14 December 2001
CLONED MONKEY EMBRYOS - A "GALLERY OF HORRORS"
1. Cloned monkey embryos are a "gallery of horrors"
2. IVF technique may increase birth abnormalities
1. Cloned monkey embryos are a "gallery of horrors"
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.
IVF technique may increase birth abnormalities
12 December 2001
Rachel Nowak, Melbourne
A popular IVF technique may increase the risk of babies being born with abnormalities such as ambiguous genitalia.
For roughly five per cent of men seeking fertility treatment because they have few or no sperm, the cause is a tiny mutation in the Y chromosome called a microdeletion. As long as the man still produces a few sperm, however, it is sometimes possible to inject one directly into the egg - a technique called intracytoplasmic sperm injection.
One of the reasons ICSI is controversial is that if there's a genetic reason for the man's infertility, it will be passed on to his sons. Many couples are prepared to use ICSI anyway, arguing that it will also be available to their children.
But evidence presented at a symposium at the Monash Institute of Reproduction and Development in Melbourne last week suggests that microdeletions on the Y chromosome are a precursor to more serious genetic faults.
Ken McElreavey of the Pasteur Institute in Paris found that in eight men with microdeletions, Y chromosomes were missing in about 10 per cent of the cells in their bodies. In the three who had enough sperm to test, up to 18 per cent of the sperm lacked a Y chromosome.
These findings suggest that the microdeletion is a sign of a chromosomal instability that causes some cells to lose the entire Y chromosome, McElreavey says. The loss of the Y chromosome in some of a baby's cells - called genetic mosaicism - can cause either ambiguous genitalia or Turner's syndrome, or both. Women with Turner's have normal female genitals, but they are unusually short and do not go through puberty.
Another study to be published soon also indicates a problem with ICSI and the sex chromosomes. Andre Van Steirteghem of the Free University in Brussels (VUB), who originally developed ICSI, found through tests on amniotic cells that in ICSI pregnancies there are three times as many sex chromosome abnormalities, including loss of the Y chromosome.
But the risk was still very low - only 10 out of almost 1600 fetuses created by ICSI had the defects.
That doesn't mean there isn't a problem, says McElreavey. Men with Y chromosome microdeletions make up just a small fraction of those using
ICSI, but they might be largely responsible for offspring with Y chromosome losses. If so, then the technique may be too risky to use on them. Every fertility clinic should be checking for these microdeletions, McElreavey says. "We need much greater follow-up of these men."
ICSI has been under fire ever since it was introduced. While most studies suggest the rate of abnormal births is no higher than usual, some indicate that it's twice as high. Worldwide, 35,000 ICSI babies were born in 1998.
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