Atrioventricular Junction Development

项目摘要 房室交界区(AVJ)对心脏的发育和功能起着至关重要的作用。房室结肌细胞 在心房和心室之间提供形态发生和电生理边界，指示 心内膜垫形成，并招募额外的心脏冠脉干细胞到心脏。AVJ中的缺陷 传导延迟、垫层形成和/或额外的心肌细胞进入心脏均可普遍存在。 人类几种先天性心脏病综合征的威胁成分。然而，尽管有超过一个 经过一个世纪的研究，诱发和指定AVJ命运和功能的机制仍然很差 明白了。 目前的学说认为，aVJ肌细胞起源于初级心场，并独特地维持 原始心管心肌的分子和生理特征。还有一种假设是，反馈 围绕BMP2和转录因子Tbx2/3的环维持这种幼年心肌状态，因此 指定AVJ命运。 与这些模型相反，我们的初步研究表明：(I)aVJ肌细胞既不是来源于 (Ii)慢传导aVJ心肌细胞表现出特殊的电生理和 不同于原始心管肌细胞的分子特征；(Iii)AVJ直接暴露于 内胚层来源的快速传导命运诱导aVJ心肌细胞Cx40表达上调并消除aVJ 延迟而不抑制BMP2或Tbx2/3的表达；(Iv)aVJ可转换为快速传导 通过去除将aVJ肌细胞与心内膜分开的心脏凝胶；最后(Iv)aVJ 心肌细胞通过心前膜形成搏动的钙波，心外冠脉干从心外膜发出 细胞出现了。 基于这些令人惊讶的发现，该应用程序建议对以下新模型进行实验测试 对于aVJ的发育和功能：(I)aVJ心肌细胞的身份在新鉴定的NKX2.5/ ISL1-阴性的三级心脏，而不是NKX2.5/Ist1阳性的初级和次级心脏区域；(Ii) BMP2-Tbx2/3信号轴是形态发生的信号，而不是肌细胞自主的细胞命运 房室结慢传导区形成的决定因素；和(Iii)房室交界处肌细胞的空间模式 定向伸展时心外膜细胞间通过钙波的搏动性细胞间通讯 朝向心脏。 使用体内和体外方法，这一提议将提供对AVJ起源的第一次洞察和 AVJ心肌对心脏正常发育和功能的作用以前不为人知。

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.