Hyaluronan and atrioventricular canal morphogenesis

在原始心脏中分离心肌和内膜的脱细胞心脏胶基质在心脏的两个区域（房室（AV）管和流出道）中形成内膜垫。随着发育的进行，垫内衬的内皮细胞群体在心肌源性刺激的影响下经历上皮向间充质的转化。由此产生的迁移间充质细胞侵入垫基质成为心脏瓣膜前体。在小鼠中的分子遗传学研究表明，肌钙蛋白聚糖（HA）和多功能蛋白聚糖都需要在心脏垫上形成。缺乏这些基质分子多功能蛋白聚糖的动物是形成心脏垫所必需的。缺乏这些基质分子的动物，细胞外基质在内膜垫形成中的作用的令人信服的证据，目前还不清楚，如果基质分子积极参与瓣膜结构的形成或在基质中只提供了一个支持性的环境，细胞迁移和分化。我们假设HA在AV管形态发生中起两种作用：a）通过与其他基质组分（多功能蛋白聚糖和VI型胶原）结合，从而形成心胶的结构组分，以及B）通过Ras上游的细胞表面受体介导机制进行信号传导。实验的目的是检查HA在这些建议的能力的功能和调节。具体目标是：1.表征心脏发育过程中HA主要来源透明质酸合酶-2（Has 2）的发育表达模式。此外，使用体外胶原凝胶转化试验，确定小鼠和鸡内膜垫中垫形态发生的分子标志物的表达，以确定该试验对哺乳动物AV管的适用性。2.确定HA在体外内膜垫形态发生过程中的功能作用。3.表征负责在心脏垫中表达的Has 2基因的顺式调控元件。总之，这些研究将提供一个更好的了解细胞外基质在发育中的心脏的生物学作用，并提供独特的试剂和技术，为未来的AV管形态发生的分析。

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.