AMELIN - AN ENAMEL-RELATED PROTEIN, TRANSCRIBED IN THE CELLS OF EPITHELIAL ROOT SHEATH

Since 1974, when Slavkin and his collaborators proposed the epithelial origin of cementum, many experiments have been carried out to provide evidence for deposition of enamel-related proteins along the root sur face. However, neither amelogenin nor other proteins have fully satisf ied expectations, In previous studies, we have identified a novel mRNA coding for an extracellular-like protein which,ve called amelin. It w as expressed at high levels in secretory and postsecretory ameloblasts in rat molars and incisors. In situ hybridization experiments describ ed in the present study also localized the amelin message to epithelia l cells adjacent to the peripheral surface of newly deposited dentin i n the root end and to cells embedded in cellular cementum in molars. I n incisors, the amelin RNA positive cells were detected in the area wh ere cementum formation had been initiated. No amelogenin RNA signal wa s found in the cells at the root surface. We postulate that the epithe lial cells of the root sheath as well as the ameloblasts are synthesiz ing amelin which might be one of the key proteins coupled to the proce ss of cementogenesis.