Stable long term germ-line transmission of transgene integration sites in mice

Transgenic mice provide a valuable tool in all fields of basic and applied biological and medical research. In this study, we describe the fate of int egrated transgenes in the mammalian host genome over a large number of gene rations. The stability of the germ-line transmission of integrated tyrosina se transgene copies was monitored up to generation F20 in a large number of individuals from seven transgenic mouse lines. Phenotypic and molecular ge netic analysis of the offspring both within the different lines and in cros s-breeding experiments revealed the high stability of the transgene integra tion sites in mice. Only very few individuals were affected by a transgene copy loss. These results indicate that, once homozygous transgenic lines ar e established, breeding programs can be continued to a high number of gener ations without further stringent molecular genetic analysis.