Studies on mutations in male germ cells of transgenic mice following exposure to isopropyl methanesulfonate, ethylnitrosourea or X-ray.

Transgenic mice have recently been used for mutagenesis assays in vivo. The present study was undertaken to clarify whether such assays can detect mutations induced after treatment of male germ cells in mouse with isopropyl methanesulfonate (iPMS), ethylnitrosourea (ENU) or X-ray irradiation. The transgenic mice used for assay are Muta Mouse (MM) strain, which carries 80 copies of the bacterial lacZ gene per cell as targets for mutagenesis. Male MM animals were given a single intraperitoneal injection of 200 mg/kg iPMS, 150 mg/kg ENU or were irradiated with 500 rads of X-rays. Vasa deferential sperm, caudal epididymal sperm and/or whole testes were extracted at various times after treatment with each agent. After the genomic DNA was extracted from each tissue, mutation analysis at the lacZ locus was carried out by the method of Myhr et al. The spontaneous lacZ- mutant frequencies were on the order of 10(-5)-10(-6). The lacZ- mutant frequencies in all treatment groups were increased over the control animals. The iPMS-induced mutant frequency in postmeiotic stages was low. However, ENU induced relatively high mutant frequencies in the spermatogonia. X-rays induced mutant frequencies in the late spermatid and early spermatid stages that were higher than the mutant frequencies in spermatogonia. Mutant frequencies in MM detected after treatment of male germ cells with ENU or X-rays were lower than mutant frequencies detected by the mouse specific-locus test in previous reports. Hence, considering the lower resolution power of the transgenic animal mutagenesis assays using the target lacZ gene compared with the specific locus test, to detect mutations induced in male germ cells, it is not clear whether this assay is a practical alternative to the specific locus test.