Quantitative Analysis of Chemotactic Motility Cycle of Ameboid Cells

描述（由申请人提供）：真核细胞运动对许多生理过程至关重要，如胚胎发育、组织更新和免疫系统功能。盘状盘基骨柱已被证明是变形虫细胞（如白细胞）趋化迁移的良好模型。变形虫迁移是假足突缩连续重复的结果，并由产生的牵引力驱动。牵引力的强度和时空组织是由肌动蛋白导向的马达、f -肌动蛋白调节、肌动蛋白交联、马达蛋白介导的收缩性和细胞粘附的协调相互作用决定的。然而，由于缺乏定量信息和分析，这些过程的生物物理协调的精确知识受到限制。我们和其他人已经观察到，在变形虫迁移过程中发生的细胞形状变化的相当一部分是由于周期性的重复事件，这使得使用条件统计方法来分析细胞运动中涉及的生化过程网络成为可能。本研究的主要目标是通过研究已知或怀疑参与运动周期不同阶段的候选细胞骨架和调节分子的作用，以统计稳健的定量方式确定牵引力时空分布和运动周期每个阶段持续时间的生化基础。我们假设肌球蛋白II不仅对运动周期的收缩期至关重要，而且对假足突出期也至关重要。牵引力的产生不仅取决于Myosin II的收缩作用，还取决于它的肌动蛋白交联作用。基于初步结果，我们进一步假设牵引力的时空分布和细胞每周期移动的平均距离取决于肌动蛋白聚合。为了验证上述假设，我们提出了三个具体目标。具体目的1是应用我们新的3D力细胞术方法来测量细胞对底物施加的力的三个组成部分。第二个和第三个目标是通过对野生型细胞和具有肌动蛋白交联或运动蛋白收缩性缺陷（Specific Aim 2）和f -肌动蛋白调节缺陷（Specific Aim 3）的突变株进行系统比较，研究已知或怀疑参与运动的候选细胞骨架和调节分子的作用。我们的方法包括同时测量荧光标记的信号（或细胞骨架）蛋白分布的空间和时间变化以及介导细胞运动周期每个阶段的3D牵引力，同时还记录细胞形状的变化。我们将应用条件统计和主成分分析（PCA）来将特定的生化过程与运动周期中的每个物理事件联系起来。我们的研究将为开始构建控制细胞迁移的生化过程的复杂网络提供必要的基础。

DESCRIPTION (provided by applicant): Eukaryotic cell motility is essential for many physiological processes such as embryonic development, tissue renewal, and the function of the immune system. Dictyostelium discoideum has proven to be an excellent model for the chemotactic migration of amoeboid cells such as leukocytes. Amoeboid migration is the result of the sequential repetition of pseudopod protrusions and retractions and is driven by the generation of traction forces. The strength and spatiotemporal organization of traction forces is determined by the coordinated interactions of actin-directed motors, F-actin regulation, actin crosslinking, motor protein-mediated contractility, and cell adhesions. However, precise knowledge of the biophysical coordination of these processes has been limited by the lack of quantitative information and analysis. We and others have observed that a considerable portion of the changes in cell shape occurring during amoeboid migration are due to periodic repetitive events, which enables the use of conditional statistics methods to analyze the network of biochemical processes involved in cell motility. The primary goal of this research is to determine in a statistically-robust, quantitative manner the biochemical basis for the spatiotemporal distribution of traction forces and the duration of each phase of the motility cycle by studying the role of candidate cytoskeletal and regulatory molecules with known or suspected involvement in the different stages of the motility cycle. We hypothesize that Myosin II is essential not only to the contractility phase of the motility cycle but also to the pseudopod protrusion phase. The generation of the traction forces depends not only on the contractile action of Myosin II, but also in its actin crosslinking effect. Based on preliminary results, we further hypothesize that the spatiotemporal distribution of traction forces and the average distance a cell travels per cycle depend on actin polymerization. To test the above hypotheses, we propose three Specific Aims. Specific Aim 1 is to apply our new 3D force cytometry method to measure the three components of the forces exerted by the cells on the substrate. The second and third aims are aimed at studying the role of candidate cytoskeletal and regulatory molecules with known or suspected involvement in the motility by undertaking systematic comparison of wild type cells and mutant strains with actin crosslinking or motor protein contractility defects (Specific Aim 2), and F-actin regulation defects (Specific Aim 3). Our method consists of simultaneously measuring the spatial and temporal changes in the distribution of fluorescently tagged signaling (or cytoskeletal) proteins and the 3D traction forces that mediate each stage of the cell motility cycle, while also recording the changes in cell shape. We will apply conditional statistics and Principal Component Analysis (PCA) to connect specific biochemical processes to each of the physical events in the motility cycle. Our studies will provide the necessary building blocks to begin constructing the complex network of biochemical processes controlling cell migration. PUBLIC HEALTH RELEVANCE: Motility of eukaryotic cells is essential for many physiological processes such as embryonic development, and tissue renewal, as well as for the function of the immune system. Incorrect regulation of motility plays an important part in many diseases (cancer, destructive inflammation, osteoporosis, mental retardation, etc.), and therefore, future therapeutic approaches will benefit from a precise quantitative understanding of the biophysical processes controlling cell motility. The aim of this study is to establish the mechanisms whereby each individual stage of the motility cycle is related to specific biochemical signaling events, and to elucidate the effects that the regulation of these signaling pathways has on cell motility, with the ultimate goal of developing a level of understanding of the biomechanical processes sufficient to predict and control cell motility.