Figure 6. Disruption of Slit-Robo signaling results in ectopic motor neurons.

(A, B) β-galactosidase and Isl1 labeling of cryosections of Robo1^lacZ/+ (n=3 embryos, n=6 sections) and Robo2^lacZ/+ (n=3 embryos, n=6 sections) embryos. (C–J) Anti-Robo1 and anti-Robo2 antibody labeling of cryosections (C, D; n=3 embryos, n=6 sections) and dissociated cells (E–J, n=3 embryos) from ventral spinal cords. Robo receptors are present on Isl1⁺ cell bodies. (K–N) Isl1 antibody labeling of spinal cord sections at brachial levels. Robo1^−/−;2^−/− and Slit1^−/−;2^−/−;3^−/− embryos have numerous Isl1⁺ cell bodies outside the neural tube at the lumbar level. (O–R) Graphs show numbers of ectopic motor neurons at different levels of the spinal cord, and the numbers of motor neurons within the spinal column of Robo and Slit mutant embryos. (S–V) Isl1 and β–tubulin immunostaining of sections of E9.75 Robo1^−/−;2^−/− embryos. Adjacent sections were immunostained for Krox20. Inset shows high power image of Isl1⁺ motor neurons in the periphery (U). Error bars represent SEM. *p < 0.05, ***p < 0.001 vs. control; unpaired Student’s t-test; n.s., not significant. Scale bars: A–D, K–N, 50 μm; E–J, 20 μm; S–V, 50 μm.