A RECOMBINATION-BASED TRANSGENIC MOUSE SYSTEM FOR GENOTOXICITY TESTING

It is well established that mutagens induce recombination in cultured cells and experimental organisms. Presumably, this is a consequence of the DNA-damage-triggering cellular-repair mechanisms. The relationshi p between recombination and mutagenicity has been exploited in submamm alian organisms, such as yeast, to assay the ability of chemical agent s and radiation to induce a form of recombination called gene conversi on - the non-reciprocal transfer of genetic information. This work has demonstrated the efficacy of predicting mutagenicity on the basis of recombination induction. Here, we describe the utilization of a transg enic mouse system for efficient detection of germ-line gene-conversion events as a mutagen-screening tool. These mice contain two mutually d efective reporter (lacZ) genes under the regulatory control of a sperm atogenesis-specific promoter. A particular intrachromosomal gene conve rsion event must occur for the generation of functional lacZ activity. Conversion events are visualized by histochemical staining or flow cy tometric analysis of transgenic spermatids. The highly mutagenic compo und chlorambucil induced a several fold percentage-wise increase of la cZ-positive spermatids, whereas acrylamide, a weak genotoxin, produced no marked increase in converted spermatids. The results indicate that recombination-based transgenic mouse models for genotoxin screening p resent a viable option for inexpensive and rapid whole-animal mutagen testing. The particular mice we describe may ultimately prove to be a useful tool for identifying agents which can cause heritable genetic m utations in humans.