Required for the migration of axonal growth-cones and distal tip cells (DTC) along the dorsal-ventral axis of the body wall (PubMed:9685266, PubMed:19169249, PubMed:9473333). Acts cell nonautonomously and independently of the classical daf-4, sma-6 or daf-1 TGFbeta receptor signaling (PubMed:9685266, PubMed:11018016, PubMed:19169249). During axon migration, facilitates long-range repulsive guidance of unc-6/netrin by enhancing unc-5-unc-40 signaling at the expense of unc-5 alone signaling, probably through direct interaction with receptor unc-5 (PubMed:19169249, PubMed:9473333). Involved in cell-cell contact formation in sensory rays in the developing male tail, via a pathway involving plx-2 and mab-20/semaphorin-2A (PubMed:15030761). Interacts with netrin receptor unc-5; the interaction is direct. Expressed first at late gastrulation stage in cells that include descendants of the AB and E lineages (PubMed:9685266). Expression detected in dorsal body wall muscle (BWM) at the 1.5-to 2-fold stage of embryogenesis; also in some of cells in the head, including one ventral muscle (PubMed:9685266, PubMed:27341757). Between 520 min and hatching, expressed in the DA and DB motor neurons, excluding DA8 and DA9 (PubMed:9685266). This pattern of expression persists into adulthood (PubMed:9685266). Belongs to the TGF-beta family.