Fig. 6

In situ hybridization revealed expression patterns of miRNAs in four types of teeth during three tooth developmental stages. (A1–C4) At E40, miR-103 was expressed in both the epithelium and mesenchyme of the incisor, canine, and molar, but expression in the premolar was lower and expression in the molar was not as strong as in the incisor and canine (A1–A4). At E50, miR-103 expression in all four types of teeth stayed the same for the most part, but the expression level was lower and more restricted in the inner enamel epithelium, which contains the most important structure of morphogenesis: the enamel knot in incisor and canine. Expression in the molar was increased and restricted in the inner enamel epithelium as well (B1–B4). At E60, mir-103 expression in the premolar increased substantially, while in the other three types of teeth, the location was restricted in the inner enamel epithelium (C1–C4). (D1–F4) At E40, miR-127 was expressed in both the epithelium and mesenchyme of the incisor, canine, premolar, and molar, but the expression levels among the four types of teeth were different. There was a strong signal in the molar, in contrast to a weak signal in the other three types of teeth (D1–D4). At E50, miR-127 expression in all four types of teeth stayed almost the same, but expression in the premolar was not observed and the expression level was lower and more restricted in the inner enamel epithelium of the molar (E1–E4). At E60, mir-127 expression in the incisor, canine, and premolar increased, while expression decreased in the molar. The location of mir-127 was restricted in the inner enamel epithelium of the incisor, canine, and premolar (F1–F4). (G1–I4) At E40, miR-133a was expressed in both the epithelium and mesenchyme of all four types of teeth, with a higher signal in the incisor (G1–G4). At E50, miR-133a expression in all four types of teeth stayed nearly the same, but with a lower signal in the incisor (H1–H4). At E60, expression was more restricted in the inner enamel epithelium and increased expression was found in the premolar and molar (I1–I4). Scale bar, 200 μm. Di, first deciduous incisor; Dc, deciduous canine; Dpm, second deciduous premolar; Dm, deciduous molar; E40, embryonic day 40; E50, embryonic day 50; E60, embryonic day 60