シンポジウム（Symposium）

Symposium Matching matters: Roles of trans-synaptic protein interactions シンポジウムマッチングがすべて: シナプス間隙タンパク相互作用の役割 Sponsored by IBRO-APRC Lecturer Exchange Program

7月25日（木）9:00～9:24　第5会場（朱鷺メッセ　3F　302） 1S05m-1 Neuroliginによる入力依存的恒常性シナプス可塑性の制御 Kensuke Futai（二井健介）¹，Motokazu Uchigashima（内ヶ島基政）^1,2，Takuya Watanabe（渡辺拓也）¹，Amy Cheung（Cheung Amy）¹，Manabu Abe（阿部学）³，Kenji Sakimura（﨑村建司）³，Masahiko Watanabe（渡辺雅彦）² ¹Dept. Neurobiology, Univ. Massachusetts Medical School, Worcester, U.S.A. ²北海道大院医解剖発生 ³新潟大脳研基礎神経科学細胞神経生物 Each year, the number of children diagnosed with autism spectrum disorders (ASDs) steadily increases (today, the prevalence is 1 in 68 children). Despite this increase in diagnosis, treatment of ASD remains a major challenge as current therapeutic interventions are limited. One approach to this issue, taken in this presentation, is to elucidate the pathophysiology of ASDs, thereby identifying potential novel drug targets to treat these disorders. Neuroligin isoforms (NL1 - 4) are postsynaptically localized and form trans-synaptic protein complexes with presynaptic neurexin isoforms (Nrxn1 - 3). These trans-synaptic protein interactions play critical roles in synaptic transmission and plasticity. Importantly, NL and Nrxn gene mutations are found in individuals with ASD and schizophrenia. Mouse models support the significance of NL and Nrxn isoforms in behavior, synaptic transmission and plasticity, emphasizing the critical roles of these adhesion molecules in modulating cognitive functions. Emerging evidence has suggested that key components of ASD pathophysiology is the dysregulation of neuronal homeostasis and faulty development of inhibitory synapses. However, the function of Nrxn-NL trans-synaptic interaction on inhibitory neuronal homeostasis is largely unknown. Thus, it is particularly important to understand how specific Nrxns and NLs interactions regulate inhibitory neuronal homeostasis. Here, we identified that NL3 localizes at inhibitory synapses in a presynaptic input-specific manner and regulates homeostatic plasticity. In this session, I will present our preliminary data addressing the roles of NL3 in inhibitory homeostatic plasticity.		7月25日（木）9:24～9:48　第5会場（朱鷺メッセ　3F　302） 1S05m-2 補体ファミリーが作り上げるシナプスの橋～両方向性シナプス構築と伝達制御～ Keiko Matsuda（松田恵子）慶應大医生理 So far, many synaptic organizers involving the differentiation and/or maturation of synapses have been identified. Recently, secreted factors which serve as a scaffold at the synaptic cleft are found essential in synaptic adhesion or accumulation of postsynaptic receptors. Cbln1, secreted C1q/ TNF&alpha superfamily member, plays a crucial role in the formation and function of parallel fiber-Purkinje cell synapses. This synaptogenic activity depends on the ""trans-synaptic bridge"" across over synaptic cleft, which is composed of the presynaptic neurexin with a splice site 4 insertion and the amino-terminal domain (ATD) of ionotropic glutamate receptor (iGluR), GluD2 localized in postsynaptic Purkinje cells. Another C1q/TNFα superfamily member, C1ql2 and C1ql3 produced in dentate gyrus granule cells, serve as anterograde synaptic organizers, recruiting functional postsynaptic kainate-type of glutamate receptors (KARs) at mossy fiber synapses through direct binding to ATD of GluK2 and GluK4 subunits of KAR. Not only to postsynaptic KARs, C1ql2 and C1ql3 also bind to neurexin3 containing sequences encoded by exon25b insertion at splice site 5, indicating the possible ""trans-synaptic bridge"" of neurexin and KAR at certain synapses. In this talk, I would like to discuss the generality of the strategy of complex formation of C1q family members and the function of ATD of iGluR.

