Syb2^−/− embryos display morphological defects similar to loss of Sema3A. (A) E18 brain from Syb2^+/+ and Syb2^−/− embryos were cut in 100-µm slices and stained with Nrp1 (red), L1 (green), and DAPI (blue; Syb2^+/+, n = 3; Syb2^−/−, n = 4 embryos). Bar, 500 µm. (B, left) Schematic view of loss of compaction of Nrp1-positive fibers in Syb2^−/−. (B, right) Profile of Nrp1 fluorescence measured in corpus callosum of Syb2^+/+ and Syb2^−/− embryos (2–3 slices quantified for each embryo). ***, P < 0.0005 by two-way analysis of variance test.