The novel HRD motif kinase SPE-60 is required for sperm development and motility in Caenorhabditis elegans

Sexual reproduction requires sperm development, activation and motility. Many of these post-meiotic processes remain incompletely understood. We identified the gene spe-60, which encodes a tau-tubulin kinase with a conserved catalytic HRD motif. Localisation via immunostaining reveals that SPE-60 is present in sperm and dynamically colocalises with membranous organelles (MOs), that store factors essential for activation and fertility. spe-60 null mutants are sterile due to immotile sperm that undergo normal MO-plasma membrane fusion but fail to extend normal pseudopods essential for motility and fertilisation. Furthermore, mutant sperm exhibit arrested spermatocyte development. The functional loss observed in spe-60 null sperm is phenocopied by sperm carrying a CRISPR/Cas-mediated point mutation within the HRD motif. Genetic epistasis places SPE-60 downstream of the serine/threonine kinase SPE-6 in the canonical sperm activation pathway. Thus, SPE-60 is required for sperm development and motility, but not MO fusion. These findings suggest that the HRD-containing kinase SPE-60 fulfils a dual function as a key evolutionarily conserved factor.