Spermatogenesis in C. elegans involves dramatic reorganization of membranous structures in spermatocytes and the morphogenesis of specialized vesicles known as the membranous organelles (MOs). Ultrastructural analyses revealed that MOs first emerge as vesicular derivatives of Golgi complexes (Wolf et al. 1978. J Ultrastruct Res 63:155-169). Recent genetic and cell biological data strongly suggest that membrane traffic from the Golgi to the developing MOs requires many elements that are either common or related to those of generic lysosomal trafficking pathways. SPE-39, which is required for fusion of intermediate vesicles during the formation of MOs, interacts with CeVPS33A and CeVPS33B, both of which are homologs of the yeast homotypic fusion and vacuole protein sorting (HOPS) complex subunit Vps33p. Knockdown of CeVPS33B by RNAi induced cytokinesis defects during spermatogenesis that are similar to those observed in
spe-39 mutants. Although SPE-39 shares limited homology with another yeast HOPS subunit Vps16p, SPE-39 and its orthologs in other species form a separate phylogenetic branch that is distinct from that of VPS16 orthologs. While VPS16 orthologs are conserved in both unicellular and multicellular eukaryotes, SPE-39 orthologs are found only in animals, suggesting they participate in an animal-specific aspect of vesicular trafficking. We also tested other known components of lysosomal transport for involvement in spermatogenesis. RNAi directed against C. elegans adaptins indicated that the adaptor protein complex AP-3 plays an important role in spermatogenesis, probably through mediating vesicular transport during MO morphogenesis. Our knowledge of C. elegans spermatogenesis and the availability of powerful forward and reverse genetic tools make the MO an increasingly attractive metazoan model for studying lysosomal biogenesis.