Mutation assays in male germ cells from transgenic mice: overview of study and conclusions.

Three confirmed mouse germ cell mutagens, ethyl nitrosourea (ENU), isopropyl methanesulphonate (iPMS) and methyl methanesulphonate (MMS), have been evaluated for their activity as mutagens to the germ cell DNA of two strains of transgenic mice (lac I, Big Blue and LacZ, Muta Mouse). Both testicular DNA and epididymal sperm DNA were evaluated. A range of sampling times was studied, from 3 days post-dosing to 100 days post-dosing. ENU and iPMS were mutagenic to both testicular DNA and epididymal sperm DNA. Mutant frequencies were higher for both chemicals in DNA recovered from testicular tissue than in epididymal sperm DNA. Likewise, mutant frequencies were higher for both DNA samples at the later sampling times. MMS was not mutagenic under any condition of test. A good level of qualitative agreement in test results was seen for the two assays and for the same assays conducted in different laboratories. The level of quantitative agreement was not as high, but was, nonetheless, generally good. Recommendations for the future conduct of transgenic rodent germ cell mutation assays are made. The test data are discussed within the context of the larger question of how such assays should be integrated into the chemical hazard assessment process.