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 against
spe-27 uncovered a pathway that inhibits spermiogenesis. Members of the spermiogenesis inhibition pathway include
spe-4 and
spe-6. Here, I report on a mutation in another member of the inhibitory pathway, allele
hc198. While
hc198 was isolated as a suppressor of
spe-27, it also suppresses other members of the
spe-8 group, bypassing the spermiogenesis signal transduction pathway in a manner similar to mutations in
spe-4 and
spe-6. This, and premature activation defects indicate the gene affected by
hc198 is also an inhibitor of spermiogenesis. Although
hc198 is a recessive suppressor of
spe-27, it does not restore full fertility. In a wild-type
spe-27 background,
hc198 mutants have compromised fertility that is restored by mating, characteristic of a spermatogenesis defective phenotype. Genetic mapping places the
hc198 mutation at -2.30 on Chromosome I. We are currently performing complementation tests with sperm genes in the mapped region. Identification of this gene will add another member to the spermiogenesis inhibition pathway, which, combined with the
spe-8 group signal transduction pathway, provides for exquisite control over the timing of sperm activation. Furthermore, spermiogenesis in C. elegans involves regulated fusion of vesicles called membranous organelles and the controlled polymerization of the Major Sperm Protein. One gene,
spe-4, whose role in the inhibitory pathway was discovered in our lab, is homologous to human Presenilin-1, an Alzheimer''s Disease gene. Therefore, the spermiogenesis inhibition pathway involves mechanisms shared by many cellular systems.