Gene expression of beta-catenin is up-regulated in inner dental epithelium and enamel knots during molar tooth morphogenesis in the mouse.

Beta-catenin is a multi-functional molecule that is involved in both cell-cell adhesion and signaling. We analyzed changes in beta-catenin gene expression during mouse molar tooth development by in situ hybridization. Prominent up-regulation of the expression of this gene was evident exclusively in the enamel knot at the early cap stage. During the cap and bell stages, the enamel knot, inner dental epithelium, and differentiating stratum intermedium expressed the beta-catenin gene more strongly than other parts of the enamel organ. During these stages, the strength of the gene expression changed heterogeneously within the inner dental epithelium and stratum intermedium. However, the heterogeneity was not evident at the late bell stage, when the cells in the inner dental epithelium had differentiated into ameloblasts at the cusp tip. No spatiotemporal change in beta-catenin gene expression was apparent in the dental papilla except for the cells that differentiated into odontoblasts, which became negative for the expression of the gene after their differentiation. Thus, the up-regulated expression of the beta-catenin gene was strongly associated with epithelial morphogenesis. These findings raise the possibility that the up-regulation of the gene expression and the stabilization of the protein by Wnt signaling play a role in the regulation of the activities of beta-catenin in tooth morphogenesis.