We have investigated the mutagenic effects of ENU, a potent mutagen in mouse spermatogonia, and of the two postmeiotic germ cell mutagens MMS and iPMS in germ cells, using a transgenic mouse mutation assay(lacZ/Muta(TM) Mouse, positive selection system). The test compounds were administered to 6-week-old animals by a single intraperitoneal injection. Seminiferous tubule germ cells were isolated from the testes after an expression time of 52 days and genomic DNA was extracted to examine induced mutations in the lacZ target gene. The spontaneous mutant frequencies observed in the control animals (n=7) ranged from 3.5 to 17.9x10(-5) (mean value 9.5+/-5.3x10(-5)). ENU (150 mg/kg; n=8) induced a 6.9-fold increase over controls, iPMS (100 mg/kg; n=7) a 2.4-fold increase, and no effect at all was found following MMS treatment (80 mg/kg; n=8). The study demonstrates that the transgenic mouse mutation assay is able to detect the germ cell mutagens ENU and iPMS in the target tissue. The critical steps of the assay, however, seem to be dosing and sampling time. In contrast, MMS has failed to induce germ cell mutations in seminiferous tubules of transgenic mice at the tested dose and after an expression period of 52 days.
