In situ signal of Prtg mRNA is noted in the developing tooth germ. (A) The whole mount in situ expression in an E10.5 embryo reveals that Prtg mRNA is present in the maxilla and mandible as well as in the central nervous system. (B) A higher magnification of Fig. 5A; mx, maxilla; md, mandible. (C) At E10.5, strong in situ Prtg signals were present in the mesenchymal cells in the first branchial arch and throughout the oral epithelial layer (OPL). (D) At E12.0, an in situ signal is observed in the OPL and underlying mesenchymal cells. (E) Control section with sense probe to Fig. 5D. (F) At E14.0, the Prtg mRNA is conspicuous in the enamel organ and the surrounding mesenchymal cells. (G) At E16.0, in situ signals are detected in the enamel organ and the dental papilla. (H) At E18.0, a faint mRNA signal is marginally detected in the inner enamel epithelium. In the dental papilla, the positive cells are noted in the presumptive caspal areas. The signal is undetectable in the other areas. (I)Control section with sense probe in an E18.0 tooth germ. The left side of Figs. 5C-H corresponds to the lingual side, and the right side is the buccal side. Scale bars: C- H, 200 μm.