Fig. 7. Interneuron and oligodendrocyte specification. The status of developing interneurons and oligodendrocytes was examined on coronal sections at E12.5. Gad67 marks developing inhibitory neuron populations and is significantly reduced in Nkx2.1^–/–;Gsh2^–/– double-mutant mice (D) compared with control (A), Gsh2^–/– (B) or Nkx2.1^–/– (C) single mutant mice. Gad67 expression, although reduced and restricted to the ventral midline, persists in Shh^–/– mutants (E). Olig2 is expressed in the VZ of the LGE and MGE (F). In Gsh2^–/– mutants, Olig2 expression is reduced in the mutant LGE (G). By contrast, Olig2 expression appears unaffected in Nkx2.1^–/– mutants (H). Olig2 expression is reduced in Nkx2.1^–/–;Gsh2^–/– mutants (I), and is absent in Shh^–/– mutants (J). Arrows show dorsal limit of expression of Gad67 (A-D) and Olig2 (F-I) in control and mutant brains. Expression of Pdgfra is normally observed in the MGE as punctate staining (K; arrow). In Gsh2^–/– mutants, Pdgfra is ectopically expressed in the VZ of the MGE and the ventral LGE (L), but is completely absent in Nkx2.1^–/– mutants (M). Pdgfra is ectopically expressed in the lateral domain in Nkx2.1^–/–;Gsh2^–/– double mutants (N), and is absent in Shh^–/– mutants (O). By contrast, Plp/DM20 expression (P; arrows) is unaffected in Gsh2^–/– (Q) or Nkx2.1^–/– (R) single, or Nkx2.1^–/–;Gsh2^–/– double (S), mutants. However, in Shh^–/– mutants expression of Plp/DM20 is lost (T). Scale bar in A: 200 µm for A-D,F-I,K-N,P-S; 275 µm for E,J,O,T.