Tensile stress in orienting planar cell polarity

描述（由申请人提供）：在许多器官系统中，突出数百个跳动的纤毛的细胞，称为多纤毛细胞，产生强烈的流体流动，沿着腔体表面运输生物材料。多纤毛虫细胞分布在呼吸道、生殖道和脑室中，它们产生的流动对人类健康有重大影响。为了有效地发挥器官功能，纤毛流必须沿着特定的轴流动：例如，在肺中，纤毛流将粘液排出而不是深入气道。为了产生定向流动，发育中的上皮需要获得平面轴，从而定向细胞内和细胞间的纤毛跳动。为了确定多纤毛虫细胞如何获得平面细胞极性（PCP），我们开创了一个模型系统，即X. laevis幼虫皮肤。多纤毛细胞在原肠胚形成后不久就开始在发育中的皮肤中分化，产生强有力的纤毛流，且纤毛流总是由前向后。已知在原肠胚形成期间发生的全局模式事件可以固定纤毛流的方向，但对介导这种模式事件的机制一无所知，就像所有其他已知的PCP例子一样。在这个探索性的提议中，我们将测试一个新的模型，其中平面极性的方向部分由胚胎发生期间组织中发生的拉伸应力的方向决定。在皮肤的情况下，这种拉伸应力在原肠胚形成期间通过中胚层在内化和轴向伸长期间产生的力发生。具体来说，我们将采用一种称为牵引器拉力的装置，在平面轴通常建立的阶段对孤立的发育中的皮肤施加定向应力。这些实验将扩展初步发现，确定定向应力可以指定平面轴的参数，并确定定向应力是与PCP信号通路上游还是平行工作。总之，本文提出的实验将提供重要的原理证明，从而为研究胚胎中的力如何塑造和塑造组织建立一个新的模型。

DESCRIPTION (provided by applicant): In many organ systems, cells projecting hundreds of beating cilia, called multiciliate cells, produce a vigorous fluid flow that transports biological materials along luminal surfaces. Multiciliate cells populate the respiratory and reproductive tracts, and the ventricles of the brain, and the flow they produce has significant implications for human health. To be effective in organ function, ciliary flow has to direct along a specific axis: in the lung, for example, flow propels mucus out of rather than deeper into the airways. To produce directed flow, developing epithelia need to acquire a planar axis, thus orienting cilia beating within a cell, as well as between cells. To determine how multiciliate cells acquire planar cell polarity (PCP), we have pioneered a model system, namely the X. laevis larval skin. Multiciliate cells begin to differentiate in the developing skin soon after gastrulation, producing a vigorous ciliary flow that invariably is directed from anterior to posterior. A global patterning event that occurs during gastrulation is known to fix the direction of ciliary flow, but nothing is known about the mechanisms that mediate this patterning event as is the case in all other known examples of PCP. In this exploratory proposal, we will test a new model where the direction of planar polarity is dictated in part by the orientation of tensile stress that occurs in the tissue during embryogenesis. In the case of the skin, this tensile stress occurs during gastrulation via the forces generated by mesoderm during involution and axial elongation. Specifically, we will employ a device, called the tractor pull, to apply oriented stress to isolated developing skin, at stages when the planar axis is normally established. These experiments will extend on preliminary findings, determine the parameters by which oriented stress can specify a planar axis, and determine whether oriented stress works upstream or in parallel with the PCP signaling pathway. In sum, the experiments proposed here will provide an important proof of principle, thus establishing a new model for studying how forces in the embryo sculpt and pattern tissues. PUBLIC HEALTH RELEVANCE: Multiciliate cells play important roles in human health by generating directed fluid flow in the brain, lung and reproductive tract, but the mechanisms that orient flow direction in relation to an organ axis are poorly understood. To study these mechanisms, the proposed research will employ a model system to test a novel hypothesis where tensile stress incurred by a developing tissue acts to orient the direction of ciliary flow. Results from the proposed experiments will potentially establish a new paradigm for how the direction of ciliary flow is established during development, and will have implications for diagnosis and treatment of human disease that affect ciliated epithelia, such as the ciliary defects that occurs during primary ciliary dyskinesia and Kartegener's syndrome.