Cilia in cardiac morphogenesis

先天性心脏病是最常见的严重出生缺陷，影响0.8%的活产婴儿。正常 心脏发育取决于遗传和表观遗传因素之间复杂的相互作用。特别是， 血流和心脏功能对于心脏形态发生是必不可少的：然而， 这些机械信号被感测和解释仍然不清楚。纤毛，这也是必不可少的， 通过它们在胚胎组织者（节点）的功能发展心脏LR不对称性，最近已经被 发现在其他管状的充满液体的器官如肾脏中起机械传感器的作用。我们已经确定 一组纤毛，称为心脏纤毛，在小鼠心脏中，在e8.5 - e12.5，对应于发育中的时间 从血流开始延伸通过瓣膜形成和分隔。本提案的目的是 定义了心脏纤毛在心脏形态发生中直接起作用的机制， 在产生LR不对称性中的作用。纤毛不动但结构正常的小鼠， 器官沿着LR轴的定位。虽然在7-50%的受影响小鼠中观察到心内缺陷， 相当多的人存活到成年，心脏结构和功能正常。相比之下， 纤毛或纤毛感觉完全缺失的患者有严重的心脏缺陷， 在妊娠中期，胚胎致死率与LR轴发育无关。这些观察提示 纤毛在心脏发育中是必需的，独立于它们在LR发育中的功能。我们假设 心脏纤毛作为细胞外信号如血流、心脏功能或分泌配体的传感器 影响形态发生在本提案的具体目标1中，我们将定义心脏纤毛的作用：它们是 机械传感器、刺猬受体或能动结构？为此， 检查心脏纤毛。组成性纤毛突变对心脏发育的作用将是 通过分析具有导致纤毛缺陷突变的小鼠胚胎的心脏表型进行评价， 运动性、纤毛生物发生或纤毛机械感觉。心脏缺陷和纤毛分布将被 在小鼠胚胎中进行了评估，突变导致心脏跳动消失。纤毛在LR中的作用 发展将区别于它们的辐射内功能。在规范目标2中，我们将确定 心脏纤毛通过使用Cre-lox技术从心外膜特异性地去除纤毛而发挥其作用， 心内膜、心包和心前区。最后，在规范目标3中，我们将寻求定义心脏如何 纤毛直接形态发生。在此，连接纤毛感觉与心脏感觉的下游信号传导途径（一个或多个）被激活。 将通过分析上皮-间充质转化、增殖和 纤毛功能和生物发生突变的小鼠胚胎心脏中的hedgehog信号传导。

Congenital heart disease is the most common serious birth defect, affecting .8% of liveborn infants. Normal cardiac development depends on complex interplay between genetic and epigenetic factors. In particular, blood flow and cardiac function are essential for cardiac morphogenesis: however, the mechanism by which these mechanical signals are sensed and interpreted remains unclear. Cilia, which are also essential in the development of cardiac LR asymmetry via their function at the embryonic organizer (node), have recently been found to function as mechanosensors in other tubular, fluid-filled organs such as the kidney. We have identified a set of cilia, called cardiac cilia, in the mouse heart at e8.5 - e12.5, corresponding to the time in development extending from the onset of blood flow through valve formation and septation. The goal of this proposal is to define the mechanism by which cardiac cilia function directly in cardiac morphogenesis independent of their role in the generation of LR asymmetry. Mice with immotile, but structurally normal cilia have abnormal positioning of organs along the LR axis. Although intracardiac defects are observed in 7-50% of affected mice, a significant number survive to adulthood with structurally and functionally normal hearts. In contrast, mice with complete absence of cilia or ciliary sensing have severe cardiac defects with 100% penetrance that result in mid-gestational embryonic lethality independent of LR axis development. These observations suggest that cilia are required in cardiac development independently from their function in LR development. We hypothesize that cardiac cilia function as sensors for extracellular signlas such as flow, cardiac function or secreted ligands to affect morphogenesis. In Spec. Aim 1 of this proposal, we will define what cardiac cilia do: are they mechanosensors, hedgehog receptors or motile structures? To this end, the distribution and composition of cardiac cilia will be examined. The role of constitutive ciliary mutations on cardiac development will be evaluated by analysis of the cardiac phenotype of mouse embryos with mutations resulting in defective ciliary motility, ciliary biogenesis or ciliary mechanosensation. The cardiac defects and distribution of cilia will be evaluated in mouse embryos with a mutation resulting in an absent heart beat. The role of cilia in LR development will be distinguished from their intracradiac function. In Spec. Aim 2, we will identify where cardiac cilia exert their effect by using Cre-lox technology to delete cilia specifically from the epicardium, endocardium, pericardium and anterior heart field. Finally, in Spec. Aim 3 we will seek to define how cardiac cilia direct morphogenesis. Here, the downstream signaling pathway(s) connecting ciliary sensing with cardiac morphogenesis will be investigated by analyzing epithelial-mesenchymal transformation, proliferation and hedgehog signaling in mouse embryo hearts with mutations in ciliary function and biogenesis.