Localization of Six1, Six2, Six4 and Six5 mRNAs in the tooth germs at the late cap stage (E16.5). (A1,B1,C1,D1,E1,F1) Low magnification images of expression patterns of Six family genes at the anterior level including first molars on serial frontal sections. (A2–A5) Six1 expression in the inner enamel epithelium (IEE) of the upper incisor tooth germ (arrow in A2,A3), and in the IEE and dental follicle (DF) in the upper and lower molar tooth germs (arrow and arrowhead in A4,A5). (B2–B5) Restricted expression of Six2 in the dental papilla (DP) and DF (asterisk and arrowhead in B4,B5, respectively). (C2–C5) No expression of Six3 mRNA in any tooth germs. (D2–D5) Expression of Six4 in the IEE and DF in the upper incisor tooth germ (arrow and arrowhead in D2,D3) and the intense expression in the IEE of the molar tooth germs (arrow in D4,D5). (E2–E5) Six5 is expressed in the neural retina (NR) shown as in E1. Expression of Six5 in the IEE (arrow in E2,E3) and DF (arrowhead in E2–E5) in the tooth germs, and the expression in the DP (asterisk in E2–E5). (F2–F5) Expression of Six6 in the NR shown as in F1. NE, nasal epithelium; Md, mandible; Mx, maxilla; Tg, tongue. Scale bars = 400 μm (A1,B1,C1,D1,E1,F1), 200 μm (A2–A5,B2–B5,C2–C5,E2–E5,F2–F5).