Mechanisms of axon guidance during development

发育过程中轴突引导的机制

基本信息

批准号：
7735301
负责人：
edward giniger
金额：
$ 104.63万
依托单位：
NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE
依托单位国家：
美国
项目类别：
财政年份：
资助国家：
美国
起止时间：
至
项目状态：
未结题

来源：
https://reporter.nih.gov/project-details/7735301
关键词：
Actins Adult Affect Aging Alzheimer&apos s Disease Amyotrophic Lateral Sclerosis Animals Axon Behavioral Biochemical Genetics Biological Models Biology Birth Brain Brain region Cancer Etiology Cell Adhesion Cell Nucleus Cell Shape Cell Surface Receptors Cell membrane Cells Cessation of life Characteristics Class Complex Coupling Cytoskeletal Proteins Cytoskeleton Defect Dendrites Development Disabled Persons Disease Drosophila genus Drosophila notch protein Elements Embryo Endopeptidases Event Genes Genetic Growth Growth Cones Head Health Histology Homologous Gene Human Image Invertebrates Lead Learning Lesion Life Ligands Link Localized Longevity Malignant Neoplasms Mammals Methods Modeling Modification Molecular Molecular Genetics Morphology Motor Mus Muscle Rigidity Mutate Mutation Nerve Nerve Degeneration Nervous system structure Neurodegenerative Disorders Neurofibrillary Tangles Neurons Neuropil Notch Signaling Pathway Orthologous Gene Pathway interactions Patients Pattern Peptide Hydrolases Phosphotransferases Play Population Process Property Protein Kinase Protein Tyrosine Kinase Proteins Receptor Signaling Regulation Rhabdomyosarcoma Role Signal Pathway Signal Transduction Standards of Weights and Measures Stroke Structure Synapses Syndrome Tauopathies Tissues Tyrosine Tyrosine Phosphorylation Week abl Oncogene axon guidance base cell motility cell type computerized data processing embryonic stem cell fly genetic manipulation human disease interest intracellular protein transport leukemia malignant breast neoplasm medulloblastoma mutant neuronal cell body neuronal survival notch protein null mutation prevent protein localization location receptor relating to nervous system research study response tissue fixing trafficking

项目摘要

How is the proper pattern of neural connections established during development? And how is that pattern maintained in the adult nervous system? These are the questions that the Axon Guidance and Neural Connectivity Unit seeks to answer. To understand the mechanisms underlying the establishment of neural connections, we focus on what might be termed the "elementary event" in the process of neural wiring, the mechanism by which a single cell-surface receptor tells a developing neuron where to grow in order to find its synaptic partners. We study a particular cell surface receptor called Notch. Notch is notable because, in addition to directing nerve growth, it also controls the branching of dendrites, the identities of neurons (and many other types of cells), how many neurons are born and whether cells live or die. As such, it controls many aspects of animal development and is responsible for a wide array of human diseases, including some kinds of cancer and stroke. What we learn about Notch in axons, therefore, has implications for biology and health far beyond the particular process we are examining. Previous studies of Notch have focused on a single signaling mechanism for this ubiquitous receptor. We have found, however, that this is only half of the story. About 5% of the Notch protein in the embryo is tyrosine phosphorylated, and this population of molecules associates specifically with an alternate group of downstream effectors, the Abl oncogene and its associated accessory factors, to directly control cell-cell contacts, cell shape and cell migration. We have shown, moreover, that this alternate Notch signaling pathway acts at the plasma membrane (as opposed to the standard signaling pathway, which targets events in the cell nucleus), and that it acts via a protein called Rac that is a direct regulator of the actin cytoskeleton and of cell-adhesion complexes. In growing nerves, the activity of the Notch/Abl/Rac machinery is revealed as regulation of the direction and extent of nerve growth. Current experiments are directed at continuing to elucidate the molecular mechanism of this alternate signaling pathway, and to determine where besides growing axons it may act in biology and disease. We are particularly interested by evidence that the alternate Notch signaling pathway we have discovered may be central to controlling the survival of neural and embryonic stem cells, and that it is key to the mechanism by which activation of Notch can cause cancers, including medulloblastoma, leukemia, rhabdomyosarcoma and breast cancer. There is a great deal of interest in developing models of neurodegenerative diseases in simple, invertebrate model systems that provide unequaled experimental power for characterizing the cellular events of a complex process and establishing its molecular genetic basis. Use of Drosophila for studies of neurodegeneration have been problematic, however, since in general they have either relied on highly artificial manipulations, such as high-level expression of mutated human genes in the fly, or have identified genes that clearly affect neuronal survival in the fly but are not related to any gene or pathway demonstrated to play a role in neurodegeneration in mammals. We have now identified a natural, adult-onset neurodegenerative syndrome of Drosophila in flies mutant for the ortholog of a gene directly implicated in human diseases including Alzheimer Disease and ALS. The protein kinase Cdk5, together with its regulatory subunit, p35, is one of the major kinases that phosphorylates cytoskeletal proteins to generate the neurofibrillary tangles that are characteristic of the "tauopathy" class of neurodegenerative diseases. Moreover, activated Cdk5 is found concentrated in degenerating tissue in the brains of Alzheimer patients, and experimental activation of Cdk5 induces degenerating lesions in the mouse brain. We have generated a null mutation of the gene encoding the fly homolog of the Cdk5 activating subunit, p35. We find the mutants are viable and fertile, and are behaviorally normal at birth. However, within a few weeks they show progressive loss of motor coordination, culminating in rigidity and then death, with a significantly shortened lifespan (30% shorter than matched controls). Sectioning the heads of aging p35 mutant flies reveals degenerative lesions in the brain, initially in the neuropil but also around the cell bodies. Remarkably, these lesions are highly localized, being present bilaterally in specific brain nuclei, but not generally distributed through the brain, even though p35 and Cdk5 are present and active throughout the brain. Therefore, these mutants may allow us not only to uncover the genetic pathway leading to Cdk5-associated neurodegeneration, but also to understand how and why disease processes that occur throughout the brain lead to very specific and characteristic structural and behavioral defects in particular brain regions. Moreover, in mutant animals we observe widespread defects in axon patterning, synaptic morphology and protein localization within axons long before we see overt degeneration, raising the possibility that late onset degeneration may actually reflect a delayed response to defective nervous system structure early in development.

