Fig. 4. Dorsoventral patterning of the telencephalon is largely restored in Shh^-/-;Gli3^+/- mutants. Lateral (A-C) and dorsal (A'-C') views of the heads from wild-type, Shh^-/- and Shh^-/-;Gli3^+/- E12.5 embryos, showing the extent of the phenotypic rescue. The telencephalon of Shh^-/-;Gli3^+/- embryos is formed of two paired vesicles (arrows), in sharp contrast to the phenotype of Shh^-/- embryos. Note that the eye phenotype is also partially rescued as indicated by the presence of two distinct eyes, albeit fused at the midline and the proboscis observed in Shh^-/- animals is reduced in size (asterisks in B,C; arrows in E,G,K,M; arrowheads in B-C'). (D-O) Coronal sections of wild-type and Shh^-/-;Gli3^+/- E12.5 embryos assayed for various region-specific homeobox gene expression. Dlx2 (D,E), Mash1 (J,K) and Gsh2 (L,M) expression in the mutants closely resembles that in wild-type embryos, showing that ventrolateral patterning is established normally in this context. Double immunohistochemistry for Gsh2 and Pax6 further demonstrate that LGE- and cortex-like structures are properly established in Shh^-/-;Gli3^+/- animals (N,O). Arrowheads delineate the boundary between the LGE and the cortex. In the ventral midline, a small region of Nkx2.1 expression is observed in Shh^-/-;Gli3^+/- embryos (G,I, asterisks). Overlay of Nkx2.1 (red) and Dlx2 (green) RNA in situ hybridization from adjacent sections using Adobe Photoshop 4, shows the nested pattern of Nkx2.1 within a broader Dlx2 domain in both wild-type and mutant embryos (H,I). (P-S) Coronal sections of wild-type and Shh^-/-;Gli3^+/- E12.5 embryos assayed for Gli1 (P,Q) and Ptch (R,S) expression, showing that the Shh pathway is not active. Brackets in P,R indicate the extent of Gli1 (P) or Ptch (R) expression.

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