During spermatogenesis of C. elegans, when primary spermatocytes undergo meiosis and form four haploid spermatids, the cytoplasmic contents of the spermatocytes segregate so that haploid spermatids are void of any ribosomes and endoplasmic reticulum . These are partitioned off into a separate cytoplast, the residual body. We have isolated spermatogenesis defective (spe) mutations that disrupt this segregation. Mutations in one such gene,
spe-26, result in defective spermatocytes which undergo normal nuclear division but fail to segregate the cell contents into spermatids and residual body. To further understand the function of the
spe-26 gene product, we have cloned the
spe-26 gene by transformation rescue of sterile mutations with genomic clones. A 3.9 kb Hind III, Bam Hl fragment was identified to encode the
spe-26 gene. Differential Northern analysis using probes from this fragment identified two transcripts, a 2.4 kb sperm specific transcript and a 1.5 kb transcript present in both males and mutant hermaphrodites that produce only oocytes. This result suggests that the 2.4 kb sperm specific transcript is the
spe-26 gene product. A search of the existing sequence data with the genomic clone sequence and partial cDNA clone sequence has not revealed any significant matches. All 5 alleles of
spe-26 have similar phenotypes which do not change over the deficiency. This suggests that the
spe-26 gene product has a very specific role during a stage in spermatogenesis, the cytolocalization of cell contents during the formation of spermatids. This is further supported by the temperature shift experiments.
spe-26 gene product could be a member of the cytoskeletal machinery specialized for the localization of components during the formation of spermatids.