Immunohistochemical expression of Prtg is also observed in the developing tooth germ. (A) At E10.5, immunohistochemical Prtg signals were present in the mesenchymal cells in the first branchial arch and throughout the oral epithelial layer (OPL). (B) A higher magnification of Fig. 6A. The signal of the Prtg protein is localized around the cell, suggesting protein localization on the cell surface. (C) At E12.0, an immunohistochemical signal is also present in the thickened area of the OPL and in the underlying mesenchymal cells. The Prtg-expressing is strong in the mesenchymal cells localized beneath the thickened OPL (indicated by the square). (D) A higher magnification of the boxed area in the Fig. 6C. (E) At E14.0, the Prtg expression is notable in the enamel organ and the surrounding mesenchymal cells. (G) At E16.0, immunohistochemical signals are marginally detected in the enamel organ and the dental papilla. (F, H) Higher magnifications of the boxed areas in the Figs. 6E and G, respectively. (I) The immunohistochemical signal was detected in the dental papilla as well as in the enamel organ. (J) A higher magnification of the boxed area in the Fig. 6I. The left side of Figs. 6A, C, E, G and I corresponds to the lingual side, and the right side is the buccal side. Scale bars: A, C, E, G and I, 200 µm; B, D, F, H and J, 40 µm.