Spontaneous mutants recovered from liver and germ cell tissue of low copy number lacI transgenic rats.

The finding of a large discordance between animal species in their response to a carcinogenic challenge, has led to the realization that the useful extrapolation of animal test data to humans requires a better understanding of animal interspecies differences. With the development of transgenic shuttle vector based animal systems we are now able to study mutation of the same genetic target in both mice and rats. We have begun to analyze mutants recovered from rat lines carrying low copy numbers of the same lambda/lacI constructs carried by the Big Blue mouse. A large database on mutations in lacI transgenic mice is already available for comparison. The data indicate that the differences between the mutations recovered from rat liver and germ cell tissues are similar to those recovered from transgenic mice, but when compared with a large database of mutations available for mice, some site-to-site differences may exist. This study represents the first interspecies look into the molecular nature of mutations in the lacI transgenic rodents.