UNC-13 and UNC-10/rim localize synaptic vesicles to specific membrane domains.
Synaptic vesicles undergo a maturation step, termed priming, in which they become competent to fuse with the plasma membrane. To morphologically define the site of vesicle priming and identify fusion-competent synaptic vesicles, we combined a rapid physical-fixation technique with immunogold staining and high-resolution morphometric analysis at Caenorhabditis elegans neuromuscular junctions. In these presynaptic terminals, a subset of synaptic vesicles contact the plasma membrane within approximately 100 nm of a presynaptic dense projection. UNC-13, a protein required for vesicle priming, localizes to this same region of the plasma membrane. In an unc-13 null mutant, few synaptic vesicles contact the plasma membrane, suggesting that membrane-contacting synaptic vesicles represent the morphological correlates of primed vesicles. Interestingly, a subpopulation of membrane-contacting vesicles, located within 30 nm of a dense projection, are unperturbed in unc-13 mutants. We show that UNC-10/Rim, a protein implicated in presynaptic plasticity, localizes to dense projections and that loss of UNC-10/Rim causes an UNC-13-independent reduction in membrane-contacting synaptic vesicles within 30 nm of the dense projections. Our data together identify a discrete domain for vesicle priming within 100 nm of dense projections and further suggest that UNC-10/Rim and UNC-13 separately contribute to the membrane localization of synaptic vesicles within this domain.
Weimer
Robby M
RM
Ecole Normale Supérieure, Biologie Cellulaire de la Synapse, and Institut National de la Santé et de la Recherche Médicale, U789, F-75005 Paris, France,.
Gracheva
Elena O
EO
Meyrignac
Olivier
O
Miller
Kenneth G
KG
Richmond
Janet E
JE
Bessereau
Jean-Louis
JL
D000818:Animals; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D021962:Membrane Microdomains / Q000378:metabolism* / Q000648:ultrastructure*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D013572:Synaptic Vesicles / Q000378:metabolism* / Q000648:ultrastructure*
D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D009419:Nerve Tissue Proteins; C485548:UNC13B protein, human; C437625:unc-10 protein, C elegans