Animals cloned by somatic cell nucleus transfer are a gallery of horrors, some more than others.
Nine out of 10 cloned lambs die soon after birth at the South Australian Research and Development Institute that produced Australia’s first cloned sheep, Matilda. Many are destroyed at birth because their lungs are too immature for breathing or their kidney and urinary systems underdeveloped.
Matilda, unveiled 18 months ago, was cloned, like Dolly, by somatic cell nuclear transplant. Since then, the Institute has had little success. Instead of the flock of 30 cloned merinos expected, there are about six, not even enough to find out why they go wrong.
The Institute’s chief scientist, Dr Simon Walker admitted to doubts about the use of cloned sheep for commercial breeding.
It is even worse when it comes to attempts to clone monkeys. A high percentage of cloned monkey embryos that look healthy are really a "gallery of horrors" within, according to a researcher at Advanced Cell Technology, the company that claimed to have produced the first cloned human embryos. Tanja Dominko presented the results at a conference in December, in Washington DC. The work was done before she joined ACT, 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.
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.
Dominko looked at 265 cloned rhesus macaque embryos created by nuclear transfer. She said that the trauma of removing the nucleus from the egg might be responsible for the defects. Eggs whose nuclei are removed without adding a nucleus show the same abnormalities, in addition to evidence of programmed cell-death.
Surprisingly the cells keep dividing, some embryos developed to the stage known as a blastocyst (a hollow ball with a small mass of cells inside), but by day six or seven they had started to look abnormal.
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.
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, where the success rates are not high, so the same abnormalities may occur in them. It’s just that everyone focuses on the few successes, he was reported to have said.
Article first published February 2002