DESIGNED ENAMEL DEFECTS

牙本质间充质基质细胞外形成牙釉质 通过有序组装一种蛋白质支架来调节 微晶尺寸。牙釉质基质的两种研究蛋白质是 釉原蛋白和塔夫特林。我们发现釉原蛋白的自组装依赖于 氨基末端42个残基与17个残基结构域相互作用 羧基区域。我们预测表达釉原蛋白的动物 带有这两个组装结构域之一缺失的蛋白质将 对牙釉质基质组装有不利影响，因此对矿物质有不利影响 阶段性发展。我们预测棱镜到棱镜的大量缺陷 将观察到牙釉质和牙本质牙釉质结合部(DEJ)缺陷 在转基因小鼠中，错误表达的釉原蛋白被截断为其 组装区域，但不是在它们的非转基因产仔对照中。 我们预测牙釉质缺陷将可以用新的 测试方法。最终，这些转基因动物将是有用的 研究影响人类的遗传性釉质缺陷的模型，如 釉质发生不完全。具体目标是：1)衡量和比较 正常牙釉质和转基因牙釉质的断裂韧性和硬度 小鼠，2)测量和比较DEJ界面断裂韧性 3)对正常小鼠和转基因小鼠进行鉴定、定位和比较 正常小鼠和转基因小鼠的DEJ失败机制。这些 调查将与釉原蛋白中的一种特定遗传缺陷有关 错误表达转基因小鼠的装配结构域对由此产生的变化的影响 在它们的釉质结构中。牙釉质的结构变化将是 通过测量两种材料的断裂韧性和硬度 垂直平面。这将提供有关 缺陷相对于釉质棱镜方向的空间取向。 牙釉质的结构变化，影响其相互作用的能力 与牙本质形成的正常DEJ将通过测量 DEJ的界面断裂韧性。具体的失效机制 将被鉴定为DEJ，并与釉质缺陷有关。釉质 与DEJ相关的缺陷将通过断裂韧性和 跨DEJ和相邻牙齿结构的硬度分析。总而言之， 例如，错误表达转基因小鼠的牙齿结构将是 与正常对照组相比。与以前对牙釉质缺陷的研究不同 一些遗传病因不明或有缺陷的孤立个体 由全身性中毒产生，这些研究是可重复的，并且 单一的遗传原因是已知的。

Enamel forms extracellularly on mesenchymally derived dentin matrix through the ordered assembly of a protein scaffold that regulates crystallite dimensions. Two studied proteins of the enamel matrix are amelogenin and tuftelin. We show amelogenin self-assembly depends on the amino-terminal 42 residues interacting with a 17 residue domain in the carboxyl region. We predict that animals expressing amelogenin proteins bearing deletions of either of these two assembly domains will have an adverse effect on enamel matrix assembly and hence upon mineral phase development. We predict that prism to prism defects in bulk enamel as well as dentino-enamel junction (DEJ) defects will be observed in transgenic mice mis-expressing amelogenins truncated to their assembly domains, but not in their non-transgenic litter mate controls. We predict that the enamel defects will be identifiable using novel testing methods. Ultimately, these transgenic animals will be useful models to study inherited enamel defects that affect humans such as amelogenesis imperfecta. Specific aims are: 1) To measure and compare enamel fracture toughness and hardness between normal and transgenic mice, 2) To measure and compare DEJ interfacial fracture toughness between normal and transgenic mice, 3) To identify, localize and compare DEJ failure mechanisms in normal and transgenic mice. These investigations will related a specific genetic defect in the amelogenin assembly domain of mis-expressing transgenic mice to resultant changes in their enamel structure. Structural changes in enamel will be quantified by measurement of fracture toughness and hardness in two perpendicular planes. This will provide important information about the spatial orientation of defects with respect to enamel prism orientation. Structural changes in enamel that compromise its ability to interact with dentin and form a normal DEJ will be quantified by measuring the interfacial fracture toughness of the DEJ. Specific failure mechanisms of the DEJ will be identified and related to enamel defects. Enamel defects related to the DEJ will be localized by fracture toughness and hardness profiling across the DEJ and adjacent tooth structures. In all cases, tooth structure from the mis-expressing transgenic mice will be compared to normal controls. Unlike prior studies of enamel defects on a few isolated individuals of unknown genetic etiology, or on defects produced by generalized poisoning, these studies are repeatable and the single genetic cause is known.