Spermiogenesis is the process by which spermatids differentiate to become mature spermatozoa. During spermiogenesis in C. elegans, pseudopods extend from the spermatids and enable the sperm to crawl to the fertilization site within the hermaphrodite reproductive tract. A signal transduction pathway that activates spermiogenesis involves genes in the
spe-8 group (
spe-8,
spe-12,
spe-19,
spe-27, and
spe-29). Mutations in any of the
spe-8 group genes disrupt spermiogenesis. A suppressor screen of
spe-27(
it132ts)I identified numerous mutations that bypass the need for an activation signal altogether. Two genes previously identified from this suppressor screen were
spe-4 and
spe-6. SPE-4 is a presinilin 1 homolog localized to the membrane of the membranous organelle, while SPE-6 is a predicted cytosolic serine threonine protein kinase. Here we identify and characterize three additional genes from the
spe-27 suppressor screen:
spe-46 (W06D4.2) and Y23H5A.4 on Chromosome I, and K01D12.7 on Chromosome V. The
spe-46(
hc197) mutation causes defects in spermatogenesis in addition to premature sperm activation, and the null phenotype is sterility. SPE-46 has a predicted transmembrane domain and is expressed solely in sperm. The Y23H5A.4
(hc198) mutation results in excessive loss of sperm that appear normal, lowering fecundity. The Y23H5A.4 protein is sperm expressed and has an MSP domain, which is disrupted by the
hc198 suppressor mutation. This protein localizes to the mitochondria (see our poster on Y23H5A.4 for additional information). Finally, the K01D12.7
(hc201) mutation causes a sperm defect in addition to premature spermatid activation. The K01D12.7 protein is very small and has a predicted signaling function and potential
eri-1 interaction. We have also mapped and studied several additional suppressor mutations that are all on Chromosome I. While it has been known that membranous organelle fusion with the plasma membrane occurs during spermiogenesis, our results now show the involvement of a novel putative signaling molecule (K01D12.7) and the mitochondria (Y23H5A.4).