シンポジウム（Symposium）

Symposium New trends in study on plasticity-related gene Arc/arg3.1: regulations and cognitive functions シンポジウム可塑性関連因子Arc研究の新展開:分子制御機構と認知機能への関与協賛：新学術領域「脳情報動態」

7月25日（木）16:52～17:16　第7会場（朱鷺メッセ　2F　201B） 1S07e-1 活動依存的Arc発現によるAMPA型グルタミン酸受容体動態制御 Haruhiko Bito（尾藤晴彦）^1,2，Yuichiro Ishii（石井雄一郎）¹，Hajime Fujii（藤井哉）¹，Takashi Hayashi（林崇）^1,3，Michiko Okamura（岡村理子）¹，Yayoi Kondo（近藤弥生）¹，Manabu Abe（阿部学）⁴，Kenji Sakimura（崎村建司）⁴，Hiroyuki Okuno（奧野浩行）⁵ ¹東京大院医神経生化 ²東大IRCN ³国立精神・神経セ神経研 ⁴新潟大脳研 ⁵鹿児島大院医歯・生化分子生物 Deciphering the intricate and interactive relationship between the information encoded in the genome and the ongoing synaptic activity is critical for understanding the molecular and cellular signaling underlying long-term memory formation and maintenance. To systematically dissect this question, we have investigated the molecular basis of the signaling from synapses to the nucleus and from the nucleus to the synapses, which crucially determines the persistence of synaptic plasticity. Activity-induced Arc/Arg3.1 expression has been proposed to regulate surface expression of AMPA receptors (AMPA-Rs), although the mechanisms involved remain unclear. We previously found an inverse synaptic tagging rule by which Arc preferentially targeted weaker, rather than stronger, synapses. Whether this critically affected the temporal dynamics of spine AMPA-R turnover, however, remained unexplored. To address this issue, we analyzed subunit-specific AMPA-R lateral diffusion during structural plasticity in wildtype and Arc-knockout hippocampal neurons. Long-term potentiation (LTP) of surface GluA1/GluA2 in expanded spines was normal both in wildtype and Arc-KO neurons. However, removal of surface GluA1/GluA2 from non-expanded spines was slow but significant in wildtype neurons, during the late phase of plasticity. This late-phase heterosynaptic depression was disrupted in Arc-KO neurons, consistent with inverse synaptic tagging. Additionally, we found another GluA subunit-specific effect of Arc during LTP. Thus, activity-dependent Arc expression may regulate dynamics of distinct AMPA-R complexes during multiple phases of LTP in an input-regulated manner.		7月25日（木）17:16～17:40　第7会場（朱鷺メッセ　2F　201B） 1S07e-2 Arc protein structure and oligomerization control: from synaptic plasticity to retroviral-like capsids Clive Bramham（Bramham Clive） University of Bergen The extraordinary plasticity of the brain enables memory formation and shapes human behavior and cognition.The immediate early gene, Arc, has emerged as a pivotal regulator of long-term synaptic plasticity, memory formation and cognitive flexibility. Research in my lab aims to resolve the molecular basis of synaptic plasticity. This is crucial for elucidating how control systems at the subcellular level impact functional properties of neuronal networks, as well as high-order brain function and dysfunction. Arc protein is expressed in a neuronal activity-dependent manner. But what is Arc protein, how does it work, and how is its function regulated? Recent work has provided surprising insights into the structural and biochemical properties of the Arc protein. Inside the neuron, Arc appears to function as a protein interaction hub, capable of binding to a variety of effector proteins in neuronal subcompartments (dendrites, nucleus). In this scenario, Arc dynamically controls signaling pathways underlying the major forms of synaptic plasticity: long-term potentiation (LTP), long-term depression (LTD), and homeostatic synaptic scaling. In radical contrast, Arc protein can also self-assemble into large retrovirus-like capsids that are released in extracellular vesicles and capable of intercellular transfer of RNA. Thus, Arc appears to have radically different functional states as: 1) hub protein and 2) retroviral-like capsid. Resolving this dichotomy is of major importance for understanding how neuronal activity shapes connectivity in neural networks.

