Radiation induction of mutations affecting sperm morphology in mice

To investigate the basis of the sperm abnormality assay, studies have been made of the frequency of sperm abnormalities in the genital tracts of the progeny of irradiated males. Male C57BL/6 mice were irradiated (75-600 rad X-rays to the testes) and were then bred in the pre-sterile period to untreated C57BL/6 females. The sperm of their male progeny were examined for the frequency of sperm abnormalities. Variant males with clearly elevated levels of sperm abnormalities were more frequently seen amongst the progeny of irradiated fathers than with the progeny of sham-irradiated controls (10 in 170 compared with 2 in 188; P less than 0.02). Although no clear dose-response relation could be discerned with the number of animals studied, similar differences were observed with irradiated male SWR, C3H/He in inbred crosses and with C57BL/6 in hybrid crosses with C3H/He females. In contrast, matings of males made at longer times following irradiation did not lead to a significant increase in the number of affected progeny for the number tested. Breeding experiments with the affected F1 males showed that the sperm morphology defect could be transmitted in 7 of 19 cases. Parallel cytogenetic studies showed that 3 of the initial affected progeny had detectable reciprocal translocations and that in 2 of these cases the translocation was transmitted with the sperm defect. The studies thus showed that radiation can induce mutations that affect the levels of sperm abnormalities and that these mutations can be associated with reciprocal translocations.