Shh is a target of Fgf10/Fgfr2b signaling. (A) FGF10-impregnated bead stimulates palatal epithelial proliferation (arrow). (B) BSA-impregnated bead had no effect on proliferation. (C) Shh bead stimulated proliferation in isolated palatal mesenchymal explants. (D) FGF10 induced Shh in vitro, in the oral side of WT palatal epithelium (arrow), but not in Fgfr2b_/_ mutant mice (E). (F) FGF10 also induced Ptc1 in the mesenchyme immediately adjacent to the bead in palatal explants (arrows). Ptc1 is a known target of Shh and an indicator of the level of hedgehog signaling. (G_L) In situ hybridization to detect Shh mRNA. Shh was expressed in the MEE and the oral side of the palatal epithelium, as well as in the dorsum of the tongue. (H, I, K, and L) In Fgfr2b_/_ and Fgf10_/_ mutants, Shh expression was reduced and concentrated to discrete patches of palatal epithelium. Shh remained expressed throughout the tongue dorsum epithelium (arrow). (M and N) Frontal histological sections through the posterior oral region of NB WT (M) and K14-Cre;Shhc/n (N) mice, stained with Ladewig’s trichrome. (M) In the WT mouse, the palatal shelves had elevated and fused in the midline forming a barrier between the oral cavity and the nasopharynx (asterisk). (N) The palatal shelves of K14-Cre;Shhc/n mutants failed to develop beyond rudimentary processes. (O) In situ hybridization to detect Smo mRNA at E13. Transcripts were detected in the mesenchyme of the palate (arrow). G_I, L and O, same magnification; scale bars: 200 ∝m. J and K: original magnification, ∞12.5.