Long-distance Wnt transport in axons highlights cell type-specific modes of Wnt transport in vivo .

Wnt signaling performs critical functions in development, homeostasis, and disease states. Wnt ligands are secreted signaling proteins that often move between cells to activate signaling across a range of distances and concentrations. In different animals and developmental contexts, Wnts utilize distinct mechanisms for intercellular transport including diffusion, cytonemes and exosomes [1]. Mechanisms for intercellular Wnt dispersal remain controversial in part due to technical challenges with visualizing endogenous Wnt proteins in vivo , which has limited our understanding of Wnt transport dynamics. As a result, the cell-biological bases for long-range Wnt dispersal remain unknown in most instances, and the extent to which differences in Wnt transport mechanisms vary by cell type, organism, and/or ligand remain uncertain. To investigate processes underlying long-range Wnt transport in vivo , we utilized C. elegans as an experimentally tractable model where it is possible to tag endogenous Wnts with fluorescent proteins without disrupting signaling [2]. Live imaging of two endogenously tagged Wnt homologs revealed a novel mode for long-distance Wnt movement in axon-like structures that may complement Wnt gradients generated by diffusion and highlighted cell type-specific Wnt transport processes in vivo .