Fig. 4. Absence of floor plate, reduction of ventral neural progenitor population in response to attenuated Shh signaling in Disp1 hypomorphic mutants. Sections through the neural tube of control (A-D), Disp1 hypomorphic mutants (as indicated). In Disp1^2/2 mutant (E-H): the floor plate is absent (E); Nkx2.2 and Olig2 positive cells are reduced by over 50% (F); Nkx2.2 cells occupy the ventral midline (F); and Nkx6.1-positive cells are also affected (G). The dorsal marker Pax7 is restricted to the dorsal domain (G). In Disp1^2/C829F mutant (I-L), both Nkx2.2 and Olig2 are further reduced (J). The Pax7 and Pax6 domains move ventrally (K,L). In Disp1^2/C829F, Shh+/– mutant (M-P), Nkx2.2-positive cell is absent (N). Reducing the sequestration by Ptch1 rescues the Disp1^2/2 spinal cord phenotype in Disp1^2/2, Ptch1+/– mutant (Q-T).