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Good morning, class.
Nice to see you here,

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you loyal holdouts, the stalwarts
who haven't gone home early for

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Thanksgiving. You recall that
last time we were talking about the

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Matevoidic system, and
much of the rationale for

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studying it stems from two reasons.
First of all, it recapitulates in a

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formal sense what happens
during embryogenesis,

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i.e. one has relatively
undifferentiated stem cells which

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are able to differentiate into a
number of different directions by

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committing themselves to either
the myeloid or lymphoid compartment,

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and then going down yet other
pathways, more detailed pathways to

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generate a whole
variety of cell types.

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Secondly, we really understand
the differentiation pathways of

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Matevoisis better than we
understand any tissue in the body,

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in no small part because it's much
easier to study the soluble cells in

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the blood and in the immune system
than it is to study how these

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processes happen in normal
tissues. But having said that,

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I want to emphasize the fact that
in each of our tissues there are

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oligopotential stem cells.
When I say oligopotential I mean

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they can go down several different
pathways. Recall up there on that

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diagram we talked about
pluripotential which means multiple,

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and today we're going to talk a
bit about todipotential stem cells,

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which are able to disperse
descendants into all the different

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differentiation
lineages in the body.

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At the end of our last lecture,
we were focusing on the red blood

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cells. And this is sometimes
called erythropoiesis,

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which is to say the process by
which red blood cells are generated.

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We mentioned the concept of
homeostasis, and homeostasis just

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refers to the fact that all of these
systems are in very delicate balance

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so that the body can respond to the
physiologic needs of the organism at

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any one point in time. We
talked about the fact that for

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example when there's a
massive infection in the body,

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then the homeostatic mechanisms
allow an increase in these kinds of

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immune cells in order to
encounter the infection.

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And at the end of our last lecture,
we were talking about this specific

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branch, and how in fact
homeostasis is maintained there.

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And what we see here is a
series of committed progenitors.

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So when I talk about committed
progenitors I'm referring to cells

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that have already made the
commitment to go down one

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or another pathway. They're
not yet fully differentiated.

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As you can see here, we
have first forming cells and

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colony forming cells. We
don't need to remember all the

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different abbreviations except to
say that these cells here are in a

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relative undifferentiated
state. And the only end stage

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differentiation comes at the very
end here when we get to red blood

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cells. We said in general that
it's the case that most highly

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differentiated cells are
post-mitotic, which is to say

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they're never going to reenter into
the growth and division cycle of the

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cell that we talked about
earlier in the semester.

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And that's obviously dictated here
by the fact that this erythrocyte

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lacks a nucleus, i.e.
during the final stage of

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differentiation, in addition
to accumulating large

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amounts of hemoglobin in its
cytoplasm, this cell actually pops

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out its nucleus, and that
obviously represents an

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irrevocable change in that cell
can never again enter into growth

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and division cycle. The
immediate precursor of an

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erythrocyte is often called an
erythroblast. And the term blast

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here refers to a cell of embryonic
appearance. Blast is used often to

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indicate, we'll mention that again
shortly, a cell which looks very

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primitive, and embryonic, and
undifferentiated. And that ends

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up going into an erythrocyte,
which we said is actually a synonym

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for a red blood cell,
an RBC, a red blood cell.

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And we talked about the fact
that this progression is actually

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maintained and furthered by the
stimulus of the compound called

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erythropoietin. So, we're
using some of the same

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words over and over again. And
erythropoietin is essentially a

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growth factor which stimulates the
end stage differentiation of the

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erythroblast into
the erythrocyte.

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Epo, as erythropoietin's often
abbreviated, is actually made in the

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kidneys. And it's made in
the kidneys in response to the

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physiological stimulus of
hypoxia. Hypoxia means inadequate

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oxygenation of the tissues.
You might ask, well, why is red

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blood cell contractions controlled,
as they are, in the kidney?

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And the fact is, we don't
really know why evolution

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has chosen the kidney as the site of
monitoring the degree of oxygenation

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of the blood. And in response to
hypoxia, it begins to crank out

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erythropoietin, or
Epo. You can think of

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erythropoietin as an extracellular
liggon just like a growth factor.

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It has its own cognate receptor
on the surface of the erythroblast,

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and when Epo released by the kidney
hits an erythroblast in the context

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of the bone marrow, it
actually has two effects.

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It happens to be the case that
roughly even 95% of the erythroblast

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that are made routinely are forced
to go into apitosis under routine

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conditions. So, this is
an enormously wasteful

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system, i.e. as every moment we
speak, 90 or 95% of the erythroblast

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that have come into existence
in your bone marrow apitose.

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They never go into end
stage differentiation.

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But when Epo is around, Epo
provides a strong anti-apoptotic

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signal to the red blood saves
some and maybe even all of the

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erythroblasts from their normal
fate of undergoing apitosis.

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So here, if we imagine
there are actually two fates,

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one is to become an erythrocyte,
and the other is to apitose, where

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the aptisosis is paradoxically
enough the dominant fate of the cell,

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the moment that an Epo comes on the
scene, it blocks this alternative

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fate, allowing these cells to mature.
Epo at the same time stimulates the

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erythroblast to differentiate.
Now, you might as yourself the

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question, why is there this
enormously inefficient process?

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An enormous effort is made to crank
out large, astronomical numbers of

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erythroblasts, and yet
most of them are wasted even

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before they've had a chance to
undergo end stage differentiation.

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And the rationale here is as
follows. This is a terrific system

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for rapidly ramping up the level of
red blood cells in your circulation

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because here, within a matter of
a day or two, one can crank up,

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actually in a matter of hours,
you can crank up the rate of

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production of red blood cells
by maybe even a factor of ten.

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Instead of having 90% of
the erythroblast apitose,

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let's say 0% of them do so, and
therefore, instead of having 10%

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of the erythroblasts becoming red
blood cells, 100% of them will do so.

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And therefore, you have
the virtually miraculous

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response that if you go from here
high up in the rocky mountains at

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ten or 12,000 feet, within a
matter of two or three days,

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your red blood cell concentration
actually has compensated,

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has risen up to create the oxygen
caring capacity that enables you to

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deal with the thin oxygen, with
the low oxygen tension that's

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present at high altitudes.
Now, having said that,

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the fact is that there is an Epo
receptor on the surface of the

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erythroblast, and what we
see there is the following.

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Let's talk about the erythroblast
and just blow it up a little bit.

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So, here's the erythroblast.
That's the undifferentiated

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precursor. And by the way, the
erythroblast is actually still a

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white blood cell. Often we
call a white blood cell a

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leukocyte. You may know
that gluco means white. So,

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a leukocyte, it's still white.
And after the erythropotent

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impinges on it, one of the
things it starts doing is

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to make the hemoglobin, which
turns it into a red blood cell.

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At this stage, it's still white.
On the surface of the erythroblast

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are these Epo receptors. I'll
just abbreviate them like this,

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Epo receptor, and once it binds
the liggon Epo just like the growth

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factor receptors, we talked
early in the receptors

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signals are sent into the
erythroblast to stimulate both

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differentiation and to prevent
the initiation of the cell suicide

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program that we call apitosis.
Interestingly, one of the things

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that happens normally is the
following, that when these signals

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come in, there is an enzyme called
a phosphotase which is attracted

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to the receptor. The
Epo receptor works like a

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tyrosine kinase growth factor
receptor that we talked about

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earlier in the semester.
And here, we have an enzyme,

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a phosphotase, which actually
counteracts the function of the

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tyrosine kinases. So,
after the Epo receptor has

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bound its liggon, here's
the plasma membrane,

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it has a whole series of
I'll draw Y here for tyrosine.

