The company's claims are being greeted with a mixture of enthusiasm and scepticism by other biologists, who warn its results have yet to be independently confirmed. "But if it works the way they claim, it's revolutionary," says Tom Rosenquist of Stony Brook University in New York.
Introducing genes into mammals is laborious and expensive at present, so the technique is only used for research and to create animals that yield high-value medical products. But if making GM mammals becomes cheap and easy, companies could soon be modifying everything from the farm animals that produce our food to our pets. Tosk's method could even be used to correct genetic faults in people.
At the moment, GM mammals are usually made by injecting naked DNA directly into an egg. But the success rate is extremely low: to get just one GM animal, a skilled technician has to carry out dozens of injections and then implant the resulting embryos. An alternative is to start with ordinary cells and then try to clone the few that integrate the extra DNA. But this isn't very efficient either.
Tosk's method cuts out this tedious manipulation, New Scientist has learned. The extra DNA is simply injected into an animal's bloodstream. Within a couple of weeks, it is integrated into a high proportion of cells in many different tissues, says Tosk's chief executive Patrick Fogarty. Since some sperm and egg cells are also altered, normal breeding can then produce animals in which every cell carries the extra DNA. When mice are modified by injecting DNA into their tails, Fogarty claims, 40 per cent of their offspring on average carry the extra DNA-an amazingly high proportion.