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. In order to identify additional genes involved in spermatid activation, a suppressor screen was performed on
spe-27(
it132ts)I mutants. Numerous suppressor mutants were recovered; most were discovered to harbor
spe-6 mutations. Here we report on several non-
spe-6 suppressor mutants and their phenotypes. The suppressor mutations described here are in separate genes and include
spe-4(
hc196)I,
hc197,
hc198,
hc201,
hc202,
zq9, and
zq10. None of these suppressors are allele specific: they suppress other
spe-8 group genes such as
spe-19 and
spe-29. These suppressor mutations do not restore wild type fertility to
spe-27(
it132ts), resulting instead in lifetime fecundity ranging from only four progeny to nearly 20 progeny. However, the suppressor mutations in a wild-type background vary significantly from one another.
hc196 and
hc197 mutants produce fewer than 20 progeny at 25C, whereas
hc198 and
hc201 exhibit near wild type fecundity at 25C. Male suppressor mutants all harbored activated sperm, suggesting that these mutations bypass the spermiogenesis activation pathway resulting in premature spermatid activation. SNP mapping revealed that
spe-4(
hc196),
hc197,
hc198, and
hc202 are on Chromosome I, and
hc201 is on Chromosome V. Illumina sequencing achieving 25x coverage was performed on all but the
spe-4 mutation, and the data were analyzed using the Genious Pro software package. Single candidate mutations were identified for
hc197 and
hc198, and two candidates were found for
hc201. Resequencing confirmed the mutations. Transformation rescue is ongoing, and we will discuss rescue of phenotypes such as these where the mutant phenotype is difficult to identify on an individual basis. Taken together, the suppressor mutations define a set of genes whose products inhibit spermatid activation until relived by the
spe-8 group gene products. These inhibitory gene products appear to involve the membranous organelles and MSP packaging. We hypothesize that prevention of MSP polymerization is crucial to maintaining the spermatid stage.