Scientists find gene that built mighty mouse

It sounds like something from an Arnold Schwarzenegger science fiction film: bodybuilders of the future could be produced in the womb, rather than by steroids.

But a team of American scientists have produced genetically altered mice which would win their species' bodybuilding contests, by knocking out a gene involved in regulating muscle growth. They produced mice with unusually large shoulders, three times the muscle mass, which were a third larger than normal.

The finding by a team at Johns Hopkins University, Baltimore - reported today in the science journal Nature - could have important implications both for humans, in offering treatments for wasting diseases like muscular dystrophy, and for producing extra large farm animals such as cows, chickens and pigs without the use of chemical additives or hormones.

It is more likely that the farming uses would come first - rather as cloning has been done first with sheep rather than humans, because it involves the use of large numbers of embryo cells.

To produce the mice, the American researchers first took "stem cells" and disabled the gene called GDF-8, which codes for a growth-regulatingchemical called myostatin.

The targeted stem cells were cloned and injected into normal embryos. After being transferred into the wombs of female mice, the altered embryos developed normally. But once they matured, the mutant mice had individual muscles up to three times the mass of regular mice, and pronounced shoulders and hips.

As well as having potential for the treatment of neuromuscular diseases, the scientists believe the approach might also yield benefits for cancer patients suffering severe weight loss.