Wnt signaling and contact-mediated repulsion shape sensory dendritic fields.

UNLABELLED: The complete and non-redundant coverage of sensory tissues by neighboring neurons enables effective detection of stimuli in the environment. How the neurites of adjacent neurons establish their boundaries to achieve this completeness in coverage remains incompletely understood. Here, we use distinct fluorescent reporters to study two neighboring sensory neurons with complex dendritic arbors, FLP and PVD, in C. elegans . We quantify the sizes of their dendritic fields, and identify CWN-2/Wnt and LIN-17/Frizzled as a ligand and receptor that regulate the relative dendritic field sizes of these two neurons. Loss of either cwn-2 or lin-17 results in complementary changes in the size of the dendritic fields of both neurons; the FLP arbor expands, while that of PVD shrinks. Using an endogenous knock-in mNeonGreen-CWN-2/Wnt, we find that CWN-2/Wnt is localized along the path of growing FLP dendrites. Dynamic imaging shows a significant braking of FLP dendrite growth upon CWN-2/Wnt contact. We find that LIN-17/Frizzled functions cell-autonomously in FLP to limit dendritic field size and propose that PVD fills the space left by FLP through contact-induced retraction. Our results reveal that interactions of dendrites with adjacent dendrites and with environmental cues both shape the boundaries of neighboring dendritic fields.

HIGHLIGHTS: ▫ Secreted Wnt CWN-2 and cell-autonomous activity of neuronal LIN-17/Frizzled receptors restrict FLP dendritic field sizes▫ Endogenously tagged CWN-2/Wnt is punctate and visible in the same plane of growing FLP dendrites▫ Growth of developing FLP dendrites is inhibited upon contact with extracellular CWN-2/Wnt and with PVD dendrites.