Cloned monkey embryos a "gallery of horrors"

John Aboud jathree at panix.com
Wed Dec 12 16:11:52 EST 2001


Attack of the blah blah blah.

-ja3


http://www.newscientist.com/news/news.jsp?id=ns99991679

Cloned monkey embryos are a "gallery of horrors"

19:00  	12  December  01
Sylvia Pagán Westphal, Boston

A high percentage of cloned monkey embryos that look healthy are 
really a "gallery of horrors" deep within, says a researcher at 
Advanced Cell Technology, the company that last month published the 
first paper on cloned human embryos.

This could mean that there is something unique about primate eggs 
that will make cloning monkeys or people far more difficult than 
cloning other animals. At the very least, the experiments show that 
there's a lot to learn before primates can be cloned.

Tanja Dominko, who presented the results last week at a conference in 
Washington DC, did the work before joining ACT, while she was working 
for the reproductive biologist Gerald Schatten at the Oregon Regional 
Primate Research Center in Beaverton.

Several groups have been trying for years to clone monkeys, but while 
the embryos look normal, no one has ever got them to develop further.

Uneven scatter
To try and figure out what was going wrong, Dominko looked at 265 
cloned rhesus macaque embryos created by nuclear transfer - plucking 
out an egg's nucleus and then adding a nucleus from a donor cell. She 
followed development of the embryos through several divisions, from 
the two-cell stage until the 32-cell stage.

Though they appeared superficially healthy, the cells in the vast 
majority of Dominko's embryos did not form distinct nuclei containing 
all the chromosomes. Instead, the chromosomes were scattered unevenly 
throughout the cells.

"The surprising thing is that these cells keep dividing," says 
Dominko. Some embryos developed to the stage known as a blastocyst, 
but by day six or seven they had started to look abnormal.

The cloned human embryos created by ACT didn't even get this far. 
Only one reached the six-cell stage.

Trauma of removal
Dominko says that the trauma of removing the nucleus from the egg 
might be what triggers the defects. Eggs whose nuclei are removed and 
then put back inside show the same abnormalities, as well as evidence 
of programmed cell suicide. "This is not to say that normal embryos 
can't be made, but not on a regular basis," says Dominko.

Ian Wilmut, who cloned Dolly the sheep, told the conference that 
Dominko's results were not surprising in the light of experience of 
nuclear transfer in mice and cows. Even in these animals the success 
rates are not high, so the phenomena observed by Dominko probably 
occur in them as well - it's just that everyone focuses on the few 
successes, he says.

Even so, researchers hoping to publish work on nuclear transfer in 
humans may now have to come up with better evidence that embryos are 
healthy. William Haseltine, editor of the journal in which ACT 
published details of its cloned human embryos, now agrees that 
pictures alone aren't enough.
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