THE ROLE OF TGF-BETA3 IN PALATOGENESIS

本研究的长期目标是明确tgf - β - 3诱导腭融合的具体分子机制。在发育过程中，tgf - β 3的表达在空间和时间上都受到限制。在融合前腭上皮中发现了异常高的表达水平。与tgf - β 3表达激增相一致的是，纯合子tgf - β 3缺陷小鼠出现双侧次腭裂。研究表明，在上皮融合过程中，tgf - β 3触发上皮-间充质转分化和相关的基底膜降解，这是腭融合成功的必要过程。结合TGF-beta3在预融合腭架中的表达模式和水平、TGF-beta3零突变小鼠腭裂的完全外显率、缺乏TGF-beta3的内边缘上皮细胞无法从上皮细胞向间质细胞转分化等数据，可以提出以下假设：TGF β 3是一个主开关，能够启动一系列分子事件，导致腭发育过程中成功的中线上皮融合。为了验证这一假设，我们将利用TGF-beta3零突变小鼠来研究TGF-beta3信号传导和下游生物反应。这些研究被组织为三个不同的目的：tgf - β I型受体及其下游信号分子的表达和功能，Aim 1中的Smads， Aim2中上皮融合过程中上皮主基因和关键分子开关在上皮-间质转分化中的作用，以及Aim 3中金属蛋白酶及其抑制剂在基底膜相关降解中的功能。这些研究将最终提高我们对导致腭裂形成的发病机制的理解，腭裂是人类最常见的先天性出生缺陷之一。

The long-term goal of this proposal is to define specific molecular mechanisms of TGF-beta3-induced palatal fusion. During development TGF-beta3 expression is both spatially and temporally restricted. Exceptionally high expression levels have been found specifically in prefusion palatal epithelium. Concordant with this surge of TGF-beta3 expression, homozygous TGF-beta3-deficient mice suffer from bilateral clefting of the secondary palate. It has been suggested that during epithelial fusion, TGF-beta3 triggers epithelio-mesenchymal transdifferentiation and associated degradation of the basement membrane, processes necessary for successful palatal fusion. The combined data, including expression pattern and level of TGF-beta3 in prefusion palatal shelves, complete penetrance of cleft palate in TGF- beta3 null mutant mice and failure of TGF-beta3-deficient medial edge epithelial cells to transdifferentiate from epithelial cells to mesenchymal cells lead to the formulation or the following hypotheses: TGF beta3 is a master switch, capable of initiating a cascade of molecular events leading to successful midline epithelial fusion during palatogenesis. To test this hypothesis we will utilize TGF-beta3 null mutant mice to investigate TGF-beta3 signaling and downstream biological responses. The proposed studies have been organized to three different Aims: expression and function of TGF-beta type I receptors and their down- stream signaling molecules, Smads in Aim 1, role of epithelial mastergenes and key molecular switches in epithelio-mesenchymal transdifferentiation during epithelial fusion in Aim2, and function of metalloprotemases and their inhibitors during associated degradation of the basement membrane in Aim 3. These studies will eventually improve our understanding of the pathogenetic mechanisms that lead to formation of cleft palate, one of the most common congenital birth defects in human.