Fig. 3. Morphology and gene expression in Gli2 null brains. (A) Dorsal view of the morphology of wild-type (left) and Gli2^-/- (right) dissected E18.5 brains. Anterior is to the top. (B,C) Comparison of lateral views of dissected cortex, and dorsal views of tectum and cerebellum in wild-type (B) versus Gli2^-/- (C) brains. Arrows point to the posterior cortex in the two hemispheres, tectum and cerebellum. Gli2^-/- mutant mice have an apparently normal choroid plexus (not shown). The ballooning of the telencephalic vesicle may be due to the inability of the tissue, which is thinner than normal, to sustain the same degree of intravesicular pressure. (D) Comparison of wild-type and Gli2^-/- cortices seen in parietal sagittal sections stained for Hematoxylin and Eosin. The intermediate zone and cortical plate layers appear of normal size and cell density. (E-G) BrdU incorporation in wild-type (F) and mutant (G) cortices, and quantification of cell proliferation (E). The mean number of BrdU⁺ cells per section from wild-type and Gli2^-/- animals is shown. For simplicity, the vz was considered as the zone in between the ventricle and 5-cell diameters away, and the svz as that in between 5- and 10-cell diameters from the ventricle (svz cells, P<0.05; vz cells, P<0.01). (H,I) Comparison of Neurod1 expression by in situ hybridization in the cerebellum of wild-type (H) and Gli2^-/- (I) E18.5 animals. (J-S) Images of in situ hybridization analyses of sagittal sections from E18.5 (J-Q), and coronal sections from E15.5 (R,S), wild type (J,L,N,P,R) and Gli2^-/- (K,M,O,Q,S) animals probed with Gli1 (J,K), Gli2 (L,M), Gli3 (N,O), Neurod1 (P,Q) or clone 53 (R,S). Neocortical Gli1 expression is absent in Gli2^-/- animals, but a domain of its expression in the striatum was still present (inset, K). Note the small hippocampus in the Gli2^-/- brain (Q, arrow), compared with in wild type (P). Forebrain pattern appeared largely unchanged as expression of the Pax6 anteroposterior gradient and of Dlx2 ventrally were not grossly affected (not shown). (T,U) Quantification of the number of Neurod1⁺ (T) and clone 53⁺ (U) cells in the dorsal telencephalon of wild-type versus Gli2^-/- animals (Neurod1⁺, P<0.001; clone 53⁺, P<0.001). cb, cerebellum; cp, cortical plate; ctx, cortex; h, hippocampus; iz, intermediate zone; Med, medulla; st, striatum; svz, subventricular zone; tct, tectum; vz, ventricular zone. Scale bar in A: 800 µm for A; 1.3 mm for B,C; 75 µm for D; 50 µm for F,G,H,I; 130 µm for J-Q; 300 µm for R,S.