[Paleopsych] Nature: Biologists come close to cloning primates
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Wed Oct 27 21:13:25 UTC 2004
Biologists come close to cloning primates
Cloned monkey embryos transferred into mothers.
US biologists have created cloned monkey embryos, and successfully
transferred them into monkey mothers. Although none of the resulting
pregnancies lasted more than a month, this is by far the closest
scientists have come to cloning a primate.
The study was unveiled yesterday by reproductive biologist Gerald
Schatten of the University of Pittsburgh, Pennsylvania, at the annual
meeting of the American Society for Reproductive Medicine in
Philadelphia. Schatten's group copied a technique used earlier this
year to clone a human embryo and extract embryonic stem cells.
If researchers are able to repeat this process in monkeys, it might
help them to refine the tricky technique without experimenting on
human eggs and embryos, which are very difficult to obtain and raise a
host of ethical objections. This in turn might help to resolve whether
human embryonic stem cells, which can grow into a variety of tissues,
will prove useful in medicine.
Previously, Schatten and his colleagues had struggled to create
healthy monkey embryos by cloning, which involves removing the
DNA-containing nucleus from an adult cell and inserting it into an egg
stripped of its own nucleus.
In a 2003 study published in Science, Schatten suggested that
extracting the nucleus from a monkey egg also robs it of two proteins
essential for survival^1. He found that all the resulting embryos
had fatal chromosomal defects, and speculated that cloning any
primate, including humans, might be impossible.
That view proved false in February this year, when scientists from
South Korea announced in Science that they had successfully cloned
human embryos, and used them to grow embryonic stem cells capable of
morphing into numerous different tissue types^2. One aim of such
research is to grow replacement tissues to fight human disease.
In the Korean work, the cloned human embryos were allowed to divide in
culture for just five or six days before being terminated. But, by
adopting the Koreans' technique, Schatten's team made 135 cloned
monkey embryos and transferred them into 25 mothers. The team
experimented with transferring the nuclei from skin cells and from
cumulus cells, which are found in the ovary.
Why does it work?
Schatten says he is not yet sure why the Korean method is so
successful. Rather than sucking the nucleus out of the recipient eggs,
the technique involves gently squeezing it out. This may remove less
of the cell's cytoplasm and leave more of the essential molecules
needed by the egg to direct embryo development; or it may simply cause
less damage to the eggs.
None of the cloned monkey embryos resulted in a pregnancy that lasted
more than a month. But Schatten says it is too early to say whether
cloned monkeys will ever be born; it may just take more attempts. It
is also impossible, he says, to use these results to predict whether a
cloned human baby could survive long in development.
Schatten adds that his preliminary attempts to make embryonic stem
cells from cloned monkey embryos failed. But at least his study
confirms that the Korean cloning method works, something that has been
difficult to prove because very few research groups work in such
areas. "It shows that at least part of the technique is reproducible,"
1. Simerly C., et al. Science, 300. 297
(2003). | Article | PubMed | ISI |
2. Hwang W. S., et al. Science, 303. 1669 - 1674
(2004). | Article | PubMed | ISI | ChemPort |
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12 February 2004
Korea's stem-cell stars dogged by suspicion of ethical breach
06 May 2004
Stem-cell research: Crunch time for Korea's cloners
06 May 2004
Human clones doomed?
11 April 2003
Silence of the clones
11 March 2003
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