Cloning primates is turning out to be a real challenge

December 12, 2001

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 (New Scientist, 1 December, p 4). 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.
-end-
Author: Sylvia Pagan Westphal, Boston

New Scientist issue: 15TH December 2001

PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS STORY AND, IF PUBLISHING ONLINE, PLEASE CARRY A HYPERLINK TO: http://www.newscientist.com

New Scientist

Related Embryos Articles from Brightsurf:

Zebrafish embryos help prove what happens to nanoparticles in the blood
What happens to the nanoparticles when they are injected into the bloodstream, for example, to destroy solid tumours?

Artificial intelligence system developed to help better select embryos for implantation
Investigators from Brigham and Women's Hospital and Massachusetts General Hospital are developing an artificial intelligence system with the goal of improving IVF success by helping embryologists objectively select embryos most likely to result in a healthy birth.

Embryos taking shape via buckling
The embryo of an animal first looks like a hollow sphere.

Who's your daddy? Male seahorses transport nutrients to embryos
New research by Dr Camilla Whittington and her team at the University of Sydney has found male seahorses transport nutrients to their developing babies during pregnancy.

Study suggests embryos could be susceptible to coronavirus
Genes that are thought to play a role in how the SARS-CoV-2 virus infects our cells have been found to be active in embryos as early as during the second week of pregnancy, say scientists at the University of Cambridge and the California Institute of Technology (Caltech).

Spawning fish and embryos most vulnerable to climate's warming waters
Spawning fish and embryos are far more vulnerable to Earth's warming waters than fish in other life stages, according to a new study, which uniquely relates fish physiological tolerance to temperature across the lifecycles of nearly 700 fish species.

Animal embryos evolved before animals
A new study by an international team of researchers, led by scientists from the University of Bristol and Nanjing Institute of Geology and Palaeontology, has discovered that animal-like embryos evolved long before the first animals appear in the fossil record.

Choosing the best embryos
Struggling with infertility? You are not alone. Infertility affects one out of every six Canadian couples.

Turtle embryos play a role in determining their own sex
In certain turtle species, the temperature of the egg determines whether the offspring is female or male.

Early in vitro testing for adverse effects on embryos
ETH researchers have combined embryonic cells and liver cells in a new cell culture test.

Read More: Embryos News and Embryos Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.