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Organisation and Roles of Axonal Endoplasmic Reticulum

轴突内质网的组织和作用

基本信息

批准号：
BB/L021706/1
负责人：
Cahir O'Kane
金额：
$ 51.97万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2015
资助国家：
英国
起止时间：
2015 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=BB%2FL021706%2F1
关键词：
Organisation Roles Axonal Endoplasmic Reticulum

项目摘要

Animal and human movement depends on the ability of nerve cells to carry signals along narrow projections known as axons, which in humans can extend as much as a metre from the centre of the cell, the cell body - and even several metres in giraffes or whales. If the cell body has the size of a lecture theatre in Cambridge, the axon is like a corridor reaching out of it as far as Edinburgh or Paris, allowing transport of materials and communication. Maintaining the structure and function of long axons requires a lot of engineering. The importance of this is reflected in problems that occur when it goes wrong - diseases with effects such as axon degeneration, paralysis, or lack of sensation. Some of these preferentially affect long axons, or the ends of axons furthest from the cell body - suggesting impairment in communication or transport, that the parts of axons furthest from the cell body are most susceptible to. How does communication along axons maintain their form and function? Axons have many internal organelles that are bounded by membranes, whose transport and organisation contributes to the engineering and communication to maintain longer axons. Some of them are transported along tracks called microtubules, and carry materials and signals forward and back along axons. Another membrane-bound structure within axons are tubules known as smooth endoplasmic reticulum (ER), which run lengthwise along the axon. Due to their length and continuity, and the ensuing potential to conduct signals for long distances within neurons, they have been likened to a "neuron within a neuron". However, the mechanisms that form them, their function in axons, and the relationship between their form and function, are poorly understood. Mechanisms to maintain function and integrity of long axons can be revealed by indentifying the genetic causes of axon degeneration. In support of a role for ER in this, the disease Hereditary Spastic Paraplegia (HSP), characterised by degeneration of longer spinal motor axons, is often caused by mutations in proteins with roles in modeling ER membrane. These proteins insert in one face of the membrane, thus curving it, and some have additional roles such as fusing tubules into a network, or severing microtubules (tracks along which organelles are transported). In yeast, removing two groups of these proteins even deletes nearly all tubular ER. We aim to understand the mechanisms that govern the architecture of ER in axons, and the importance of this for axon function. We use the fruitfly Drosophila, given the ease of generating mutant and transgenic flies that lack particular proteins or express altered forms of them, and the availability of reagents and methods to study nerve cells, including axons. Some mutations in Drosophila HSP genes even have similar phenotypes to human HSP: larvae whose anterior (controlled by shorter axons) moves normally, but whose posterior (controlled by longer axons) cannot. We have also shown that a Drosophila HSP protein is important for shaping ER in non-neuronal cells, and for normal amounts of ER in longer axons - the first direct evidence that HSP genes affect ER in longer axons, and implying that axonal ER is important for axon survival. We will therefore examine the detailed organisation of tubular ER in axons, using high resolution electron microscopy. We will develop ways to visualise ER in live animals, in single axons, and in high resolution electron microscopy, and will use these to assess in detail the roles of a range of proteins on the presence, extent, morphology and network organisation of axonal ER. We will also assess how far axonal ER contributes to signaling in axons by release of an important signaling molecule, calcium ions, and how this signaling depends on ER form as determined by HSP and related proteins. In the longer term, our approach can illuminate roles of ER in axonal injury and long-range signaling in neurons.

动物和人类的运动依赖于神经细胞沿着被称为轴突的狭窄突起沿着传递信号的能力，在人类中，轴突可以从细胞中心（细胞体）延伸一米，在长颈鹿或鲸鱼中甚至延伸数米。如果细胞体有剑桥的演讲厅那么大，轴突就像一条走廊，从它延伸到爱丁堡或巴黎，允许物质的运输和交流。维持长轴突的结构和功能需要大量的工程。这一点的重要性反映在当它出错时发生的问题上--具有轴突变性、瘫痪或感觉缺失等影响的疾病。其中一些优先影响长轴突，或距离细胞体最远的轴突末端-表明通讯或运输受损，距离细胞体最远的轴突部分最容易受到影响。沿着轴突的通讯是如何保持它们的形式和功能的？轴突有许多内部细胞器，这些细胞器由膜限制，其运输和组织有助于工程和通信，以维持较长的轴突。它们中的一些是沿着被称为微管的轨道运输的，并沿着沿着轴突向前和向回携带物质和信号。轴突内的另一种膜结合结构是被称为平滑内质网（ER）的小管，其沿轴突纵向沿着延伸。由于它们的长度和连续性，以及随之而来的在神经元内长距离传导信号的潜力，它们被比作“神经元中的神经元”。然而，形成它们的机制，它们在轴突中的功能，以及它们的形式和功能之间的关系，知之甚少。通过确定轴突变性的遗传原因，可以揭示维持长轴突功能和完整性的机制。为了支持ER在其中的作用，遗传性痉挛性截瘫（HSP）疾病的特征是较长的脊髓运动轴突变性，通常是由蛋白质突变引起的，蛋白质在ER膜建模中起作用。这些蛋白质插入膜的一面，从而使其弯曲，并且一些具有额外的作用，例如将小管融合成网络，或切断微管（细胞器被运输的沿着的轨道）。在酵母中，去除两组这些蛋白质甚至删除几乎所有的管状ER。我们的目标是了解的机制，支配结构的ER在轴突，这对轴突功能的重要性。我们使用果蝇，因为很容易产生缺乏特定蛋白质或表达改变形式的突变和转基因果蝇，以及研究神经细胞（包括轴突）的试剂和方法的可用性。果蝇HSP基因中的一些突变甚至与人类HSP具有相似的表型：幼虫的前部（由较短的轴突控制）正常移动，但其后部（由较长的轴突控制）不能。我们还表明，果蝇HSP蛋白是重要的塑造ER在非神经元细胞，并为正常量的ER在较长的轴突-第一个直接证据表明，HSP基因影响ER在较长的轴突，并暗示轴突的ER是重要的轴突生存。因此，我们将使用高分辨率电子显微镜检查轴突中管状ER的详细组织。我们将开发方法来可视化ER在活的动物，在单一的轴突，并在高分辨率电子显微镜，并将使用这些详细评估的存在，程度，形态和轴突ER的网络组织的一系列蛋白质的作用。我们还将评估轴突ER通过释放一种重要的信号分子钙离子对轴突信号传导的贡献程度，以及这种信号传导如何取决于HSP和相关蛋白所确定的ER形式。从长远来看，我们的方法可以阐明ER在轴突损伤和神经元长距离信号传导中的作用。