The effects of treating drosophila females with actinomycin-D on the yields of dominant lethals, translocations and recessive lethals recovered from X-irradiated spermatozoa

Abstract

Drosophila females were injected with Actinomycin-D. After a day they were mated (for 24 h only) to males that had been exposed to 2000 or 2500 R X-irradiation, so that only mature spermatozoa were sampled. The radiation-induced frequencies of dominant lethals, II–III translocations and recessive sex-linked lethals in the paternal genome were determined. When compared to the appropriate controls, it is found that such treatment of the females with Actinomycin leads to an inrease of the frequency of dominant lethals and to a decrease of those of translocations and recessive lethals. Characteristic is the delayed expression of the Actinomycin effect, in that the modification of translocation and recessive lethal frequencies is most pronounced in oocyte stages utilized 4–6 days after injection. The present findings are interpreted to mean that Actinomycin acts by partially inhibiting the restitution of chromosome breaks, thereby increasing the frequency of dominant lethals, and decreasing that translocations and recessive lethals. This implies that maternal repair processes acting at the stage of pronucleus formation are required for the repair (restitution) or misrepair (reunion giving rise to translocations) of chromosome breaks induce mature spermatozoa.