Direct interactions between C. elegans RAB-3 and Rim provide a mechanism to target vesicles to the presynaptic density.
Rim is a multi-domain, active zone protein that regulates exocytosis and is implicated in vesicle priming and presynaptic plasticity. We recently demonstrated that synaptic defects associated with loss of Caenorhabditis elegans Rim (termed UNC-10) are accompanied by a reduction in docked vesicles adjacent to the presynaptic density. Since Rim is known to interact with the vesicle-associated GTPase Rab3A, here we asked whether UNC-10-dependent recruitment of synaptic vesicles to the presynaptic density was through an UNC-10/Rab-3 interaction. We first established that C. elegans Rab3 (termed RAB-3) in its GTP but not GDP-bound state interacts with UNC-10. We then demonstrated by EM analysis that rab-3 mutant synapses exhibit the same vesicle-targeting defect as unc-10 mutants. Furthermore, unc-10;rab-3 double mutants phenocopy the targeting defects of the single mutants, suggesting UNC-10 and RAB-3 act in the same pathway to target vesicles at the presynaptic density. Endogenous release of unc-10;rab-3 double mutants was similar to that of unc-10 single mutants, but more severe than rab-3 mutants, suggesting the common targeting defects are reflected by the milder rab-3 release defect. Rim has recently been shown to positively regulate calcium influx through direct interactions with calcium channels. Consistent with this notion we found UNC-10 colocalized with the calcium channel, UNC-2 at C. elegans presynaptic densities and synaptic release in unc-10 and rab-3 mutants exhibit reduced calcium-sensitivity. Together these results suggest that vesicles targeted to the presynaptic density by RAB-3/UNC-10 interactions are ideally positioned for efficient calcium-dependent release.
Gracheva
Elena O
EO
Department of Biological Sciences, University of Illinois at Chicago, 840 West Taylor St., Chicago, IL 60607, United States.
Hadwiger
Gayla
G
Nonet
Michael L
ML
Richmond
Janet E
JE
D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D013572:Synaptic Vesicles / Q000502:physiology*; D020692:rab3 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; C437625:unc-10 protein, C elegans; D020692:rab3 GTP-Binding Proteins