Hyaluronan and atrioventricular canal morphogenesis

原始心脏中分离心肌和心内膜的脱细胞心脏果冻基质在心脏的两个区域，房室管和流出道形成心内膜缓冲肿胀。随着发育的进行，在心肌源性刺激的影响下，衬里的内皮细胞群经历上皮细胞向间质细胞的转化。由此产生的迁移间充质细胞侵入缓冲基质，成为心脏瓣膜前体。小鼠分子遗传学研究表明，肌脲酸（HA）和桃聚糖都是形成心脏垫所必需的。缺乏这些基质分子的动物是形成心脏缓冲所必需的。动物缺乏这些基质分子——细胞外基质在心内膜缓冲层形成中作用的有力证据，尚不清楚基质分子是否积极参与瓣膜结构的形成，或者基质中仅为细胞迁移和分化提供支持性环境。我们假设HA在房室管形态发生中起两个作用：a)与其他基质成分（versican和VI型胶原）结合，从而形成心脏胶状物的结构成分；b)通过Ras上游的细胞表面受体介导的机制发出信号。实验旨在检查HA在这些提议的能力中的功能和调节。具体目标是：1。描述心脏发育过程中HA的主要来源透明质酸合酶-2 （Has2）的发育表达模式。此外，通过体外胶原凝胶转化实验，确定缓冲层形态发生分子标记在小鼠和鸡心内膜缓冲层中的表达，以确定该方法对哺乳动物房室管的适用性。2. 确定HA在体外心内膜缓冲层形态发生中的功能作用。3. 描述Has2基因中负责心垫表达的顺式调控元件。综上所述，这些研究将有助于更好地理解细胞外基质在心脏发育中的生物学作用，并为未来分析房室管形态发生提供独特的试剂和技术。

The acellular cardiac jelly matrix that separates the myocardium and endocardium in the primitive heart forms endocardial cushion swellings in two regions of the heart, the atrioventricular (AV) canal and the outflow tract. As development proceeds, a population of the endothelial cells lining the cushions undergoes an epithelial to mesenchymal transformation under the influence of myocardial-derived stimuli. Resultant migratory mesenchymal cells invade the cushion matrix to become cardiac valve precursors. Molecular genetic studies in the mouse demonstrate that both myaluronan (HA) and versican are required for formation on the cardiac cushions. Animals lacking these matrix molecules versican are required for formation of the cardiac cushions. Animals lacking these matrix molecules the compelling evidence for the role of the extracellular matrix in endocardial cushion formation, it is unclear if matrix molecules actively participate in the formation of valve structures or in the matrix provides only a supportive environment for cellular migration and differentiation. We hypothesize that HA plays two roles in AV canal morphogenesis: a) By binding to other matrix components (versican, and type VI collagen) and thus forming a structural component of the cardiac jelly and b) By signaling via a cell surface receptor-mediated mechanism upstream of Ras. Experiments are designed to examine the function and regulation of HA in each of these proposed capacities. The specific aims are: 1. Characterize the developmental expression patterns for the principal source of HA during heart development, hyaluronan synthase-2 (Has2). In addition, define the expression of molecular markers of cushion morphogenesis in mouse and chick endocardial cushions using an in vitro collagen gel transformation assay to establish the applicability of this assay for the mammalian AV canal. 2. Determine the functional role of HA during in vitro endocardial cushion morphogenesis. 3. Characterize the cis regulatory elements of the Has2 gene that are responsible for expression in the cardiac cushions. Taken together, these studies will provide a greater understanding of the biologic role of the extracellular matrix in the developing heart and provide unique reagents and techniques for future analysis of AV canal morphogenesis.