Subcellular localization of beta-catenin and cadherin expression in the cap-stage enamel organ of the mouse molar.

We analyzed the subcellular distribution of beta-catenin in the cap-stage enamel organ and compared it with the expression of E- and P-cadherin by using confocal laser microscopy. The amounts of the molecules in the cytoplasm and the nucleus showed regional variations in the enamel organ, whereas cell surface-associated beta-catenin was ubiquitous. In both the enamel knot and the inner dental epithelium, beta-catenin was detected in the cytoplasm and in the nucleus. However, the amount of nuclear beta-catenin was apparently higher in the enamel knot than in the inner dental epithelium. P-cadherin also gave a stronger signal in the enamel knot than in other parts of the enamel organ. In the stellate reticulum, where E-cadherin was preferentially expressed, as well as in the cervical loop and outer dental epithelium, beta-catenin was localized in the cytoplasm but not in the nucleus. The nuclear localization of beta-catenin in the enamel knot suggests a specific activation of the canonical Wnt signaling pathway. A coincident upregulation of P-cadherin was observed in this area. Altogether, these observations suggest the possibility of a linkage between cell adhesion and Wnt signaling in the enamel knot.