7月25日（木）9:48～10:12　第5会場（朱鷺メッセ　3F　302） 1S05m-3 小脳におけるシナプスオーガナイザーの役割 Takeshi Uemura（植村健）^1,2,3 ¹信州大・基盤研究支援センター・遺伝子実験支援部門 ²信州大・先鋭領域融合研究群バイオメディカル研究所 ³独立行政法人科学技術振興機構, CREST Synapses are formed and maintained by trans-synaptic interaction between pre- and postsynaptic cell adhesion molecules called synapse organizers. To date, at least ten kinds of synapse organizers have been identified. In the cerebellum, postsynaptic glutamate receptor δ2 (GluD2) interacts with presynaptic neurexins (NRXNs) through secreted cerebellin precursor protein 1 (Cbln1), which regulates parallel fiber (PF)-Purkinje cell (PC) synapse formation. The functional importance of this ternary complex in synapse formation is well supported by both conventional and conditional GluD2 or Cbln1 knockout mice, in which the number of PF-PC synapses decreased to approximately half of those in wild-type mice. As a result, the question arises of how the remaining synapses are formed. One possible mechanism is that NRXNs sustain remaining PF-PC synapse formation through the interaction with other types of postsynaptic synapse organizers, such as neuroligins and leucine-rich repeat transmembrane proteins. To investigate the role of NRXNs in PF-PC synapses, we generated cerebellar granule cell (GC)-specific Nrxn1, Nrxn2, and Nrxn3 triple knockout (TKO) mice. The cerebellar GC-specific Nrxns TKO mice showed severe ataxia and reduced cerebellar size. Unexpectedly, most of all cerebellar GCs were disappeared in these mutant mice, suggesting that NRXNs are essential for cerebellar GCs survival. The requirement of NRNXs for cerebellar GCs survival was reproduced in cultured cerebellar GCs. We found that the formation of synaptic vesicle clustering in the axonal varicosities and the axonal activity-dependent neurotrophic factor release were impaired in cultured Nrxns TKO GCs. Notably, the majority of axonal varicosities of cultured GCs are not apposed to definite postsynaptic structures. These results suggest the possibility that NRXNs function independent of their postsynaptic ligands. Here, we report our recent advances in the functional analysis of NRXNs in cerebellar GCs.		7月25日（木）10:12～10:36　第5会場（朱鷺メッセ　3F　302） 1S05m-4 ニューロリジン３の担うシナプス形成の古典経路と非古典経路の役割 Tomoyuki Yoshida（吉田知之）¹，Ayako Imai-Tabata（今井ー田端彩子）¹，Atsushi Yamagata（山形敦史）²，Hironori Izumi（和泉宏謙）¹，Tomoko Shiroshima（城島知子）²，Juhyon Kim（金主賢）³，Masaki Fukata（深田正紀）⁴，Keizo Takao（高雄啓三）⁵，Hisashi Mori（森寿）¹，Shuya Fukai（深井周也）² ¹富山大医分子神経 ²東京大定量研 ³富山大工電気電子システム ⁴生理研分子細胞生理生体膜 ⁵富山大生命科学先端セ The initiation, organization, and specification of synapses are governed by selective pairs of presynaptic and postsynaptic adhesion molecules called synapse organizers. Neurexins (NRXNs; NRXN1, 2, and 3) and 2A type receptor protein tyrosine phosphatases (RPTPs; PTPδ, PTPσ, and LAR) are the two major presynaptic organizers. The canonical postsynaptic partners of NRXNs include neuroligins (NLGNs), LRRTMs and GluDs while those of 2A type RPTPs include IL-1RAcP, IL1RAPL1, Slitrks and SALMs. NLGN 3 and NRXNs are well-established synapse-organizing pairs implicated in autism spectrum disorders and thus in social development. Nevertheless the fundamental regulatory mechanism and functional role of NLGN3-mediated synapse organization and specification remains obscure. We identified a non-canonical interaction between NLGN3 and protein tyrosine phosphatase (PTP) δ. PTPδ and NRXNs compete with each other for binding to NLGN3. Atomic-level characterization of NLGN3-PTPδ interfaces and comparison to NLGN-NRXN interfaces enabled the design of NLGN3 mutations that selectively interfere with the binding to either PTPδ or NRXNs. We generated Nlgn3 knock-in mutant mice carrying these mutations by CRISPR/Cas9-based gene editing to differentiate the roles of the canonical NRXN- and the non-canonical PTPδ-mediated transsynaptic signaling of NLGN3. These mice exhibited differential biochemical, electrophysiological, and behavioral phenotypes, suggesting distinct roles of the canonical and non-canonical trans-synaptic signaling by NLGN3.

