Structural and functional analysis of zebrafish visual circuits specified by teneurin-3

大脑是通过在发育过程中形成的连接来构建的。这些连接必须非常精确，才能让大脑完成对我们的行为至关重要的功能。此外，它们还必须具有特异性，以便具有特定功能的神经细胞能够相互交流。因此，毫不奇怪，神经科学的主要挑战之一是理解导致这种特异性的机制：一个细胞如何识别其合适的伙伴并与之形成联系？当这些连接没有正确形成时会发生什么？近年来，一些主要在细胞培养实验中进行的研究已经发现了一些位于细胞表面的分子，这些分子在细胞识别过程中起作用。然而，这张蛋白质列表还远远不能完全解释大脑中发现的连接的多样性。此外，迫切需要的是一个强大的系统，在这个系统中，这些连接的形成和功能可以在生物体中进行研究。我们在这个提案中描述的模型，斑马鱼的视觉系统，满足了这一要求，非常适合此类研究。视觉系统中的不同神经元负责将视觉信息的各个方面传递给大脑，例如颜色、光线强度或运动方向。功能相关的神经元在眼睛和大脑的特定位置相互连接。在之前发表的一项研究中，我们发现，在眼睛和大脑中发现的神经元表面的一种特定蛋白质的缺失会导致细胞连接和涉及运动的特定视觉功能的缺陷。这表明1)这种蛋白质对于某些神经元和2)这些细胞之间的适当连接很重要，它们的连接负责传递特定的视觉信息。然而，要完全理解这一过程还有很多未知之处。例如：候选蛋白质存在于哪些神经元中，它们的功能是什么？在发育过程中，这些细胞是如何形成彼此之间的联系的？是否所有含有这种蛋白质的细胞都相互连接并传递相同的功能属性，或者它们是不同的？其他相关的蛋白质有类似的功能吗？通过这个项目，我们将在一个明确的工作计划中解决这些问题。我们的实验是基于我们以前成功应用过的技术。在第一步，我们将使用遗传方法标记所有对我们的基因呈阳性的细胞，这样我们就可以分析这些细胞的样子以及它们与其他细胞的连接。然后我们将描述这些细胞的功能特性。我们之前的数据表明，这种视觉功能与眼睛看到的物体的特定运动有关，但我们也有可能发现其他功能。我们将分析当我们删除基因时，神经连接会发生什么变化。重要的是，我们已经在本应用程序中提出的初步工作中生成了这些实验所需的遗传工具。一旦我们发现了这些含有我们蛋白质的细胞的功能，我们将确定信息发送和信息接收神经元是否都需要它的存在。这将对这些蛋白质的作用机制提供重要的见解。最后，我们将评估与我们的候选蛋白相关的其他蛋白质是否在指定连接和功能相关的神经元中发挥类似的功能。我们在这个项目中描述的工作影响了对大脑中建立连接的一般理解。这些知识不仅对我们理解大脑发育很重要，而且因为它可以帮助我们制定脑损伤后功能恢复的策略，因为创伤或疾病。

The brain is built through connections that are formed during development. These connections have to be very precise in order to allow the brain to fulfil the functions important for our behaviour. Moreover, they also have to be specific so that nerve cells for particular functions are able to communicate with each other. It is therefore not surprising that one of the major challenges in Neuroscience is to understand the mechanisms that lead to such specificity: How does one cell recognise its appropriate partner and form a connection with it? What happens when these connections are not formed correctly? In recent years, several studies, mostly done in cell culture experiments, have identified a number of molecules localised on the surface of cells that play a role in this cell recognition process. However, this list of proteins is far from complete to fully explain the diversity of connections found in the brain. Moreover, what is urgently needed is a robust system where the formation and function of such connections can be studied in the living organism. Our model described in this proposal, the visual system in zebrafish, fulfils this requirement and is excellently suited for such studies. Different neurons in the visual system are responsible to transmit various aspects of visual information to the brain, for example colour, light intensity, or the direction of a movement. Functionally related neurons connect to each other at specific places in the eye and the brain. In a previous published study, we have found that the deletion of a particular protein at the surface of neurons found in the eye and the brain leads to defects in both, cell connectivity and a specific visual function involving motion. This suggests that 1) this protein is important for the appropriate connectivity between certain neurons and 2) these cells and their connections are responsible for transmitting a specific visual information. However, there are still a lot of unknowns to fully understand this process. For example: In which neurons is the candidate protein present and what is their function? How do these cells form the connections with each other during development? Are all cells containing this protein connected to each other and transmit the same functional property or are they diverse? Do other, related proteins have a similar function? With this project we will address these questions in a clear and defined work plan. Our experiments are based on techniques that we have successfully applied before. In a first step, we will use genetic methods to label all the cells, which are positive for our gene, so that we can analyse how these cells look like and with which other cells they connect. We will then characterise the functional properties of these cells. Our previous data suggests that this visual function has to do with a specific motion of objects that are seen by the eye, but it is possible that we will uncover additional functions as well. We will analyse what happens to nerve connections when we delete the gene. Importantly, we already have generated the genetic tools needed for these experiments in our preliminary work presented in this application. Once we have uncovered the function of these cells containing our protein, we will determine if its presence is needed on both, the information-sending and information-receiving neuron. This will give important insights on the mechanism of action for these proteins. Finally, we will assess if other proteins that are related to our candidate fulfil similar functions in specifying connections and for functionally related neurons. Our work described in this project impacts on the general understanding of building connections in the brain. Such knowledge is important not only for our comprehension on brain development, but also because it can help us to develop strategies for a functional recovery after brain damage through trauma or disease.