Sperm activation protein Sneaky localizes to the acrosome and defines a new protein family. K.L. Wilson, A. Altares, B.T. Wakimoto. Dept of Biology, Univ Washington, Seattle, WA.

   In Drosophila, sperm activation following egg entry involves plasma membrane breakdown, decondensation of the sperm nucleus and male pronuclear formation. Although these steps are essential for successful fertilization, mechanisms triggering sperm activation have remained a mystery. To elucidate these mechanisms, we have focused on five male sterile mutants that arrest sperm activation: sneaky (snky), space needle (spnl), aghino (agho), kugi and popsickle (pskl) . In all of these mutants, sperm successfully enter the egg but remain peripheral and do not undergo nuclear decondensation. The snky gene encodes a predicted multi-pass transmembrane protein with regions of high similarity to proteins of numerous species, including C. elegans and H. sapiens. This group of proteins defines a previously unidentified family; Snky is the only member for which functional data exist. To examine Snky localization we generated flies with an EGFP-tagged snky gene that rescues the male sterile phenotype. In these flies Snky-GFP is present in an array of cytoplasmic vesicles in early spermatids. However, the GFP signal is confined to the acrosomal region in elongated spermatids and mature sperm. We next examined the localization of Snky-GFP in sperm activation mutants agho, kugi, and spnl. Aberrant localization was observed in agho and kugi mutant testes but not in spnl. In both agho and kugi mutants, Snky-GFP is missing in the acrosomal region of mature sperm. However, Snky-GFP in the agho mutant is mislocalized and lost earlier in spermatid development than in the kugi mutants. These results suggest a pathway from Agho to Kugi to Snky that is required for proper acrosomal localization of Snky. Further studies of this class of mutants will illuminate acrosomal biogenesis and the role of the acrosome in fertility.