Regulation and Function of Arc in the Nucleus

学习和记忆的分子基础是神经元突触响应电活动的修饰，这一过程称为突触可塑性。记忆的形成有两个阶段。短期记忆是由改变突触功效的预先存在的蛋白质的修饰引起的，而长期记忆的形成需要新的基因转录来稳定这些变化。活性调节的细胞骨架蛋白Arc是唯一已知的长期记忆形成所需的蛋白质。在Arc敲除（KO）小鼠中，短期学习不受影响，但记忆的巩固和维持丧失。Arc也是唯一已知的活性诱导基因，其mRNA转录物被特异性转运到刺激位点。Arc然后在神经元树突中局部翻译并调节突触强度。这允许它以与其诱导刺激在时间和空间上相关的方式修改突触功能。 有趣的是，Arc蛋白在细胞核中也高度富集，并且活性导致细胞核内Arc蛋白的增加。在细胞核中，Arc与早幼粒细胞白血病肿瘤抑制蛋白核体（PML-NB）相关，后者通常调节转录。由于长期记忆的形成需要转录，并且在Arc KO小鼠中丢失，Arc可能有助于细胞核内的转录调控。这一发现，结合Arc在激活突触处的局部翻译，可能有助于解释一个具有数千个突触和只有一个核的神经元如何以突触特异性和依赖于核过程（如新基因表达）的方式存储信息。 该提议旨在确定活动诱导的Arc定位到细胞核是否作为一种机制来调节长期记忆形成中的新基因转录。拟议的实验将阐明Arc在细胞核中的调节和功能，目的是阐明巩固新记忆的分子基础。这项工作最终不仅对我们理解正常记忆存储背后的分子过程非常重要，而且还将揭示影响记忆形成和巩固的神经系统疾病中被破坏的过程。 具体目标1：确定核弧是否通过转录抑制调节总AMPAR水平。 具体目标2：确定Arc是否以活性依赖性方式增加PML-NB作为调节转录的手段。具体目标3：阐明Arc核输出的机制。

The molecular basis of learning and memory is the modification of neuronal synapses in response to electrical activity, a process termed synaptic plasticity. There are two phases of memory formation. Short-term memory results from modifications of preexisting proteins that change synaptic efficacy, while long-term memory formation requires new gene transcription to stabilize these changes. The activity-regulated cytoskeletal protein Arc is the only protein known to be specifically required for long-term memory formation. In Arc knock- out (KO) mice, short-term learning is not affected, but consolidation and maintenance of memory is lost. Arc is also the only known activity-induced gene for which the mRNA transcript is transported specifically to the site of stimulation. Arc is then locally translated in neuronal dendrites and regulates synaptic strength. This allows it to modify synaptic functions in a way that correlates both temporally and spatially with its inducing stimulus. Interestingly, Arc protein is also highly enriched in the nucleus and activity causes an increase in Arc protein within the nucleus. In the nucleus, Arc associates with promyelocytic leukemia tumor suppressor protein nuclear bodies (PML-NBs), which typically regulate transcription. As long-term memory formation requires transcription and is lost in Arc KO mice, Arc might contribute to transcriptional regulation within the nucleus. This finding, combined with the local translation of Arc at activated synapses, might help to explain how a neuron with thousands of synapses and only one nucleus stores information in a manner that is both synapse-specific and dependent on nuclear processes, such as new gene expression. This proposal aims to determine if the activity-induced Arc localization to the nucleus functions as a mechanism to regulate new gene transcription in long-term memory formation. The proposed experiments will clarify the regulation and function of Arc in the nucleus with the goal of elucidating the molecular basis for the consolidation of new memories. This work will ultimately be important not only in our understanding of the molecular processes behind normal memory storage but also will shed light on the processes that are disrupted in neurological disease that affect memory formation and consolidation. Specific Aim 1: To determine if nuclear Arc regulates total AMPAR levels through transcriptional repression. Specific Aim 2: To determine if Arc increases PML-NBs in an activity-dependent manner as a means of regulating transcription. Specific Aim 3: To elucidate the mechanism of Arc nuclear export.