Role of BMP and Wnt signaling in early tooth development

描述（由申请人提供）：多个家族的信号分子，包括BMP、FGF、Shh和Wnt蛋白，已涉及介导控制牙齿发育的组织相互作用。尽管在过去的二十年中，BMP4被确定为牙齿形成过程中的潜在形态发生素，但这些信号通路的功能机制以及它们如何协调作用以调节牙齿形成仍然是难以捉摸的。我们的长期目标是阐明牙齿发生的分子机制，这将有助于更好地了解人类与遗传相关的牙齿异常和牙齿再生。基于我们之前和初步的研究，我们假设BMP和Wnt信号通路在控制牙上皮发育方面发挥不同但协同的功能，其中Wnt/B-连环蛋白信号调节牙源性命运，而BMP介导的非经典信号调节细胞增殖，而Smad4非依赖性典型BMP信号传导（称为非典型BMP信号）通过调节Msx 1的表达，在牙间充质中发挥作用，控制牙发生过程。提出了两个目标来检验这一假设。在目的1中，我们将几个独特的转基因/敲除小鼠系解剖不同的和协同的生物学功能的Wnt和BMP介导的信号通路在早期牙齿发育的调节。为此，我们会：（1）确定Noggin作为Wnt信号拮抗剂的新功能;（2）确定BMP信号作为牙上皮细胞增殖的主要调节因子，但不作为牙源性命运的主要调节因子;（3）确定BMP和Wnt信号在早期牙齿发育中的协同作用;（4）确定β-catenin在牙齿发育中的明确信号功能。目的2：利用转基因/基因敲除小鼠，结合细胞培养、生物化学和分子生物学方法，研究非典型BMP信号在牙间充质中的作用和调控。为此，我们将：（1）确定TGF β信号主要负责牙上皮中Smad1/5/8的激活;（2）确定牙间充质中非典型BMP信号的功能操作;和（3）研究牙间充质中非典型BMP信号的调节机制。这些研究结果将极大地提高我们对BMP和Wnt信号在牙齿发育中的功能机制的理解，并挑战目前的经典BMP信号模型。

DESCRIPTION (provided by applicant): Multiple families of signaling molecules, including BMP, FGF, Shh, and Wnt protein, have been implicated in mediating tissue interactions that govern tooth development. Despite significant progresses in the last two decades since BMP4 was identified as a potential morphogen in during tooth initiation, functional mechanisms of these signaling pathways and how they act coordinately to regulate tooth formation remain elusive. Our long-term goal to delineate the molecular mechanisms underlying odontogenesis, which shall shed light on for better understanding of genetic related dental abnormalities and tooth regeneration in humans. Based on our previous and preliminary studies, we hypothesize that BMP and Wnt signaling pathways exert distinct but synergistic functions in controlling dental epithelium development, with Wnt/b- catenin signaling regulating odontogenic fate and BMP-mediated non-canonical signaling regulating cell proliferation, while Smad4-independent canonical BMP signaling (named as atypical canonical BMP signaling) acting in the dental mesenchyme to control odontogenic program by regulating Msx1 expression. Two aims are proposed to test this hypothesis. In Aim 1, we will several unique transgenic/knockout mouse lines dissect distinct and synergistic biological functions of Wnt- and BMP-mediated signaling pathways in the regulation of early tooth development. In this aim, we will: (1) Establish a novel function for Noggin as a Wnt signaling antagonist; (2) Establish BMP signaling as a major regulator for cell proliferation but not for odontogenic fate in the dental epithelium; (3) Define synergistic function of BMP and Wnt signaling in early tooth development; (4) Establish definite signaling function for β-catenin in tooth development. In Aim 2, we will use several transgenic/knockout mouse line combined with cell culture, biochemistry, and molecular biology approaches to investigate the role and regulation of atypical canonical BMP signaling in the dental mesenchyme. In this aim, we will; (1) Establish that TGFb signaling is primarily responsible for Smad1/5/8 activation in the dental epithelium; (2) Determine functional operation of atypical canonical BMP signaling in the dental mesenchyme; and (3) Investigate regulatory mechanism of atypical canonical BMP signaling in the dental mesenchyme. Results from these proposed studies will greatly enhance our understanding of functional mechanisms of BMP and Wnt signaling in tooth development and challenge the current model of the canonical BMP signaling.