Radiation Induction of Germline Mutation at a Hypervariable Mouse Minisatellite Locus

Abstract

Paternal ⁶⁰Co γ-irradiation was tested for the induction of germline mutation at the mouse hypervariable minisatellite locus, Ms6hm. Male C3H/HeN mice were exposed to 3 Gy ⁶⁰Co γ-ray and mated with C57BL/6N females. Matings were made at 1–7, 15–21 and 71–77 days post-treatment to test spermatozoa, spermatids and spermatogonia stages. Reciprocal crosses were also made with irradiated C57BL/6N males. Southern analysis was carried out on DNA from parents and F₁ mice. The paternal mutation frequencies per gamete of the Ms6hm locus were 8·3, 13, 28 and 15% for the C3H/HeN control, exposed spermatozoa, spermatids and spermatogonia stages, respectively. The paternal mutation frequencies per gamete were 7·7% for the C57BL/6N control and 13% for the C57BL/6N exposed spermatozoa stage. The increase in the paternal germline mutation frequency was statistically significant for C3H/HeN spermatids irradiation (p<0·005). The induced mutation frequencies were of the order of 10⁻¹, and was too high to be accounted for by the direct action of radiation on the locus. These results suggest the presence of a previously unexpected mechanism of radiation induction of germline mutation. In addition, we demonstrate that the hypervariable minisatellite locus can serve as a sensitive monitor for genetic damages to germline cells.