Synaptic vesicle clustering requires a distinct MIG-10/Lamellipodin isoform and ABI-1 downstream from Netrin

Abstract

The chemotrophic factor Netrin can simultaneously instruct different neurodevelopmental programs in individual neurons in vivo. How neurons correctly interpret the Netrin signal and undergo the appropriate neurodevelopmental response is not understood. Here we identify MIG-10 isoforms as critical determinants of individual cellular responses to Netrin. We determined that distinct MIG-10 isoforms, varying only in their N-terminal motifs, can localize to specific subcellular domains and are differentially required for discrete neurodevelopmental processes in vivo. We identified MIG-10B as an isoform uniquely capable of localizing to presynaptic regions and instructing synaptic vesicle clustering in response to Netrin. MIG-10B interacts with Abl-interacting protein-1 (ABI-1)/Abi1, a component of the WAVE complex, to organize the actin cytoskeleton at presynaptic sites and instruct vesicle clustering through SNN-1/Synapsin. We identified a motif in the MIG-10B N-terminal domain that is required for its function and localization to presynaptic sites. With this motif, we engineered a dominant-negative MIG-10B construct that disrupts vesicle clustering and animal thermotaxis behavior when expressed in a single neuron in vivo. Our findings indicate that the unique N-terminal domains confer distinct MIG-10 isoforms with unique capabilities to localize to distinct subcellular compartments, organize the actin cytoskeleton at these sites, and instruct distinct Netrin-dependent neurodevelopmental programs.

Abelson interactor-1 (ABI-1) interacts with MRL adaptor protein MIG-10 and is required in guided cell migrations and process outgrowth in C. elegans

“…Two other groups working concurrently have now also shown that MIG-10 and ABI-1 interact (Quinn and Xu, 2012; Stavoe et al, 2012). Our results demonstrate that MIG-10A and ABI-1 interact in a yeast two-hybrid system, and that either MIG-10A or MIG-10B co-immunoprecipitate with ABI-1 in insect cells, suggesting that these proteins physically interact.…”

“…Three MIG-10 isoforms are predicted, MIG-10A, B, and C (Fig 1). Cell autonomous expression of MIG-10A has been shown to be sufficient to rescue some mig-10(ct41) axon outgrowth defects (Chang et al, 2006; Quinn et al, 2006; Quinn et al, 2008), while cell autonomous expression of MIG-10B is sufficient to rescue defects in synaptic vesicle clustering observed in mig-10(ct41) animals (Stavoe et al, 2012). MIG-10C has not been shown to be required for rescue of any mutant phenotype.…”

“…These authors suggest a model in which MIG-10B interacts with ABI-1 to organize the actin cytoskeleton, which then leads to vesicle clustering (Stavoe et al, 2012). The presence of a Q-SNARE domain at the ABI-1 N-terminus suggests that ABI-1 might even participate more directly in vesicle fusion, since SNARE proteins are known to mediate the fusion of vesicles with their target membranes (Jahn et al, 2003).…”

The actin cytoskeleton in presynaptic assembly

“…These findings suggest that F-actin functions within or near synaptic vesicle pools. 17,43,62 At the Drosophila NMJ, actin is observed as distinct puncta in synaptic boutons. 63 Similarly, several proteomic studies have identified actin as a component of the synaptic vesicle and active zone proteomes.…”

“…17,62 Interestingly, the RacGEF involved in this pathway, CED-5/DOCK180, while required for vesicle clustering, is not required for proper localization of active zone proteins to presynaptic sites. These findings suggest that active zone assembly and synaptic vesicle clustering are instructed by two different signaling pathways downstream from Netrin.…”