Cardiomyocyte Proliferation & Ventricular Morphogenesis

描述(申请人提供)：促进心肌细胞的机制 胎儿期的增殖，而在胎儿期不能引起增殖 出生后的生活，人们对此知之甚少。我的实验室研究了心脏 缺乏维甲酸受体RXRA的小鼠胚胎发育 脑室内致密区的形成未能启动，导致 在一个发育不良的房间里，这与胎儿的生存能力不相容。我们有 之前描述了这种表型，并显示了对 维甲酸在脑室发育过程中不会出现在心肌中， 而是发生在一种不同的细胞谱系中，这种细胞谱系继而支持 心肌增殖和随后的室腔形态发生。 模型：根据本申请中提供的新数据，我建议维甲酸 酸性信号最初由RXRA在心外膜转导，从而 诱导一种或多种营养分泌生长因子的表达 对于心肌来说。老年胚胎和出生后动物的心肌 对这些因素的刺激不敏感。为了解决这一模式，我建议 以下是具体目标： 具体目标1：明确RXRA在心外膜中的作用。组织特异性 小鼠胚胎的失活和转基因操作，以及病毒感染 在鸡胚中，被提议证明RXRA功能发生在 心外膜。 特异性目的2：鉴定心外膜细胞分泌的S因子 对对心肌有营养作用的维甲酸的反应。生化 提出了纯化加基于基因发现的方法来鉴定 维甲酸和RXRA依赖的心外膜细胞分泌的因子 举止。 具体目标3：确定心肌反应的关键成分 心外膜细胞分泌型营养因子(S)。我建议识别信号 胎儿心肌细胞中介导反应的转导元件 营养刺激，以及导致缺乏反应的变化 在出生后心肌中。

DESCRIPTION (provided by applicant): The mechanisms which promote cardiomyocyte proliferation during fetal life, and which fail to induce proliferation during postnatal life, are only poorly understood. My lab has studied cardiac development in mouse embryos lacking the retinoic acid receptor RXRa, in which compact zone formation in the ventricular chamber fails to initiate, resulting in a hypoplastic chamber that is incompatible with fetal viability. We have previously described this phenotype and shown that the initial response to retinoic acid during ventricular development does not occur in the myocardium, but rather occurs in a distinct cell lineage which then secondarily supports myocardial proliferation and subsequent ventricular chamber morphogenesis. Model: Based on new data presented in this application, I propose that retinoic acid signaling is initially transduced by RXRa in the epicardium, thereby inducing expression of one or more secreted growth factors which are trophic for the myocardium. Myocardium in older embryos and in postnatal animals is refractory to stimulation by these factors. To address this model, I propose the following Specific Aims: Specific Aim 1: To define the role of RXRa in the epicardium. Tissue-specific inactivation and transgenic manipulation in mouse embryos, and viral infection in chick embryos, are proposed to demonstrate that RXRa function occurs in the epicardium. Specific Aim 2: To identify the factor(s) secreted by epicardial cells in response to retinoic acid that are trophic for the myocardium. Biochemical purification plus gene-based discovery approaches are proposed to identify the factors secreted by epicardial cells in a retinoic acid- and RXRa-dependent manner. Specific Aim 3: To define the critical components of the myocardial response to epicardial cell secreted trophic factor(s). I propose to identify the signal transduction elements in fetal cardiocytes which mediate the response to trophic stimulation, as well as changes which account for the lack of response in postnatal myocardium.