Fig. 6. Ebf1 inactivation affects the pathfinding of early thalamic axons and Sema6a expression in the primordium of the basal ganglia. (A-H) Coronal hemisections of E13.5 (left) and E15.5 (right) wild-type and Ebf1^-/- brains where a DiI crystal was introduced in the lateral part of the neocortex (A-D) or of the dorsal thalamus (E-H). In both wild-type and Ebf1^-/- embryos, axons labeled by cortical DiI crystals make a sharp turn and enter the ganglionic eminences (open arrowhead in A-D). Crystals placed in the dorsal thalamus of wild-type embryos show that DiI-labeled thalamic axons (white arrowhead in E,G) make a sharp turn into the ganglionic eminences in the direction of the neocortex. On the contrary, in Ebf1^-/- embryos thalamic axons run closer to the pial surface of the brain (white arrowhead in F,H). In E13.5 brains, a group of retrogradely labeled cells is detected (arrow in F) at the position where thalamic axons are located in wild-type embryos (compare arrow in F with arrowhead in E). These cells of the perireticular nucleus are intermingled with the thalamic axons in wild-type embryos. (I-P) Coronal hemisections of E13.5 (left) and E15.5 (right) wild-type and Ebf1^-/- brains processed for Sema6a (I-L) and netrin 1 (M-P) in situ hybridization. In E13.5 controls (I), Sema6a is expressed in the mantle of the dorsal thalamus (black arrowhead), in a group of cells in the mantle of the ganglionic eminences (open arrow) and in the ventral pallium (black arrow). In Ebf1^-/- mutant E13.5 embryos (J), although the thalamic expression is unaffected (black arrowhead), Sema6a expression in the mantle of the ganglionic eminences is greatly reduced. In E15.5 wild-type embryos (K), thalamic fibers (open arrowhead) grow dorsally to a group of Sema6a-expressing cells (open arrow). However in Ebf1^-/- mutant embryos (L), Sema6a expression is strongly reduced and thalamic axons (open arrowhead) invade a zone that would be Sema6a positive in wild-type embryos. Netrin 1 expression, in E13.5 controls (M) is detected in the dorsal thalamus mantle (black arrowhead), in a group of cells in the mantle of the ganglionic eminences (open arrow) and in the ventral pallium (black arrow). At E15.5 (O), two groups of netrin 1-positive cells (black arrows) are located on both sides of the incoming thalamic axons (open arrowhead) and another group of labeled cells is located more laterally (open arrowhead). In Ebf1^-/- mutant embryos (N,P) this expression pattern was not clearly changed, except for a slight reduction at E13.5, in the expression domain in the ganglionic eminences (compare M with N). dTH, dorsal thalamus; GE, ganglionic eminence; Ncx, neocortex.