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Babies for gay couples remain science fiction

发布时间:2019-03-06 14:09:01来源:未知点击:

By Claire Ainsworth Lesbian couples have a long wait before the technology that allows them to create their own babies materialises, say scientists. Despite press reports highlighting this possibility, there is scant evidence that major biological barriers blocking the way could be overcome. In theory, a new technique being developed by Orly Lacham-Kaplan and her team at the Monash Institute for Reproduction and Development in Australia could allow a gay woman to “fertilise” her partner’s egg using the nucleus of, say, one of her skin cells as an artificial sperm. As New Scientist magazine reported on 5 July, this technique, and another which creates artificial eggs, is being developed to help patients who cannot make eggs or sperm. But it is far from clear whether either technique will overcome genomic imprinting – a major biological obstacle to same-sex couples creating babies. What’s more, the same safety concerns that haunt human reproductive cloning are also likely to apply to artificial eggs and sperm. “We may not get there because it is indeed too complicated,” says Alan Trounson, deputy director of the Monash Institute. “But I think it’s a worthwhile area of research to pursue.” Artificial eggs and sperm are made using nuclear transfer techniques similar to those used in reproductive cloning. But a key difference is that scientists can now make the nuclei of body cells halve the number of chromosomes they contain, mimicking the situation in natural eggs and sperm. These chromosomes will then link with the complementary set from the partner’s egg or sperm to mimic natural fertilisation. But scientists have known for nearly 20 years that some of the genes a child inherits from its father behave differently from those it gets from its mother. This is the result of “imprinting”; chemical markers that switch genes on or off and which are essential for normal embryonic development. In the early 1980s, Azim Surani, now at the Wellcome /CRC Institute for Cancer and Developmental Biology in Cambridge and his colleagues showed that mouse embryos created from two sperm nuclei or two egg nuclei develop abnormally and die long before birth. This is due to the different imprints on the genes in sperm and eggs. So, for the time being, it is impossible for gay couples to create children together. No-one knows how or when imprinting happens in human eggs or sperm – or even what all the imprinted genes actually do, says Surani. To complicate matters further, the genes in specialised adult body cells, such as those used to create artificial eggs and sperm, acquire additional molecular marks to switch cell-type-specific genes on or off. To create a viable artificial egg, for example, you would have to wipe off all these marks and put the correct ones on. “This is very difficult,” says Surani. “At the present time, it won’t be very easy to say what will happen.” “It’s a little bit of a black box at the moment,” agrees Lacham-Kaplan. But she points out that before the arrival of Dolly the sheep, no-one thought it was possible to de-program an adult nucleus to make a clone. Imprinting may not be insurmountable, she says. A decisive moment will be provided by the outcome of Lacham-Kaplan’s current experiments to implant mouse embryos fertilised with artificial sperm into surrogate female mice. If they produce healthy offspring, it would prompt a Dolly-style rethink of the biology of imprinting, as well as making same-sex couple babies a real possibility. But even if this long-shot comes off, problems still remain. Many of the health problems that plague cloned animals are thought to be down to faulty imprinting. Much safety testing and research in animals would need to be done before the technology could be applied to humans, says Gianpiero Palermo of Cornell University,