Linking Hedgehog and Nodal/TGF-beta signaling in the establishment of left-right asymmetry

项目摘要/摘要 左-右(LR)不对称性的建立是正确定位内固定所必需的关键事件 器官。人类LR轴形成缺陷会导致心脏、血管、肺和肠道的先天缺陷 一条小路。导致LR不对称产生的基因网络是高度保守的 脊椎动物。在鼠标中，建立LR轴的初始不对称信号在节点中通过以下方式确定 纤毛驱动的流体向左流动(节流)。这些信号然后被传递到左侧板中胚层 (LPM)，它将经历不对称的器官形态发生。节蛋白是一种分泌蛋白质，属于 转化生长因子-b(转化生长因子-b)超家族在结节中表达，并在很长一段时间内到达 Left LPM，在那里它启动一个瞬时自动调节电路(涉及Nodal和Lefty)，该电路传播Nodal 信号转导并激活左侧决定子配对样同源域转录的表达 系数2(Pitx2)。Hedgehog(HH)信号通路在LR模式形成中也起着至关重要的作用。在老鼠身上， HH信号是建立分隔胚胎左侧和右侧的中线以及 以激活LPM中的节点相关自动调节电路。然而，HH 信号转导调节LPM对结节反应的能力还不是很清楚。因此，标识 HH和转化生长因子-b通路的特定汇聚点对于理解深入的机制至关重要。 确定潜在的LR不对称性，从而提供更好的诊断、预防和治疗 干预针对 与LR不对称相关的出生缺陷。 我们最近发现了HH途径的一个新靶点--神经元衍生神经营养因子(Ndnf)， 调节小鼠的轴向旋转和肠循环。在拟议的工作中，我们将纳入 生物化学、分子和遗传学方法(目标1)评估来源，(目标2)确定 转录调控，以及(目标3)研究Ndnf在LR中的潜在分子机制 决心。

Project summary/abstract The establishment of left-right (LR) asymmetry is a critical event required for the correct positioning of internal organs. Defects in human LR axis formation cause birth defects of the heart, vasculature, lungs, and intestinal tract. The gene network contributing to the generation of LR asymmetry is highly conserved across vertebrates. In the mouse, the initial asymmetric signals establishing LR axis are determined in the node by cilia-driven leftward fluid flow (nodal flow). These signals are then transferred to the left lateral plate mesoderm (LPM), which will undergo asymmetric organ morphogenesis. Nodal, a secretory protein that belongs to the transforming growth factor-b (TGF-b) superfamily, is expressed in the node and travels a long distance to the left LPM, where it initiates a transient auto-regulatory circuit (involving Nodal and Lefty) that propagates Nodal signaling and activates expression of the left-sided determinant Paired-Like Homeodomain transcription factor 2 (Pitx2). The Hedgehog (Hh) signaling pathway also plays a crucial role in LR patterning. In the mouse, Hh signaling is required to establish the midline that separates the left and right sides of the embryo, as well as to activate the Nodal-dependent auto-regulatory circuit in the LPM. However, the mechanism by which Hh signaling regulates the competence of the LPM for Nodal response is not well understood. Thus, identifying the specific convergence point of the Hh and TGF-b pathways is critical for understanding the in-depth mechanism underlying LR asymmetry determination, and therefore to provide better diagnosis, preventive and therapeutic intervention against LR asymmetry-related birth defects. We recently found that a novel target of the Hh pathway, Neuron-Derived Neurotrophic Factor (Ndnf), regulates axial rotation and intestinal looping in the mouse. In the proposed work, we will incorporate biochemical, molecular, and genetic approaches to (Aim 1) assess the source, (Aim 2) determine the transcriptional regulation, and (Aim 3) investigate the underlying molecular mechanisms of Ndnf in LR determination.