During spermiogenesis, round nonmotile spermatids are rapidly transformed into asymmetrical crawling spermatozoa. In addition to
spe-8 and
spe-12, we found two new genes,
spe-27 and
spe-29, that when mutated, disrupt spermiogenesis in an identical manner: mutant hermaphrodites are self-sterile, while mutant males are fertile. Sperm from both sexes activate abnormally in vitro, suggesting that these gene products are expressed in both sperm, but only hermaphrodites require them for activation. The hermaphrodite's spermatids, however, can be activated by mating. This phenotype has been explained by a model that has two distinct pathways of activation, one for males and one for hermaphrodites (Shakes and Ward, 1989). The four genes are needed only for the hermaphrodite pathway.
spe-27 and
spe-12 have been cloned. Their mRNA is found exclusively in the germline during spermatogenesis. Their predicted protein sequences show no similarities to known proteins. We are currently cloning
spe-29. To further understand how these genes act during spermiogenesis we are determining the subcellular localization of their gene products. In addition, suppressor analysis is under way (see abstract by Paul Muhlrad and Samuel Ward) to look for other genes in this pathway and for interactions between these genes.