POTENTIAL MSXL DOWNSTREAM GENES IN TOOTH DEVELOPMENT

正在发育的臼齿牙胚为鉴定哺乳动物器官发生中涉及的遗传途径提供了一个强大的发育系统。 Msx 1的突变导致人类和小鼠的缺牙。 在小鼠Msx 1突变体中，牙齿发育的停滞发生在芽阶段，此时牙齿诱导电位通常从牙齿上皮转移到牙齿间充质。 成牙潜力的转变与TGF β超家族成员骨形态发生蛋白-4（Bmp 4）的表达从上皮到间充质的转变相一致。Msx 1是需要这种转变Bmp 4表达的牙齿间充质;在Msx 1突变体牙齿上皮Bmp 4的表达被保存，但在牙齿间充质是缺席。 FGF构成了另一个生长因子家族，其在牙上皮和间充质之间的信号级联中可能发挥类似的作用。 我最近表明，上皮FGF如FGF 8可以诱导FGF 3在牙齿间充质中的表达，这种诱导需要Msx 1。 这些结果表明，FGF 8，像BMP 4，构成上皮诱导信号，可以诱导其各自的家族成员在牙齿间充质中的Msx 1依赖性的方式表达。 然而，BMP 4和FGF 3作为Msx 1下游信号在牙齿发育过程中的作用以及Msx 1调节其各自基因转录的机制仍然未知。 这项建议的具体目标有两个方面。 首先，我将确定Msx 1下游信号BMP 4和FGF 3的发育作用。 为此，将采用体外和体内技术来解决BMP 4单独或与FGF 3组合可以绕过Msx 1需求并挽救Msx 1牙齿表型的假设。 第二，Msx 1与辅助蛋白相互作用以赋予其下游基因足够的激活的假设将在本提案的第二个具体目标中得到解决。 生物化学和遗传学实验都将用于解决后一种假设。

The developing molar tooth germ provides a powerful developmental system for identifying the genetic pathways involved in mammalian organogenesis. Mutations in Msx1 are responsible for anodontia in both humans and mouse. In mouse Msx1 mutants, arrest of tooth development occurs at the bud stage when tooth inductive potential normally shifts from dental epithelium to dental mesenchyme. The shift of odontogenic potential coincides with the shift of expression of Bone morphogenicetic protein-4 (Bmp4), a TGFbeta superfamily member, from epithelium to mesenchyme. Msx1 is required for this shift in Bmp4 expression to the dental mesenchyme; in Msx1 mutants dental epithelial Bmp4 expression is preserved, but that in the dental mesenchyme is absent. FGFs constitute another family of growth factors which potentially play an analogous role in the signaling cascade between dental epithelium and mesenchyme. I have recently shown that epithelial FGFs like FGF8 can induce Fgf3 expression in dental mesenchyme and that this induction requires Msx1. These results indicate that FGF8, like BMP4, constitutes an epithelial inductive signal which can induce the expression of its respective family members in dental mesenchyme in an Msx1-dependent manner. Nevertheless, the role of BMP4 and FGF3 as Msx1 downstream signals during tooth development and the mechanism by which Msx1 functions to regulate transcription of their respective genes remains unknown. The specific aims of this proposal are twofold. First I will determine the developmental role of the Msx1-downstream signals BMP4 and FGF3. For this purpose, in vitro and in vivo techniques will be employed to address the hypothesis that BMP4, alone or in combination with FGF3, can bypass the Msx1 requirement and rescue the Msx1 tooth phenotype. Second, the hypothesis that Msx1 interacts with accessory proteins in order to confer sufficiency for activation of its downstream genes will be addressed in the second specific aim of this proposal. Both biochemical and genetic experiments will be used to address this latter hypothesis.