Molecular control of mechanical forces driving buckling morphogenesis of the small intestine

项目摘要/摘要 这项工作的广泛目标是理解分子线索如何协调并与物理 推动脊椎动物形态发生的力量。具体地说，我们关注的是小肠的循环，这是一个过程 对于腹部内的长肠的填充是必不可少的，当缺陷时会导致毁灭性的 先天性疾病。由于肠管在约束条件下伸长时发生弯曲而产生环状结构 它附着的肠系膜。由此产生的环路波长和曲率可以从少数几个 实验测量的物理特性，包括组织几何形状、生长速度和硬度。屈曲 已经成为塑造胚胎中各种组织和器官的核心机制。然而，优雅的 屈曲机制的简单性往往暴露了产生和制约这一点的生物复杂性 物理过程。事实上，对屈曲形态发生的理解将物理学与 在大多数情况下，缺乏潜在的分子线索和动态细胞行为。我们最近发现了BMP 信号转导是控制肠道循环的关键途径。有了这条途径，本申请利用一种 对分子和细胞生物学控制的相关机制有深入的了解。 屈曲形态发生，以及在发育过程中产生的力如何反馈以调节这些 控制。我们首先要问的是，肠系膜中依赖骨形态发生蛋白的肌球蛋白活性对组织有何贡献。 通过操纵细胞外基质组织的力学(目标1)，重点关注这一能力 组织在僵硬之前适应大应变(&gt；100%)；这种行为称为结构性 非线性，是环状形态的关键决定因素，但其生物学基础和形态功能 在发展过程中常常被忽视。接下来，我们建立在BMP建立的惊人观察的基础上 以不依赖于增殖的方式限制肠系膜伸长的差异生长(目标2)，测试 该假说认为BMP调节细胞大小以建立差异生长，从而驱动屈曲。因此，目标1 2主要研究BMP依赖的肠系膜弹性储能机制。这股能量 存储必须与能量消耗精确平衡，才能生成刻板印象的循环。为了解决这个问题， 我们研究了肠系膜增殖性生长的控制(目标3)，重点是河马信号转导。 以及差异生长所产生的力量如何对扩散进行反馈。这些交叉的- 学科研究结合了逆转录病毒基因错误表达、细胞行为、力和硬度的分析 测量、张力式生物反应器研究和数学建模。我们的长期愿景是建立 胚胎发生的机械-分子规则或设计原则，使真正的工程方法能够 再生医学，其中僵硬、应力和应变可以与细胞类型一起进行生物编程 指导功能三维组织和器官组装的规范。

PROJECT SUMMARY/ABSTRACT The broad goal of this work is to understand how molecular cues orchestrate and interact with the physical forces to drive vertebrate morphogenesis. Specifically, we focus on looping of the small intestine, a process essential for packing of the lengthy intestine within the abdomen, that when defective leads to devastating congenital disorders. Loops arise due to buckling of the intestinal tube as it elongates against the constraint of its attached mesentery. The resulting loop wavelength and curvature can be predicted from a handful of experimentally measured physical properties, comprising tissue geometry, growth rate, and stiffness. Buckling has emerged as a core mechanism of shaping various tissues and organs in the embryo. However, the elegant simplicity of buckling mechanics often betrays the biological complexity that engenders and constrains this physical process. Indeed, an understanding of buckling morphogenesis that integrates physics with the underlying molecular cues and dynamic cell behaviors is lacking in most contexts. We recently identified BMP signaling as a key pathway controlling gut looping. With this pathway in hand, the present application exploits a well-developed understanding of the associated mechanics to study the molecular and cell biological control of buckling morphogenesis, as well as how forces generated during development feed back to modulate these controls. We begin by asking how BMP-dependent acto-myosin activity in the mesentery contributes to tissue mechanics through manipulation of extracellular matrix organization (Aim 1), focusing on the ability of this tissue to accommodate large strains (>100%) before stiffening; this behavior, known as constitutive nonlinearity, is a critical determinant of looping morphology, but its biological basis and morphological function are often overlooked in development. Next, we build upon the striking observation that BMP establishes differential growth by restricting mesentery elongation in a proliferation-independent manner (Aim 2), testing the hypothesis that BMP regulates cell size to set up differential growth, driving buckling. Therefore, Aims 1 and 2 focus on BMP-dependent mechanisms of elastic energy storage within the mesentery. This energy storage must be precisely balanced with energy dissipation to generate stereotyped looping. To address this, we examine the control of proliferative growth of the mesentery (Aim 3), focusing on the Hippo signaling pathway and how forces generated by differential growth may feedback on proliferation. These cross- disciplinary studies combine retroviral gene misexpression, analyses of cell behavior, force and stiffness measurements, tensile bioreactor studies, and mathematical modeling. The long term vision is to establish mechano-molecular rules or design principles of embryogenesis, enabling a true engineering approach to regenerative medicine, wherein stiffness, stress, and strain can be biologically programmed alongside cell type specification to instruct the assembly of functional three dimensional tissues and organs.