Ciliary Protein NPHP-8 Is Required For Ciliogenesis And Chemosensation In C. Elegans And The Coupling Of Exocytosis And Endocytosis In INS-1 Cells

This paper contains two parts:(1) Caenorhabditis elegans ciliary protein NPHP-8 is required for ciliogenesis and chemosensationNephronophthisis (NPHP) is the most frequent genetic cause of end-stage renal failure in children and young adults. To date, causative mutations in 10 genes(NPHP1-9 and NPHP11) have been associated with this autosomal recessive cystic kidney disease. NPHP8/RPGRIP1L is a novel ciliary gene that when mutated also causes Joubert syndrome (JBTS) and Meckel syndrome (MKS). The exact function of NPHP8 and how defects in NPHP8 lead to human diseases are poorly understood. Here, we studied the C. elegans homolog nphp-8 (C09G5.8) and explored the possible function of NPHP-8 in ciliated sensory neurons. We determined the gene structure of nphp-8 through RACE analysis and discovered an X-box motif that had been previously overlooked. Moreover, while NPHP-8 colocalized with NPHP-4 at the transition zone at the base of cilia, disruption of either gene did not affect the correct localization of the other protein. Mutation of nphp-8 led to abnormal dye filling (Dyf) and shorter cilia lengths in a subset of ciliary neurons. In addition, chemotaxis to several volatile attractants was significantly impaired in the nphp-8 mutants. Our data suggest that NPHP-8/RPGRIP1L plays an important role in cilia formation and cilia-mediated chemosensation in a cell type-specific manner.(2) Vesicle fusion navigates clathrin puncta migration towards release sites to rapidly recycle vesicle components in pancreatic beta cellsDue to the long time required for de novo formation of deeply invaginated clathrin-coated pits that mostly appear at sites different from exocytosis before fission, clathrin-dependent vesicle recycling in secretory cells is usually regarded as a slow process. Here we show that a group of triggered vesicle fusion in pancreatic beta cells is associated with glucose-dependent fast or slow recruitment of clathrin and dynamin-1 puncta at the release sites. The subsequent disassembly of these clathrin puncta mediates internalization of synaptotagmin 7 clusters in the plasma membrane.Triggered by vesicle fusion, the fast endocytosis involves either fission of stable clathrin structures docked near release sites, or movement of clathrin puncta towards release sites prior to fission. These results have revealed an unexpected close spatio-temporal coupling of clathrin-dependent endocytosis to vesicle fusion in pancreatic beta cells, and highlighted a novel role of the movement of clathrin-coated structures in the plasma membrane to rapidly recycle vesicle membrane components.