Suryanarayanan, S. | bioRxiv Science

bioRxiv2025

Sperm activation for fertilization requires robust activity of the TAT-5 lipid flippase

During fertilization, sperm and egg membranes signal and fuse to form a zygote and begin embryonic development. Here, we investigated the role of lipid asymmetry in gametogenesis, fertilization, and embryogenesis. We find that phosphatidylethanolamine asymmetry is lost during meiosis prior to phosphatidylserine exposure. We show that TAT-5, the P4-ATPase that maintains phosphatidylethanolamine asymmetry, is required for both oocyte formation and sperm activation, albeit at different levels of flippase activity. Loss of TAT-5 significantly decreases fertility in both males and hermaphrodites and decreases sperm activation. TAT-5 localizes to the plasma membrane of primary spermatocytes but is sorted away from maturing spermatids during meiosis. Our findings demonstrate that phosphatidylethanolamine asymmetry plays key roles during gametogenesis and sperm activation, expanding the roles of lipid dynamics in developmental cell fusion.

developmental biology↗

bioRxiv2025

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. 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.

developmental biology↗