DNA repair processes in germ cells demonstrated in ejaculated sperms of rabbits treated with methyl methane sulfonate

Abstract

Male rabbits were treated with a single i.v. injection of 22.5 mg/kg methyl methane sulfonate (MMS). 0–24 h later [³H]-thymidine was injected in both testicles. Incorporation of the isotope in germ cell DNA was demonstrated in ejaculated sperms. In controls labeled sperms were demonstrated first on day 40–43. These cells were in the preleptotene spermatocyte phase at the time of [³H]-thymidine injection. In rabbits treated with MMS significant radioactivity occurred in sperms collected from day 19 onwards. These cells were in late spermatocyte and early spermatid phase of maturation when [³H]-thymidine was injected. Incorporation of thymidine in these cell populations is interpreted as an expression of unscheduled DNA synthesis, a repair process initiated after chemical damage of germ cell DNA by MMS. The usefulness of the rabbit test system within the framework of conventional mutagenicity screening tests is discussed.