Fig. 7. Tangential migration from the septum is severely impaired in Vax1^-/- embryos. (A,B) Nissl staining of coronal sections from wild-type and mutant brains at E16.5. There is complete loss of the septum in Vax1^-/- telencephalon. (C,F) (Top) The experimental procedure. The red spots represent DiI crystals placed at E13.5 in an organotypic slice culture assay. (Bottom) Bright-field images of wild-type (C) and mutant (F) slices corresponding to those shown in the scheme. Sections are taken at comparable rostrocaudal levels. (D,E,G,H) Fluorescent images of the same slices from wild-type (D,E) and Vax1^-/- (G,H) embryos; (E,H) high-magnification photographs of the region boxed in D and G, respectively. Cells that migrate along a lateral-tangential pathway are present in the wild-type slice (E, white arrows) but there is complete loss of this stream in the mutant brain (H). lv, lateral ventricle; lge, lateral ganglionic eminence; sa, septal area; sa^*, presumptive septal area.