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It has a whole series of phosphates
attached to it because of the

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actions of tyrosine kinase enzymes
that are associated with its

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cytoplasmic domain indirect analogy
to what we talked about in the case

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of growth factor receptors. But,
one of the things that happens

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is that this phosphotase, which
removes phosphates, then gloms

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onto the receptor like this.
It grabs hold of some of these

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tyrosine kinases. And what
this phosphotase does is

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reach around. It reaches around and
it begins to prune off all of these

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phosphates because that's
what a phosphate does.

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It cuts away all the phosphates,
thereby directly reversing the

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previous actions of the tyrosine
kinase that led to the formation of

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these phosphates, and that
in turn allows downstream

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signaling to occur. This
is obviously a functional

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negative feedback loop, i.e.
whenever there is an agonist

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you want an antagonist.
Whenever there's a stimulus which

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is induced in the body, there
has to be an inhibitory signal,

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and this is part of the
whole issue of homeostasis,

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the balance between forward and
backward. Interestingly enough,

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there's a family in Finland, I
believe, which has a mutant receptor.

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And their mutant receptor
lacks this tyrosine.

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And what happens as a consequence
is that that particular tyrosine

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doesn't get phosphorolated.
Because that tyrosine doesn't get

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phosphorolated, the
phosphotase cannot be attracted

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to the receptor because
there isn't a tyrosine there.

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There's some other amino acid
residue. I don't know what it is.

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It's not important, but it's not
a tyrosine. And this cannot happen

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because they don't have this
tyrosine. This phosphotase could

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not be attracted to the receptor
to shut it down as it normally

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would be. So normally
homeostasis is

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imbalanced, and several members
of this family have become Olympic

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cross-country ski winners.
They've become Olympic champions.

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Why? Because their Epo receptor's
hyperactive. Because the Epo

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receptor's hyperactive, they
have higher than normal levels

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of red blood cells in the
circulation, and this clearly allows

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them to function better
in cross country skiing,

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which as you know is a really
physically demanding task.

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Again, I'm not saying this is a
good thing for them necessarily.

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There are other things in life
besides, believe it or not,

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winning cross country Olympic
competitions because as I mentioned

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last time, having too many red
blood cells in your circulation,

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there's a downside to it which
is that you have a much greater

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tendency to have occlusions,
to have blood clots in your

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circulation which obviously is
not a very good thing to have.

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Oh, so is there
a threshold of Epo

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receptor activation before
phosphotase shuts it down?

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These things are not really well
understood, are not well studied.

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The fact is, you might be able to
say we should make a mathematical

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model of all of these different
circuitry. But the fact is if you

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want to make a mathematical
model, you have to know some of the

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constants. You have to know some
of the parameters, the binding

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constants. And in
fact, for most of the

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signaling interactions, no
one's ever really studied them in

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such great detail. So,
one really doesn't know how

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much phosphate you need here before
the phosphotase becomes really

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active. And so, there's
not a really good

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mathematical model of this feedback
loop, even though we know without

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any doubt that it exists. So,
I want to get into other issues

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that are related to the whole
issue of accumulated differentiation

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traits as one moves
down this pathway.

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Again, we've used this as a model
for how differentiation takes place

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in the entire body. The
faith that's been implicit in

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this kind of scheme for the last 20
or 30 years is that this acquisition

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of different kinds of phenotypes is
not accompanied by genetic changes,

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that is, in the genomes of these
cells. I.e. one can accomplish

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these different kinds of
differentiation not by rearranging

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genes but just by rearranging
transcriptional programs,

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and that the DNA sequence of
these cells as they proliferate and

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differentiate is fully unchanged.
And that's a matter of faith

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because you could say to me,
how do you know that it's really

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true. The fact is that people have
looked at genes in many kinds of

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cell types, but it's essentially
impossible, or it has been at least

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until recently, to preclude
the possibility that as

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cells move down these
differentiation pathways,

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they begin to change the
nucleotide sequences of different

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ones of their genes. In fact,
I've already told you about

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one instance where that's clearly
the case. And that is in the

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differentiation of the B
cells of the immune system,

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which happen to be right up here
on this chart, because as you recall

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from our discussion vis-à-vis
immunology, the B cells actually do

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rearrange their genes in order to
cobble together DNA sequences that

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together are able to enable them
to make antibodies that are able to

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react to specific antigens. So
there, there's no doubt at all

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that there's a somatic rearrangement
of the genes, somatic meaning it's

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not a germ line change. It's
happening in the soma outside

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of the germ line. There's
a somatic mutation.

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It's not a mutation that's
deleterious, but rather is directed

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towards a physiologically
normal and desirable end point.

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But for example, how do you know
that when you remember things in the

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brain, part of the memory does
not derive from changing the DNA

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sequence and different
neurons in the brain?

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What's the molecular basis of memory?
Could it be that each time we learn

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some things that there are
different nucleotide sequences,

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critical nucleotide sequences,
that are changed in neurons in the

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brain, and that those nucleotide
sequence changes represent an

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important basis for ensuring that
memory is retained over decades of

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time. Or, rather than having
genetic changes in the brain,

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might it all be epigenetic, i. .
all the other changes that happen

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to the cell besides changing DNA
sequences in the chromosomal DNA.

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So, here we're dealing with the
dialectic between epigenetic and

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genetic. And, have we
talked about DNA methylation

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here? Yes, so we talked about DNA
methylation, and do you recall or

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having discussed the fact
that when DNA gets methylated,

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that suppresses the
transcription of a gene.

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But that doesn't change
the nucleotide sequence,

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and that methylation configuration
of a gene can be passed to one cell

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generation to the next.
It's heritable, but it's not

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genetic in the strictest
sense of the term, i.e.

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it doesn't involve a change
in nucleotide sequence,

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which is what we want to
limit this term to referring.

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So, epigenic can represent all the
changes in the cell including DNA

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methylation, alterations
in transcription,

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and all other downstream events
that result in changes in the cell.

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And how can one address this?
Well, there are different ways of

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addressing this question or
addressing the possibility that in

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fact there are changes in the
nucleotide sequence of the gene.

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One way to do this is the following.
And that is to take cells from an

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early embryo, and here we see
an early vertebrate embryo.

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This looks really more like a frog
embryo or a slightly different shape,

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and here we see an early embryo.
It's after a blastula. It's called

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a blastocyst. Here again
we have the word blast.

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How about one question per lecture?
We have to have some equity here.

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Other people can ask questions.
It's good to ask questions,

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00:19:02,000 --> 00:19:06,000
but how about one per lecture;
that's fair, equitable.

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00:19:06,000 --> 00:19:10,000
All right, so here's an
early vertebrate embryo.

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Here we see the blastocyst. This
comes after the earlier stages

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in the embryo, and here
we see the inner cell mass.

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And as it turns out, the inner cell
mass is going to be the precursor of

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many of the tissues of the
ultimately arising embryo.

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And here, one can do an interesting
experiment. One can take cells out

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of the inner cell mass. And
one can begin to propagate them

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in culture. And what one ends
up with is embryonic stem cells.

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And the intrinsic interest of
embryonic stem cells is manifold.

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For one thing, you can take
embryonic stem cells and you can

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genetically alter them.
You can put a new gene in,

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in the case of a mouse, or
you can take another gene out.

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And then what you can do is you
can inject the genetically altered

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embryonic stem cell into the
blastocyst of another embryo.

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00:20:04,000 --> 00:20:08,000
So let's say we take the cells
out of the inner cell mass.

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We develop embryonic stem cells.
We can call them ES cells. That's

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00:20:13,000 --> 00:20:17,000
what they're called in the trade,
ES cells. We take them out. We can

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00:20:17,000 --> 00:20:22,000
propagate them in culture. And
then, what we can find is we'll

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put a genetic marker in those ES
cells. Let's say we put in those

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00:20:26,000 --> 00:20:31,000
embryonic stem cells the marker
for the gene beta-galactosidase.

