Fig. 3. Pathfinding defects of layer 5 cortical projections in the telencephalon of Nkx2-1 mutants. Coronal sections through the telencephalon of E14.5 (A,E) or E18.5 (B,C,F,G,H) wild-type (A-C) or Nkx2-1 mutant mice (E-H) showing anterogradely labeled fibers (A-C,E,F,H) and retrogradely labeled thalamic cells (B,C,H) after DiI crystal placements in the neocortex. Arrowheads point to corticofugal fibers following a normal course, whereas arrows indicate corticofugal fibers abnormally projecting towards the surface of the telencephalon. (G) Coronal section through the telencephalon of an E18.5 Nkx2-1 mutant mice showing retrogradely labeled cells in the cortex after a DiI crystal placement in the ventral surface of the telencephalon (at the approximate location of the arrow in F). The dotted line indicates the surface of the cortex. (D,I) Schematic drawings showing the paths followed by pyramidal tract (blue), corticothalamic (pink) and thalamocortical (purple) axons in wild-type (D) and Nkx2-1 mutant mice (I). The hatched areas (D,I) indicate the presumptive territory patterned by Nkx2-1 function. A, amygdala; c, cortical plate; cp, cerebral peduncle; DT, dorsal thalamus; GP, globus pallidus; H, hippocampus; ic, internal capsule; NCx, neocortex; Str, striatum; Str*, mutant striatum; V, layer 5 cortical neurons; VI, layer 6 cortical neurons; VT, ventral thalamus. Scale bar: 200 µm in A,E; 400 µm in B,C,F,H; 100 µm in G.