Msx2 function in tooth crown morphogenesis

描述（由申请人提供）：牙齿是上皮附属物，其形态发生受保守信号级联调节。牙冠的形态和形状是由牙尖的位置、取向、形状和高度以及邻近上皮细胞的增殖和折叠决定的。在分子水平上，牙冠的图案和形状是由来自牙釉质结的信号及其转录介质控制的，牙釉质结是一种上皮结构，被认为是牙齿形态发生的组织中心。超过10种信号蛋白在牙釉质结中有限制性表达，包括成纤维细胞生长因子（fgf）、刺猬蛋白（HH）、wnt和转化生长因子b （TGFb）超家族以及信号介质如p21、Edar、Lef1和Msx2。缺乏同源盒基因Msx2的小鼠在冠形态发生方面表现出缺陷。我们的研究表明，在Msx2敲除小鼠中(1)牙尖形成，但它们是畸形的；(2)臼齿的牙上皮折叠异常，表现出局部的，细胞增殖增加；(3)牙釉质结中的Bmp4信号依赖于Msx2，这表明Bmp4和Msx2基因在相同的遗传途径中起作用。这些观察结果为我们提出的假设提供了基础，即Msx2依赖信号BMP4通过控制牙尖形状和牙冠正常形态发生，是Msx2在牙釉质结中功能的潜在主要影响因子。在这种背景下,进一步研究Msx2在牙齿发育的作用,我们将(i)识别基因受Msx2搪瓷结,通过调查基因的表达模式,像Bmp4,发生在搪瓷Msx2结和(2)确定Msx2下游基因,Bmp4, Msx2函数的主要效应在搪瓷结,通过测试的充分性Bmp4营救尖端形状和冠形态发生缺陷在体外和体内。总的来说，这些实验将从遗传和分子角度确定Msx2及其下游基因Bmp4在牙齿发育后期的调控层次，并为理解牙尖形状和牙冠形态发生提供分子框架。

DESCRIPTION (provided by applicant): Teeth are epithelial appendages whose morphogenesis is regulated by conserved signaling cascades. The patterning and shape of tooth crowns is determined by the location, orientation, shape and height of tooth cusps, and by the proliferation and folding of the adjacent epithelium. At the molecular level, the patterning and shape of tooth crowns is controlled by signals and their transcriptional mediators derived from the enamel knot, an epithelial structure considered the organizing center for tooth morphogenesis. More than 10 signaling proteins have restricted expression in the enamel knots, including fibroblast growth factors (FGFs), hedgehog (HH), WNTs and transforming growth factor b (TGFb) superfamilies as well as mediators of signaling such as p21, Edar, Lef1 and Msx2. Mice lacking the homeobox gene Msx2 exhibit defects in crown morphogenesis. Our studies show that in the Msx2 knock out mice (i) the cusps are formed but they are misshapen, (ii) the folding of the dental epithelium is aberrant in the molars exhibiting localized, increased cell proliferation and that (iii) Bmp4 signaling in the enamel knot is Msx2-dependent suggesting that Bmp4 and Msx2 genes function within the same genetic pathway. These observations serve as the basis for our proposed hypothesis that an Msx2-dependent signal BMP4 is a potential major effector of the Msx2 function in the enamel knot by controlling the shape of cusps and crown normal morphogenesis. In this context and to further investigate the role of Msx2 during tooth development, we will (i) identify genes regulated by Msx2 in the enamel knot, by investigating the expression patterns of genes that, like Bmp4, are co-expressed with Msx2 in the enamel knot and (ii) determine whether the Msx2 downstream gene, BMP4, is a major effector of the Msx2 function in the enamel knot, by testing the sufficiency of BMP4 to rescue the cusp shape and crown morphogenesis defect in vitro and in vivo. Collectively these experiments should define a regulatory hierarchy between Msx2 and its downstream gene Bmp4 in both genetic and molecular terms during late tooth development and provide a molecular framework for understanding cusp shape and crown morphogenesis. Narrative: Teeth are epithelial appendages whose morphogenesis is regulated by complex genetic pathways. Several craniofacial and ectodermal dysplasia disorders affect tooth development by affecting their early development (tooth agenesis) or late development (dysplastic crown, enamel hypoplasia). Msx2 mutant teeth are dysplastic, exhibiting crown shape abnormalities. Although, Msx2 is critical for tooth crown morphogenesis when mutated, its function remains unknown. This project aims at understanding the role of Msx2 in the pathogenesis of tooth dysmorphias. To accomplish this aim, a search for genes regulated by Msx2 will be conducted, using powerful molecular biology, transgenic and organ culture approaches. It is anticipated that these results will provide valuable insight on the function of Msx2 gene, on the pathogenetic mechanism of tooth development and may also provide valuable information towards treatment of tooth dysmorphias. 4