PHILADELPHIA - Scientists at the University of Pennsylvania School of Veterinary Medicine have successfully used a retrovirus to modify genes in spermatogonial stem cells in a mouse - the first instance, in any species, of a transgenic animal created by inserting a gene into male germ-line stem cells.

The inserted gene subsequently appeared in approximately 4.5 percent of offspring of mice transplanted with the altered stem cells, and was transmitted to at least three succeeding generations.

The work is the cover story in the Nov. 6 issue of the Proceedings of the National Academy of Sciences, and will appear tomorrow on the journal web site. The findings should enable the creation of transgenic individuals in a wide range of species, permitting scientists to develop research models for study of numerous human diseases.

Led by Ralph L. Brinster of Penn Department of Animal Biology, the scientists succeeded in inserting a foreign gene - in this case the common reporter gene lacZ, whose product is the enzyme