Figure 2. Bell stage (E17.0) mRNA expression of Tfap2a, Tfap2b, Yeats4, and Kctd1 (A-P) in wild-type mouse embryos.

mRNA transcripts detected by in situ hybridization on cryosections in the frontal plane are shown in the upper incisor (A-D), lower incisor (E-H), upper molar (I-L), and lower molar (M-P). The dental epithelium is outlined. Note the spatially restricted expression of Tfap2a in the molars (I, M) and the overlapping expression domains of Tfap2b and Yeats4 in the incisors (B, C, F, G). Scale bar in A, G: 500um, all images are at the same scale. Pmx: premaxilla, Mx: maxilla, Md: mandible, T: tongue. Summary of gene expression results highlighting differences between incisors and molars at the cap (Q, R) and bell stages (S, T). In cap stage incisors (Q), Tfap2a, Tfap2b, Kctd1, and Yeats4 are expressed in the epithelium but only Tfap2a is expressed throughout the mesenchyme. In the molars (R), Tfap2b is expressed in the mesenchyme, while Tfap2a, Kctd1, and Yeats4 transcripts are present in both the epithelium and mesenchyme. In bell stage incisors (S), the expression of each gene is similar to that of the cap stage incisors, however, Kctd1 was not detected. In molars at the bell stage (T), Tfap2a was expressed in the epithelium only, Tfap2b expression was restricted to the mesenchyme, and minimal to no expression of Kctd1 and Yeats4 was detected, indicated by gray text (T). DE: dental epithelium, DM: dental mesenchyme.