THE USE OF SHUTTLE VECTORS FOR MUTATION ANALYSIS IN TRANSGENIC MICE AND RATS

The establishment in recent years of transgenic shuttle vector-based m utagenicity assays has provided improved systems for analysis of mutag enic and carcinogenic processes. Results in the mouse have stimulated the development of an alternate species suitable for mutation analysis and have increased our understanding of the existing models. A previo usly described shuttle vector (lambda LIZ), based on a lacI target gen e, was constructed in this laboratory for the study of mutagenesis in transgenic mice and in cultured cell lines. The shuttle vector allows for several options in its recovery from the host genome and in mutant identification. Of the 9 transgenic lineages that were generated with the lambda LIZ vector, one was chosen for use in a standardized mutag enicity assay (Big Blue(R), mouse lineage A1). Characterization of thi s lineage included copy-number determination, chromosomal localization of transgene integration and analysis of copy-number stability. As pa rt of the validation process, the standardized color-screening assay h as been tested in the mouse, both for spontaneous mutant frequencies a nd with a variety of model mutagenic compounds, and has been shown to identify most major classes of mutations as evidenced by mutant spectr a data. A discussion of the relative sensitivity of the shuttle vector to each of these classes of mutations is included. These studies have now been extended to the generation of transgenic rats containing the same shuttle vector for cross-species analysis. Spontaneous mutant fr equencies in two transgenic rat lineages were measured in liver and in germ cells. Preliminary data suggest that spontaneous mutant frequenc ies in somatic tissue are lower in rats than in mice, a result consist ent with historical observations of DNA damage and repair in these two species. Also under evaluation are alternative selectable systems for mutant identification, and hybrid animals obtained from mating lambda LIZ transgenics with genetically engineered mice possessing an inacti vated tumor suppressor gene. It is expected that each of these widely varying endeavors will contribute, not only in furthering our understa nding of the role transgenic systems should play in human risk assessm ent, but in illuminating the mechanisms of mutation in general.