Hyaluronan and atrioventricular canal morphogenesis

在原始心脏中，分隔心肌和心内膜的无细胞心脏凝胶基质在心脏的两个区域--房室管和流出道--形成心内膜垫肿胀。随着发育的进行，在心肌源性刺激的影响下，衬垫内的内皮细胞群体经历了从上皮到间充质的转变。由此产生的移行间充质细胞侵入垫层基质，成为心脏瓣膜前体。在小鼠身上的分子遗传学研究表明，肌醛酸(HA)和万西康都是在心脏垫上形成所需的。缺乏这些基质分子的动物是形成心脏垫所必需的。缺乏这些基质分子的动物是细胞外基质在心内膜缓冲形成中作用的令人信服的证据，目前尚不清楚基质分子是否积极参与瓣膜结构的形成，或者基质中是否只为细胞迁移和分化提供了支持环境。我们推测，HA在房室管形态发生中起两个作用：a)通过与其他基质成分(通用型和VI型胶原)结合，形成心脏凝胶的结构成分；b)通过细胞表面受体介导的RAS上游机制进行信号传递。实验旨在检验HA在每一种拟议能力中的功能和调节。其具体目的是：1.研究心脏发育过程中HA的主要来源--透明质酸合成酶-2(Has2)的发育表达模式。此外，利用体外胶原凝胶转化试验确定垫层形态发生的分子标志物在小鼠和鸡心内膜垫中的表达，以建立该方法在哺乳动物房室管中的适用性。2.确定透明质酸在体外培养的心内膜垫形态发生中的作用。3.鉴定Has2基因的顺式调控元件，这些元件负责在心脏垫中表达。综上所述，这些研究将对细胞外基质在发育心脏中的生物学作用提供更多的了解，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.