Uncovering the role of the ESCRT machinery in neuron pruning

就像电脑或任何其他复杂的电子设备一样，我们的大脑需要精确地“连接在一起”才能正常工作。目前的想法表明，神经线路的中断可能是许多精神疾病的基础，因此了解神经系统中的线路是如何出错的，对于帮助治疗这类疾病非常重要。因此，这项工作可能会对医疗保健部门做出贡献，从而对我们的社会做出贡献。随着神经系统的形成，神经细胞开始相互连接，就像电子设备的电线一样。当神经细胞生长时，它们以一种旺盛的方式生长，经常产生许多延伸分支。其中一些分支进入了错误的领域，或者是多余的，需要删除。我们称之为“修剪”。修剪多余或多余的树枝对调节神经系统很重要，这样它就能精确地工作。在许多情况下，修剪是通过切断树枝来进行的，因此有了“修剪”这个词。尽管我们对神经系统是如何发育的了解很多，但我们对树枝是如何被物理切断的理解仍然是一个谜。我们一直在用果蝇来尝试回答这个问题。我们使用苍蝇是因为它们与人类共享大部分基因，所以我们在苍蝇身上学到的东西可以很容易地转化为人类。与此同时，果蝇的神经系统相对简单，比老鼠更复杂的神经系统更容易接近和研究。苍蝇是应用遗传学来研究它们的生物学的完美选择。例如，果蝇生长迅速，因此可以进行基因筛选；ie。破坏基因，这是揭示事物如何运作的有力途径。在这个项目中，我们关注的是神经系统的修剪。在这里，苍蝇提供了一个很好的机会，因为当蛆变成苍蝇时，它的许多神经细胞在变态过程中被循环利用。修剪对回收过程很重要。我们通过使用水母的荧光“发光”基因来研究神经细胞是如何被修剪的，这使我们能够看到活体动物体内的神经细胞。利用这些发光的神经细胞和果蝇遗传学，我们发现一种叫做运输所需的内体分选复合物（ESCRT）的蛋白质家族对修剪很重要。这些ESCRT蛋白聚集在一起形成了一个切割细胞膜的机器。因为细胞实际上是一个包含不同成分的大膜系统，这组蛋白质很重要，在细胞的不同部位用于许多不同的过程，例如，当细胞分裂成两半时也使用它们。为了安排这些蛋白质完成每一项特定的任务，它们有非常特殊的适配器来指导它们在正确的时间在正确的地方工作。我们认为，类似于细胞分裂时发生的切割，也发生在神经细胞分支修剪的过程中。我们是第一个有证据表明ESCRT机制参与切断神经细胞分支的人。因为这一观察结果为我们提供了关于神经系统中调节修剪的基因和机制的新线索，这是一个非常重要的观察结果。我们现在要证实这些观察结果并加以扩展。我们想知道哪些ESCRT家族成员对修剪很重要，哪些不重要；这些机器是如何组装的，它们是否在分支切割的地方实际上是直接需要的，切割过程是如何由适配器控制的。我们希望我们的工作能够解开这个谜团的一部分，并且在未来，我们的工作能够帮助我们理解当人类神经系统紊乱时，当线路出现问题时会发生什么，进而开发出什么样的治疗方法来纠正这些缺陷或减轻它们对心理健康和福祉的影响。

Like a computer or any other complex electronic device our brain needs to be accurately 'wired together' to function properly. Current thinking suggests that disruptions in wiring may underlie a number of psychiatric disorders, so to understand how wiring in the nervous system goes wrong is very important for aiding therapeutic approaches for such disorders. As such this work is likely to contribute to the healthcare sector and thus to our society. As the nervous system forms, nerve cells grow to make connections with one another and as such are like the wires of an electrical device. When nerve cells grow, they do so in an exuberant manner, often generating many extension branches. Some of these branches enter the wrong territory or are redundant and need to be removed. We call this removal of branches 'pruning'. Pruning of excess or redundant branches is important for adjusting the nervous system so that it can work with precision. In many cases pruning happens by branches being cut off, hence the term 'pruning'. Although we know a great deal about how the nervous system develops, our understanding of how branches are physically cut away remains a mystery. We have been using the fruitfly Drosophila to try and answer this question. We use flies because they share most of their genes with humans, so what we learn in the fly can be easily translated to humans. At the same time, fruitflies have a relatively simple nervous system that is more accessible and easier to study than more complex nervous systems as found in mouse. Flies are perfect for applying genetics to investigate their biology. For example, fruitflies grow quickly so one can do genetic screens; ie. breaking genes, which is a powerful way uncovering how things work. In this project we are focusing on pruning in the nervous system. Here, the fly provides a great opportunity, as many of its nerve cells are recycled during metamorphosis, when a maggot turns into a fly. Pruning is important for the recycling process. We study how nerve cells undergo pruning by using fluorescent 'glowing' genes from a jellyfish, which allows us to see nerve cells inside the living animal. Using these glowing nerve cells and fly genetics we found that a family of proteins called the Endosomal Sorting Complexes Required for Transport (ESCRT) are important for pruning. These ESCRT proteins assemble and together form a machine that cuts cell membranes. Because cells are really a large system of membranes containing different components, this group of proteins is important and used for many different processes in different parts of cells e.g. they are also used when cells divide in two. To schedule these proteins for each specific task, they have very specific adaptors that direct them to work in the right place at the right time. We think that something like the cutting that occurs when a cell divides is also happening during nerve cell branch pruning. We are the first people to have any evidence to suggest that the ESCRT machinery is involved in cutting nerve cell branches. Because this observation gives us a new clue as to the genes and mechanisms that regulate pruning in the nervous system, this is a very important observation. We would now like to confirm these observations and extend them. We want to know which of the ESCRT family members are important for pruning and which are not; how these machines assemble, whether they are actually needed directly at the place where the branch is cut and how the cutting process is controlled by the adaptors. We hope our work will resolve part of this mystery and that in future the new insights that our work can help up understand what happens when wiring goes wrong in human disorders of the nervous system, and, by extension what therapeutic approaches could be developed to correct such defects or lessen their impact on mental health and well being.