Dopey-dependent regulation of extracellular vesicles maintains neuronal morphology

Mature neurons maintain their distinctive morphology for extended periods in adult life.Compared to developmental neurite outgrowth, axon guidance, and target selection,relatively little is known of mechanisms that maintain morphology of mature neurons.Loss of function in C. elegans dip-2, a member of the conserved lipid metabolicregulator Dip2 family, results in progressive overgrowth of neurites in adults. We findthat dip-2mutants display specific genetic interactions with sax-2, the C.elegans ortholog of Drosophila Furry and mammalian FRY. Combined loss of dip2 and sax-2 results in failure to maintain neuronal morphology and elevated release ofneuronal extracellular vesicles (EVs). By screening for suppressors of dip-2(0) sax2(0)double mutant defects we identified gain-of-function (gf) mutations in theconserved Dopey family protein PAD-1 and its associated phospholipid flippase TAT5/ATP9A that restore normal neuronal morphology and normal levels of EV releaseto dip-2(0) sax-2(0) double mutants. Neuron-specific knockdown suggests PAD-1(gf)can act cell autonomously in neurons. PAD-1(gf) displays increased association withthe plasma membrane in oocytes and inhibits EV release in multiple cell types. Ourfindings uncover a novel functional network of DIP-2, SAX-2, PAD-1, and TAT-5 thatmaintains neuron morphology and modulates EV release.