UNCP-18 is a C. elegans STXBP homolog that is required for full fertility

Exocytosis supplies the plasma membrane with lipids and proteins, and is essential for release of molecules to the cell exterior. The capture and efficient fusion of vesicles with the plasma membrane relies on SNARE and SEC1/MUNC18 (SM) proteins. The human SM protein STXBP1 is required for exocytosis of neurotransmitters, and mutation is associated with human neuronal disease. In contrast, mutations in STXBP2 and -3 primarily affect the function of non-neuronal cell types. Here we characterize the role of the C. elegans SM protein UNCP-18 in the germline. Endogenously tagged UNCP-18 is broadly expressed and primarily localized to the plasma membrane, consistent with a role in exocytosis. Loss of UNCP-18 led to reduced brood size which can be partially rescued by mating. Additional germline defects are evident, however, suggesting a role beyond the sperm. Our results demonstrate that UNCP-18 plays non-neuronal roles and suggest that C. elegans might provide a useful model for understanding the non-neuronal functions of SM proteins.