Why does cloning create abnormalities? Scientists take a step towards finding out
Berlin, Germany: Significant abnormalities observed in cloned mice help reinforce the need to continue to avoid the reproductive cloning of humans, a scientist said today (Wednesday 30 June 2004) at the 20th annual conference of the European Society of Human Reproduction and Embryology. Dr. Takumi Takeuchi, from Cornell University, New York, USA told a media briefing that he and Dr. Gianpiero Palermo's team had compared imprinting abnormalities (the process where specific genes inherited from both parents are silent) in mice embryos derived from assisted reproduction techniques and from cloning.
"We found significantly impaired development in the cloned embryos compared with those derived from more conventional ART techniques", said Dr. Takeuchi, "and this has made us more convinced that reproductive cloning is unsafe and should not be applied to humans."
Drs. Takeuchi and Palermo were prompted to undertake the research by concerns about the increased incidence of imprinting abnormalities in children born after ARTs. The most prominent of these is Beckwith-Wiedemann syndrome, where children are born larger than normal.
Scientists also knew that cloned animals had been born with a similar condition, called 'large offspring syndrome'. Dr.Takeuchi's team set out to study whether the disorders arising in the ART system and those in cloned animals were comparable. The team took mouse oocytes and divided them into three groups. 68 were inseminated by ICSI, 37 activated parthenogenetically (without involving male gametes), and 77 were cloned by injected a cell nucleus into an egg where the nucleus had been removed. Of this latter group, 43 underwent first embryonic cleavage (the first few divisions of an embryonic egg) and 15 became full blastocysts.
"The embryos created by parthenogenesis and those from ICSI reached the blastocyst stage at the same rate, unlike the clones, where only 30% got that far", said Dr. Takeuchi. "This appears to be due to the abnormal gene expression we saw in the cloned group. This not only explains the developmental impairment of the cloned group, but may in future be helpful in identifying environmental culture condition that are deleterious to the development of ART embryos," he said.
Dr. Takeuchi said that as yet it was difficult to make a direct link with a specific cause for the abnormalities. "But there are a number of possibilities", he said. "They could be linked to fertility medications utilized to induce superovulation, or the progesterone employed to help implantation; in vitro culture conditions which could be related to the length of the culture or the concentrations of certain media components such as serum or even a specific amino acid. Finally, we cannot exclude the contribution of the peculiar genetic makeup of patients' gametes, together with the specific ART procedure", he said.
Identification of gene expression abnormalities would help to monitor the development of reproductive techniques prior to their application to routine medical practice, said Dr. Takeuchi.
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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