Mechanosensory neurite termination and tiling depend on SAX-2 and the SAX-1 kinase

Mechanosensory neurons provide accurate information about stimulus location by restricting their sensory dendrites to nonoverlapping regions, a pattern called tiling. Here, we show that C. elegans sax-1 and sax-2 regulate mechanosensory tiling by controlling the termination point of sensory dendrites. During development, the posterior PLM mechanosensory dendrite overlaps transiently with the anterior ALM mechanosensory neuron. This overlap is eliminated during a discrete period of paused or slowed PLM process growth, between an early period of rapid outgrowth and a later period of maintenance growth. In sax-2 mutants, the PLM sensory dendrite fails to slow between the active growth and maintenance growth phases, leading to sustained overlap of anterior and posterior mechanosensory processes. sax-2 encodes a large conserved protein with HEAT/Armadillo repeats that functions with sax-1, an NDR cell morphology-regulating kinase. High-level expression of sax-2 leads to premature neurite termination, suggesting that SAX-2 can directly inhibit neurite growth.