Fig. 5. The cytoplasmic domain of Fra is not required for proper localization. (A-E') Stage 16 embryos stained with BP102 to visualize all axons. (C'-E') Same embryos as C-E. Staining with anti-Myc or anti-HA reveals Fra receptor expression. Anterior is up. (A) Wild-type embryos stained with BP102 exhibit a ladder-like CNS scaffold with distinct thick anterior and posterior commissures. (B) Commissural bundles are thin or absent in fra mutant embryos (arrowheads). (C) Expressing a full length Fra receptor in all neurons using elavGal4 rescues fra mutant defects. (C') Wild-type Fra localizes to the axons scaffold when expressed in all neurons. (D) When a weak insert of FraC is expressed panneurally in a fra mutant background, many axons fail to cross the midline (arrowheads). (D') Despite the inability of FraC to rescue fra guidance defects, this truncated receptor is still localized to the axon scaffold as well as the wild-type full-length receptor. (E) Expression of FraC^Robo67Myc does not rescue the defects seen in fra mutant embryos (arrowheads); however, in contrast to FraC, FraC^Robo67Myc does not efficiently localize to axons (E') perhaps because the exongenous Robo sequence interferes with normal Fra receptor distribution.