EXPRESSION OF E-CADHERIN AND P-CADHERIN DURING TOOTH MORPHOGENESIS AND CYTODIFFERENTIATION OF AMELOBLASTS

Cell-cell adhesion is fundamental in morphogenesis and is known to be mediated by several groups of cell adhesion molecules. Cadherins are a group of such molecules involved in the Ca2+-dependent cell-cell adhe sion mechanism and are found in most kinds of tissue. In this study us ing indirect immunofluorescence microscopy, we analyzed the distributi on of two kinds of cadherins, E- and P-cadherin, in developing tooth g erms. In the molar tooth germs at the early bud stage, marginal cells of the epithelial tooth bud expressed both E- and P-cadherin, whereas central cells expressed only E-cadherin. At the cap stage, in addition to the cells of the inner and outer enamel epithelium, which outline the enamal organ, cells of the enamel knot, which is thought to contro l tooth morphogenesis, strongly expressed P-cadherin. The expression o f P-cadherin was prominent in the inner enamel epithelium during the e arly to mid bell stage, and was also evident in the non-dividing cell masses at future cusp tips, which are the so-called secondary enamel k nots. In the tooth germ at the late bell stage when the cells of the i nner enamel epithelium began to polarize to differentiate into amelobl asts, the polarizing ameloblasts lost P-cadherin and strongly expresse d E-cadherin. However, E-cadherin was also lost from polarized amelobl asts at later stages. The stratum intermedium and the stellate reticul um were E-cadherin positive from the bell stage onward even at the sta ges when the ameloblasts became E-cadherin negative again. These resul ts suggest that the differential expression of E- and P-cadherin durin g morphogenetic stages plays a role in the regulation of tooth morphog enesis, whereas alteration of E-cadherin expression during later stage s of tooth development is related to differentiation and function of t he ameloblasts and other cells supporting amelogenesis.