Fig. 7. Ventral expansion of Olig1/Olig2 expression in neuroepithelium and increased production of oligodendrocyte progenitor cells in the Nkx2.2 mutant spinal cord. Spinal cord sections from E13.5 (A-D,G-H) and E15.5 (E,F) wild-type (A,C,E,G) and mutant (B,D,F,H) embryos were labeled for Olig1 (A,B) or Olig2 (C-F) or double-labeled for Olig2 and Shh (G,H). In the wild-type embryos, Olig1 and Olig2 are expressed in the same ventricular cells, which are separated from the Shh-expressing floor plate by the Nkx2.2 domain (arrow, G). In the mutants, the Olig1/Olig2 domain is ventrally expanded into the Nkx2.2 domain and becomes directly adjacent to the floor plate (H). The number of Olig1/Olig2-positive cells in the surrounding regions is accordingly increased.