Identification of a Phosphatase-encoding Sperm Gene in the Nematode Caenorhabditis elegans
Precise activation of sperm cells is critical for prospective fertilization for most organisms and the same is true for the nematode Caenorhabditis elegans. Sperm cells from C. elegans remain as inactive spherical spermatids and only activate after an external signal. Activation reorganizes the cell to produce a pseudopod and induce motility. I determined that a previously unstudied gene, F55F8.7, is involved in spermatid activation. The gene was identified from the mutation zq9 that causes premature sperm activation. The mutation was found because it restores partial fertility to worms harboring the it132 mutation in the spe-27 gene. Genome mapping and whole genome sequencing were employed to identify the mutation. The results indicated the zq9 mutation occurred in a small region on chromosome I. F55F8.7 was the only mutated sperm gene in the region. Zq9 mutants were transformed with a normal copy of the F55F8.7 gene, and normal function was restored, confirming that zq9 resides in F55F8.7. Further, RT-PCR data corroborated that the gene is expressed solely in sperm. F55F8.7 is predicted to have protein tyrosine phosphatase activity. The C. elegans genome contains 58 similar copies of this gene, many of which are sperm expressed. The substantial number of these paralogs could explain why a knockout mutation of F55F8.7 produces no phenotype. The gene is widely represented in animals with two ortholog genes in humans: PTPRG and PTPRZ1. Future work will include making a transcriptional fluorescent fusion to study expression and protein localization in spermatogenesis.