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00:20:31,000 --> 00:20:35,000
And beta-galactosidase in the
presence of a proper indicator,

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00:20:35,000 --> 00:20:39,000
if you put a proper indicator
and make a cell turn blue.

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00:20:39,000 --> 00:20:43,000
So now we have an ES cell line
that produces the beta-galactosidase

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00:20:43,000 --> 00:20:47,000
enzyme. The beta-galactosidase
enzyme beta-gal itself has no effect

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00:20:47,000 --> 00:20:51,000
on the biology of the cells.
It's only a marker. And now,

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00:20:51,000 --> 00:20:55,000
we take those ES cells, and we
inject them into another embryo,

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00:20:55,000 --> 00:21:00,000
a wild type embryo that
lacks this beta-gal marker.

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00:21:00,000 --> 00:21:05,000
And what we can see is that we
inject the ES cells into this

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00:21:05,000 --> 00:21:10,000
blastocyst. The injected ES cells
will now insinuate themselves,

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00:21:10,000 --> 00:21:15,000
will now intrude into the massive
cells in this embryo into which we

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00:21:15,000 --> 00:21:20,000
injected the ES cells, and
they will become part of the

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00:21:20,000 --> 00:21:25,000
entire embryo genesis that follows.
I.e. soon these foreign ES cells

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00:21:25,000 --> 00:21:30,000
will weasel their way
into this inner cell mass.

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00:21:30,000 --> 00:21:34,000
And they will become established
and become functionally equivalent to

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00:21:34,000 --> 00:21:38,000
the inner cell mass cells that
were resident there prior to this

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00:21:38,000 --> 00:21:42,000
injection. And what you can do then
is follow the subsequent fate of,

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00:21:42,000 --> 00:21:46,000
in this case, a mouse. And what
will happen often is that you can

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00:21:46,000 --> 00:21:50,000
find blue cells all over the
mouse sometimes in the paws,

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00:21:50,000 --> 00:21:54,000
sometimes in the coat. Let's
imagine that the hair would turn

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00:21:54,000 --> 00:21:58,000
blue, which in fact is not the case.
But let's imagine the hair would

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00:21:58,000 --> 00:22:02,000
turn blue. So
here's the mouse,

305
00:22:02,000 --> 00:22:06,000
happy because it's part
of an important experiment.

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00:22:06,000 --> 00:22:11,000
And what you'll sometimes see is
that, well, remember that art was

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00:22:11,000 --> 00:22:16,000
not my forte. Anyhow, here
you might see stripes of blue

308
00:22:16,000 --> 00:22:20,000
cells on the skin. The hair
won't turn blue actually,

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00:22:20,000 --> 00:22:25,000
but the skin may if you
give it the proper indicator.

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00:22:25,000 --> 00:22:29,000
And what this indicates is that
in this case, the cells that were

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00:22:29,000 --> 00:22:34,000
injected into the blastocyst
could become part of lineages which

312
00:22:34,000 --> 00:22:39,000
committed themselves
to becoming skin cells.

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00:22:39,000 --> 00:22:43,000
Or, the cells in the brain might
be blue. Or, the cells in the gut

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00:22:43,000 --> 00:22:47,000
might be blue. Or under
certain conditions,

315
00:22:47,000 --> 00:22:51,000
the cells in the intestine might
be blue. In telling you that,

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00:22:51,000 --> 00:22:55,000
I mean to indicate that the
cells that we injected into this

317
00:22:55,000 --> 00:23:00,000
blastocyst, which carry
beta-gal were totipotent.

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00:23:00,000 --> 00:23:04,000
They could create all the tissues
of the mouse under the proper

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00:23:04,000 --> 00:23:08,000
conditions. The proper conditions
are obviously being put into this

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00:23:08,000 --> 00:23:12,000
very special environment in
which all kinds of differentiation

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00:23:12,000 --> 00:23:16,000
inducing signals, which
we don't really understand,

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00:23:16,000 --> 00:23:20,000
can induce this cell to commit
itself to enter into one or another

323
00:23:20,000 --> 00:23:24,000
differentiation lineage. And
in principal, you can make a

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00:23:24,000 --> 00:23:28,000
whole organism out of an ES cell.
ES cell has as much plasticity, as

325
00:23:28,000 --> 00:23:32,000
much flexibility,
as a fertilized egg.

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00:23:32,000 --> 00:23:36,000
It has not yet lost the ability
to make all the parts of the body.

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00:23:36,000 --> 00:23:40,000
On some occasions, the ES cell
will even get into the gonads of the

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00:23:40,000 --> 00:23:45,000
mouse, which are down here
somewhere. And if that's so,

329
00:23:45,000 --> 00:23:49,000
if the ES cell which you injected
has been able to seed the formation

330
00:23:49,000 --> 00:23:54,000
of these cells down here, then
what will happen is that either

331
00:23:54,000 --> 00:23:58,000
the sperm or the egg coming
from this mouse will now transmit

332
00:23:58,000 --> 00:24:04,000
the blue gene. And now,
in the next generation,

333
00:24:04,000 --> 00:24:10,000
all of the mice will inherit the
blue beta-galactosidase gene in all

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00:24:10,000 --> 00:24:16,000
of their cells because now this
will have entered into the germ line.

335
00:24:16,000 --> 00:24:22,000
If these blue cells happen
to colonize the testes,

336
00:24:22,000 --> 00:24:28,000
the ovary, or the testes, then
these blue cells will become

337
00:24:28,000 --> 00:24:32,000
ancestors to the sperm or the egg.
And now, in the next generation,

338
00:24:32,000 --> 00:24:36,000
mice will inherit a blue
gene in all of their cells.

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00:24:36,000 --> 00:24:40,000
And now this mouse is really
happy because it's now part of an

340
00:24:40,000 --> 00:24:44,000
extremely important experiment
because now all of its cells will

341
00:24:44,000 --> 00:24:47,000
become blue, having inherited them
as part of the oocyte which led to

342
00:24:47,000 --> 00:24:51,000
its formation. In
this kind of an animal,

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00:24:51,000 --> 00:24:55,000
we call this animal a kind of
a chimera. Chimera is a mythical

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00:24:55,000 --> 00:24:59,000
beast which is, let's say,
half human and half horse

345
00:24:59,000 --> 00:25:02,000
or something like that.
Or a chimera means it has

346
00:25:02,000 --> 00:25:06,000
genetically different parts in it.
That is not to say that these parts

347
00:25:06,000 --> 00:25:09,000
carrying the blue gene
are necessarily defective,

348
00:25:09,000 --> 00:25:13,000
they're just genetically different,
one from the other. But they can

349
00:25:13,000 --> 00:25:16,000
participate in embryogenesis in
a fashion that's indistinguishable

350
00:25:16,000 --> 00:25:20,000
from the non-blue cells. They
just do everything they're

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00:25:20,000 --> 00:25:23,000
supposed to do, and they
pretend as if they were in

352
00:25:23,000 --> 00:25:27,000
this embryo from the get go,
from the very beginning, from the

353
00:25:27,000 --> 00:25:31,000
moment of fertilization.
So they are totipotent.

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00:25:31,000 --> 00:25:34,000
There's an alternative experiment
you can do, and you can take the ES

355
00:25:34,000 --> 00:25:38,000
cells, and you can inject
them under the skin of a mouse,

356
00:25:38,000 --> 00:25:41,000
let's say. So now, you're
putting them in a very unfamiliar

357
00:25:41,000 --> 00:25:45,000
environment. And what you see
then on many occasions is you can

358
00:25:45,000 --> 00:25:49,000
actually get a tumor. You
can get what's called an

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00:25:49,000 --> 00:26:00,000
embryonal carcinoma.

