Genotoxic effects of ethyl methanesulfonate and X-rays at different stages of rat spermatogenesis, studied by inhibition of DNA synthesis and induction of DNA repair in vitro

Abstract

Novel in vitro techniques have been developed for evaluation of genetic effects in rat spermatogenesis. The effects of chemical and physical model mutagens, ethyl methanesulfonate (EMS) and X-rays, on DNA synthesis have been compared at different stages of the seminiferous epithelial cycle. Inhibition of DNA synthesis, measured by (3H)-thymidine (3HTdR) and (125I)-iododeoxyuridine (125IUdR) incorporation assays, was observed in all stages in a dose dependent manner after EMS administration, whereas X-rays had only a slight inhibiting action. Unscheduled DNA synthesis (UDS) was analyzed by autoradiography of spermatogenic cell squashes. EMS induced UDS in all cell types except the most mature spermatids (steps 13–19). Highest induction was found in mid- and late pachytene primary spermatocytes at stages VII-XII, and a variable response in haploid cells. Step-12 spermatids were particularly sensitive, showing high induction of UDS. X-irradiation mainly affected mid- and late pachytene spermatocytes, but spermatids were only slightly affected. During meiosis and spermiogenesis, DNA is most susceptible to mutagen insult during maximal transcriptional activity at late steps of meiotic prophase. In addition, nuclear condensation phase at steps 9–12 of spermiogenesis is sensitive, which suggests a capacity of the germ cells to repair their genetic damage before the final inactivation of their chromatin.