Mechanisms of Mitochondrial Distribution

描述（由申请人提供）：在真核细胞中，线粒体运动或“运输”是通过将细胞器连接到驱动蛋白或肌球蛋白马达蛋白上而发生的，驱动蛋白或肌球蛋白马达蛋白分别沿着微管或肌动蛋白丝行走。这些线粒体运输事件是将线粒体分布在细胞质内所必需的，并且对于分裂期间子细胞的线粒体遗传也是必不可少的。线粒体转运机制的分子理解对人类健康至关重要，因为损害线粒体分布的遗传病变与越来越多的人类疾病有关，包括某些形式的肌营养不良症，心肌病，截瘫和神经变性。从酵母到人类，线粒体运输的基本调控机制是保守的。啤酒。酵母线粒体运输缺陷干扰子细胞（芽）的线粒体遗传。以前的研究确定了两个独立的途径，调节酵母线粒体遗传。第一种途径利用称为Mmr 1的外周线粒体衔接蛋白。Mmr 1与Myo 2形成复合物，Myo 2是一种V类肌球蛋白马达蛋白。本申请中的实验将测试Mmr 1丰度、活性和/或定位的变化协调Mmr 1介导的线粒体遗传与细胞周期的模型。第二个线粒体遗传途径需要一个位于内质网（ER）的Rab GTdR，称为Ypt 11。Ypt 11还与Myo 2形成复合物。ER锚定的Rab如何控制线粒体膜的遗传尚不清楚。在本申请中，提出并测试了两种替代模型来解释ER定位的Ypt 11如何影响线粒体遗传。主要研究者的实验室最近描述了线粒体遗传所需的第三种途径。该途径利用Gem 1/Miro，一种尾锚定的线粒体外膜蛋白，含有两个GTdR结构域和两个Ca 2+结合EF-手基序。Gem 1/Miro是从酵母到人类的保守基因，突变型Miro在培养细胞中的表达导致细胞凋亡，Gem 1/Miro缺陷的果蝇表现出神经元缺陷。实验拟确定Gem 1/Miro是否通过Myo 2起作用，并确定其GTdR结构域的特定效应子。最后，主要研究者的实验室将研究在遗传筛选中鉴定的线粒体遗传途径的新组分。这些研究可能会确定哺乳动物的同源物，这将使未来的研究线粒体分布机制在人类细胞和组织。公共卫生相关性：概述的研究将促进对基于肌动蛋白的线粒体转运机制的理解。结果将与人类发育和健康相关，因为几种感兴趣的分子具有人类同源物，包括Myo 2（人类肌球蛋白Va）和Gem 1（人类Miro 1和Miro 2）。人肌球蛋白Va的缺陷导致胚胎死亡，肌球蛋白Va功能降低的患者患有Griscelli综合征，这是一种以免疫缺陷、神经和色素沉着缺陷为特征的通常致命的疾病。突变型哺乳动物Miro的表达改变了线粒体形态并诱导培养细胞中的细胞死亡，并且果蝇Miro中的缺陷破坏了轴突线粒体运输，这是一种可能在人类中保守的功能。一些拟议的实验可能会导致同源物的识别，控制肌动蛋白为基础的线粒体分布过程中的人类细胞和组织。在这个过程中学到的东西可能会让科学家和临床医生操纵这些分子的活动，以造福人类健康。

DESCRIPTION (provided by applicant): In eukaryotic cells, mitochondrial movement or `transport' occurs by attaching the organelle to kinesin or myosin motor proteins that walk along microtubules or actin filaments, respectively. These mitochondrial transport events are required to distribute mitochondria within the cytoplasm and are also essential for inheritance of mitochondria by daughter cells during division. A molecular understanding of mitochondrial transport mechanisms is critical for human health, as genetic lesions that compromise mitochondrial distribution are linked to a growing list of human disorders, including some forms of muscular dystrophy, cardiomyopathy, paraplegia, and neurodegeneration. The basic mechanisms regulating mitochondrial transport are conserved from yeast to man. This proposal focuses on the molecules and machineries that mediate actin-based mitochondrial transport during division in the budding yeast, S. cerevisiae. Defects in yeast mitochondrial transport interfere with mitochondrial inheritance by daughter cells (buds). Previous studies identified two independent pathways that regulate yeast mitochondrial inheritance. The first pathway utilizes a peripheral mitochondrial adaptor protein called Mmr1. Mmr1 forms a complex with Myo2, a class V myosin motor protein. Experiments in this application will test the model that changes in Mmr1 abundance, activity and/or localization coordinate Mmr1-mediated mitochondrial inheritance with the cell cycle. The second mitochondrial inheritance pathway requires an endoplasmic reticulum (ER)- localized Rab GTPase called Ypt11. Ypt11 also forms a complex with Myo2. How an ER-anchored Rab controls inheritance of mitochondrial membranes is not understood. In this application, two alternative models to explain how ER-localized Ypt11 influences mitochondrial inheritance are proposed and tested. The principle investigator's laboratory recently described a third pathway required for mitochondrial inheritance. This pathway utilizes Gem1/Miro, a tail-anchored outer mitochondrial membrane protein containing two GTPase domains and two Ca2+binding EF-hand motifs. Gem1/Miro is conserved from yeast to man. Expression of mutant Miro in cultured cells leads to apoptosis, and flies with defective Gem1/Miro display neuronal defects. Experiments are proposed to determine whether Gem1/Miro acts via Myo2 and to identify specific effectors of its GTPase domains. Finally, the principle investigator's laboratory will study novel components of mitochondrial inheritance pathways identified in genetic screens. These studies will likely identify mammalian homologs that will allow future investigation of mitochondrial distribution mechanisms in human cells and tissues. Public Health Relevance: The studies outlined will advance the understanding of actin-based mitochondrial transport mechanisms. The results will be relevant to human development and health, as several of the molecules of interest have human homologs, including Myo2 (human myosin Va) and Gem1 (human Miro1 and Miro2). Defects in human myosin Va cause embryonic lethality, and patients with reduced myosin Va function suffer from Griscelli's syndrome, an often fatal disorder characterized by immunodeficiency, and neurological and pigmentation defects. Expression of mutant mammalian Miro alters mitochondrial morphology and induce cell death in cultured cells, and defects in fly Miro disrupt axonal mitochondrial transport, a function that is likely conserved in humans. Some of the proposed experiments may lead to the identification of homologs that control actin-based mitochondrial distribution processes in human cells and tissues. What is learned in the process may allow scientists and clinicians to manipulate the activities of these molecules for the benefit of human health.