Fig. 1. Mid/hindbrain phenotype in the absence of total or Gli2A-mediated Shh signaling. (A-L) Dorsal view of whole-mount brains (A-F), and Hematoxylin and Eosin staining of midline sagittal sections (G-L) of P0 wild-type (control) and cko embryos or E18.5 null embryos. (B,H) In Shh-null mutants, cerebral cortex (Ctx), dorsal midbrain (tectum, Tec), ventral Mb (tegmentum, Teg) and ventral anterior hindbrain (vHb) are not discernible, and the cerebellum (Cb) is abnormal. (H, inset) Calbindin-positive Cb Purkinje cells (red, arrow) and Hoechst staining (blue) of the area indicated by the square. A cell dense layer probably corresponds to the Cb external granule cells (arrowhead). (C,I) In Smo-En1 cko mutants, the size of the Mb/Cb is reduced, the ventricle is absent (arrow) and the Tec is not divided into superior (SC) and inferior colliculi (IC). (D,J) In Smo-Nes cko mutants, the IC is truncated (arrow) and the Cb is reduced in size. The Ctx is also reduced in size. (E,F,K,L) In Gli2-null and Gli2-En1 cko mutants, the Teg, vHb and Cb are reduced in size. The Tec thins in Gli2-null mutants because of hydrocephaly. (M-R) Hematoxylin and Eosin staining of midline sagittal sections of E12.5 wild-type (control) and mutant embryos. (N) In Shh-null mutants, the mes/r1 is severely reduced in size. Dorsal and ventral neural tube is joined at the isthmus (Is) (arrow). (O) A close apposition of ventral and dorsal isthmus (vIs, dIs) is visible in Smo-En1 cko mutants (arrow), and dorsal mes (d-mes) and r1 (d-r1) are truncated. (P) In Smo-Nes cko embryos, d-r1 and the posterior d-mes are reduced in size (arrow), but no obvious defect is observed in ventral mes (v-mes) or r1 (v-r1). (Q,R) There is no obvious dorsal phenotype in Gli2-null or Gli2-En1 cko mutants, but ventral mes/r1 is altered (arrows). Scale bars: 700 µm in A-F; 300 µm in G-L; 75 µm in M-R.