Fig. 4. Regulation of Gli3 repressor (Gli3R) levels is required for dorsal mes/r1 development and growth. (A-D) Hematoxylin and Eosin staining of E18.5 and E12.5 sagittal sections. (A,B) Dorsal mes/r1 development is severely affected in the Gli3^Xt/Xt-null mutants. (A) At E18.5, IC and SC are not discernible and the Cb is reduced in size and abnormal. (B) The dorsal isthmus (d-Is) and r1 region are enlarged at E12.5. (C,D) The Shh^-/- phenotype (compare Fig. 1H,N) is partially rescued by removing one copy of Gli3. Ventral (Teg/vHb and v-mes/r1) and dorsal structures are present and dorsal Mb appears to be organized into IC and SC. Insets in A and C show calbindin-positive Purkinje cells in the Cb. (E) The N-terminal Gli3R form is increased whereas full-length Gli3 (Gli3F) is decreased in Shh^-/- brain compared with Shh^+/+ or Shh^+/- mes/r1 at E12.5. Gli3F is slightly reduced in Shh^+/- mes/r1. Whole brain extracts were used for Shh^-/- mutants, as the size of the mes/r1 is severely reduced by E12.5. Scale bars: 300 µm in A,C; 75 µm in B,D.