FIGURE 9:

Crk is not required for proper expression of Robo and Slit but may play a more subtle role in Slit/Robo signaling. (A–F) Stage 15 embryos, antigens, and genotypes indicated. (A–C) Representative images of Robo localization in control and Crk knockdown embryos. (A) In wild type, Robo is strongly enriched in longitudinal axon bundles (A–A”, cyan arrows) and excluded from commissural axon bundles crossing the midline (A–A”, magenta arrows). (B, C) Following Crk knockdown, Robo expression is still largely restricted to longitudinal axon tracks (B–C’’, cyan arrows). In most cases, midline-crossing axon bundles are Robo-negative (B–C’’, magenta arrows); however, a subset of Robo-positive axons appear to cross the midline in Crk knockdown embryos (C–C’’, green arrows), suggesting Slit/Robo signaling may be impaired following Crk loss. (D–F) Representative images of Slit localization in control and Crk knockdown embryos. (D) In wild type, Slit expression is confined to the midline glia along the ventral midline (magenta arrows). (E, F) In Crk knockdown embryos, Slit expression remains confined to midline glia, generally forming a stereotypical line along the ventral midline (E–E”, magenta arrows). However, Crk knockdown embryos with more severely disrupted CNS patterning defects can have mispositioned Slit-expressing midline glia (F–F”, yellow arrows). Scale bars = 50 µm.