7月25日（木）17:40～18:04　第7会場（朱鷺メッセ　2F　201B） 1S07e-3 The Temporal Dynamics of Arc Expression Regulate Cognitive Flexibility Angela M Mabb（Mabb Angela M） Georgia State University, Atlanta, United States The activity-regulated protein Arc/Arg3.1 (Arc) is essential for spatial memory acquisition and consolidation. Arc is required for protein-synthesis-dependent synaptic plasticity related to learning and memory, making it one of the key molecular players in cognition. Arc protein expression is highly dynamic: increasing and then rapidly declining following increased network activity or exposure to a novel environment. Retrieval of a memory also induces Arc expression which then rapidly decays. The regulation of Arc protein induction occurs at the level of mRNA transcription, mRNA trafficking, and protein translation. Although the importance of Arc induction is clear, the role of Arc protein degradation in synaptic plasticity and learning-related behaviors is still unknown. The temporal expression of Arc protein is largely mediated through the ubiquitin-proteasome pathway. We disrupted the temporal control of Arc degradation by creating an Arc knock-in mouse (ArcKR) wherein the predominant Arc ubiquitination sites were mutated. Arc mRNA and protein expression are altered in ArcKR mice, leading to reduced metabotropic glutamate receptor dependent long-term depression (mGluR-LTD) threshold and enhanced mGluR-LTD amplitude. ArcKR mice had intact spatial learning but showed specific deficits in selecting an optimal strategy during reversal learning. Alterations in reversal learning suggest a global deficit in cognitive flexibility and is likely a result of underlying changes in neural coding mediated through proper turnover of Arc.		7月25日（木）18:04～18:28　第7会場（朱鷺メッセ　2F　201B） 1S07e-4 The role of Arc/Arg3.1 protein in the regulation of alcohol seeking Kasia Radwanska（Radwanska Kasia） Nencki Institute of Experimental Biology, PAS Alcohol addiction involves dysregulation of the glutamatergic system. Here we tested the role of Arc, one of the key regulators of the glutamatergic transmission, in the regulation of alcohol addiction. We observed that Arc KO mice drink as much alcohol as wild-type (WT) animals, but they are more persistent in alcohol seeking during alcohol withdrawal and relapse induced by alcohol-associated cues. Furthermore, we found that Arc protein is upregulated at the synapses of Basolateral (BLA) and Central Amygdala (CeA) (but not the hippocampus) in wild-type mice after withdrawal from long-term alcohol training. To test the function of Arc in the amygdala we developed and tested gRNAs for Arc knockdown with CrispR/Cas9 system. The most efficient gRNA was introduced on AAV vector together with CrispR/Cas9 into CeA and mice were trained to drink alcohol or sucrose. The mice with local indel mutation of arc gene were more persistent in alcohol seeking during cue-induced relapse, they had decreased levels of Arc protein in CeA and increased levels of AMPA receptor subunit GluR2, as compared to the control animals. Local mutation of arc did not affect sucrose seeking and consumption. In conclusions, our data show the novel role of Arc protein in CeA, as a specific regulator of alcohol seeking during relapse induced by alcohol-associated cues.

7月25日（木）18:28～18:50　第7会場（朱鷺メッセ　2F　201B） 1S07e-5 Arc欠損は記憶の正確性と認知的切り替えの障害を引き起こす Hiroyuki Okuno（奥野浩行）鹿児島大院医歯生化学・分子生物学 The neuronal immediate early gene Arc plays critical roles in synaptic plasticity and homeostatic scaling by regulating AMPA receptor (AMPA-R) trafficking. We previously proposed the inverse synaptic tagging mechanism of Arc for synapse-specific AMPA-R regulation (Okuno et al., Cell, 2012), and recently confirmed that this mechanism is indeed critically involved in experience-dependent neuronal plasticity in the visual cortex in vivo (El-Boustani, Science, 2018). However, the roles of synapse-specific regulation of Arc in cognitive functions have not been fully investigated so far although several studies have reported Arc's role in learning and memory formation. Here, we investigated ability of target-switching in Arc knockout (KO) mice using the spatial reference task Barnes maze. Contrary to the previous reports, Arc-KO mice showed normal performance during the initial acquisition as well as the first reversal session. However, interestingly, these mice exhibited specific impairments in target-switching during subsequent repeated reversal sessions. Network analysis of behavior during the reversal sessions revealed poor target precision in Arc-KO mice. Such deficits in behavioral switching were clearly reproduced in a different behavioral task. Taken together, our findings suggest an Arc-dependent synaptic mechanism that regulates cognitive refinement processes such as memory precision and behavioral flexibility.