360
00:26:00,000 --> 00:26:03,000
Now you'll say, well,
so what? That's not so

361
00:26:03,000 --> 00:26:07,000
interesting. But it's
very interesting. Why?

362
00:26:07,000 --> 00:26:10,000
Because if you look at the genome
of those embryonal carcinoma cells

363
00:26:10,000 --> 00:26:14,000
which we can call EC cells if you
want, those cells are genetically

364
00:26:14,000 --> 00:26:17,000
full wild type. And yet,
we're getting a tumor here.

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00:26:17,000 --> 00:26:21,000
So, it means that these cells,
which have been placed in a fully

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00:26:21,000 --> 00:26:24,000
unfamiliar environment under the
skin or in the belly of a mouse will

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00:26:24,000 --> 00:26:28,000
begin to form a tumor. And
in fact, they represent the

368
00:26:28,000 --> 00:26:31,000
only type of cell that we know
about where a cell having a wild type

369
00:26:31,000 --> 00:26:35,000
genome can actually
give you a tumor.

370
00:26:35,000 --> 00:26:39,000
As you sensed from our previous
discussions, all other kinds of

371
00:26:39,000 --> 00:26:44,000
human cancer cells we know about
have to have mutant genes in order

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00:26:44,000 --> 00:26:48,000
for them to grow as a malignancy.
These cells are fully wild type and

373
00:26:48,000 --> 00:26:53,000
can grow as an embryonal carcinoma.
They are very primitive. These

374
00:26:53,000 --> 00:26:57,000
cells have quite a bit of autonomy.
They're not so responsive to all

375
00:26:57,000 --> 00:27:02,000
the growth factors that normally
are required by many cells throughout

376
00:27:02,000 --> 00:27:07,000
the soma of an animal
throughout the tissues.

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00:27:07,000 --> 00:27:10,000
So this allows us to begin to move
on and ask other kinds of questions.

378
00:27:10,000 --> 00:27:14,000
For example, you can take
these embryonal carcinoma cells.

379
00:27:14,000 --> 00:27:18,000
You put them in a Petri dish, and
you can actually induce them to

380
00:27:18,000 --> 00:27:22,000
differentiate into different
cell types in vitro.

381
00:27:22,000 --> 00:27:26,000
How can you do that? Well,
we're just beginning to learn

382
00:27:26,000 --> 00:27:30,000
how to do that. We don't
really know how to do that.

383
00:27:30,000 --> 00:27:34,000
But, if you give them the right
cocktail of growth factors,

384
00:27:34,000 --> 00:27:38,000
they might begin to form muscle
cells. If you give them another

385
00:27:38,000 --> 00:27:43,000
cocktail of growth factors, they
might begin to give pancreatic

386
00:27:43,000 --> 00:27:47,000
eyelid cells that form insulin,
or in this case cartilage cells.

387
00:27:47,000 --> 00:27:52,000
And presumably, the cocktail of
growth factors you're providing each

388
00:27:52,000 --> 00:27:56,000
one of these cells with in vitro,
i.e. in the Petri dish, is mimicking

389
00:27:56,000 --> 00:28:00,000
the growth factor environment
that each of these cell types is

390
00:28:00,000 --> 00:28:04,000
experiencing within the
embryo. In other words,

391
00:28:04,000 --> 00:28:08,000
cells in different parts of
the embryo experience different

392
00:28:08,000 --> 00:28:12,000
combinations of growth factors that
persuade them to commit themselves

393
00:28:12,000 --> 00:28:16,000
to becoming these kind of cells,
these kind of cells, and these kind

394
00:28:16,000 --> 00:28:20,000
of cells. And therefore, one
of the promises of embryonic

395
00:28:20,000 --> 00:28:24,000
stem cell research is the
possibility of being able to

396
00:28:24,000 --> 00:28:28,000
regenerate different kinds of
tissues in a fashion that I just

397
00:28:28,000 --> 00:28:32,000
showed you here. But this
whole experiment in the

398
00:28:32,000 --> 00:28:36,000
case of human beings is
ethically extremely controversial.

399
00:28:36,000 --> 00:28:40,000
Why? Because the experiment starts
out making these ES cells here,

400
00:28:40,000 --> 00:28:44,000
and if we want to start out
with an early embryo like this,

401
00:28:44,000 --> 00:28:48,000
start out with a blastocyst, in
the case of a human blastocyst,

402
00:28:48,000 --> 00:28:52,000
this human blastocyst has
the potential under the proper

403
00:28:52,000 --> 00:28:56,000
conditions of becoming a newborn
human being. And therefore,

404
00:28:56,000 --> 00:29:00,000
we have this enormous ethical
conflict in this country.

405
00:29:00,000 --> 00:29:04,000
Is this blastocyst already a human
being? Can you already afford to

406
00:29:04,000 --> 00:29:08,000
truncate the life of this blastocyst
at this stage of development,

407
00:29:08,000 --> 00:29:13,000
and in so doing, are you
actually extinguishing human life,

408
00:29:13,000 --> 00:29:17,000
or is this organism, if you want to
call it that, already still much too

409
00:29:17,000 --> 00:29:22,000
primitive to consider it
to be equal to human life?

410
00:29:22,000 --> 00:29:26,000
And here, I would not,
unlike my political views,

411
00:29:26,000 --> 00:29:31,000
be forward enough to venture
an opinion because it's really

412
00:29:31,000 --> 00:29:35,000
something that no one really can
argue about in any objective way.

413
00:29:35,000 --> 00:29:40,000
It's all a matter of opinion.
Is this a human being already,

414
00:29:40,000 --> 00:29:44,000
or is it simply an inanimate
cluster, a clump of cells?

415
00:29:44,000 --> 00:29:48,000
Now, in principal,
how could we do this?

416
00:29:48,000 --> 00:29:52,000
How could we actually create
this kind of tissue therapy?

417
00:29:52,000 --> 00:29:56,000
Because the fact is, as you get
older, your tissues start falling

418
00:29:56,000 --> 00:30:00,000
apart. You haven't
experienced that.

419
00:30:00,000 --> 00:30:04,000
But I have. And the fact is that
even if you try to stay in shape,

420
00:30:04,000 --> 00:30:09,000
things just start falling
apart. And the older you get,

421
00:30:09,000 --> 00:30:13,000
the more they fall apart.
Even people who eat well,

422
00:30:13,000 --> 00:30:18,000
which I do, and exercise well,
which I don't, even they fall apart.

423
00:30:18,000 --> 00:30:22,000
And so the question is, are there
way of replacing and repairing

424
00:30:22,000 --> 00:30:27,000
tissue? And this would, in
principal, represent one such

425
00:30:27,000 --> 00:30:31,000
strategy because it means that you
could possibly inject replacement

426
00:30:31,000 --> 00:30:36,000
cells into an agent tissue and
generate cells which could then

427
00:30:36,000 --> 00:30:40,000
restore and regeneration function
which has somehow inevitably

428
00:30:40,000 --> 00:30:45,000
deteriorated over the decades.
Well, that raises the question of

429
00:30:45,000 --> 00:30:50,000
how you can actually get a
blastocyst, how you can make a

430
00:30:50,000 --> 00:30:56,000
blastocyst like this. To state
an obvious thing which you

431
00:30:56,000 --> 00:31:01,000
might already have intuited,
let's say you had such cells

432
00:31:01,000 --> 00:31:05,000
differentiated from various cell
types that you want to inject into

433
00:31:05,000 --> 00:31:09,000
somebody's muscle or into their
liver if they had diabetes and had

434
00:31:09,000 --> 00:31:13,000
lost their beta cells, or
into their cartilage if they

435
00:31:13,000 --> 00:31:17,000
banged up their knee during
basketball practice or something

436
00:31:17,000 --> 00:31:21,000
like that, or jogging, which
is allegedly good for you.

