Figure 4

robo2 and robo3 are required for commissure formation. A-B Confocal microscopic images of WT and ast^−/− commissures from individual CoPA axons (lateral view). ast^ti272z CoPA axons ascend in the midline while WT CoPA axons cross immediately. Anterior is to the left, dorsal is up. Gray dotted line indicates ventral midline of spinal cord. C Measurements of axon length within the midline of the spinal cord, in the anteroposterior axis (arbitrary units) in wild-type, ast^ti272z, and twt embryos. ast^ti272z commissure length is 36 ± 3.2 (n = 7), which is 2.8 times that of wild type, which measures 13.3 ± 1.1 (n = 19) . In affected twt^tx209embryos, the average length is roughly 15 times that of WT (204 ± 22.9; n = 9).