Fig. 4.

The Abl FABD and SH2 motifs are necessary for commissural axon guidance. (A-C) Stage 16 Abl² mutant embryos expressing the indicated Abl-GFP fusions in EW neurons using eg-Gal4. Four segments are shown. Anterior is up. (A) Abl^KNGFP has no effect in these embryos. (B) Abl^WTGFP expression has no effect. (C) Abl^NGFP interferes with midline crossing of EW neurons (arrow). (D) Quantification of EW crossing defects in Abl² mutants expressing the indicated Abl constructs. Abl^N, unlike Abl^WT, interferes with EW midline axon crossing. (E) Quantification of EW axon crossing defects in Abl² mutant embryos expressing DNFra along with the indicated constructs. Abl^WT rescues midline crossing defects though Abl^RK and Abl^ΔFABD do not. Data from control and Abl^WT rescue are also presented in Fig. 2B. For D and E, error bars indicate s.e.m.; number of segments scored is shown in parentheses; ^*P<0.05. n.s., not significant. (F) Multiple sequence alignment of the predicted FABD of Mus musculus (Mm) Abl1 and Arg (Abl2) along with that of Drosophila melanogaster (Dm) Abl using ClustalW. Identical residues are shaded in dark blue, similar residues are shaded in light blue. Similarity plot and consensus sequence are shown below. Amino acids 1499-1638 are shown for D. melanogaster Abl.