Fig. 8. Both cortical and thalamic axons pathfinding defects contribute to the formation of an abnormal internal capsule in Dlx1/2^-/- embryos. Coronal hemisections of E14 (A-F) and E16.5 (G-J) Dlx1/2 heterozygous (upper panel) and homozygous (lower panel) mutant brains where DiI crystals were introduced in the lateral part of the neocortex (A,B) or of the dorsal thalamus (C-J). Stars in E,F,I,J indicate DiI crystal positions. (A,B) DiI crystals in the lateral neocortex of control embryos label axons that make a turn and enter the ganglionic eminences (open arrowhead in A). In Dlx1/2^-/- embryos, these axons, do not make a sharp turn and grow into the ganglionic eminences towards the pial surface (open arrowhead in B). (C-F) DiI crystals in the dorsal thalamus of control embryos label thalamic axons that make a sharp turn into the ganglionic eminences (white arrowhead in E). In more rostral sections (C), axons grow in direction of the neocortex (white arrowhead in C) reaching the region where cortical axons enter the ganglionic eminences (compare C with A). In Dlx1/2^-/- embryos, thalamic axons fail to make a sharp turn (white arrowhead in F) and grow towards the pial surface of the ganglionic eminences (white arrowhead in D). Note that misrouted thalamic and cortical axons both travel in a more superficial domain of the ganglionic eminences (compare A with C and B with D). (G-J) A DiI crystal (star in I,J) in the lateral part of the dorsal thalamus labels the internal capsule, which is displaced closer to the pial surface in Dlx1/2^-/- mutant embryos. Furthermore, in addition to axons that navigate to the neocortex (open arrowheads), axons diving into the amygdalar region (white arrowhead in J) were detected. These axons were detected in more rostral sections (H), running in the ventral pallium (white arrowhead), whereas axons of the superficially displaced internal capsule run dorsally into the necortex (compare open arrowheads in G,H). dTH, dorsal thalamus; GE, ganglionic eminences; IC, internal capsule; Ncx, neocortex; Str, striatum.

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