MATING AND SEX PEPTIDE STIMULATE THE ACCUMULATION OF YOLK IN OOCYTES OF DROSOPHILA-MELANOGASTER

Mating elicits two reactions in many insect females: egg deposition is increased and receptivity to males is reduced. Central to the control of receptivity and oviposition in Drosophila melanogaster is the sex peptide (SP), a 36-amino-acid peptide sex pheromone synthesized in the male accessory glands and transferred to the female during copulation . To identify regulatory mechanisms involved in the maintenance of the oviposition response, we have compared the effects of mating and SP a pplication with respect to oogenesis. The distribution of the various stages of oogenesis in the ovary, yolk protein (YP) synthesis by the f at body, as well as YP content, uptake and synthesis by the ovary were investigated. Transcripts of the yolk protein genes (yp) were quantif ied by Northern blotting. Based on our results, we conclude that matin g and SP injection into virgin females stimulate yp gene transcription in the fat body only moderately above the background level. However, uptake into the ovary and transcription of the yp genes in the ovary i s strongly enhanced after either mating or SP injection. These data ar e supported by the finding that the abundance of the vitellogenic stag e 10 oocytes is also increased. In contrast, early vitellogenic stages 8 and 9 of oogenesis are present in the same numbers in virgin, mated , and SP-injected females, which suggests a control point at about sta ge 9 determining vitellogenic oocyte progression. The finding that SP can elicit equally all changes observed after copulation suggests that in the sexually mature female it is the major component controlling a nd stimulating oogenesis after mating.