7月25日（木）10:36～11:00　第5会場（朱鷺メッセ　3F　302） 1S05m-5 Postsynaptic Calsyntenin-3 Requires Direct Interactions with Presynaptic Neurexins to Orchestrate Excitatory Synapse Development in the Hippocampus Ji Won Um（Um Ji Won）¹，Hyenho Kim（Kim Hyenho）¹，Dongwook Kim（Kim Dongwook）¹，Hee-yoon Lee（Lee Hee-yoon）²，Hyeyeon Kang（Kang Hyeyeon）¹，Dongseok Park（Park Dongseok）¹，Soo-Jeong Kim（Kim Soo-Jeong）¹，Keiko Matsuda（Matsuda Keiko）³，Fredrik H Sterky（Sterky Fredrik H）⁴，Michisuke Yuzaki（Yuzaki Michisuke）³，Jin Young Kim（Kim Jin Young）⁵，Se-Young Choi（Choi Se-Young）²，Jaewon Ko（Ko Jaewon）¹ ¹DGIST, Daegu, South Korea ²Seoul National University, Seoul, Korea ³Keio University, Tokyo, Japan ⁴University of Gothenburg, Gothenburg, Sweden ⁵Korea Basic Science Institute, Cheongju, Korea A number of synaptic cell adhesion molecules have recently emerged as factors that are crucial for dictating various stages of synapse and circuit organization. These adhesion molecules perform both overlapping and nonoverlapping roles in mediating excitatory and inhibitory synapse formation, transmission, and plasticity. A subset of these molecules has been classified as synapse organizers, which control connectivity and validate distinct signaling pathways. The list includes neurexins, neuroligins, leucine-rich repeat transmembrane proteins (LRRTMs), netrin-G ligands (NGLs), synaptic adhesion-like molecules (SALMs), Slit- and Trk-like family (Slitrks) proteins, and leukocyte common antigen-related receptor protein tyrosine phosphatases (LAR-RPTPs). Among others, calsyntenin-3 (Clstn3) is a postsynaptic adhesion molecule that induces presynaptic differentiation via presynaptic neurexins (Nrxns), but whether Nrxns directly bind to Clstn3 has been a matter of debate. Here, using affinity chromatography analyses, we show that β-Nrxns directly interact via their LNS domain with Clstn3 through its cadherin domains in a Calcium-dependent manner. In addition, Clstn3 binds β-Nrxns with a slight preference for SS4 insert-positive splice varients. Expression of splice site 4 (SS4)-insert-positive β-Nrxn variants, but not insert-negative variants, reversed the impaired Clstn3 synaptogenic activity observed in Nrxn-deficient neurons. Consistent with this, Clstn3 selectively formed in vivo complexes with SS4-positive Nrxns. Moreover, expression of Clstn3 cadherin domains in CA1 hippocampal neurons of Clstn3-knockout mice rescued structural deficits in excitatory synapse development, especially within the stratum radiatum layer. Collectively, these results suggest that Clstn3 physically and functionally links to SS4-positive Nrxns to induce presynaptic differentiation and to orchestrate excitatory synapse development in hippocampal neurons in vivo.