Cloned monkey embryos a "gallery of horrors"
jathree at panix.com
Wed Dec 12 16:11:52 EST 2001
Attack of the blah blah blah.
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.
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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