The Caenorhabditis elegans spe-21 gene that encodes a palmitoyltransferase is necessary for spermiogenesis.

In most animals, spermatids that are produced must further differentiate into fertilization-competent spermatozoa after completing meiosis. In Caenorhabditis elegans, this process is known as spermiogenesis or spermatid activation and it results in the transformation of round, non-motile spermatids into amoeboid, motile spermatozoa. Spermatid activation in C. elegans is also associated with the fusion of Golgi-derived vesicles called the membranous organelles (MOs) with the plasma membrane. This fusion process is required for producing a fertilization-competent surface on the sperm by placing MO-carried, resident proteins onto the spermatozoon membrane. We have identified, cloned, and characterized the role of spe-21, also designated as dhhc-5, during both hermaphrodite and male spermatid activation. Putative spe-21 null mutant worms are severely sub-fertile at all studied growth temperatures. spe-21 mutant spermatids fail to activate either in vivo or in vitro after treatment with known chemical activators. We have found that spe-21 is necessary for MO fusion and pseudopod formation in spermatids. The spe-21 gene encodes a predicted four pass transmembrane protein with a conserved Asp-His-His-Cys (DHHC) tetrapeptide zinc finger motif embedded in a cysteine rich region (DHHC-CRD type zinc finger motif). Generally, proteins with DHHC-CRD motifs catalyze the post-translational addition of palmitate to their protein substrates and are called palmitoyltransferases or palmitoylacyltransferases (PATs). We also found that mNeonGreen-tagged SPE-21 localizes to the MOs in spermatids. Together, our findings show that SPE-21 is an MO localized palmitoyltransferase required for proper spermatid activation and creation of fertilization-competent spermatozoa.