RAB-5 regulates regenerative axonal fusion by controlling EFF-1 endocytosis

Abstract

Following a transection injury to the axon, neurons from a number of species have the ability to undergo spontaneous repair via fusion of the two separated axonal fragments.In the nematode C. elegans, this highly efficient regenerative axonal fusion is mediated by Epithelial Fusion Failure-1 (EFF-1), a fusogenic protein that functions at the membrane to merge the two axonal fragments. Identifying modulators of axonal fusion and EFF-1 is the next step towards harnessing this process for clinical applications. Here, we present evidence that the small GTPase RAB-5 acts to inhibit axonal fusion, a function achieved via endocytosis of EFF-1 within the injured neuron. Consequently, we find that perturbing RAB-5 activity increases the capacity of the neuron to undergo axonal fusion, through enhanced membranous localization of EFF-1 and the production of extracellular EFF-1-containing vesicles. These findings identify RAB-5 as a novel regulator of axonal fusion and the first regulator of EFF-1 in neurons.

How cells fuse

“…A system to cut axons using laser microsurgery (axotomy) was implemented in C. elegans (Yanik et al, 2004) and was used in a breakthrough experiment which determined that EFF-1 fuses cut axons in the PLM mechanosensory neuron (Ghosh-Roy and Chisholm, 2010). EFF-1 directly mediates the reconnection process, and RAB-5–mediated endocytosis of EFF-1 controls the axonal fusion remodeling (Linton et al, 2018). Based on rescue experiments, EFF-1 acts cell-autonomously in the PLM neuron during the axonal auto-fusion process (Fig.…”