Expression of BmprIa and BmprIb in developing tooth and palate. (A, E) At E13.5, BmprIa expression is detected in the epithelium and mesenchyme of upper incisor (A), but is restricted in the epithelium in lower incisor (E). (B, D) BmprIb is expressed in the epithelium of both upper (B) and lower (D) incisor at the same stage. (E, F) In the developing molars at E13.5, BmprIa (E) and BmprIb (F) is expressed in the epithelium and mesenchyme. Note that BmprIb exhibits a higher level of expression in the upper molar mesenchyme as compared to its expression in the lower molar (F). (G-J) At E14.5, BmprIa is continuously expressed in both the epithelial and mesenchymal compartments of upper (G) and lower (H) molars, but BmprIb expression is restricted to molar epithelium, particularly in the inner enamel epithelium (I, J). (K-N) Expression of BmprIa (K, M) and BmprIb (L, N) in E13.5 palatal shelf. In the anterior palate, both BmprIa (K) and BmprIb (L) are expressed in the palatal epithelium and mesenchyme. In the posterior palate, BmprIa expression is observed in the epithelium and mesenchyme at relatively lower levels (M); however, no BmprIb expression is detected (N). Dashed lines demarcate dental epithelium. T, tongue; de, dental epithelium; dm, dental mesenchyme; PS, palatal shelf.