Cardiac Pacemaker Development

描述（由申请人提供）：窦房结的心脏起搏器细胞对于产生有节奏的心跳至关重要。尽管这种特殊的心脏细胞类型的重要性，很少知道他们的个体发生或规范和分化的机制。我们的初步数据显示，虽然原代心管最初显示有节奏的跳动，但起搏细胞不会分化为窦房结。相反，起搏器前体起源于已知心源野后方的中胚层，在心脏循环过程中接管起搏功能。令人惊讶的是，起搏器前体中胚层可以在没有其他周围胚胎组织的情况下进行分化。它们表现出持续的节律性心跳速率，并对起搏器细胞特异性离子通道阻滞剂敏感。此外，它们还具有调节其他心肌细胞群的能力。我们的全球RNA分析已经确定了一组独特的wnt相关基因在起搏器前体中表达。这些有些令人惊讶的发现导致了三个中心假设：(1)起搏器前体来自与心脏区分离的特定中胚层群体；(2)起搏器细胞的命运在心管形成之前被诱导；(3) wnt相关信号在起搏器细胞特化过程中作为促进信号，对心脏场具有抑制作用。我们将用实验来检验这些假设。这一建议将为确定起搏器前体的胚胎起源（Aim 1），特定中胚层亚群进入起搏器细胞命运的能力（Aim 2），以及在短暂的时间窗口和胚胎中特定位置指定和指导这种重要细胞类型分化的新分子机制（Aim 3）提供第一个基础。

DESCRIPTION (provided by applicant): Cardiac pacemaker cells of the Sinoatrial Node are essential for producing rhythmic heartbeats. Despite the importance of this specialized cardiac cell type, little is known about their ontogeny or mechanisms of specification and differentiation. Our preliminary data show that although the primary heart tube initially displays rhythmic beating, the cells pacing it do not differentiate into the Sinoatrial Node. Instead, pacemaker precursors arise from the mesoderm posterior to the known cardiogenic field and take over the pacing function during heart-looping. Surprisingly, the pacemaker precursor mesoderm can differentiate in culture without any other surrounding embryonic tissues. They display sustained rhythmic beat rates, and sensitivity to pacemaker cell specific ion channel blockers. Furthermore, they have the ability to pace other cardiomyocyte populations. Our global RNA profiling has identified a unique set of Wnt-related genes expressed in pacemaker precursors. These somewhat surprising findings lead to three central hypotheses: (1) the pacemaker precursors arise from a specific mesoderm population separate from the heart field; (2) pacemaker cell fate is induced prior to heart tube formation; and (3) Wnt-related signaling, which is inhibitory to the heart field, acts as a promoting signal during pacemaker cell specification. We will test these hypotheses experimentally. This proposal will provide the first basis for identifying the embryonic origin of pacemaker precursors (Aim 1), the ability of a specific mesoderm subpopulations to enter the pacemaker cell fate (Aim 2), and novel molecular mechanisms that specify and direct the differentiation this important cell type during a brief temporal window and at a defined site in the embryo (Aim 3). PUBLIC HEALTH RELEVANCE: The cardiac pacemaker is essential for cardiac function and survival. Limited options of effective treatments contribute to the continued prevalence of arrhythmic heart disease. The proposed study will explore the molecular mechanisms that regulate the earliest developmental steps leading to the generation of this essential cardiac tissue and may provide a basis for future therapeutic approaches.