Abstract
To know the difference in sensitivity to ionizing radiation for mutation induction between somatic and male germ cells, we have carried out mutation assays using the transgenic mice, which is the gpt-delta mouse strain carrying the bacterial gpt gene as targets for mutagenesis. The spontaneous gpt gene mutation frequency in embryo cells was 1.04 x 10-5. The mutation frequencies after exposure to 1, 2.5 or 5 Gy of X rays in embryo cells were 1.50, 2.43 or 3.46 x 10-5, respectively. The induced mutation frequencies in embryo cells were increased linearly with increasing doses of X rays. The mutation frequencies (spontaneous or induced with 5 Gy of X rays) in spleen cells were 1.10 or 2.93 x 10-5, respectively. The mutation frequencies for both somatic cells were nearly the same. To measure the induced mutation frequencies in male germ cells (spermatogonial cell stage), sperms were extracted at 65-83 days after irradiation of 1, 2.5 or 5 Gy of X rays, corresponding to the spermatogonial stem cell stage at the time of treatment. The spontaneous mutation frequency in male germ cells was 0.36 x 10-5. The mutation frequencies in male germ cells irradiated with 1, 2.5 or 5 Gy of X rays at the spermatogonial stem cell stage were 0.39, 0.53 or 1.05 x 10-5, respectively. The mutation frequencies (both spontaneous and induced) in spermatogonial cell stage were about three times lower than those in somatic cells. This difference would be due to the high base excision repair activity in male germ cells.
