Beyond cell shape: Actin exerts systems-level control during morphogenesis

 描述（由申请人提供）：细胞形状的变化驱动形态发生，肌动蛋白缺乏导致细胞形状变化失败和出生缺陷。然而，我们对肌动蛋白对形态发生的影响的了解主要限于分子列表和总体表型的描述。虽然肌动蛋白丝（F-肌动蛋白）被认为是细胞形状的主要结构决定因素，但基本问题仍然没有答案：F-肌动蛋白是如何重塑的？它是如何与细胞膜接触的？它如何适应环境或遗传变异？我们需要这些答案来理解发展和人类疾病。 我们的长期目标是充分了解肌动蛋白在形成健康组织中的作用。我们专注于果蝇细胞化，这是在胚胎中建立第一个上皮层的过程。在细胞化过程中，胚胎的每个新细胞都发生了三个细胞表面重塑事件：（i）微绒毛分解;（ii）膜沟进入;（iii）肌动球蛋白环收缩。我们已经表明，虽然这三个重塑事件在空间上隔离了几十微米，但它们仍然在动力学上相互耦合，并与肌动球蛋白环中可测量的变化耦合。我们还确定了特定的F-肌动蛋白调节剂的肌动球蛋白环，促进鲁棒性的细胞化对环境和遗传干扰。这些结果表明，肌动蛋白不仅仅是赋予细胞形状。我们的工作模型是，肌动蛋白为基础的机制也有助于协调，动力学和稳健的形态发生。 在这项拟议的工作中，我们将测试我们的模型如下：在目标1中，我们将测试的假设，质膜张力，产生的沟内陷，抑制F-肌动蛋白聚合微绒毛，导致他们“展开”或分崩离析。在目的2中，我们将测试他的假设，不同的动力学阶段的肌动球蛋白环收缩是由不同的机制F-肌动蛋白的调节。在目的3中，我们将检验以下假设：F-肌动蛋白调节剂Srya和Spt稳定收缩环内的F-肌动蛋白，以确保在细胞中的稳健细胞化。 面对环境和基因的干扰。 我们已经组建了一个由物理学家、数学家和技术专家组成的多学科团队;我们将采用多种方法的强大组合，包括定量实时成像、物理力测定、遗传学和基因组编辑，以不寻常的细节来研究细胞化事件。由于驱动细胞化的肌动蛋白机制是广泛保守的，我们的发现将与其他器官有关，包括人类。我们将建立个人重塑事件是如何在空间和时间上进行调节的，同时也展示了这些事件是如何相互协调以高保真度完成细胞化的。在这项工作中，我们还将揭示基因，力学和环境如何调节F-肌动蛋白。

 DESCRIPTION (provided by applicant): Changes in cell shape drive morphogenesis and actin deficiencies cause failed cell shape change and birth defects. Yet our knowledge of actin's influence on morphogenesis is largely limited to lists of molecules and descriptions of gross phenotypes. While actin filaments (F-actin) are recognized as the major structural determinant of cell shape, basic questions remain unanswered: How is F-actin remodeled? How does it inter- face with cell membranes? How does it adapt to environmental or genetic variability? We need these answers to understand development and human disease. Our long-term goal is to fully understand actin's role in forming healthy tissues. We are focused on Drosophila cellularization, the process that builds the first epithelial sheet in the embryo. During cellularization, three cell surface remodeling events are going on in every new cell of the embryo: (i) microvilli disassemble; (ii) a membrane furrow ingresses; and (iii) an actomyosin ring contracts. We have shown that while these three remodeling events are spatially segregated over tens of microns, they are still kinetically coupled to each other and to measurable changes in the actomyosin ring. We have also identified specific F-actin regulators in the actomyosin ring that promote the robustness of cellularization against environmental and genetic perturbation. These results argue that actin does more than just give cells their shape. Our working model is that actin- based mechanisms also contribute to the coordination, kinetics, and robustness of morphogenesis. In this proposed work, we will test our model as follows: In Aim 1, we will test the hypothesis that plasma membrane tension, generated by furrow ingression, suppresses F-actin polymerization in microvilli, causing them to "unfold" or fall apart. In Aim 2, we will test he hypothesis that distinct kinetic phases of actomyosin ring contraction are governed by distinct mechanisms of F-actin regulation. In Aim 3, we will test the hypothesis that F-actin regulators, Srya and Spt, stabilize F-actin within the contractile ring to ensure robust cellularization in the face of environmental and genetic perturbation. We have assembled a multidisciplinary team of physicists, mathematicians and technologists; and we will employ a powerful combination of approaches, including quantitative live imaging, physical force assays, genetics, and genome editing to examine the events of cellularization in uncommon detail. Because the actin- based machinery that drives cellularization is widely conserved, our findings will be relevant to other organ- isms, including humans. We will establish how individual remodeling events are regulated in space and time, while also showing how the events are coordinated with each other to accomplish cellularization at high fidelity. In doing this work, we will also reveal how genes, mechanics, and environment regulate F-actin.