Biology subjects

Singson, A.

Publications and source records attributed to Singson, A..

4 recordsLinked to original sources

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↗

bioRxiv2021

The EGF-motif containing protein SPE-36 is a secreted protein required for sperm function at fertilization in C. elegans

The growing number of genes specifically required for fertilization suggests that there is a significant amount of molecular complexity at the sperm-egg interface. Thus, we have adopted a model of a "fertilization synapse" where specialized zones of interaction and multi-protein complexes mediate gamete interaction and fusion. The fertilization synapse is likely to be composed of both trans and cis protein-protein interactions at the surface of each gamete. Mutations in the Caenorhabditis elegans spe-36 gene result in a sperm-specific fertility defect. Surprisingly, spe-36 encodes a secreted EGF-motif containing protein that functions cell autonomously. Despite the fact that morphology and migratory behavior of spe-36 sperm are indistinguishable from wild-type sperm, spe-36 sperm make close contact with oocytes but fail to fertilize them. The genetic requirement for a secreted sperm-derived protein for fertilization is novel and represents a paradigm-shifting discovery in the molecular understanding of fertilization.

developmental biology↗

bioRxiv2017

spe-43 is required for sperm activation in C. elegans

Successful fertilization requires that sperm are activated prior to contacting an oocyte. In C. elegans, this activation process, called spermiogenesis, transforms round immobile spermatids into motile, fertilization-competent spermatozoa. We describe the phenotypic and genetic characterization of spe-43, a new component of the spe-8 pathway, which is required for spermiogenesis in hermaphrodites; spe-43 hermaphrodites are self-sterile, while spe-43 males show wild-type fertility. When exposed to Pronase to activate sperm in vitro, spe-43 spermatids form long rigid spikes radiating outward from the cell periphery instead of forming a motile pseudopod, indicating that spermiogenesis initiates but is not completed. Using a combination of recombinant and deletion mapping and whole genome sequencing, we identified F09E8.1 as spe-43. SPE-43 is predicted to exist in two isoforms; one isoform appears to be a single-pass transmembrane protein while the other is predicted to be a secreted protein. SPE-43 can bind to other known sperm proteins, including SPE-4 and SPE-29, which are known to impact spermiogenesis. In summary, we have identified a membrane protein that is present in C. elegans sperm and is required for sperm activation via the hermaphrodite activation signal.

developmental biology↗