Kinesin and +TIP-based microtubule steering

描述(由申请人提供)：微管细胞骨架的适当组织是许多细胞功能的基础，如神经元的极化运输、上皮细胞的营养运输和有丝分裂。虽然控制有丝分裂细胞中微管排列的机制已经被广泛研究，但对分化细胞中微管排列的探讨要少得多。果蝇神经元的树突可以作为一个系统来识别控制微管极性的机制，因为它们含有均匀的极性减去末端输出的微管。在果蝇神经元中的活体实验导致了树突中微管排列的模型，在该模型中，生长微管正端的运动蛋白-2和正端相互作用蛋白(TIPS)的复合体与分支点的静止微管相互作用，并积极地将生长的正端导向细胞体。这种微管导向机制可以作为控制不同细胞类型(如上皮细胞)中微管极性的通用模型。这项提议的目的是利用果蝇神经元的体外重建、计算模拟和分析来了解基于尖端动蛋白的微管操纵。这项工作的第一个目的是使用纯化的蛋白质和微制造的通道来开发一种新的实验系统，用于体外研究末端-动蛋白复合体对微管的操纵。这种体外重组将验证和扩大体内观察，并将提供一个系统，以量化该蛋白质复合体的活性。第二个目标将是测量系统特定组件之间的结合亲和力，以建立用于建模研究的定量生化参数。第三个目标是利用实验产生的定量参数，在体内和体外开发基于尖端动蛋白的微管操纵的计算模拟，然后使用体内实验测试模型的预测。这些模拟将结合已知的微管和运动蛋白马达的机械特性，并将提供有关TIPS承受持续微管弯曲所需的机械载荷的能力的见解。这些实验和计算研究将探索Kinesin马达和TIP蛋白的新功能角色，这里开发的框架将为理解分化细胞中微管极性建立的普遍方面提供基础。许多人类神经退行性疾病与调节微管细胞骨架的基因突变有关，突显了了解神经元中适当的微管组织的重要性。

DESCRIPTION (provided by applicant): Proper organization of the microtubule cytoskeleton underlies many cellular functions such as polarized transport in neurons, nutrient transport in epithelial cells, and mitosis. While mechanisms that control microtubule alignment in mitotic cells have been extensively studied, alignment of microtubules in differentiated cells has been probed much less. Dendrites of Drosophila neurons can be used as a system to identify mechanisms that control microtubule polarity as they contain uniform-polarity minus-end-out microtubules. In vivo experiments in fly neurons have led to a model of microtubule alignment in dendrites in which a complex of kinesin-2 and plus-tip interacting proteins (+TIPs) at growing microtubule plus-ends interacts with stationary microtubules at branch points and actively directs the growing plus- end toward the cell body. This microtubule steering mechanism may serve as a general model for control of microtubule polarity in diverse cell types such as epithelial cells. The goal of this proposal is to use in vitro reconstitution, computational simulations, and analysis of Drosophila neurons to understand +TIP-kinesin based microtubule steering. The first aim of the work is to use purified proteins and microfabricated channels to develop a novel experimental system for studying microtubule steering by +TIP-kinesin complexes in vitro. This in vitro reconstitution will validate and extend in vivo observations, and will provide a system for quantifying the activity of this protein complex. The second aim will be to measure binding affinities between specific components of the system to establish quantitative biochemical parameters for modeling studies. The third aim will be to develop computational simulations of +TIP-kinesin based microtubule steering in vivo and in vitro, using quantitative parameters generated from the experiments, and then test predictions of the models using in vivo experiments. The simulations will incorporate known mechanical properties of microtubules and kinesin motors, and will provide insights into the ability of +TIPs, to withstand the mechanical loads necessary for sustained microtubule bending. These experimental and computational studies will explore novel functional roles for both kinesin motors and the +TIP proteins, and the framework developed here will provide a foundation for understanding universal aspects of microtubule polarity establishment in differentiated cells. The importance of understanding proper microtubule organization in neurons is underscored by the numerous human neurodegenerative diseases that are linked to mutations in genes involved in regulating the microtubule cytoskeleton.