New method for making transgenic mice

Japanese researchers have produced genetically altered mice by injecting genes into the testes of immature males. The researchers, based at Kyoto University in Japan, then mated the mice with normal females and found that a small number of the offspring carried the added gene in all their cells. The scientists say their method provides a new way for producing genetically altered animals, especially those for which existing transgenic technology has proved inefficient or impossible.

Most techniques used to produce genetically altered laboratory animals, which rely on adding genes to eggs or early embryos, have a success rate of less than one per cent. The new method, details of which are published in the journal, the Biology of Reproduction, targets the sperm stem cells present in the testes of immature males. The researchers used a virus to deliver the gene to the stem cells, which then produced genetically altered sperm in the adult mouse. But the technique only works in immature mice, the researchers stress.

Of the 31 mice used in the experiment, eight later mated with normal females to produce offspring, of which an average of three per cent carried the genetic alteration. The 'transgene' was also passed on to a second generation, turning up in six out of eight pups from a male transgenic mouse, and one of three offspring of a female transgenic mouse. The researchers say their technique should be suitable for producing genetic alterations in a wide range of animals, including pigs and cattle. And because genetically altered stem cells continue to produce large numbers of transgenic sperm throughout the animal's life, many transgenic offspring can be produced from a single 'founder' male.

Last year, Japanese and US researchers managed to create transgenic zebrafish, using genetically modified sperm grown in the laboratory. At the time, the authors speculated that if the procedure could be adapted to human sperm, then it could one day be used to correct genetic diseases before fertilisation. However, such germ-line gene therapy is currently outlawed in the UK and many other countries.