437
00:31:21,000 --> 00:31:25,000
Who knows? How could you deal
with that? Well, the fact is,

438
00:31:25,000 --> 00:31:29,000
let's imagine there were such a
blastocyst which we'd produce in

439
00:31:29,000 --> 00:31:34,000
this fashion that we
differentiated like this.

440
00:31:34,000 --> 00:31:37,000
OK, this is now the sequence
of events. There's an important

441
00:31:37,000 --> 00:31:40,000
consideration we have to take
into account, and that is if this

442
00:31:40,000 --> 00:31:44,000
blastocyst came from a
different person than you,

443
00:31:44,000 --> 00:31:47,000
and we induced these
cells to differentiate,

444
00:31:47,000 --> 00:31:51,000
and we injected those
differentiation cells into your

445
00:31:51,000 --> 00:31:54,000
muscle, things wouldn't work.
Why? Because these cells, if the

446
00:31:54,000 --> 00:31:57,000
blastocyst originated in a different
person than yourself would be

447
00:31:57,000 --> 00:32:01,000
genetically different from you,
and would be recognized as foreign

448
00:32:01,000 --> 00:32:04,000
tissue by your immune system. So
even though you were getting an

449
00:32:04,000 --> 00:32:08,000
injection of cells which could
regenerate your muscle perfectly

450
00:32:08,000 --> 00:32:11,000
well, those cells would never
be given a chance to establish

451
00:32:11,000 --> 00:32:15,000
themselves and to thrive, and
to reconstruct the tissue simple

452
00:32:15,000 --> 00:32:18,000
because the immune system would
regard those cells as being

453
00:32:18,000 --> 00:32:22,000
foreigners and would go after them
hammer and tongs trying to get rid

454
00:32:22,000 --> 00:32:25,000
of them in the same way it tries
to get rid of all kinds of foreign

455
00:32:25,000 --> 00:32:29,000
invaders. I.e. the only
way you could avoid it is

456
00:32:29,000 --> 00:32:33,000
if this blastocyst was
genetically identical to you.

457
00:32:33,000 --> 00:32:37,000
But how can you make a blastocyst
which is genetically identical to

458
00:32:37,000 --> 00:32:41,000
you? Well, I'm glad I asked that
question. That's really the big

459
00:32:41,000 --> 00:32:45,000
challenge we have here because we
don't want to create a situation

460
00:32:45,000 --> 00:32:49,000
where we have to restore somebody's
tissues, but the only way we can

461
00:32:49,000 --> 00:32:53,000
restore them is to leave them
immunosuppressed for the rest of

462
00:32:53,000 --> 00:32:57,000
their lives. When I say
immunosuppressed I mean we have to

463
00:32:57,000 --> 00:33:01,000
prevent their immune system from
attacking all of these cells that

464
00:33:01,000 --> 00:33:05,000
we've injected in them, these
foreign cells, in the same way

465
00:33:05,000 --> 00:33:09,000
that we have to suppress the
immune system of any person who has

466
00:33:09,000 --> 00:33:13,000
received a graft from another
individual including often bone

467
00:33:13,000 --> 00:33:18,000
marrow transplants. In all
cases, we have at least for a

468
00:33:18,000 --> 00:33:24,000
while to prevent their immune system
from attacking and eliminating these

469
00:33:24,000 --> 00:33:29,000
engrafted cells. And this
is where the whole strategy

470
00:33:29,000 --> 00:33:33,000
comes for the whole process of
cloning. You may recall the case of

471
00:33:33,000 --> 00:33:37,000
Dolly about five years ago,
and let's remember what happened

472
00:33:37,000 --> 00:33:41,000
here because this would a momentous
experiment in mammalian biology.

473
00:33:41,000 --> 00:33:45,000
It asked the question, really, if
you take cells from a somatic tissue,

474
00:33:45,000 --> 00:33:49,000
from here, or here, or
here, are those cells,

475
00:33:49,000 --> 00:33:53,000
in principal, still totipotent,
i.e. is the nucleus, is the genome

476
00:33:53,000 --> 00:33:57,000
of those cells totipotent, or
has the genome, the chromosomal

477
00:33:57,000 --> 00:34:01,000
complement of cells in their cells
undergone some kind of irrevocable,

478
00:34:01,000 --> 00:34:05,000
irreversible change, which
precludes those cells from ever

479
00:34:05,000 --> 00:34:08,000
becoming totipotent?
Well, in fact,

480
00:34:08,000 --> 00:34:12,000
if you take mammary epithelial cells
from the breast of a human being or

481
00:34:12,000 --> 00:34:15,000
from the breast of a ewe and
you put them into the blastocyst,

482
00:34:15,000 --> 00:34:18,000
nothing's going to happen. Those
introduced mammary epithelial

483
00:34:18,000 --> 00:34:22,000
cells will not be able to establish
themselves in the blastocyst.

484
00:34:22,000 --> 00:34:25,000
And, we will not be able to
insinuate themselves amidst the

485
00:34:25,000 --> 00:34:29,000
inner cell mass, and
they will not be able to

486
00:34:29,000 --> 00:34:33,000
participate in embryogenesis. So
therefore, the epigenetic program

487
00:34:33,000 --> 00:34:38,000
in these somatic cells seems to
be irrevocably set to preclude the

488
00:34:38,000 --> 00:34:44,000
participation of the already
differentiated mammary epithelial

489
00:34:44,000 --> 00:34:49,000
cells in subsequent embryogenesis.
Therefore, you could not do this

490
00:34:49,000 --> 00:34:54,000
experiment all over again of
introducing cells into the inner

491
00:34:54,000 --> 00:35:00,000
cell mass as I just described over
here, injecting them into this.

492
00:35:00,000 --> 00:35:04,000
But still, that doesn't answer the
question. The issue is not whether

493
00:35:04,000 --> 00:35:08,000
the mammary epithelial cell is
irrevocably committed to being a

494
00:35:08,000 --> 00:35:12,000
mammary epithelial cell. The
issue: is its genome capable

495
00:35:12,000 --> 00:35:16,000
under the proper circumstances of
becoming an early embryonic cell.

496
00:35:16,000 --> 00:35:21,000
And therefore, what was done is
the following. One took mammary

497
00:35:21,000 --> 00:35:25,000
epithelial cells, in this
case from Dolly's quote

498
00:35:25,000 --> 00:35:29,000
unquote "mother, one
prepared nuclei from these

499
00:35:29,000 --> 00:35:33,000
cells, taking them out of the
cytoplasm, and then one got

500
00:35:33,000 --> 00:35:38,000
fertilized eggs or eggs that
have been induced to become.

501
00:35:38,000 --> 00:35:42,000
So here's an oocyte. An
oocyte is an unfertilized egg.

502
00:35:42,000 --> 00:35:46,000
In principle, you can activate
an oocyte by putting a sperm in,

503
00:35:46,000 --> 00:35:51,000
or in fact it's actually better if
you take the oocyte and you fool it

504
00:35:51,000 --> 00:35:55,000
into thinking it's become fertilized
by treating it with different salts,

505
00:35:55,000 --> 00:36:00,000
high potassium
concentration, and so forth.

506
00:36:00,000 --> 00:36:04,000
And that will induce the egg
to say I've been fertilized.

