Nematode extracellular protein interactome expands connections between signaling pathways

The nematode Caenorhabditis elegans is a favorable model for studying cell-surface protein interactomes, given its well-defined and stereotyped intercellular contacts. Here, we report an extracellular interactome dataset for C. elegans. Most of these interactions were unknown, despite recent datasets for flies and humans, as our collection contains a larger selection of protein families. We uncover interactions for all four major axon guidance pathways, including ectodomain interactions between three of them. We demonstrate that a protein family, previously known for maintaining axon positioning, functions as secreted binders for insulins and that their overexpression in vivo extends lifespan, consistent with inhibition of insulin signaling. We reveal interactions of cystine-knot proteins with putative signaling receptors, which may extend the study of neurotrophins and growth factors to nematodes. Finally, our dataset constitutes a resource for uncovering the logic of neuronal connectivity, intercellular communication and adhesion, and signaling pathways involved in aging and disease.