Articles

Pigeons from Chickens: Michael McGrew at TEDxDeExtinction

September 12, 2019


Translator: Yasmine Wong
Reviewer: Mary Beth Strawn (Applause) What I have to tell you first is that we actually don’t have the technology to bring back extinct birds to life. And we’re really going to have to– the problem, because of that, is because we can’t clone birds. And you see on this slide, this large egg here. So that yoke there, that you had
for your breakfast, is a single cell. And to clone an animal,
you would have to take a nucleus from the egg, and put in the nucleus
that you want to clone. And we’ve tried that
for many years in the chicken, and it was just impossible. So that brings me to this saying
by Salvador Dali. And he said, “Either things are easy
or they’re impossible.” So, if we can’t clone birds, we’re just going to have to find
a better way to do this. And the way I see
we’re going to do this, is that we’re going to use
these special cells called germ cells or sex stem cells to propagate endangered species and bring back extinct birds. Let me give you a bit of biology. In every animal,
in every human, in every bird,
in every fish, there are these special
group of cells, stem cells, that are called the germ cells,
or the sex stem cells. And they’re set aside
very early in development. And they’re carried within
the body, in the testees. So, these cells only do one thing. In the female, they make eggs. In the male, they make sperm. And during their development,
they undergo miosis, they lose half their chromosomes, and they make a functional gamete. Then the two of them come together, form a new zygote and make the next animal. So the problem with birds, is that these sex stem cells form very early in development. They’re there right at
the beginning in the laid egg. And they migrate through the embryo, to colonize the gonad. So, the problem is– you heard Robert Lanza talk
about making induced pluripotent cells. So if we make those from a bird, and we put them back at this early stage, they’re never going to make a germ cell. They’re never going
to give rise to offspring. They’ve arrived too late.
The germ cells have already been defined. The one thing we can do in birds– and that’s for chickens now, we haven’t done it for other species the one thing we can do that
you can’t do for any other species, is that we can take these germ cells, from the early embryo
and put them into culture. And in culture, they’ll grow. They’ll make millions
and millions of cells. So then, what we can do
with these cells in culture is that we can add
a gene to mark them. In this case, green fluorescent protein. So the cell turns green;
We can see it. And then we can take that cell, and put it in a surrogate host. In this case, another chicken. And we implant that in. We grow up that surrogate host
until it becomes an adult cockerel. We mate it and
what we see is actually some of the offspring are green. So it means that one germ cell, that one sex stem cell, that we took from one embryo, put it into culture, we were able to modify it,
put it into another host, and actually generate
offspring from that. This offers us a new opportunity. We’re actually going to make
a different sort of frozen zoo. And we’re calling that a frozen aviary. What we can do is
we can actually take germ cells from many types of chicken, grow them in culture, and freeze them in test tubes. And we’re going to do this
with industrial breed chickens that we eat. We’re also going to do this
with rare breeds, the chickens that we think are going to be lost from the world. We’re going to freeze them down
and then actually, very easily if we need these birds,
if they’re lost by disease, we’re going to be able
to file these cells put them into surrogate hosts
(other chickens) breed, and get back these chickens. My title was, “Pigeons from Chickens”. What does it have to do with germ cells? What does it have to do
with freezing cells? Well, the thing about these
sex stem cells in birds is that they’re promiscuous. In this case, this is a very unusual family. This chick actually has two parents,
which are here. The hen was the mother. And the duck was the father. And what happened– and this is a pure bred chick. What they did– actually, my friends at the CVRL– is that they took the sex stem cells
from a chicken and implanted them into a duck embryo. That duck hatched, grew up and it was mated back to a hen. And what happened was that
those germ cells functioned and gave rise to
a pure chicken offspring. What that means for us is if we want to bring back
an extinct bird, we actually don’t have
to have a close relative to be a host for these germ cells. We can use any bird
from any species to do this, even a chicken. The problem is this process
was very inefficient. There were very few
chick offspring that were born. What we want to do is we want to make a better host
for these germ cells that we’re going to freeze away. And the way we’re going to do that is to use Talen technology. We’re going to take one of
these cultured germ cells, and we’re going to mutate a gene that is important for
its own germ cells to develop. And then we’re going to inject that
back into a chicken, raise it up, and generate
a line of chickens with this mutated gene. What will happen then is that when we breed that chicken, and it has two mutant alleles, it will have no germ cells of its own. Then we can use it, actually, as a host, for our frozen germ cells. So, we can take germ cells
from our frozen bank, introduce them into this host chicken, and then all the offspring
from those two birds, both male and female, will be the chickens. And what we’re hoping to do with this is actually we can use germ cells
from endangered species, and inject them into these same hosts. And then when we breed these chickens, in this case, we’re hoping to get
this endangered bird, which is the houbara, which is an endangered bustard
from the Middle East. I’m going to put
the whole story together now. What we need to do is to be able
to cultivate germ cells, or sperm sex cells, from many different bird species. And we can only do that
for chicken now. That’s the big jump we have to take. Once we can do that, we’ll be able to take the technology
of George Church, to introduce DNA into these, to put in genes. In this case, from
the passenger pigeon, into the band-tailed pigeon. The cells from these are then put into a surrogate host. Most conservatively, it’ll be another band-tailed pigeon. These will be mated
and will generate offspring, which are band-tailed pigeon,
with passenger pigeon genes. And this process can be repeated
over and over again. What we’re hoping to do
to accelerate this process is to actually use one of these chickens,
with no germ cells. So we can actually mate that chicken, to the pigeon and get offspring,
with passenger pigeon traits. And I’m finished. Thank you for your attention. (Applause)

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