Figure 2.

The Wnt/β-catenin signaling pathway is activated in a dynamic fashion in molar tooth development. Summary of data from analyses of Wnt/β-catenin pathway activity in developing molar teeth in vivo with immunostaining for nuclear β-catenin; X-gal staining of embryos carrying Wnt reporter transgenes that contain multimerized LEF/TCF binding sites upstream of a minimal promoter and a lacZ reporter (TOPGAL, BAT-gal, and Lef/Tcf-lacZ); and X-gal staining of embryos in which lacZ has been inserted into the endogenous Axin2 locus, a direct Wnt target gene (Liu et al., 2008; Lohi et al., 2010). While expression patterns vary slightly for different reporters, these studies, taken together, indicate that Wnt/β-catenin signaling localizes specifically to the epithelium of the dental lamina at the placode stage; to the primary epithelial enamel knot and underlying mesenchymal cells at the bud and cap stages; and to the secondary enamel knots and underlying mesenchymal cells at the bell stage. Wnt/β-catenin pathway activity is indicated by grey or blue shading in the print and online versions, respectively. Dashed black lines indicate epithelial-mesenchymal borders. Diagrams are not to scale.