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

项目概要/摘要 左右（LR）不对称的建立是正确定位内部组织所需的关键事件。 机关人类LR轴形成缺陷导致心脏、脉管系统、肺和肠的出生缺陷。 道。导致LR不对称性产生的基因网络在整个基因组中是高度保守的。 脊椎动物在小鼠中，建立LR轴的初始不对称信号在节点中通过以下方式确定： 纤毛驱动的微流体流动（节流）。然后这些信号被传递到左侧板中胚层 (LPM)，其将经历不对称的器官形态发生。Nodal是一种分泌蛋白，属于 转化生长因子-b（TGF-b）超家族在淋巴结中表达，并长距离移动到淋巴结。 左LPM，在那里它启动一个瞬态自动调节电路（涉及Nodal和Lefty），传播Nodal 信号传导并激活左侧决定簇配对样同源结构域转录的表达 因子2（Pitx 2）。Hedgehog（Hh）信号通路在LR模式中也起着至关重要的作用。在老鼠体内， Hh信号是建立分隔胚胎左右两侧的中线所必需的， 激活LPM中的节点依赖性自动调节电路。然而，Hh 信号传导调节LPM对Nodal响应的能力还不清楚。因此，识别 Hh和TGF-b通路的特定汇合点对于理解深入的机制至关重要 潜在的LR不对称性测定，从而提供更好的诊断、预防和治疗 干预反对 LR不对称相关的出生缺陷。 我们最近发现Hh通路的一个新靶点，神经元源性神经营养因子（NdNF）， 调节小鼠的轴向旋转和肠循环。在拟议的工作中，我们将 生物化学、分子和遗传学方法（目的1）评估来源，（目的2）确定 目的3：探讨NdNF在LR中的分子机制 保持战略定力

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.