Differential responses to ultraviolet irradiation of the polar cytoplasm ofDrosophila eggs.

The posterior pole ofDrosophila melanogaster eggs was irradiated with ultraviolet light of 253.7 nm wavelength; different batches were irradiated at different times after oviposition, ranging from less than 10 mins to 125 mins. Two different experiments were run at different dose levels: 280 μW/mm² and 530 μW/mm². A differential response to irrariation was observed in relation to the age of the treated eggs. Embryo mortality increased with egg age in both experiments (Fig. 1).No differential effects onlarval mortality were found in egg batches irradiated between 15 and 95 mins of age in either experiment (Fig. 3).The incidence ofsterility in the survivors was higher when the eggs were irradiated before 55 mins or when pole nuclei were present. The overall incidence of sterility was much higher in the high-dose experiment (Fig. 4).Sterility is considered as a measure of damage to germ cell precursors, most probably involving RNA. On this basis the probability of the affected RNA being messenger RNA stored in polar granules is discussed.