abelson, trio, and enabled interact genetically with frazzled. D.J. Forsthoefel 1, E.C. Liebl 2, M.A. Seeger 1. 1) Dept. of Molecular Genetics and Neurobiotech Center,Ohio State Univ.,Columbus,OH; 2) Dept. of Biology,Denison Univ.,Granville,OH.
In order to better understand the roles of the Abelson kinase (Abl) and the GEF Trio during axon guidance, we have begun to examine Abl's and Trio's interactions with receptors known to function at the embryonic CNS midline in Drosophila. We previously observed that abl,trio double mutant embryos stained with MAb BP102 exhibited a dramatic CNS phenotype in which commissural axon pathways were disrupted in 100% of segments, consistent with a role for these gene products in modulation of the growth cone cytoskeleton during attractive signaling (Neuron 26:107-118). We now report that mutations in both abl and trio dominantly enhance CNS defects in embryos that are homozygous mutant for frazzled (fra), which encodes the attractive Netrin receptor. In homozygous fra embryos, commissural axon pathways are thin or missing in only 14% of segments scored (n=242). In fra/fra;abl/+ embryos the percentage of defective segments increases to 26% (n=299). Likewise, in fra/fra;trio/+ embryos 42% of segments exhibit a loss of commissural axons (n=208). Mutations in trio and abl also enhance CNS defects in embryos hemizygous for Df(1)NP5, a deletion which removes the Fra ligands Netrin A and Netrin B. Interestingly, we find that heterozygosity for enabled (ena) reduces the severity of the CNS phenotype in homozygous fra or hemizygous Df(1)NP5 embryos. For example, in Df(1)NP5/Y embryos 24% (n=277) of segments have disrupted commissures versus only 7% in Df(1)NP5/Y;ena/+ embryos (n=308). Abl, Trio, and/or Ena may be engaged directly by Fra to modulate the growth cone cytoskeleton. Alternatively, dominant modification of the fra phenotype may reflect these proteins' integration into signaling networks downstream of multiple guidance cues, exclusive of or in addition to Fra signaling. In order to distinguish between these possibilities, we are characterizing biochemical interactions between Fra, Abl, Ena, and Trio.