How do neurons recognize self from non-self?

项目摘要 本文旨在了解神经元的一个基本特性：它们的自我识别和自我调节能力。 避免。自我回避是神经元功能的一个重要方面，因为它确保来自同一个神经元的分支 细胞最小化它们的重叠，同时最大化它们与来自其他细胞的分支的交互。在哺乳动物中， 该过程的核心是产生足够的原钙粘蛋白（Pcdh）蛋白同种型多样性， 基本上，大脑中的每个神经元在其表面都有不同的条形码， 其他神经元Pcdh蛋白异构体多样性的产生需要复杂的Pcdh机制 转录和前体mRNA剪接，使得不同的Pcdh mRNA分子-携带不同的5'末端 （可变外显子）但相同的3'端（恒定外显子）-在个体细胞中表达。了解如何 不同的Pcdh mRNA分子的产生代表了神经科学领域的一个长期的谜团。 揭开这个基本的谜团是阐明神经元自我回避过程的关键， 代表了剖析这种Pcdh调节异常如何介导自我回避的第一个重要步骤 可能导致严重的神经系统疾病，例如自闭症谱系障碍和精神分裂症。 然而，尽管它们在大脑中发挥着重要作用，但在了解它们如何发挥作用方面取得的进展有限。 Pcdh mRNA被转录并适当剪接，作为基因表达调控的一般模型， 未能概括这一复杂的机制，并且由于直接在体内研究它所需的工具已经落后， 后面在这个提议中，我们的目标是（i）测试Pcdh RNA转录的范式转换假设， 基于可变和恒定外显子的可变反式剪接的剪接， DNA链--我们认为这一机制受Pcdh基因座的3D基因组拓扑结构的调控-- 和（ii）设计技术创新，允许在体内精确操作Pcdh基因簇 直接在神经元中验证我们的假设。这些研究有可能阐明复杂的 Pcdh异构体多样性产生的机制及其在神经元自我回避和神经元连接中的作用 健康和疾病的大脑。这些研究的结果也有望开辟一个新的类别， RNA加工反应的调节机制，以前未观察到， 哺乳动物，但我们推测是由细胞利用，以克服具有挑战性的问题，前mRNA剪接 与复杂的基因结构有关。

PROJECT SUMMARY This essay aims to understand a fundamental property of neurons: their ability to self-recognize and self- avoid. Self-avoidance is an essential aspect of a neuron's function as it ensures that branches from the same cell minimize their overlap while maximizing their interactions with branches from other cells. In mammals, at the core of this process is the generation of sufficient Protocadherin (Pcdh) protein isoform diversity such that essentially every neuron in the brain is differentially barcoded at its surface and therefore appears different to other neurons. The generation of Pcdh protein isoform diversity requires complex mechanisms of Pcdh transcriptional and pre-mRNA splicing such that distinct Pcdh mRNA molecules - bearing a different 5' end (variable exon) but an identical 3' end (constant exons) - are expressed in individual cells. Understanding how different Pcdh mRNA molecules are produced represents a long-term mystery in the field of neuroscience. Answering this fundamental mystery is key in illuminating the process of neuronal self-avoidance and represents the first essential step toward dissecting how dysregulation of this Pcdh mediated self-avoidance can lead to severe neurological disorders, such as for instance autism spectrum disorder and schizophrenia. Despite their critical function in the brain, however, limited progress has been made in understanding how Pcdh mRNAs are transcribed and properly spliced as general models of gene expression regulation have failed to recapitulate this complex mechanism and as the tools required to study it directly in vivo have lagged behind. In this proposal, we aim to (i) test a paradigm-shifting hypothesis of Pcdh RNA transcription and splicing based on alternative trans-splicing of variable and constant exons encoded in tandem on the same DNA strand - a mechanism that we propose to be regulated by the 3D genome topology of the Pcdh locus - and (ii) design technological innovations that will allow precise manipulation of the Pcdh gene cluster in vivo to test our hypothesis directly in neurons. These studies have the potential to illuminate the complex mechanism of the generation of Pcdh isoform diversity and its role in neuronal self-avoidance and wiring of healthy and disease brains. The findings from these studies are also poised to open up a new class of regulatory mechanisms of RNA processing reactions, previously unobserved and uncharacterized in mammals but that we speculate are utilized by cells to overcome challenging problems of pre-mRNA splicing associated with complex gene architectures.