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Saved by sperm

作者:张阏    发布时间:2019-03-08 03:11:12    

By Jonathan Knight in San Francisco SPERM riddled with holes will revolutionise the production of transgenic animals, claim biologists in Hawaii. They have devised a more efficient way of inserting genes into mice so fewer animals will be killed after failing to take up the extra DNA. Their technique involves freezing and thawing sperm, mixing them with the foreign genes, then injecting them into eggs. To create transgenic animals, geneticists usually inject DNA into fertilised eggs before the two parents’ chromosomes have mingled. But this is very wasteful. Hundreds of eggs must be injected, and fewer than one in ten of the embryos that survive to full term take up a working copy of the injected genes. The rest are killed—a waste of life that is causing increasing alarm (This Week, 8 May, p 4). The new technique should reduce this wastage. It is the brainchild of the team at the University of Hawaii in Honolulu who last year created the first cloned mice (see “The year in news”, 19 December 1998, p 28). Tony Perry, Teruhiko Wakayama and Ryuzo Yanagimachi, working with colleagues at Osaka University and the Obihiro University of Agriculture in Japan, fertilised mouse eggs by intracytoplasmic sperm injection (ICSI)—the same technique that allows men with low sperm counts to father children. Before mixing the sperm with foreign DNA and injecting them into eggs, the researchers disrupted the cell membranes of the sperm with detergent or by rapid freezing and thawing. Ten years ago, an Italian team claimed to have made transgenic mice simply by mixing fresh sperm with the foreign DNA, but other researchers have been unable to repeat the experiment. The disruption caused by the detergent, or freezing and thawing, seems to have solved this problem. “You can think of it as shattering the membrane,” says Perry. This seems to help the foreign DNA break into the sperm and hitch a ride into the embryo. When Perry mixed his treated sperm heads with the gene for jellyfish green fluorescent protein, more than two-thirds of the eggs he injected began to develop and glowed green. He then implanted all the embryos into female mice and found that one in five of the pups that were born glowed (Science, vol 284, p 180). The green protein is mildly toxic and may have killed some embryos, so the true efficiency could be higher. Perry also expects the success rate to rise as they refine the technique. Other researchers are eager to experiment with the technique. “We’d try it,” says Arthur Lander, director of the transgenic mouse facility at the University of California at Irvine. “It could mean fewer days of work for the technician.” Animal welfare campaigners are also pleased. As well as avoiding the destruction of dozens of failed transgenic mice, there would be no need for large stocks of stud males to fertilise eggs the old-fashioned way, says Richard McGowan,

 

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