The role of Fat3 in amacrine cell dendrite development.

描述（由申请人提供）：大脑功能取决于通过轴突和树突之间精确有线连接的信息流。回路中的神经元树突的数量和排列可以有很大的不同，有些神经元只延伸一个初级树突进入一个明确的神经元，而另一些神经元则发展出多个树突，对称地延伸到细胞体周围。然而，与揭示轴突规范和指导机制的出色进展相反，对树突的初始规范和生长知之甚少。体外研究表明，神经元最初延伸多能神经突，其中一个成为轴突，剩下的分化为树突。这些结果表明，树突分化的许多方面是内在调节的。然而，在体内，树突发育还必须与周围组织协调，使得树突被适当地定位以形成适当的突触连接。细胞外信号如何诱导胞内重排，驱动树突的初始规格和随后的形态发生是未知的。在过去，由于缺乏合适的检测方法和没有任何明显的分子参与者，这个问题一直难以解决。我们一直致力于解决这些问题，建立一个系统，研究树突发育的无长突细胞的视网膜。无长突细胞通常是单极的，将单个顶端树突延伸到称为内丛状层（IPL）的离散突触层。然而，在缺乏非典型钙粘蛋白Fat 3的小鼠中，无长突细胞发育出第二个树突状细胞，其指向远离IPL。由于脂肪3是一种细胞表面受体，这些结果表明，脂肪3的行为诱导迁移前体回缩其拖尾过程中遇到的IPL的信号响应。Fat3信号最终如何促进顶端树突的发育是一个谜，没有已知的效应子或配体。为了建立更详细分析枝晶发育的知识基线，将进行两项探索性研究。首先，我们将开发一种实时成像分析，可用于描述神经突行为和高尔基体定位的动态变化，发生的主导过程成为树突和拖尾过程被收回。其次，为了在树突内部工作，我们将通过测试可能的候选蛋白质和对与Fat3细胞内结构域相互作用的蛋白质进行无偏筛选来寻找Fat3的下游效应子。总之，这些研究将定义树突规格的显着事件，并阐明发生在下游的脂肪3的信号事件。 公共卫生相关性：我们的视觉是由视网膜中精确组织的回路调节的，视网膜是位于眼睛后部的感觉组织。数以百万计的美国人是盲人，无法参与日常活动，如阅读和驾驶。了解视觉回路在发育过程中是如何连接的，将有助于确定失明的原因，并最终设计出恢复视力的神经假体。

DESCRIPTION (provided by applicant): Brain function depends on the flow of information through precisely wired connections between axons and dendrites. Neurons within a circuit can vary widely in the number and arrangement of their dendrites, with some neurons extending only one primary dendrite into a well-defined neuropil and others developing multiple dendrites that extend symmetrically about the cell body. However, in contrast to excellent progress in uncovering mechanisms of axon specification and guidance, relatively little is known about the initial specification and outgrowth of dendrites. In vitro studies suggest that neurons initially extend multipotent neurites, one of which becomes an axon, leaving the remainder to differentiate as dendrites. These results suggest that many aspects of dendrite differentiation are intrinsically regulated. However, in vivo, dendrite development must also be coordinated with the surrounding tissue, such that dendrites are properly positioned to form the appropriate synaptic connections. How extracellular signals induce the intracellular rearrangements that drive the initial specification and subsequent morphogenesis of dendrites is unknown. In the past, this issue has been hard to tackle due to the lack of a suitable assay and the absence of any obvious molecular players. We have been addressing these problems by establishing a system for studying dendrite development in the amacrine cells of the retina. Amacrine cells are typically unipolar, extending a single apical dendrite into a discrete synaptic layer called the inner plexiform layer (IPL). However, in mice lacking the atypical cadherin Fat3, amacrine cells develop a second dendritic arbor that points away from the IPL. Since Fat3 is a cell surface receptor, these results suggest that Fat3 acts by inducing migrating precursors to retract their trailing processes in response to a signal encountered in the IPL. How Fat3 signaling ultimately promotes development of the apical dendrite is a mystery, with no known effectors or ligands. To establish a baseline of knowledge for more detailed analysis of dendrite development, two exploratory studies will be performed. First, we will develop a live imaging assay that can be used to describe the dynamic changes in neurite behavior and Golgi localization that occur as the leading process becomes a dendrite and the trailing process is retracted. Second, to work our way inside the dendrite, we will search for downstream effectors for Fat3, both by testing likely candidate proteins and by performing an unbiased screen for proteins that interact with the Fat3 intracellular domain. Together, these studies will define the salient events of dendrite specification and elucidate the signaling events that occur downstream of Fat3. PUBLIC HEALTH RELEVANCE: Our sense of vision is mediated by precisely organized circuits in the retina, a sensory tissue located at the back of the eye. Millions of Americans are blind and unable to participate in daily activities such as reading and driving. Understanding how visual circuits are wired during development will improve efforts to identify the causes of blindness and eventually design neural prostheses for the restoration of sight.