appears to affect the brain so much that preclinical
research in rodents suggested that certain probiotics have antidepressant and anti-anxiety
effects. Probiotics are basically substances you can take orally to stimulate the growth
of microbes. One study even found that a Bifidobacterium infantis probiotic had anti-depressive effects
on par with that of the anti-depressant drug citalopram. I used to think that the only benefit of fiber
was that it helped you poop. However, considering dietary fiber isn’t food for us but for
our microbes, a diet rich in fiber from a variety of sources should also be good for
our mental health. This information about the gut microbiome
makes you start to wonder how many mental afflictions could be traced back to disruptions
in gut health from, for example, diets rich in fiberless processed foods and refined carbohydrates,
or from the unmitigated use of antibiotics. Antibiotics can be a life saver when absolutely
necessary as we saw at the start of the video, but the most commonly prescribed antibiotic
– a wide-spectrum antibiotic doesn’t just kill the offending bacteria, but all kinds
of other bacteria get caught in the crossfire. This is like poisoning your cat along with
a bunch of cockroaches you’re trying to kill. In the United States alone, tens of millions
of people are prescribed antibiotics for minor afflictions. 60 to 80 percent of children
taken to the doctor complaining of bad sore throats or ear pain will walk out with an
antibiotic. It’s estimated that people will take 30 courses of antibiotics by the age
of 40. But, the highest prescription rate was for children under the age of two with
1,365 courses per 1000 babies. So, could all these antibiotics affect the
young gut microbiome and the brain development of these children? A 2012 paper by Dr. Derrick MacFabe describes
what happens when rats are injected with something called Propionic Acid or PPA. The PPA injection
provoked peculiar changes in the rats’ brains like neuroinflammation, increased oxidative
stress, and glutathione depletion.The rats also displayed abnormal movements, repetitive
interests, cognitive deficits, and impaired social interactions. Basically, the results
of this injection were very similar to autism spectrum disorders. And, PPA is a fermentation
product of bacteria, namely Desulfovibrio, Bacteroidetes and Clostridia. It was found
that patients with autism have many more species of the clostridium bacteria and have high
levels of PPA in their feces. It’s estimated that in one third of patients,
autism doesn’t show up until around 18 to 24 months. Several reports from parents say
that their children were developing normally until they received antibiotics for upper
respiratory or ear infections. According to Dr. Sydney Finegold, antibiotics wipe out
or suppress several organisms in the gut, but Clostridia is one of the ones that persists. A CBC program titled “The Autism Enigma”
features Ellen Bolte who explains how her son Andrew’s behavior changed drastically
after 6 courses of antibiotics over a 2 to 3 ½ month period for an ear infection. After
this, he was diagnosed with severe autism. Digging into the research, Ellen came across
information about the Clostridia bacteria, so she started searching for a doctor who
would be willing to try an antibiotic called “vancomycin” on Andrew. Vancomycin is
specifically designed to target the Clostridia bacteria. After she finally found a doctor
who agreed to test her theory, they tried the antibiotic and it had impressive effects.
“The results were astounding. Within a matter of just a few weeks, he became calm. He was
aware of his environment… he’s putting puzzles together…” The antibiotic brought out improvements
in Andrew that were transient but drastic. This case lead to a pilot study with Dr. Finegold
and a Dr. R Sandler who found that out of 10 autistic children treated with vancomycin,
8 of them had again transient but significant improvements. Now, jumping to conclusions about the cause
autism has not been… helpful in the past… but this idea that autism could be the result
of a disturbed gut is gathering more and more data. A disturbed gut ecosystem would also
explain the very common gastrointestinal issues autistic children suffer. Some estimates say
that as high as 70% of children with autism spectrum disorders also have gastrointestinal
issues. Autism is just one of the disorders that can
be linked to a disruption in gut health, and research on the gut microbiome is growing
quickly. About 3600 related articles on this topic were published between 2010 and 2015.
At this point, saying the gut microbiome is important to health is an understatement.
Dr. Martin Blaser says that “losing your entire microbiome outright would be nearly
as bad as losing your kidneys or liver.” Unlike the kidneys or liver however, you can
change the makeup of your microbiome with what you put into your mouth. I guess Hippocrates knew what he was talking
about when he said “All disease begins in the gut,” and “Let food be thy medicine.” This video was brought to you by Squarespace.
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