DOSE-RESPONSE OF A RADIATION INDUCTION OF A GERMLINE MUTATION AT A HYPERVARIABLE MOUSE MINISATELLITE LOCUS

Dose-response of an induction of a germline mutation was studied at a hypervariable mouse minisatellite locus, Ms6hm, which consists of tandem repeats of a sequence motif GGGCA. Male C3H/HeN mice were exposed to various doses of Co-60 gamma-ray and mated with unirradiated C57BL/6N female mice. Matings were done at Various time after irradiation to assess the effects of radiation on spermatozoa, spermatids and spermatogonia. DNA samples of F-1 offsprings were analysed by Southern blotting for the repeat length mutation at the Ms6hm locus. The mutation frequency per gamete of the paternal allele was 9.1% for the unirradiated control group. The spermatids stage was most sensitive to radiation and a statistically significant dose-response was observed. The mutation frequency of the paternal allele in Fl mice increased to 22% for 1 Gy, 28% for 2 Gy, and 28% for 3 Gy. The spermatogonia stage was less sensitive to radiation, and the mutation frequencies of the paternal allele were 14% for 2 Gy, and 16% for 3 Gy. The spermatozoa stage germ cells were also less sensitive and the frequency of mutation of the paternal allele increased to 14% for 3 Gy. However, these increases were statistically not significant. Possible mechanisms of radiation induction of germline mutation at the hypervariable minisatellite locus will be discussed.