Histological analysis of secondary palate development and morphological features of Bmp7-deficient mouse embryos.

(A) Coronal sections from the middle region of the palate at E13.5-E15.5. Whereas the palatal shelves in both Bmp7^wt/wt and Bmp7^Δ/Δ embryos were similar in shape at E13.5, the shelves of the Bmp7^Δ/Δ embryos at E14.5 remained vertically oriented when compared to Bmp7^wt/wt littermate embryos. Note the increased tongue height in Bmp7^Δ/Δ embryos. At E15.5 the palatal shelves of Bmp7^Δ/Δ embryos were in the process of reorientation, while the shelves of Bmp7^wt/wt littermates already had started to fuse along their medial edges (arrow). (B) Coronal sections along the A-P axis of the developing palates at E15.5 stained with Alcian Blue and Fast Red demonstrate regional differences in palatal shelf reorientation in the Bmp7^Δ/Δ embryos. The delay in reorientation is most evident in the anterior region. The mid-palatal region was defined by the presence of the 1^st molar tooth bud (*) on the sections. n; nose, p; palatal shelf, t; tongue, Scale bar: 100 μm. (C) Ventral views of Meckeĺs cartilage (stained with Alcian Blue) at E14.5 reveal that its halves are significantly shorter and fail to fuse in the anterior region in Bmp7^Δ/Δ embryos, resulting in a shorter mandible (white dotted lines) with a protruding tongue (yellow dotted line). Upper lips are marked (red dotted lines). (D) Side views of Bmp7^Δ/Δ and Bmp7^wt/wt littermate heads show that the growth of the nasal prominence is also stunted in the mutant in addition to the shorter mandible. Yellow dotted outline in image of mutant embryo corresponds to wt littermate.