The Paternal Effect Genems(3)sneakyIs Required for Sperm Activation and the Initiation of Embryogenesis inDrosophila melanogaster

AbstractAlthough a large number of maternal factors are known to be essential for fertilization or the earliest stages of embryogenesis inDrosophila melanogaster, the role of paternally supplied products is not clearly understood. Paternal effect mutations provide a means to identify factors specifically required by the sperm after its entry into the egg. Here we describe the third strict paternal effect gene to be identified inDrosophila, ms(3)sneaky(snky), which defines the earliest developmental arrest phenotype so far described. Characterization of two independently isolatedsnkymutations showed that they affected male fertility, but not viability or female fertility. Cytological analyses showed that spermatogenesis proceeded normally insnkymales. However, thesnkydefect was evident after sperm entry into the egg;snkysperm did not undergo nuclear decondensation, form a functional male pronucleus, or initiate mitotic divisions in the egg. Immunolocalization of tubulin and Drosophila Centrosomin, a known centrosomal component, showed thatsnky-inseminated eggs failed to reconstitute a microtubule-organizing center. In addition,snkysperm chromatin retained the histochemical properties of mature sperm chromatin for several hours after sperm entry, showed reduced staining with membrane-impermeant nuclear dyes, and failed to replicate. We conclude that thesnky+product is required for the initial response of the sperm to cytoplasmic cues in the egg and for the subsequent initiation of embryogenesis inDrosophila. We suggest that all of thesnkydefects can be explained by the failure of the sperm plasma membrane to break down after entry into the egg