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Clones contain hidden DNA damage

作者:叔孙喻    发布时间:2019-03-06 14:14:01    

By Andy Coghlan Genes disrupted when stem cells are cultured in the lab might explain why cloned animals grown from them die so often, or are grossly overlarge. This discovery, by researchers in the US, rings new alarms about the dangers of cloning humans. “It’s probably a bad idea,” says Kevin Eggan, one of the team that made the discovery at the Whitehead Institute for Biomedical Research at the Massachusetts Institute of Technology in Cambridge, Massachusetts. Even when cloned animals looked normal, they still harboured genetic disruptions from the cell culturing process that could pose unseen dangers, the team found. “Disruption of those genes in humans could cause things like mental retardation,” says Eggan. “It surely adds yet more evidence that there should be a universal moratorium against copying people,” says Ian Wilmut, the scientist who cloned Dolly the sheep at the Roslin Institute in Edinburgh. “How can anybody take the risk of cloning a baby when the outcome is unpredictable?” The Whitehead team examined gene patterns in mouse embryonic stem cells. These can be used to create mice either by cloning, or by fusing the cells with eggs – leading to “chimeric” mice. When they examined six genes linked with embryonic development, they found that most of the disruptions occurred when the embryonic stem cells were being cultured in the lab, not because of the cloning or IVF process. The gene alterations were related to a phenomenon called “imprinting”. Embryos receive copies of most genes from both parents, and imprinting causes a gene from just one parent – and not the other – to be switched on. The investigators found widely varying patterns of imprinting in four of the six genes, even amongst “daughter” cells all grown in culture from the same “parent” embryonic stem cell. Eggan says that there is no obvious way to alter the culturing process to prevent the disruptions: “It shows that cloners need to pay very careful attention to how they culture cells before cloning.” Adult cells can also be used to create clones, as in the case of Dolly the sheep who was made from an udder cell. But no experiments have been carried out to assess whether imprinting is affected in this case. There is some good news, however. Imprinting is particularly important during very early embryo development, but is less so when cells specialise and become specific tissues. Therefore that the disrupted genes have less of an impact on organ formation, meaning that the conversion of embryonic stem cells into transplantable tissues through so-called “therapeutic cloning” might still be safe and possible. “Cell differentiation per se seems to be less sensitive to changes in imprinting than the overall organisation of cells and tissues in the embryo,” says Peter Andrews, professor of biomedical science at the University of Sheffield. Journal reference: Science (vol 293,

 

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