Hu Jan C-C, Yamakoshi Yasuo, Yamakoshi Fumiko, Krebsbach Paul H, Simmer James P
University of Michigan Dental Research Lab, Ann Arbor, Mich. 48108, USA.
Cells Tissues Organs. 2005;181(3-4):219-31. doi: 10.1159/000091383.
The initiation of enamel crystals at the dentino-enamel junction is associated with the expression of dentin sialophosphoprotein (DSPP, a gene normally linked with dentin formation), three 'structural' enamel proteins--amelogenin (AMELX), enamelin (ENAM), and ameloblastin (AMBN)--and a matrix metalloproteinase, enamelysin (MMP20). Enamel formation proceeds with the steady elongation of the enamel crystals at a mineralization front just beneath the ameloblast distal membrane, where these proteins are secreted. As the crystal ribbons lengthen, enamelysin processes the secreted proteins. Some of the cleavage products accumulate in the matrix, others are reabsorbed back into the ameloblast. Once crystal elongation is complete and the enamel layer reaches its final thickness, kallikrein 4 (KLK4) facilitates the breakdown and reabsorption of accumulated enamel matrix proteins. The importance of the extracellular matrix proteins to proper tooth development is best illustrated by the dramatic dental phenotypes observed in the targeted knockouts of enamel matrix genes in mice (Dspp, Amelx, Ambn, Mmp20) and in human kindreds with defined mutations in the genes (DSPP, AMELX, ENAM, MMP20, KLK4) encoding these matrix proteins. However, ablation studies alone cannot give specific mechanistic information on how enamel matrix proteins combine to catalyze the formation of enamel crystals. The best approach for determining the molecular mechanism of dental enamel formation is to reconstitute the matrix and synthesize enamel crystals in vitro. Here, we report refinements to the procedures used to isolate porcine enamel and dentin proteins, recent advances in the characterization of enamel matrix protein posttranslational modifications, and summarize the results of human genetic studies that associate specific mutations in the genes encoding matrix proteins with a range of dental phenotypes.
牙釉质晶体在牙本质-牙釉质交界处的起始与牙本质涎磷蛋白（DSPP，一种通常与牙本质形成相关的基因）、三种“结构性”牙釉质蛋白——釉原蛋白（AMELX）、釉蛋白（ENAM）和成釉蛋白（AMBN）以及一种基质金属蛋白酶——釉质溶解素（MMP20）的表达有关。牙釉质形成过程中，牙釉质晶体在成釉细胞远端膜下方的矿化前沿稳定伸长，这些蛋白质在此处分泌。随着晶体带的延长，釉质溶解素对分泌的蛋白质进行加工处理。一些裂解产物积聚在基质中，另一些则被重新吸收回成釉细胞。一旦晶体伸长完成且牙釉质层达到最终厚度，激肽释放酶4（KLK4）促进积聚的牙釉质基质蛋白的分解和重吸收。细胞外基质蛋白对牙齿正常发育的重要性在小鼠牙釉质基质基因（Dspp、Amelx、Ambn、Mmp20）靶向敲除以及在编码这些基质蛋白的基因（DSPP、AMELX、ENAM、MMP20、KLK4）发生特定突变的人类家系中观察到的显著牙齿表型中得到了最好的体现。然而，仅消融研究无法提供关于牙釉质基质蛋白如何结合以催化牙釉质晶体形成的具体机制信息。确定牙釉质形成分子机制的最佳方法是在体外重构基质并合成牙釉质晶体。在此，我们报告了用于分离猪牙釉质和牙本质蛋白的方法的改进、牙釉质基质蛋白翻译后修饰表征的最新进展，并总结了将编码基质蛋白的基因中的特定突变与一系列牙齿表型相关联的人类遗传学研究结果。
