Factors regulating the abundance and localization of synaptobrevin in the plasma membrane.
After synaptic vesicle fusion, vesicle proteins must be segregated from plasma membrane proteins and recycled to maintain a functional vesicle pool. We monitored the distribution of synaptobrevin, a vesicle protein required for exocytosis, in Caenorhabditis elegans motor neurons by using a pH-sensitive synaptobrevin GFP fusion protein, synaptopHluorin. We estimated that 30% of synaptobrevin was present in the plasma membrane. By using a panel of endocytosis and exocytosis mutants, we found that the majority of surface synaptobrevin derives from fusion of synaptic vesicles and that, in steady state, synaptobrevin equilibrates throughout the axon. The surface synaptobrevin was enriched near active zones, and its spatial extent was regulated by the clathrin adaptin AP180. These results suggest that there is a plasma membrane reservoir of synaptobrevin that is supplied by the synaptic vesicle cycle and available for retrieval throughout the axon. The size of the reservoir is set by the relative rates of exo- and endocytosis.
Dittman
Jeremy S
JS
Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA.
Kaplan
Joshua M
JM
D000818:Animals; D001369:Axons / Q000378:metabolism; D017173:Caenorhabditis elegans; D002462:Cell Membrane / Q000378:metabolism*; D002966:Clathrin / Q000378:metabolism; D005089:Exocytosis; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D034041:Monomeric Clathrin Assembly Proteins / Q000378:metabolism; D009046:Motor Neurons / Q000378:metabolism*; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000378:metabolism; D050683:R-SNARE Proteins / Q000378:metabolism / Q000502:physiology*
D002966:Clathrin; D034041:Monomeric Clathrin Assembly Proteins; D009419:Nerve Tissue Proteins; D050683:R-SNARE Proteins; C439023:clathrin assembly protein AP180; D049452:Green Fluorescent Proteins