Immunolocalization of Sex-Peptide Pheromones on D. melanogaster Sperm. J. Peng , S. Büsser , H. Liu , T. Honegger , E. Kubli. Zoologisches Inst, Uni. Zürich, Zürich, Switzerland.

   In D. melanogaster mating elicits two characteristic changes in female reproductive behavior: receptivity is reduced and oviposition is increased. Post mating responses last about one week when sperm is present (= sperm effect), without sperm 1-2 days. Sex-Peptide and DUP99B (the first two peptides characterized constituting the Sex-peptide pheromone family) are sufficient to induce these post mating responses. The two peptides are very similar in their C-terminal parts. After a normal mating, the two peptides are transferred to the female. We have tested the hypothesis that the sperm effect may be based on binding of SP and/or DUP99B to sperm. Mature sperm dissected from the seminal vesicles or female genital tracts was incubated with SP or DUP99B, respectively. The binding of the peptides to sperm was visualised with polyclonal rabbit antibodies and an anti-rabbit IgG FITC conjugate. In vitro immunolocalization with SP antibodies revealed a strong binding of SP to the head. The N-terminal part of SP is responsible for binding. DUP99B binds to the tip of the sperm head (including the acrosome region). A region near the N-terminus of DUP99B is involved in binding. The binding regions of SP and DUP99B are not homologous in sequence. Furthermore, in vivo the binding patterns of the two peptides vary in space and time. Initially SP binds to head and tail, after 5 h the label on the tail is continuously lost. 5 d after mating only the head remains labelled. DUP99B, however, binds only to the head in the first 5 h after mating. These results support the hypothesis mentioned above and suggest that SP is the more important peptide. This is further confirmed by of wild type females with males containing deletions for the DUP99B gene or a nonsense mutation in the SP gene, respectively (see presentation by Liu et al.).