Caenorhabditis elegans rab-3Mutant Synapses Exhibit Impaired Function and Are Partially Depleted of Vesicles

Abstract

Rab molecules regulate vesicular trafficking in many different exocytic and endocytic transport pathways in eukaryotic cells. In neurons, rab3 has been proposed to play a crucial role in regulating synaptic vesicle release. To elucidate the role of rab3 in synaptic transmission, we isolated and characterized Caenorhabditis elegans rab-3 mutants. Similar to the mouse rab3A mutants, these mutants survived and exhibited only mild behavioral abnormalities. In contrast to the mouse mutants, synaptic transmission was perturbed in these animals. Extracellular electrophysiological recordings revealed that synaptic transmission in the pharyngeal nervous system was impaired. Furthermore, rab-3 animals were resistant to the acetylcholinesterase inhibitor aldicarb, suggesting that cholinergic transmission was generally depressed. Last, synaptic vesicle populations were redistributed in rab-3 mutants. In motor neurons, vesicle populations at synapses were depleted to 40% of normal levels, whereas in intersynaptic regions of the axon, vesicle populations were elevated. On the basis of the morphological defects at neuromuscular junctions, we postulate that RAB-3 may regulate recruitment of vesicles to the active zone or sequestration of vesicles near release sites.

Rabphilin Potentiates SolubleN-Ethylmaleimide Sensitive Factor Attachment Protein Receptor Function Independently of rab3

“…The rab-3 phenotype is also characterized by aberrant synaptic physiology that can be assessed using the EPG, a simple extracellular recording technique developed by Raizen and Avery (1994) and Avery et al (1995). Mutations in several genes implicated in synaptic transmission significantly alter the EPG trace (Iwasaki et al, 1997;Nonet et al, 1997Nonet et al, , 1998Saifee et al, 1998). In contrast to rab-3, which exhibits EPG defects , the EPGs of most rbf-1 worms were not distinguishable from those of wild-type animals (Fig.…”

“…Indeed, rab proteins in yeast are essential components of the secretory pathways they regulate (Novick and Zerial, 1997). In contrast, previous studies of rab-3 mutants in C. elegans and rab-3a mutants in mice came to the unexpected conclusion that rab-3 was not required for synaptic vesicle release (Geppert et al, 1994a;Nonet et al, 1997). A major difference between the synapse and most other secretory pathways is that vesicles are found in abundance at most synapses.…”

Calmodulin enhances ribbon replenishment and shapes filtering of synaptic transmission by cone photoreceptors

“…Synaptotagmin (syt) 7 complexes with CaM to accelerate replenishment in hippocampal neurons (Liu et al, 2014), but there is no evidence for syt 7 at retinal ribbon synapses (Kantardzhieva et al, 2012). Another potential CaM target is Rab3a, a vesicle-associated protein involved in both long-and short-term plasticity (Castillo et al, 1997;Geppert et al, 1997;Nonet et al, 1997;Leenders et al, 2001;Schlüter et al, 2004Schlüter et al, , 2006 accelerate replenishment by quickening the transition of vesicles to release sites at the ribbon base. (d) Vesicles spend only 47 ms at the membrane surface before fusion (membrane dwell time; Fig.…”

A Conserved Mechanism of Synaptogyrin Localization

“…To assess whether localization of SNG-1 is mediated by protein-protein interactions with other SV protein(s), we examined SNG-1::GFP or native SNG-1 localization in mutants lacking distinct SV-associated proteins, including RAB-3 and RBF-1 (rabphilin), SNB-1, and SNT-1 (Table 1; Nonet et al, 1993Nonet et al, , 1997Nonet et al, , 1998; Staunton, Ganetzky, and Nonet, unpublished observations). In these single mutant backgrounds, the localization of SNG-1::GFP or native SNG-1 was indistinguishable from that in jsIs219 or wildtype animals (our unpublished results).…”