Glial adherens junction proteins act with SAX-7/L1CAM to promote dendrite extension in C. elegans

Adherens junctions (AJs) stabilize cell contacts by coupling adhesion molecules to the cytoskeleton. AJ proteins have been studied extensively in epithelia, but less is known about their roles in other cell types. Here, we describe a role for AJ proteins in C. elegans glia. Previously, we showed that C. elegans glia use the adhesion molecule SAX-7/L1CAM to anchor the dendritic endings of URX and BAG sensory neurons at the nose during embryo elongation, allowing their dendrites to stretch to their full lengths. Using cell-specific rescue and depletion experiments, we show that the AJ proteins MAGI-1 and HMR-1/Cadherin also act in glia to promote URX and BAG dendrite extension. MAGI-1 is a multi-PDZ domain protein that can simultaneously interact with PDZ-binding (PB) motifs in SAX-7 and HMP-2/β-catenin thus potentially bridging SAX-7 to the cadherin-catenin complex. The SAX-7 PB motif also binds AFD-1/afadin. Double-mutant analyses indicate that many of these players act redundantly, consistent with parallel interactions among them. As MAGI-1, HMR-1 and AFD-1 are all found in epithelial AJs, we propose that an AJ-like complex in glia promotes dendrite extension.