Required for posterior migration of cells and axon growth cones during nervous system assembly. Isoform a is required for posterior migration of the axon growth cone and the ALM cell body. Isoform a may enhance posterior migration by regulating the subcellular location or stability of guidance cue receptors such as sax-3 and unc-40; promoting their localization to the cell surface. Isoform b is specifically required for CAN cell migration. {ECO:0000269|PubMed:15539493; ECO:0000269|PubMed:17237777; ECO:0000269|PubMed:17237778; ECO:0000269|PubMed:8625818; ECO:0000269|PubMed:9581759}.