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Fig. 7 Germ layer contribution to oropharyngeal epithelium and teeth in amphibians and amniotes. (A) Ambystoma punctatum, extirpation of the ectoderm of a stage 24 embryo, ventral view (redrawn after Adams, 1924). (B) Ambystoma punctatum; sagittal section of a stage 39 embryo after extirpation of the ectoderm; teeth in the ectoderm (blue) are reduced or absent, while endoderm (green) has given rise to splenial (S) and palatine (P) tooth germs (red); FG, foregut (adapted after Adams, 1924). (C) Ambystoma punctatum; sagittal section of a stage 45 embryo showing a maxillary bulb (MB) separated from any connection with the foregut; no contact between ectoderm (blue) and endoderm (green), yet a palatine tooth (P) is present (red); FG, foregut (adapted after Adams, 1924). (D) Pleurodeles waltl, first-generation tooth, stage 36. dp, dental papilla; ide, inner dental epithelium; oe, oral epithelium (from Davit-Béal et al., 2007, with permission from the publisher). Scale bar = 10 μm. (E) Chalcides viridanus; cross section of the dental lamina on the upper jaw of a 30 mm embryo. Scale bar = 50 μm. (F) Mus musculus; frontal section through a cap-stage molar tooth germ of a Sox17-2A-iCre/R26R mouse, with the epithelium outlined with red dots; there is no contribution of the endoderm (blue) [modified from Rothova et al., 2012, courtesy of the authors ]. Scale bar = 100 μm. (G) Mus musculus; immunostaining for keratin 6 (Krt6, red) and tumor protein p63 (p63, green) in a E15.5 embryo. Krt6 is expressed uniformly in the periderm superficial to the tooth germ (arrow). mn, mandible; tg, tooth germ (from Peyrard-Janvid et al., 2014, with permission from the publisher). Scale bar = 20 μm.