507
00:36:04,000 --> 00:36:09,000
I better start embryogenesis. But
what you do in this case is the

508
00:36:09,000 --> 00:36:13,000
following. The egg has its
own haploid nucleus here,

509
00:36:13,000 --> 00:36:18,000
and you can take a little needle.
And, you suck that nucleus right

510
00:36:18,000 --> 00:36:23,000
out of the egg. So,
you've enucleated it.

511
00:36:23,000 --> 00:36:27,000
That's what you've done,
and now the egg is enucleate.

512
00:36:27,000 --> 00:36:32,000
It doesn't have a nucleus
in it. But keep in mind,

513
00:36:32,000 --> 00:36:36,000
much of what happens during early
embryogenesis is programmed not only

514
00:36:36,000 --> 00:36:41,000
by the genes but by all array
of cytoplasmic proteins that are

515
00:36:41,000 --> 00:36:46,000
present throughout the egg,
and which play critical roles in

516
00:36:46,000 --> 00:36:50,000
determining the subsequent
course of embryogenesis.

517
00:36:50,000 --> 00:36:55,000
So now what you can do is you
inject into this enucleate oocyte

518
00:36:55,000 --> 00:37:00,000
the nucleus of a
mammary epithelial cell.

519
00:37:00,000 --> 00:37:05,000
The mammary epithelial cell is
obviously highly differentiated.

520
00:37:05,000 --> 00:37:10,000
It's there to make milk. We'll
call it an MEC if you want,

521
00:37:10,000 --> 00:37:15,000
and you put that in there, and
under certain circumstances,

522
00:37:15,000 --> 00:37:20,000
and then you can treat this with
a little bit of salt to mimic the

523
00:37:20,000 --> 00:37:25,000
physiological stimulus that comes
after the sperm hits the egg.

524
00:37:25,000 --> 00:37:31,000
And now this egg will
think it's been fertilized.

525
00:37:31,000 --> 00:37:35,000
And now it will begin to divide.
But keep in mind, the genome of

526
00:37:35,000 --> 00:37:39,000
this quote unquote "unfertilized
egg" has come not from the sperm and

527
00:37:39,000 --> 00:37:44,000
the preexisting nucleus of the egg.
It's come because the nucleus has

528
00:37:44,000 --> 00:37:48,000
been injected from a
mammary epithelial cell.

529
00:37:48,000 --> 00:37:52,000
An experience over the last 30
years had indicated that this will

530
00:37:52,000 --> 00:37:57,000
never work. But finally somebody in
Scotland, a man named Ian Wilmouth

531
00:37:57,000 --> 00:38:01,000
tinkered enough with the conditions
of these cells that he could

532
00:38:01,000 --> 00:38:05,000
actually get it to work not
so often, maybe one, or two,

533
00:38:05,000 --> 00:38:10,000
or three times out of 100
tries. But on those conditions,

534
00:38:10,000 --> 00:38:14,000
this thing would begin to divide.
The nucleus would begin to divide

535
00:38:14,000 --> 00:38:19,000
its diploid. Keep in mind that
when a sperm comes into an egg,

536
00:38:19,000 --> 00:38:23,000
the egg is haploid. The sperm
is haploid. Together they make a

537
00:38:23,000 --> 00:38:27,000
diploid genome. This
introduced genomus diploid,

538
00:38:27,000 --> 00:38:32,000
and the question is, the critical
question is, can the genes in this

539
00:38:32,000 --> 00:38:36,000
introduced nucleus totally rearrange
their transcriptional program so

540
00:38:36,000 --> 00:38:41,000
that even though these genes might
all be intact in terms of nucleotide

541
00:38:41,000 --> 00:38:45,000
sequence, can the entire infinitely
complex array of DNA associated

542
00:38:45,000 --> 00:38:50,000
proteins, I.e. the
proteins that constitute

543
00:38:50,000 --> 00:38:54,000
the chromatin which is not only the
histones but also the transcription

544
00:38:54,000 --> 00:38:59,000
factors, the TF's, can they
all jump on and jump off as

545
00:38:59,000 --> 00:39:03,000
they should to mimic and replicate
the spectrum of transcription

546
00:39:03,000 --> 00:39:08,000
factors that is normally present
shortly after an egg is fertilized?

547
00:39:08,000 --> 00:39:12,000
If they can do that, then
this embryo can begin to

548
00:39:12,000 --> 00:39:16,000
replicate, and can ultimately
develop into a complete embryo.

549
00:39:16,000 --> 00:39:20,000
If they can't, then embryogenesis
is going to be truncated shortly

550
00:39:20,000 --> 00:39:24,000
thereafter maybe at the two cell
stage, at the four cell stage,

551
00:39:24,000 --> 00:39:28,000
at the 16 cell stage, but shortly
thereafter, not because of the DNA

552
00:39:28,000 --> 00:39:32,000
sequences being defective,
but because the spectrum of

553
00:39:32,000 --> 00:39:36,000
transcription factors is up and down
regulates certain genes is in fact

554
00:39:36,000 --> 00:39:40,000
not been able to re-assort
themselves in response to what?

555
00:39:40,000 --> 00:39:44,000
Initially, in response to the
signals coming from the cytoplasm

556
00:39:44,000 --> 00:39:48,000
because one might imagine,
correctly so, that the nucleus in

557
00:39:48,000 --> 00:39:53,000
here is getting signals from
the cytoplasm telling it,

558
00:39:53,000 --> 00:39:57,000
in effect, telling this nucleus,
you should behave functionally as if

559
00:39:57,000 --> 00:40:01,000
you were the nucleus of a
fertilized egg. In other words,

560
00:40:01,000 --> 00:40:05,000
the environment of proteins
here is influencing the behavior

561
00:40:05,000 --> 00:40:09,000
of this nucleus. That goes
backwards to our normal

562
00:40:09,000 --> 00:40:12,000
way of thinking because keep in mind
our normal vectoral way of thinking

563
00:40:12,000 --> 00:40:14,000
is that the nucleus is
influencing the cytoplasm.

564
00:40:14,000 --> 00:40:17,000
That's the direction of
information flow. But here,

565
00:40:17,000 --> 00:40:20,000
we're having a different situation.
Here, the cytoplasm is telling this

566
00:40:20,000 --> 00:40:23,000
injected nucleus, well,
you used to be a mammary

567
00:40:23,000 --> 00:40:25,000
epithelial cell nucleus, but
now you've got to take on a

568
00:40:25,000 --> 00:40:28,000
different job. And we're
going to force you to do

569
00:40:28,000 --> 00:40:32,000
so. And to the
extent that happens,

570
00:40:32,000 --> 00:40:36,000
then in principle, one can
end up having a normal embryo.

571
00:40:36,000 --> 00:40:40,000
And, it happened actually on
rare occasion that this worked.

572
00:40:40,000 --> 00:40:44,000
Here they used actual electrical
stimulus rather than salt to get the

573
00:40:44,000 --> 00:40:48,000
nucleus to divide. This
electrical stimulus,

574
00:40:48,000 --> 00:40:52,000
again, was to mimic the stimulus
that the sperm entering the egg

575
00:40:52,000 --> 00:40:56,000
normally provides, thereby
activating the egg and

576
00:40:56,000 --> 00:41:00,000
forcing the entire
fertilized egg to proliferate.

