unc-34 is required for cell and neuronal growth cone migrations;
unc-34 mutations disrupt nearly all cell and growth cone migrations that have been analyzed. In particular,
unc-34 mutations affect the cell migrations of the HSN, CAN, ccM, ALM, and Q cell neuroblasts as well as the growth cone migrations of the HSN, CAN, VD and DD axons. In addition,
unc-34 mutants also show a general disorganization of axon bundles of the ventral nerve cord. To address the role of
unc-34 in these migrations we cloned the gene.
unc-34 maps to a cosmid gap on the left arm of chromosome V, approximately one m.u. to the left of
unc-60. A BLAST search using the sequence of the Drosophila gene enabled (ena) detected a C. elegans homologue from a YAC sequence that covers the cosmid gap in this region. Ena is conserved from flies to mammals and has been implicated in cytoskeletal dynamics and stability through F-actin assembly; the murine homologue, mEna localizes to the cytoskeleton and binds profilin. Mutations in Drosophila ena cause defects in the CNS and PNS, including misrouted axons and disorganized axon bundles. The role of ena in cell and neuronal growth cone migrations, and the presence of an ena homologue in the
unc-34 region, suggested to us that
unc-34 may encode the C. elegans homologue of enabled. Three results showed that
unc-34 is indeed an ena homologue. First, RNA interference with C. elegans ena sequences produced an
unc-34-like phenotype. Second, genomic Southern blots of DNA from
unc-34 mutants showed that the ena homologue was deleted in
unc-34(
e951) mutants. Third, sequencing the 5' end of the ena gene from
unc-34 mutants showed that
unc-34(
gm104) is an amber stop early in the gene and
unc-34(
gm114) is an alanine to threonine mutation. Our work also demonstrates that, in addition to the requirements for Ena in nerve bundle formation seen in Drosophila, Ena plays a significant role in cell migration. We are currently investigating the function of C. elegans abl and dab, two other genes in the Drosophila enabled pathway.