开发过程中如何建立神经联系的正确模式？在成人神经系统中如何保持这种模式？这些是Axon指导和神经连接部门寻求回答的问题。为了了解建立神经联系的机制，我们将重点放在神经接线过程中可能称为“基本事件”的机制，该机制是单个细胞表面受体告诉开发的神经元的机制，以便在哪里生长以找到其突触伴侣。我们研究了一种称为Notch的特定细胞表面受体。 Notch之所以值得注意，是因为除了指导神经生长外，它还控制着树突的分支，神经元（以及许多其他类型的细胞）的身份，有多少神经元出生以及细胞是否生命或死亡。因此，它控制着动物发育的许多方面，并负责各种人类疾病，包括某些癌症和中风。因此，我们在轴突中了解到的缺口对生物学和健康的影响远远超出了我们正在研究的特定过程。先前对Notch的研究集中在该无处不在的受体的单个信号传导机制上。但是，我们发现这只是故事的一半。胚胎中约有5％的缺口蛋白是酪氨酸磷酸化的，并且该分子群专门与替代下游效应子，ABL OtoCerene及其相关的辅助因子专门与直接控制细胞细胞接触，细胞形状和细胞迁移直接控制。此外，我们已经表明，该替代的凹口信号通路起作用在质膜上（与标准信号通路相反，该途径靶向细胞核中的事件），并且它通过称为RAC的蛋白质作用，该蛋白质是肌动蛋白细胞骨架的直接调节剂和细胞粘附复合物的直接调节剂。在日益增长的神经中，凹口/ABL/RAC机械的活性被揭示为对神经生长的方向和程度的调节。当前的实验旨在继续阐明该替代信号通路的分子机制，并确定除了生长轴突外，它还可以在生物学和疾病中起作用。我们特别感兴趣的是，我们发现的备用凹槽信号传导途径可能是控制神经和胚胎干细胞存活的至关重要的，并且这对于置于癌症的激活可能引起癌症，包括髓母细胞瘤，白血病，rhabdomyosarcoma和乳腺癌的机制是关键。在简单的无脊椎动物模型系统中开发神经退行性疾病模型的模型引起了极大的兴趣，这些模型提供了无与伦比的实验能力来表征复杂过程的细胞事件并确定其分子遗传基础。然而，使用果蝇用于神经变性的研究一直是有问题的，因为通常它们要么依赖于高度人为的操纵，例如苍蝇中突变的人类基因的高级表达，或者已经鉴定出明显影响果蝇中神经元生存的基因，但与任何基因或途径无关，但表现出任何证明在Neurodeserals中发挥作用的基因。现在，我们已经确定了果蝇中的天然，成年的神经退行性综合征突变体中直接与直接与包括阿尔茨海默氏病和ALS在内的人类疾病有关的基因的直系同源物。蛋白激酶CDK5及其调节亚基P35是磷酸化细胞骨架蛋白的主要激酶之一，以产生神经纤维纤维缠结，这些神经纤维缠结是“ Tauopathy”类神经变性疾病的特征。此外，发现活化的CDK5集中在阿尔茨海默氏症患者大脑中的退化组织中，CDK5的实验激活可诱导小鼠脑中的退化病变。我们已经产生了编码CDK5激活亚基的Fly同源物的基因的无效突变，p35。我们发现突变体是可行的和肥沃的，并且在出生时行为正常。但是，在几周内，它们显示出运动协调的逐渐丧失，最终导致刚性和死亡，其寿命明显缩短（比匹配的对照短30％）。截至衰老p35突变蝇的头部揭示了大脑中的退化性病变，最初是在神经胶体中，也是细胞体周围的。值得注意的是，这些病变是高度局部的，在特定的脑核中双侧存在，但通常不会通过脑部分布，即使p35和CDK5在整个大脑中都存在并活跃。因此，这些突变体不仅可以揭示导致与CDK5相关的神经变性的遗传途径，而且还可以理解整个大脑中发生的疾病过程以及为什么会导致特别特异性和特征性的结构和行为缺陷在特别是大脑区域。此外，在突变动物中，我们观察到轴突模式，突触形态和蛋白质定位的广泛缺陷，早在我们看到明显的退化之前，就会提高迟发性变性实际上可能反映了对有缺陷的神经系统在发育早期发育早期的延迟反应的可能性。