Expression of amelin and amelogenin in epithelial root sheath remnants of fully formed rat molars

Objective. To study the expression patterns of 2 enamel proteins, amelin and amelogenin, in the epithelial cells of the root sheath of fully formed rat molars. Study design. Twelve Sprague-Dawley rats, 50, 65, and 85 days of age, were used in this study. The maxillae of the rats were dissected free, and sagittal serial sections were made through the mesial root of the first molar. In situ hybridization of amelin and amelogenin mRNAs was performed, and immunohistochemical examinations of the corresponding proteins in the epithelial cells of the root sheaths of fully formed rat molars were performed. Antibodies against epidermal keratins were used to identify epithelial root sheath remnants. Results. A group of epithelial cells, enclosed at the border between cellular cementum and dentin, expressed and synthesized amelin, but not amelogenin. Another group of epithelial cells, forming islands or strands, which were partially or totally incorporated in the matrix of the cellular cementum, expressed and synthesized both amelogenin and amelin. A third group of epithelial cells at the periphery of the cellular cementum expressed neither of the 2 proteins. Epithelial cells at the surface of acellular cementum did not express either of the 2 proteins. Conclusion. This study showed that the epithelial root sheath remnants in rat molars express and synthesize amelogenin, as well as amelin. However, there are marked regional differences. The roles of the Enamel proteins in the formation of the radicular hard tissues of the rat molars and in the maintenance of the periodontal tissues remain to be clarified.