as exciting as it sounds, cross species cloning between a cow and a
human may not be possible. The cytoplasm of an egg contains
transcription factors that must correctly interact with the nuclear
DNA to activate / deactivate certain genes during development. During
evolution, these proteins and their DNA binding region may change
(somewhat.) Also the mitochondria of the egg contains it own DNA
(meaning a cross species clone is not genetically identical to the
nucleus-donating species.) On the other hand, once the egg begins to
develop, human proteins will be produced ... whether these proteins
can correctly interact with a cow uterus to form vasculature needed
for the placenta ... I suspect it depends on how distantly related the
species are.
but instead, why not use a chimps? and just let the female chimp carry
the embryo? you could even genetically engineer a chimp with some
human DNA and mitochondria.
There is of course one other huge problem: each species contains its
own collection of viruses that are capable of entering a cell based on
surface molcules that are species specific. by using a cow or
whatever egg, you open up the door for viruses to enter the egg (while
it has maternal surface proteins) and thus invade the 'human' nucleus.
these viruses could combine with human viruses and that would be bad.
anyway, here are some sites ...
http://www.newsmax.com/archives/articles/2003/8/15/160205.shtml
http://www.mpibpc.mpg.de/inform/25years/Jaeckle.html
http://www.lirmm.fr/~guindon/ihp/IHP_Yang.pdf
here's a case where similar species cross-species cloning seems to have worked:
http://news.bbc.co.uk/1/hi/sci/tech/1113719.stm
even with closely related species virus transfer is potentially a huge
problem (and the main reason why our government sanctioned stem cell
lines cannot be used in people, since they were grown on a bed of
mouse cells to provide growth factors) of course, if you're
endangered to the point of extinction, who cares.
one other thing that I will note about your comment on using an
isolated uterus is that during pregnancy, antibodies normally pass
from mother to fetus. these antibodies protect the fetus from
infection not just during the pregnancy but for many months after
birth. if born without these antibodies, the chance of survival
through the first two years of life may be very slim. I'm not sure if
there is any data on this, but it would be modeled in animals. so if
you're going to go for it, you might need to pump in some human serum
(preferably, I suppose, with the antibodies that react to cow cells
removed.) |
