Fig. 6. Ectopic expression of Dephrin causes axonal repulsion. (A,B) Ectopic expression of Dephrin in midline cells (A) causes a severe thinning of the commissures (arrowhead) but does not interfere with the determination of midline glia (black, anti-Wrapper). As in wild type (B), midline glia still tightly enwrap the commissural fibres. (C,D) Ectopic expression of Dephrin in midline cells prevents axons from crossing the ventral midline. The lineage of one neural precursor includes glial cells and three contralateral projecting neurones (star). In embryos with ectopic midline expression of Dephrin (C), the projections of these neurones (thin arrow) are stalled at the midline. In a 1-hour younger wild-type embryo (D), the axons (thin arrow) have already crossed the midline. (E,F) Axonal repulsion by ectopic Dephrin does not depend on Slit or Robo1. Ectopic expression of Dephrin in midline cells of slit, robo1 double mutants (E, purple, arrow) is able to push axons (FasII, brown) out of the midline. In slit, robo1 double mutants (F), the longitudinal tracks collapse at the midline. (G,H) Ectopic expression of Dephrin in longitudinal glia cells (G, thick arrow) causes breaks in the axonal scaffold (green, BP102). Longitudinal glia cells expressing GFP (H, thick arrow) do not perturb the formation of the axonal scaffold (brown, BP102). Horizontal views of stage 17 embryos (except D, stage 16); anterior to the left. Dotted line marks the midline.