Wnt signals and frizzled activity orient anterior-posterior axon outgrowth in C-elegans

Secreted proteins of the Wnt family affect axon guidance, asymmetric cell division, and cell fate. We show here that C. elegans Writs acting through Frizzled receptors can shape axon and dendrite trajectories by reversing the anterior-posterior polarity of neurons. In lin-44/Wnt and lin-17/Frizzled mutants, the polarity of the PLM mechanosensory neuron is reversed along the body axis: the long PLM process, PLM growth cone, and synapses are posterior to its cell body instead of anterior. Similarly, the polarity of the ALM mechanosensory neuron is reversed in cwn-1 egl-20 Wnt double mutants, suggesting that different Wnt signals regulate neuronal polarity at different anterior-posterior positions. LIN-17 protein is asymmetrically localized to the posterior process of PLM in a lin-44-dependent manner, indicating that Writ signaling redistributes LIN-17 in PLM. In this context, Wnts appear to function not as instructive growth cone attractants or repellents, but as organizers of neuronal polarity.