Rabx-5 Regulates RAB-5 Early Endosomal Compartments and Synaptic Vesicles in C. elegans

Abstract

Early endosomal membrane compartments are required for the formation and recycling of synaptic vesicles, but how these compartments are regulated is incompletely understood. We performed a forward genetic screen in C. elegans for mutations that affect RAB-5 labeled early endosomal compartments in GABAergic motoneurons. Here we report the isolation and characterization of one mutation, rabx-5. The rabx-5 mutation leads to decreased intensity of YFP::RAB-5 in the cell soma but increased intensity in the synaptic and intersynaptic regions of the axon. This effect is due to the bias of the cycling state of RAB-5, and results from a change in the organization of the early endosomal compartment as well as the membrane binding state of RAB-5. Synaptic vesicle accumulation is altered in rabx-5 mutants, and synaptic transmission from cholinergic neurons is decreased. Early endosomal membrane compartments show disorganization with ageing and rabx-5 mutant animals age faster. These results suggest that rabx-5 regulation of RAB-5 compartments is important for maintaining proper synaptic function throughout the lifetime.

Communication breakdown: The impact of ageing on synapse structure

“…Interestingly, these reductions are more prominent in “decrepit,” nearly paralyzed individuals compared to those that maintain locomotory vigor in their “old age.” Similarly, 35-day old animals of a related species, C. briggsae that start to lose their ability to move (i.e., just prior to death) show profound breakdown of nerve tissue, including the accumulation of large, membranous structures (Epstein et al, 1972). In another study of C. elegans , mutations of a regulator of the early endosomal Rab protein, RAB-5 affects neuronal endosomal structures and synaptic vesicle accumulation and causes the animals to age faster (Sann et al, 2012). …”

C. elegans as a model for membrane traffic

“…RABX-5 is thought to activate RAB-5 on early endosomes, where it is important for homotypic early endosome fusion, degradative transport toward the late endosome, and probably recycling transport as well (Dwivedi et al, 2011; PMID 21618079; Poteryaev et al, 2010; PMID 20434987; Sann et al, 2012; PMID 22675499; Sato et al, 2005; PMID 15895077; Woodman, 2000; PMID 11208157). RABX-5 is removed from early endosomes by the action of SAND-1 and its associated proteins as the degradative process proceeds, as RAB-5 positive early endosomes mature into RAB-7 positive late endosomes (Poteryaev et al, 2010; PMID 20434987).…”

Endosome maturation factors Rabenosyn‐5/VPS45 and caveolin‐1 regulate ciliary membrane and polycystin‐2 homeostasis

“…Thus, RABS‐5 recruitment to EE‐like structures occurs independently of the RAB‐5 activation state. Next, we assessed whether RAB‐5(Q78L) or RAB‐5(S33N) overexpression, or loss of RAB‐5 GEFs ( rme‐6 or rabx‐5 ) (Sato et al , ; Sann et al , ), phenocopy the cilium structure defects of rabs‐5 mutants. In all cases, no defects in phasmid dye‐filling, cilium length, or PCMC area were observed (Figs C and EV3A and B; Hu et al , ; Kaplan et al , ; van der Vaart et al , ).…”