Drosophila melanogaster Sex-Peptide is the molecular basis of the sperm effect. E. Kubli, J. Peng, H. Liu, S. Chen, T. Honegger. Dept. of Zoology, University Zurich, Zurich, Switzerland.

   In D. melanogaster, mating leads to two behavioral responses in females, increased egg laying and reduced receptivity. Both post-mating (pm) responses persist for a few days. Seminal fluid and sperm are involved in these responses. Males that do not transfer sperm can induce these responses for only about one day (= short-term response). Manning suggested that sperm is responsible for the long-term response (= sperm effect). Sex-Peptide (SP) and Dup99B, two small peptides of the Sex-peptide pheromone family, can induce these two pm responses for one day when injected into virgin females. To study the role of the two peptides in a normal mating, we investigated null-mutants for both genes. We produced a SP null mutant with the homologous recombination targeting technique developed by Rong and Golic. We found that in matings with WT OreR females, SP null males induce only a slight increase of egg laying on the first day (elicited by Ovulin and DUP99B which are still transferred). Reduction of receptivity persists only for 1-2 days. We also found that SP does not affect sperm transfer and storage. Sperm can be stored in the female for a long time due to the low egg laying rate after copulation with SP null males. However, we could not find any changes in the females pm responses after copulation with a Dup99B null male. We conclude that DUP99B has only a minor effect in eliciting the pm responses. SP binds to sperm with its N-terminal part during copulation. The functional C-terminal part is cleaved off at a trypsin cleavage site and probably enters the hemolymph. The N-terminal end remains on the sperm. Transgenic males containing a SP gene with a modified trypsin cleavage site in a SP null background, elicit only short-term pm responses, but the modified SP is still bound to sperm 3 d after mating. We conclude that it cannot be cleaved, and thus cannot enter the hemolymph and elicit the long-term response.