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
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
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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