Relating structure to function: Development of dendritic arborisations underlying orientation selectivity in the vertebrate visual system

神经系统中的结构和功能是密切相关的，但结构和功能关系是如何发展的还不清楚。细胞结构多样性明显的一个例子是脊椎动物的视网膜。它由70多种不同类型的神经元组成，这些神经元具有将光信息转换为电化学信号并将其发送到大脑的功能。有趣的是，视觉信息已经在视网膜中进行了预处理，并被分成不同的通道，如运动、颜色或边缘。这是通过在不同的视网膜细胞之间形成不同的网络来完成的，例如无长突细胞和视网膜神经节细胞。无长突细胞是视网膜中最多样(也是研究最少)的一类神经元，具有许多不同的形状。虽然在揭示影响神经元形状、复杂性和连通性的因素方面取得了一些进展，但我们对确切机制的了解有限，许多过程仍然不清楚。这个项目将使用视网膜中两种特定类型的无长突细胞--我们之前发现的--它们在形态和功能之间具有惊人的对应关系，作为研究大脑中这种神经元结构-功能关系是如何产生的模型。这些细胞形成许多突起或树枝(称为树突)，呈细长结构，类似于椭圆形区域。我们发现，这些椭圆在眼睛内呈放射状排列，即沿着从视网膜中央到外部的轴线排列。我们的结果表明，这些细胞对定向视觉刺激的检测至关重要，而定向视觉刺激是视觉信息中的一个关键元素。然而，目前尚不清楚a)形成这些椭圆形细胞结构的发育步骤是什么，b)是什么影响了这种细胞形状的产生，以及c)这种形状与它们在视网膜中的连接细胞有什么关系。利用斑马鱼模型系统，我们将跟踪这些特定的无长突细胞的结构发展，并确定每个步骤，直到它们功能成熟。为了做到这一点，我们将使用我们实验室现有的遗传工具来专门标记这些细胞，并在显微镜下对它们在活动物身上进行成像。在第二组实验中，我们将研究不同的参数如何影响我们的无长突细胞的发育。为此，我们将改变这些神经元的活动(例如，将鱼保持在黑暗中以消除视觉输入)，改变其中某些基因的表达或改变视网膜的细胞组成，然后像以前一样跟踪结构的发展。这将回答一些关于控制细胞结构的机制的重要问题。最后，为了识别哪些其他细胞连接到这些特定的无长突细胞并绘制它们的接触点(突触)，我们将使用一种基于电子显微镜的最先进技术来创建视网膜细胞结构的非常详细的3D模型。这将使我们能够确定特定的无长突细胞结构是如何相对于其他细胞的结构安排的，从而确定它们特定功能的潜在机制。我们的工作将是朝着更好地理解神经系统中结构-功能关系如何发展的重要一步。

Structure and function in the nervous system are closely related, but it is not clear how structure-function relationships develop. One example where the structural diversity of cells is clearly evident is the vertebrate retina. It consists of over 70 different types of neurons with the function to transform light information into electrochemical signals and send them to the brain. Interestingly, visual information is pre-processed already in the retina and split into different channels, such as motion, colour or edges. This is done through the formation of distinct networks between different retinal cells, for example amacrine cells and retinal ganglion cells. Amacrine cells are the most diverse (and least studied) class of neurons in the retina, with many distinct shapes. Although some progress has been made in uncovering factors that influence shape, complexity and connectivity of neurons, our knowledge about the exact mechanisms is limited and many processes are still unclear. This project will use two specific types of amacrine cells in the retina -previously identified by us- that have a striking correspondence between morphology and function as a model to study how such neuronal structure-function relationships in the brain are generated. These cells form many processes or arbours (called dendrites) that are in the shape of elongated structures, similar to elliptic areas. We found that these ellipses are arranged radially in the eye, meaning along the axis from the middle of the retina to the outside. Our results demonstrated that these cells are crucial for detection of oriented visual stimuli, a key element in visual information. However, it is not clear a) what are the developmental steps to form these elliptic cellular structures, b) what influences the generation of this cellular shape and c) how this shape is related to their connected cells in the retina. Using the zebrafish model system, we will follow the structural development of these specific amacrine cells and identify the individual steps until they are functionally mature. To do so, we will use genetic tools already available in our laboratory to label these cells specifically and image them in live animals under the microscope. In a second set of experiments, we will investigate how different parameters will influence the development of our amacrine cells. For this we will alter activity in these neurons (for example keep the fish in the dark to abolish visual input), change the expression of certain genes in them or alter the cellular composition of the retina and then follow the structural development as before. This will answer some important questions about the mechanisms to control cellular structure. Finally, to identify which other cells connect to these specific amacrine cells and map their points of contact (synapses), we will use a state-of-the-art technology based on electron microscopy to create very detailed 3D models of the cellular structures in the retina. This will allow us to identify how the particular amacrine structure is arranged in relation to the structure of other cells and thus the underlying mechanisms for their specific function. Our work will be an important step forward towards better understanding how structure-function relationships develop in the nervous system.