Fig. 5. Pathfinding defects of layer 5 cortical projections in the diencephalon of Nkx2-1 mutants. Coronal (A,D) and horizontal (B,E) sections through the diencephalon (A,D) or pons (B,E) of E18.5 (A,B,D,E) wild-type (A,B) or Nkx2-1 mutant mice (D,E) showing anterogradely labeled fibers (A,B,D,E) and retrogradely labeled thalamic cells (A,D) after DiI crystal placements in the neocortex. The arrow indicates corticofugal fibers that follow an abnormal rostral path into the chiasmatic region of the hypothalamus. (C,F) The paths followed by pyramidal tract (blue), corticothalamic axons (pink) and thalamocortical axons (purple) in wild-type (C) and Nkx2-1 mutant mice (F). The hatched area indicates the presumptive territory patterned by Nkx2-1 function. Chr, chiasmatic region; Chr*, mutant chiasmatic region; cp, cerebral peduncle; DT, dorsal thalamus; fr, fasciculus retroflexus. Scale bar: 400 µm in A,B,D,E.