577
00:41:00,000 --> 00:41:03,000
And so, once this starts developing,
let's say, the blastocyst stage,

578
00:41:03,000 --> 00:41:07,000
here we have a blastocyst.
You can see the inner cell mass

579
00:41:07,000 --> 00:41:11,000
once again here. This
can be transferred into a

580
00:41:11,000 --> 00:41:14,000
pseudo-pregnant ewe.
Pseudo-pregnant means you take a

581
00:41:14,000 --> 00:41:18,000
female ewe and you inject it with a
series of hormones that persuade her

582
00:41:18,000 --> 00:41:22,000
reproductive system including
prolactin, and progesterone,

583
00:41:22,000 --> 00:41:25,000
or estrogen, persuade
her reproductive system,

584
00:41:25,000 --> 00:41:29,000
her uterus, that she's pregnant.
You inject this early embryo into

585
00:41:29,000 --> 00:41:33,000
her, and this early embryo will then
implant into the wall of her uterus

586
00:41:33,000 --> 00:41:37,000
and begin to develop.
And if it all works well,

587
00:41:37,000 --> 00:41:41,000
you get a Dolly is born. You get
a new sheep coming out of this.

588
00:41:41,000 --> 00:41:46,000
It doesn't work so often, one,
two, three, four times after out of

589
00:41:46,000 --> 00:41:50,000
a hundred, and very often in
the great majority of cases,

590
00:41:50,000 --> 00:41:55,000
there are mis-births, mis-carriages,
which happen in the middle of

591
00:41:55,000 --> 00:41:59,000
embryogenesis. So, almost
in the great majority of

592
00:41:59,000 --> 00:42:04,000
cases, this fails. Somehow,
the reprogramming of this

593
00:42:04,000 --> 00:42:08,000
nucleus, which is what we're talking
about, reprogramming it in terms of

594
00:42:08,000 --> 00:42:12,000
its transcriptional program,
goes awry. And therefore, bad

595
00:42:12,000 --> 00:42:17,000
things happen. The fact
that on a rare occasion

596
00:42:17,000 --> 00:42:21,000
gets and succeeds here already is
extremely interesting because it

597
00:42:21,000 --> 00:42:25,000
proves irrevocably that the genome
of a mammary epithelial cell is in

598
00:42:25,000 --> 00:42:30,000
principle competent to program
entire embryonic development.

599
00:42:30,000 --> 00:42:34,000
And that means that during the
development of Dolly's mother,

600
00:42:34,000 --> 00:42:39,000
we'll put her up here, as she
developed from one cell into 1,

601
00:42:39,000 --> 00:42:44,000
00 or 10,000 billion cells, as
that development occurred the DNA

602
00:42:44,000 --> 00:42:49,000
sequences that went from the
fertilized egg to her didn't really

603
00:42:49,000 --> 00:42:53,000
change. I.e. the DNA sequences
that were in one of her mammary

604
00:42:53,000 --> 00:42:58,000
epithelial cells were intact,
and as capable in principle of

605
00:42:58,000 --> 00:43:03,000
launching the full-fledged
development as would be

606
00:43:03,000 --> 00:43:08,000
a fertilized egg. And
that is one of the proofs,

607
00:43:08,000 --> 00:43:12,000
by the way, that in fact
differentiation does not involve,

608
00:43:12,000 --> 00:43:16,000
with some rare exceptions,
alterations in DNA sequence.

609
00:43:16,000 --> 00:43:20,000
This, in turn, ends up being
connected with the whole issue of

610
00:43:20,000 --> 00:43:24,000
embryonic stem cells. Let's
say that I wanted to have my

611
00:43:24,000 --> 00:43:28,000
muscles regenerated, although
they're still pretty good.

612
00:43:28,000 --> 00:43:33,000
So, I take a skin cell of mine,
and I inject the skin cell.

613
00:43:33,000 --> 00:43:36,000
I take the nucleus out, and
I inject it into an oocyte.

614
00:43:36,000 --> 00:43:40,000
And then I let the oocyte
develop up to this stage.

615
00:43:40,000 --> 00:43:44,000
And I don't put the oocyte back
into a sheep or another woman,

616
00:43:44,000 --> 00:43:48,000
although I could in principle. I
actually take the cells out of the

617
00:43:48,000 --> 00:43:51,000
inner cell mass.
Those are ES cells,

618
00:43:51,000 --> 00:43:55,000
and I begin to use them to
regenerate my muscles to do this

619
00:43:55,000 --> 00:43:59,000
strategy. So, the
cells are, in this case,

620
00:43:59,000 --> 00:44:03,000
not used for reproductive cloning,
which is what this is here.

621
00:44:03,000 --> 00:44:07,000
They're used for therapeutic cloning,
where instead of taking these cells

622
00:44:07,000 --> 00:44:11,000
and the ES cells and allowing
them to form a whole embryo,

623
00:44:11,000 --> 00:44:15,000
they're used to form a cell line
of ES cells from the blastocyst from

624
00:44:15,000 --> 00:44:19,000
the inner cell mass. What
we talked about before,

625
00:44:19,000 --> 00:44:23,000
here you see the blastocyst
with the inner cell mass here.

626
00:44:23,000 --> 00:44:27,000
You see it again. But now, rather
than allowing this blastocyst

627
00:44:27,000 --> 00:44:31,000
to continue development, we
simply extract cells from it and

628
00:44:31,000 --> 00:44:34,000
again create ES cells. I
could create therefore in

629
00:44:34,000 --> 00:44:38,000
principle, ES cells, which
are genetically identical to

630
00:44:38,000 --> 00:44:41,000
all the cells in my body, and
any one of you could as well.

631
00:44:41,000 --> 00:44:44,000
And here, there's not only one, but
there's two ethical complications.

632
00:44:44,000 --> 00:44:48,000
First of all, here we're starting
human life with the intent of

633
00:44:48,000 --> 00:44:51,000
truncating it very early, and
secondly, where are the oocytes

634
00:44:51,000 --> 00:44:54,000
going to come from? Well,
you could say you can get

635
00:44:54,000 --> 00:44:58,000
them from some women, but
producing oocytes from a human

636
00:44:58,000 --> 00:45:02,000
female isn't so easy. You
have to inject her with all

637
00:45:02,000 --> 00:45:06,000
kinds of stimulatory hormones,
choreogramatatrophic hormones. It's

638
00:45:06,000 --> 00:45:10,000
an unpleasant procedure.
Usually women are paid $5,

639
00:45:10,000 --> 00:45:14,000
00 or $10,000 to produce
some oocytes. Well,

640
00:45:14,000 --> 00:45:18,000
you say, that's OK, but
is that OK? I don't know.

641
00:45:18,000 --> 00:45:22,000
Is it OK to pay a woman to donate
her oocytes to make herself into an

642
00:45:22,000 --> 00:45:26,000
oocyte factory? I don't
know. You have to judge.

643
00:45:26,000 --> 00:45:30,000
I think there's arguments
both for and against it.

644
00:45:30,000 --> 00:45:34,000
Clearly, any one of us would be
extraordinarily naïve if we thought

645
00:45:34,000 --> 00:45:39,000
that this was a procedure which
had no ethical encumbrances in it.

646
00:45:39,000 --> 00:45:43,000
And, you have to think about
them for yourself. Still,

647
00:45:43,000 --> 00:45:48,000
the potentials are enormous, and
therefore the question exists.

648
00:45:48,000 --> 00:45:53,000
Will there be ways in the future
of taking differentiated cells from

649
00:45:53,000 --> 00:45:57,000
one's tissue, and in fact using
them in these ways to make ES cells

650
00:45:57,000 --> 00:46:02,000
without having to go through an
oocyte, and without having the

651
00:46:02,000 --> 00:46:06,000
potential of creating human life.
The alternative to this has been to

652
00:46:06,000 --> 00:46:10,000
do the following, to go
into our normal tissues and

653
00:46:10,000 --> 00:46:14,000
pull out adult stem cells. What
do I mean by adult stem cells?

