DESIGNED ENAMEL DEFECTS

牙釉质在间充质衍生的牙本质基质上细胞外形成 通过蛋白质支架的有序组装， 微晶尺寸 两种研究的釉质基质蛋白质是 釉原蛋白和簇蛋白。 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 具有这两个组装结构域中任一个缺失的蛋白质将 对釉质基质组装并因此对矿物质 阶段发展。 我们预测，棱镜到棱镜的缺陷， 将观察到牙釉质以及牙本质-牙釉质连接（DEJ）缺陷 在错误表达截短成其 组装结构域，但不是在其非转基因同窝交配对照。 我们预测，牙釉质缺陷将可识别使用新的 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牙釉质缺陷的模型， 釉质发生 具体目标是：1）测量和比较 牙釉质断裂韧性和硬度之间的正常和转基因 2）测量和比较DEJ界面断裂韧性 3）对转基因小鼠进行鉴定、定位和比较 正常和转基因小鼠的DEJ失效机制。 这些 研究将涉及釉原蛋白中的特定遗传缺陷， 错误表达转基因小鼠的组装结构域对结果变化的影响 在它们的釉质结构中。 牙釉质的结构变化 通过测量断裂韧性和硬度进行量化， 垂直平面 这将提供有关 缺陷相对于釉质棱柱取向的空间取向。 影响其相互作用能力的牙釉质结构变化 与牙本质和形式正常DEJ将通过测量 DEJ的界面断裂韧性。 特定失效机制 DEJ将被识别并与牙釉质缺陷相关。 釉质 与DEJ相关的缺陷将通过断裂韧性而局部化， DEJ和相邻牙齿结构的硬度分布。 在所有 例，错误表达转基因小鼠的牙齿结构将被 与正常对照相比。 不像先前的研究， 一些孤立的个体未知的遗传病因，或对缺陷 这些研究是可重复的， 只有一种遗传原因是已知的。

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.