Cas mutants display a mild but significant commissural axon defect. (a–h) Transverse cryosections through control (a,c,e,g) and Wnt1Cre;TcKO (b,d,f,h) e11.5 spinal cords immunostained for Tag1 (a–d), L1Cam (e–h, red) and laminin (e–h, green). Sections in (e–h) were counterstained with Topro (blue). (c–d), and (g–h) are higher magnification views of (a–b), and (e–f), respectively. There is a mild reduction in the width of the ventral commissure (white arrows, d,h), and the DREZ is smaller and disorganized in Wnt1Cre; TcKO embryos (yellow arrows, b,f). (i) Quantification of the normalized commissure thickness in control and Wnt1Cre;TcKO embryos. Two-tailed t-student test ***p = 0.0041. 5 brachial sections per animal, 4–5 animals for each genotype. (j) Quantification of the normalized DREZ thickness in control and Wnt1Cre;TcKO embryos. Two-tailed t-student test ***p = 6.22e-5. 5 sections per animal, 5 animals for each genotype. Error bars represent SEM. Scale bars: 50 μm; Scale bar in F corresponds to (a,b,e,f); scale bar in h for (c,d,g,h).