654
00:46:14,000 --> 00:46:18,000
These are not stem cells that are
totipotent. These are stem cells

655
00:46:18,000 --> 00:46:22,000
which are in my muscles and
regenerating muscle mass,

656
00:46:22,000 --> 00:46:26,000
which happens believe it or not.
These are stem cells which might be

657
00:46:26,000 --> 00:46:30,000
in my skin and are continually
regenerating skin cells.

658
00:46:30,000 --> 00:46:34,000
Keep in mind that in the maintenance
of all our normal tissues there are

659
00:46:34,000 --> 00:46:38,000
stem cells whose configuration can
formally be depicted like this with

660
00:46:38,000 --> 00:46:42,000
the transit amplifying
cells we talked about before.

661
00:46:42,000 --> 00:46:46,000
And maybe, if one took the stem
cells out of an adult tissue right

662
00:46:46,000 --> 00:46:50,000
here, if we had a way of extracting
them, those could be propagated in

663
00:46:50,000 --> 00:46:54,000
vitro, and then injected back
in. Those are so-called adult stem

664
00:46:54,000 --> 00:46:58,000
cells. And the
individuals who are against

665
00:46:58,000 --> 00:47:02,000
this kind of manipulation of human
embryos and so forth say that adult

666
00:47:02,000 --> 00:47:06,000
stem cells are really the solution.
You take stem cells out of a

667
00:47:06,000 --> 00:47:10,000
person's tissue, you expand
them. Ex vivo means out

668
00:47:10,000 --> 00:47:14,000
of the body, in vitro, and
then you use them. You inject

669
00:47:14,000 --> 00:47:19,000
them into somebody's tissue
to regenerate their tissue.

670
00:47:19,000 --> 00:47:23,000
There's only one problem with that.
It's ethically far less encumbered

671
00:47:23,000 --> 00:47:27,000
obviously, but it doesn't
work that well. In fact,

672
00:47:27,000 --> 00:47:31,000
some people think it hardly works at
all, that the exceptions are really

673
00:47:31,000 --> 00:47:36,000
rather far and few between. And
so, this issue will long be or

674
00:47:36,000 --> 00:47:41,000
continue to be debated. But
it obviously represents a very

675
00:47:41,000 --> 00:47:46,000
new and exciting area of biomedical
research. And interestingly enough,

676
00:47:46,000 --> 00:47:52,000
it impinges as well in a fully
unexpected way on cancer because

677
00:47:52,000 --> 00:47:57,000
this whole paradigm of stem cells,
it turns out, also applies to cancer

678
00:47:57,000 --> 00:48:01,000
cells. If you were to
have asked me two or

679
00:48:01,000 --> 00:48:05,000
three years ago, what did
the cells in the tumor look

680
00:48:05,000 --> 00:48:09,000
like? I would draw a picture like
this, that these are a series of

681
00:48:09,000 --> 00:48:12,000
exponentially growing cells
so that all the cancer cells,

682
00:48:12,000 --> 00:48:16,000
all the neoplastic cells in
the tumor mass are biologically

683
00:48:16,000 --> 00:48:20,000
equivalent to one another.
They all have the same mutant

684
00:48:20,000 --> 00:48:23,000
genome, and they all are capable
of multiplying exponentially.

685
00:48:23,000 --> 00:48:27,000
But it turns out that work in the
Matavoidic system on Matevoidic

686
00:48:27,000 --> 00:48:31,000
tumors like leukemias,
and now on breast cancers,

687
00:48:31,000 --> 00:48:36,000
yields a very different results,
because it turns out that the way

688
00:48:36,000 --> 00:48:44,000
that the tumors are organized
looks like this. The tumors also are

689
00:48:44,000 --> 00:48:52,000
organized in this hierarchical
array just like normal tissue.

690
00:48:52,000 --> 00:49:00,000
How do we know that? Again,
I'm glad I asked that question.

691
00:49:00,000 --> 00:49:04,000
Because if you take these cells out
of the tumor and put them in another

692
00:49:04,000 --> 00:49:08,000
mouse, let's say,
you get a new tumor.

693
00:49:08,000 --> 00:49:13,000
These cells are tumorogenic,
I.e. they concede a new tumor.

694
00:49:13,000 --> 00:49:17,000
If you take these cells out of the
tumor, they have the same mutant

695
00:49:17,000 --> 00:49:21,000
genome. They constitute the bulk,
the vast mass of the cancer cells in

696
00:49:21,000 --> 00:49:26,000
a tumor. You put these into a
mouse, and they're non-tumorogenic.

697
00:49:26,000 --> 00:49:30,000
And, in some kinds of tumors, the
tumorogenic cells can represent

698
00:49:30,000 --> 00:49:35,000
only 1 or 2% of the total mass
of cancer cells in the tumor.

699
00:49:35,000 --> 00:49:38,000
And from this, we begin
to realize that you look

700
00:49:38,000 --> 00:49:42,000
inside tumors: the tumors deviate
minimally from the organization of

701
00:49:42,000 --> 00:49:46,000
normal tissue. They also
depend on self-renewing

702
00:49:46,000 --> 00:49:50,000
stem cells which can make transit
amplifying cells and can give end

703
00:49:50,000 --> 00:49:53,000
stage cells, which although
they're neoplastic, have many of the

704
00:49:53,000 --> 00:49:57,000
differentiated characteristics of
the normal tissue from which they

705
00:49:57,000 --> 00:50:01,000
arose. And this has
enormous implications for,

706
00:50:01,000 --> 00:50:05,000
for example, therapies
against tumors.

707
00:50:05,000 --> 00:50:09,000
If you ask somebody, how do
you develop and how you judge

708
00:50:09,000 --> 00:50:13,000
the success of an anticancer
treatment? You talk to somebody

709
00:50:13,000 --> 00:50:17,000
like from the pharmaceutical
industry. And let's say that's easy.

710
00:50:17,000 --> 00:50:21,000
If you have a new drug, and
that drug reduces the mass of a

711
00:50:21,000 --> 00:50:26,000
tumor by 50%, that means that
you've done something really good.

712
00:50:26,000 --> 00:50:30,000
But let's look what's going on here.
If these cells are 99% of the tumor

713
00:50:30,000 --> 00:50:34,000
in terms of the mass and these
cells are 1% of the tumor,

714
00:50:34,000 --> 00:50:38,000
let's say you've invented a new drug
which wipes out all of these cells

715
00:50:38,000 --> 00:50:42,000
but doesn't touch these cells. The
bulk of the tumor has shrunk and

716
00:50:42,000 --> 00:50:46,000
everybody will say, eureka,
we've succeeded in curing

717
00:50:46,000 --> 00:50:50,000
cancer. But keep in mind that the
self-renewing capacity of the tumor

718
00:50:50,000 --> 00:50:53,000
rests in these cells. And
if these cells are allowed to

719
00:50:53,000 --> 00:50:57,000
survive, then they'll start
proliferating again and regenerate

720
00:50:57,000 --> 00:51:01,000
the entire tumor mass. And
you won't really know that you

721
00:51:01,000 --> 00:51:05,000
had any success because these cells
look like all the other tumor cells

722
00:51:05,000 --> 00:51:10,000
under the microscope. But
biologically, they're very

723
00:51:10,000 --> 00:51:14,000
different. And therefore,
the future of cancer therapy,

724
00:51:14,000 --> 00:51:19,000
and it will take five or ten years
to do this, has to begin to focus on

725
00:51:19,000 --> 00:51:23,000
getting rid of these self-renewing
stem cells which create this

726
00:51:23,000 --> 00:51:28,000
enormous regenerative
capacity on the part of tumors.

727
00:51:28,000 --> 00:51:32,000
See you next Monday.
Have a great vacation.

728
00:51:32,000 --> 00:51:37,000
Eat much turkey, and get some
exercise, and don't smoke.