The assembly of the nervous system in the nematode C. elegans requires the directed migrations of cells and growth comes along the anteroposterior and dorsoventral body axis. We show here that the gene vab-8 is essential for most posteriorly directed migrations of cells and growth cones. Mutations in vab-8 disrupt fourteen of seventeen posteriorly directed migrations, but only two of seventeen anteriorly directed and dorsoventral migrations. For two types of neurons that extend axons both anteriorly and posteriorly, vab-8 mutations disrupt only the growth of the posteriorly directed axon. vab-8 encodes two genetic activities that function in the guidance of different migrations. Our results suggest that most posteriorly directed cell and growth cone migrations are guided by a common mechanism involving the vab-8 gene.

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