Frazzled and Abelson Figure 1. Increasing Abl activity in a fra mutant reduces commissure formation. Stage 16 embryos stained with mAb BP102 are depicted with anterior up. Indicated UAS- (U) transgenes are expressed pan-neurally using the 1407-Gal4 (1407-G4) driver line recombined onto a fra3 chromosome. For this reason, phenotypes are compared to heterozygous fra3 rather than a wild-type embryo; in most cases the heterozygote is similar to wild-type. [A] Normal anterior commissures (AC), posterior commissures (PC) and longitudinal connectives (LC) are observed in a fra3 1407- GAL4 heterozygote stained with BP102. [B] Over-expression of BcrAbl in a fra3 heterozygote causes fuzzy commissures in most segments while [C] expression of Ablwt causes only a rare fuzzy commissure (black arrowheads). [D] Homozygous fra3/fra4 mutants display thinning and missing PC’s (black arrowhead) in some segments but the AC remains unaffected (white arrowhead). Over-expression of either [E] BcrAbl or [F] Ablwt in a fra3/fra4 background enhances the degree of thinning and missing PC’s (black arrowhead), and many AC’s (white arrowhead) disappear. [K] Quantification of defects in the AC and PC are graphed with percent of commissures missing in a fra3 1407-Gal4 heterozygote (white, highlighted with ‘w’), fra3 1407- Gal4/fra4 homozygote (black) and fra3 1407-Gal4/fra4 homozygote’s expressing the indicated Abl transgene (gray). All three Abl transgenes significantly enhance the loss of PCs and both BcrAbl and Ablwt affect AC formation (*P,0.05; **P,0.01; ***P,0.001). [G] Co-expression of a Frawt transgene restores the fuzzy commissure defects caused by expression of BcrAbl but [H] with the FraDP3 transgene the AC and PC commissures are more distinct. Expression of [I] Frawt or [J] FraDP3 transgenes also rescues commissure formation when Ablwt is over-expressed in a homozygous fra mutant. [L] The distribution of segments containing fuzzy (black) or distinct (white) commissures in fra3/fra4 embryos co-expressing BcrAbl and each of the Fra P-motif deletion mutants is graphed. doi:10.1371/journal.pone.0009822.g001 heterozygous fra mutants [Figure 1B, C]. This phenotype depends on the presence of Fra protein, as re-expression of Frawt in our mutants reverts the phenotype back to that seen when either BcrAbl or Ablwt is expressed alone: normal AC and PC formation is observed with Ablwt, and the fuzzy commissures seen with BcrAbl return [Figure 1G, I]. PLoS ONE | www.plosone.org 4 March 2010 | Volume 5 | Issue 3 | e9822