The role of spectraplakins as key integrators of axonal microtubule networks

神经元向其他神经元、肌肉或腺体延伸长突起（轴突）的能力是构成我们大脑和协调我们行为的神经元网络形成的关键过程。例如，轴突生长的失败通常是致命的或在脊髓损伤时引起瘫痪。为了找到治疗方法，我们必须彻底了解轴突生长的机制。生长的轴突遵循可重复的路径，这些路径由指导轴突生长的化学线索指示。轴突的伸长基本上是由细胞的丝状骨架元件驱动的，称为肌动蛋白和微管。肌动蛋白和微管必须密切合作，它们的活动必须适应通过指导化学线索的指令。解开这些不同的因素（肌动蛋白，微管和信号）如何整合和相互协调轴突生长过程中是需要解决的关键任务。为此，我们把我们的工作集中在假定的积分分子，称为spectraplakins。它们可以将微管与肌动蛋白和信号成分物理连接起来，如果没有它们，轴突生长就会受到严重抑制。然而，spectraplakins与肌动蛋白、微管和信号传导成分的联系如何帮助它们执行其生长促进功能仍有待解决。为了促进这项任务，我们研究的spectraplakin短暂停止（射击）的果蝇，这是一个最有帮助的模型。因此，可以用果蝇中可用的强大而快速的策略来研究Shot;所获得的数据是相关的，并且可以转化为生物医学研究，因为Shot的特征和功能与哺乳动物或人类spectraplakins的特征和功能几乎相同。作为我们项目的起点，我们已经确定了Shot分子的三个区域/结构域，它们可以将Shot与微管、肌动蛋白以及最有可能的信号传导因子联系起来。我们已经证明，所有这些都是轴突生长中Shot功能所必需的。在这里，我们将解决他们的功能的细节，使用先进的显微镜，结构-功能研究，和最先进的技术（质谱），以确定尚未未知的结合因子。作为一个重要的进一步战略，我们将系统地利用组合遗传学。我们将把Shot的联合收割机突变与其他已知有助于轴突生长的基因突变结合起来。组合的突变缺陷将提供Shot与其他因素的功能关系的基本见解，从而将Shot功能映射到轴突生长的系统背景中。我们的研究结果将为spectraplakins在健康和疾病中的功能以及轴突生长的调控网络提供重要的新见解。

The ability of neurons to extend long processes (axons) towards other neurons, muscles or glands, is a key process underlying the formation of the neuronal networks that make up our brain and coordinate our behaviour. For example, failure of axonal growth is often fatal or causes paralysis upon spinal injury. To find cures we have to acquire a thorough understanding of the mechanisms underlying axonal growth. Growing axons follow reproducible paths signposted by chemical cues that direct the growing axon. Axonal elongation is essentially driven by filamentous skeletal elements of cells, called actin and microtubules. Actin and microtubules have to cooperate closely, and their activity must be adaptable to instructions through the guiding chemical cues. Unravelling how these different factors (actin, microtubules and signals) integrate and cross-coordinate each other during axonal growth is the key task that needs to be addressed. To this end, we focus our work on putative integrator molecules, called spectraplakins. They can physically link microtubules to actin and signalling components and, in their absence, axonal growth is severely inhibited. However, how the links of spectraplakins to actin, microtubules, and signalling components help them to perform their growth promoting function remains to be resolved. To facilitate this task, we study the spectraplakin Short stop (Shot) of fruitflies, which represents a most helpful model. Thus, Shot can be studied with powerful and rapid strategies available in fruitflies; the data obtained are relevant and can be translated into biomedical research, since the characteristics and functions of Shot are virtually identical to those of mammalian or human spectraplakins. As the starting point of our project, we have identified three regions/domains of the Shot molecule that can link Shot to microtubules, actin and, most likely, signalling factors. We have shown that all of them are absolutely required for Shot function in axonal growth. Here we will address the detail of their function, using advanced microscopy, structure-function studies, and state-of-the art technology (mass spectrometry) to identify yet unknown binding factors. As an essential further strategy we will make systematic use of combinatorial genetics. We will combine mutations of Shot with mutations in other genes known to contribute to axonal growth. The combined mutant defects will give essential insights into the functional relationships of Shot to other factors, thus mapping Shot function into the systemic context of axonal growth. Our results will provide essential new insights into the function of spectraplakins in health and disease and the regulatory networks underlying axonal growth.