EphrinA reverse signalling in retinal axon guidance

在神经系统发育过程中，会产生大量被称为神经元的细胞，这些细胞通过被称为轴突的长电缆相互连接。这些轴突对大脑的功能非常重要。轴突通常很长，发育神经生物学的一个主要问题是这种轴突连接是如何实现的。原则上，它可以被描述为有一个路线图，由位于两个不同神经元之间的不同位置的许多不同的引导柱分子组成，告诉这些轴突走哪条路。许多这样的分子已经被识别出来，我们想知道它们是如何告诉轴突他们必须走哪条路才能找到他们的另一个神经元。它的工作原理可能是这样的：在轴突上有其他分子与引导柱分子结合，例如，对于名为Ephins的引导柱分子，轴突上有相应的被称为Ephs的反分子，它们只与Ephins相互作用，而不与例如与另一类引导柱分子‘netrins’相互作用。事实上，我们想要了解的分子就是这些Ephs和Ephin。轴突上的Eph分子与道路上的肾上腺素接触，导致轴突避开这一区域。象征性地，就路线图而言，这可能意味着汽车(电缆)将从错误的一侧接近单行道，然后掉头离开。这种行为被称为“排斥”。还有其他引导柱分子，如netrins，它们会引起相反的反应，即(在这张图片中)从正确的位置接近单行道，诱导一种“吸引力”，即汽车将驶入这条道路。对于这种由肾上腺素介导的排斥力，我们希望了解轴突/缆索的末端发生了什么，这被称为生长锥体，在显微镜下观察时，具有手形结构。在这个生长锥体内有一个管道和管道网络，这些管道不断被破坏和重建，其局部平衡决定了增长锥体迁移的方向。埃弗斯和伊弗林控制着管道和管道被摧毁和重建的位置和速度。然而，目前Ephs和Ephins之间的联系以及生长锥体内的管之间的联系并不清楚。在这种方法中，我们设计了一些实验来更好地理解这种联系(在我们的术语中是信令路径)。我们将使用视网膜中的轴突，它们通常会生长到大脑的顶盖部分。这些视网膜轴突具有很好的特征，一些测试可以用来分析Ephs和Ephins的功能。从其他引导柱系统中，有一些类型的链接已知，我们将调查这些链接是否对Ephs、eparin和这些视网膜轴突也很重要。我们想要研究的一点是一个令人惊讶的发现，引导柱分子，即Eparin，也可以表达在缆索/轴突上，并且Ephs可以被发现作为引导柱细胞。这个颠倒的表达模式的含义将是本应用程序的主要部分。

During development of the nervous system, large numbers of cells called neurons are generated, which are connected to each other by long cables called axons. These axons are very important for the function of the brain. The axons are often quite long, and a main question in developmental neurobiology is how this axon wiring is achieved. In principle, it can be described such that there is a road map consisting of a number of different guide post molecules positioned at different places between two different neurons which tell these axons which way to go. A number of these molecules have been identified and we would like to understand how they tell the axons which way they have to go to find their other neuron. It might work like this: on the axons there are other molecules which bind the guide post molecules, such that, for example, for guide post molecules named 'ephrins' there are corresponding counter-molecules called 'Ephs' on the axons, which interact only with 'ephrins', and not for example with 'netrins', which is another class of guide post molecules. In fact, the molecules which we would like to understand are these Ephs and ephrins. The contact of an eph molecule on axons with ephrins positioned on the road results in avoidance of this area by this axon. Symbolically, in terms of the road map, it might mean that the car (cable) would approach a one-way street from the wrong side and would turn away. This behaviour is called 'repulsion'. There are other guide post molecules such as netrins, which induce the opposite reaction that is (in this picture) approaching the one-way street from the correct site, inducing an 'attraction', that is the car would drive into this road. For the repulsion, mediated by ephrins, we would like to understand what happens at the very tip of the axon/cable, which is called a growth cone, and when viewed by under a microscope, has a hand-like structure. Inside this growth cone there is a network of tubes and pipes, which are constantly destroyed and re-built, the local balance of which determines the direction in which the growth cone migrates. The Ephs and ephrins control the location and the rate by which the tubes and pipes are destroyed and rebuilt. However, at present the link between the Ephs and ephrins on the one hand, and the tubes inside the growth cone is not clear. In this approach we have designed some experiments to understand this link (in our terms signalling pathways) better. We will use axons from the retina, which normally grow into a part of the brain called the tectum. These retinal axons are very good characterised and some tests are available to analyse the function of Ephs and ephrins. From other guide post systems there are some types of links known, and we will investigate whether these links are also important for Ephs, ephrins and these retinal axons. A point we would like to investigate is the surprising finding that the guide post molecules, the ephrins, can also be expressed on the cables/axons and the Ephs can be found as guide post cells. The meaning of this reversed expression pattern will be a major part of this application.