Atrioventricular Junction Development

项目摘要 房室交界区（AVJ）对心脏的发育和功能起着重要作用。AVJ肌细胞 提供心房和心室之间的形态发生和电生理边界，指示 内皮细胞垫形成，并招募额外的心脏冠状动脉干细胞到心脏。AVJ中的缺陷 传导延迟、缓冲垫形成和/或额外的心脏细胞进入心脏，都可能是普遍的， 几种人类先天性心脏病综合征的危险成分。然而，尽管超过一个 经过世纪的研究，诱导和确定AVJ命运和功能的机制仍然很差 明白 目前的教条假设AVJ肌细胞起源于原发性心脏区域， 原始心管心肌的分子和生理特征。它也被假定，反馈 包含Bmp 2和转录因子Tbx 2/3的环维持这种幼年心肌状态，因此 指定AVJ结局。 与这些模型相反，我们的初步研究表明：（i）AVJ肌细胞不是来自于 （ii）慢传导AVJ肌细胞显示特异性电生理和 与原始心管肌细胞不同的分子特征;（iii）AVJ直接暴露于 内胚层来源的快速传导命运诱导剂上调AVJ肌细胞中的Cx40并消除AVJ 延迟而不抑制Bmp 2或Tbx 2/3表达;（iv）AVJ可以转换为快速传导 通过去除将AVJ肌细胞与内皮细胞分离的心胶;以及最后（iv）AVJ 心肌细胞通过心外膜形成搏动性钙波， 细胞出现。 基于这些令人惊讶的发现，本申请提出实验性地测试以下新颖模型 对于AVJ发育和功能：（i）在新鉴定的Nkx2.5/Nkx2.5内建立AVJ肌细胞的身份。 Isl 1阴性的第三心脏而不是Nkx2.5/Ist 1阳性的初级和次级心脏场;（ii） Bmp 2-Tbx 2/3信号轴作为形态发生线索，而不是肌细胞自主细胞命运 AVJ慢传导区形成的决定因素;和（iii）AVJ肌细胞在空间上形成一种新的 定向伸展过程中心外膜细胞间通过Ca 2+波的搏动性细胞间通讯 朝着心脏。 使用体内和体外方法，该提案将首次深入了解AVJ的起源， AVJ心肌在心脏正常发育和功能中的作用尚未被认识。

Project Summary The atrioventricular junction (AVJ) plays vital roles for cardiac development and function. The AVJ myocytes provide a morphogenetic and electrophysiological boundary between the atrium and ventricle, instruct endocardial cushion formation, and recruit extra cardiac coronary stem cells to the heart. Defects in AVJ conduction delay, cushion formation, and/or extra cardiac cell entry to the heart, can all be prevalent and life threatening components of several congenital heart syndromes in humans. However, despite more than a century of investigation, the mechanisms that induce and specify the AVJ fate and function remain poorly understood. The current dogma assumes that the AVJ myocytes arise from the primary heart field and uniquely maintain molecular and physiological features of primitive heart tube myocardium. It is also postulated that a feedback loop encompassing Bmp2 and the transcription factors Tbx2/3 maintain this juvenile myocardial state, thus specifies AVJ fate. Contrary to these models, our preliminary studies show that: (i) AVJ myocytes are not derived from either the primary or secondary heart field; (ii) Slow conducting AVJ myocytes display specific electrophysiological and molecular characteristics distinct from primitive heart tube myocytes; (iii) Direct exposure of the AVJ to endoderm-derived fast conducting fate inducers up-regulate Cx40 in the AVJ myocytes and eliminate AVJ delay without suppressing either Bmp2 or Tbx2/3 expression; (iv) The AVJ can be converted to fast conducting by removal of the cardiac jelly that separates the AVJ myocytes from the endocardium; and finally (iv) AVJ myocytes pattern a pulsatile Ca2+ wave through the proepicardium from which extra cardiac coronary stem cells arise. Based on these surprising findings, this application proposes to experimentally test the following novel models for AVJ development and function: (i) Identity of AVJ myocytes is established within the newly identified Nkx2.5/ Isl1-negative tertiary heart rather than the Nkx2.5/Ist1-positive primary and secondary heart fields; (ii) The Bmp2-Tbx2/3 signaling axis acts as a morphogenetic cue, rather than a myocyte-autonomous cell fate determinant for slow conducting zone formation at the AVJ; and (iii) AVJ myocytes spatially pattern a novel pulsatile intercellular communication between proepicardial cells via a Ca2+ wave during oriented extension towards the heart. Using in vivo and in vitro approaches, this proposal will provide the first insight into the origin of the AVJ and the previously unrecognized roles of AVJ myocardiumn for proper heart development and function.