Molecular biological study of the function of matrix proteins in the early stage of tooth development, with special reference to cytodifferentiation and initial calcification

鞘蛋白(成釉蛋白)是釉质基质蛋白的主要成分之一，不仅在分泌性成釉细胞中表达，而且在其他类型的细胞中也有表达，如未成熟的成牙本质细胞和马拉色斯的其余上皮细胞。为了解鞘蛋白在牙上皮-间充质相互作用中的作用，我们尝试研究了鞘蛋白在大鼠中牙胚牙骨质形成最早阶段的表达及其与骨水泥母细胞分化的关系。研究结果总结如下：1.研究成果。赫特威格上皮根鞘的部分细胞和马拉色氏上皮细胞的其余部分细胞表达鞘蛋白，其分子形式与分泌型成釉细胞表达的分子形式相同。电子显微镜免疫细胞化学显示鞘蛋白存在于高尔基体中，位于牙周侧的马拉色氏上皮细胞的其余部分。结论：1.骨水泥基质本身不含鞘蛋白。位于根部牙本质表面附近的间充质细胞表达骨桥蛋白，骨桥蛋白是牙骨质形成的标志之一，其突起延伸至根部牙本质表面。这些细胞通常附着在其余的马拉色氏上皮细胞上。给予细胞分泌活性的抑制剂莫尼辛后，骨桥蛋白明显定位于这些间充质细胞延伸的胞浆突起中。结果表明，鞘蛋白的表达总是先于骨桥蛋白的表达，提示Hertwig上皮根鞘和Malassez上皮细胞分泌的鞘蛋白诱导间充质细胞向成牙本质细胞分化，并将细胞质突起延伸到钙化牙本质表面，形成初始的粘固层。

Sheath protein (ameloblastin), one of the main constituent of the enamel matrix protein, is expressed not only in the secretory ameloblast but also in other cell types such as immature odontoblasts and epithelial cell rest of Malassez. In order to understand the role of Sheath protein in the epithelial-mesenchymal interaction, we have attempted to demonstrate the expression of sheathe protein and the relation of cement blast differentiation of the earliest stage of the cementgenesis in the rat moral tooth germs and incisors. The results are summarized as follows.1. A part of cells in the Hertwig's epithelial root sheath and the epithelial cell rest of Malassez expressed sheath protein whose molecular form is identical to that expressed in the secretory ameloblast. Electron microscopic immunocytochemitry revealed that sheath protein is contained in the Golgi apparatus located periodontal side of the epithelial cell rest of Malassez. Cement matrix itself did not contain sheath protein.2. Mesenchymal cells located near the surface of the root dentin expressed osteopontin, one of the marker of initial cementum, and have processes extending to the surface of the root dentin. Thses cells are usually attached to the epithelial cell rest of Malassez.3. After the administration of Monesin, one of the inhibitor of the cell secretory activity, osteopontin are clearly localized in the cytoplasmic processes extending from these mesenchynal cells.4. Expression of sheath protein was always prior to that of osteopontin.These results suggested that sheath protein secreted from the cells of Hertwig's epithelial root sheath and the epithelial cell rest of Malassez induced differentiation of mesenchymal cells to odontoblasts which extend cytoplasmmic processes to the surface of calcified dentin and form initial cement layer.