Fig. 6. Axons expressing FraC are not attracted toward the midline. (A-E) Stage 16 embryos stained with mAb BP102 to visualize all axons (magenta) and anti-HA to reveal FraC-HA expression (green). Anterior is up. (A) Wild-type embryos stained with BP102 exhibit a ladder-like CNS scaffold. (B) Commissural bundles are thin when one copy of FraC is panneurally expressed in a wild-type background (arrowheads). (C) Axon commissures are almost completely absent when two copies of FraC are expressed. (D) Fewer axons cross the midline when one copy of FraC is expressed in a fra heterozygous background (arrowheads; compare this phenotype to the one in B). (E) When one copy of FraC is expressed in a fra homozygous mutant background, axons are no longer attracted toward the midline. (F) Diagram of the FraC-HA construct used in these experiments. (G,H) Stage 16 embryos stained with mAb BP102 and anti-GFP to highlight the Egl neurons. (G) When one copy of FraC is expressed specifically in the Egl neurons in a wild-type background, EW axons fail to cross the midline in many segments (arrow with star). (H) None of the EW axons cross the midline when FraC is expressed in a fra mutant background. Additionally, we also see defects in EG axon guidance (starred feathered arrow), a phenotype never observed in fra mutants (feathered arrows in G). Specifically, both EW and EG axons are often observed exiting the midline (carets).