American researchers have revealed that cloning causes abnormalities in resulting embryos, but they found no evidence of defects in those created by other assisted reproduction techniques. The researchers were trying to investigate concerns that assisted reproductive technologies increase the risk of the rare genetic disorders Beckwith-Wiedemann and Angelman syndromes.
Drs Takumi Takeuchi and Gianpiero Palermo, of Cornell University (US), presented their findings to the annual conference of the European Society for Human Reproduction and Embryology (ESHRE). They created mouse embryos by three different methods: ICSI (intracytoplasmic sperm injection), where the is injected into the egg; by parthenogenesis, where an egg is induced to become an embryo without sperm; and SCNT (somatic cell nuclear transfer - cloning, where the nucleus of an adult cell is transferred to an enucleated egg. The team then grew the embryos to the blastocyst (16 cell) stage. Survival of the ICSI and parthenogenic embryos was the same as for naturally conceived embryos, but only 30 per cent of the cloned embryos made it to the blastocyst stage. 'This appears to be due to abnormal gene expression we saw in the cloned group', said Takeuchi.
Probing the cloned embryos with fluorescent markers, the researchers found that histone proteins, which bind to DNA, had been chemically reset in the cloned embryos. This reprogramming, known as imprinting, affects gene expression and so could lead to the reduced survival rate. 'Whether it is correctly reprogrammed, we don't know,' said Palermo. The chemical groups on the histones of ICSI and parthenogenesis derived embryos were normal, the researchers found.
The results have added to the debate on reproductive cloning. 'This has made us more convinced that reproductive cloning is unsafe and should not be applied to humans', said Takeuchi, whilst ESHRE, which renewed its moratorium on the reproductive cloning at the conference, described the technique as 'irresponsible and unethical'.