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Tsai MH, Lin WC, Chen SY, Hsieh MY, Nian FS, Cheng HY, Zhao HJ, Hung SS, Hsu CH, Hou PS, Tung CY, Lee MH, Tsai JW. A lissencephaly-associated BAIAP2 variant causes defects in neuronal migration during brain development. Development 2024; 151:dev201912. [PMID: 38149472 DOI: 10.1242/dev.201912] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2023] [Accepted: 12/12/2023] [Indexed: 12/28/2023]
Abstract
Lissencephaly is a neurodevelopmental disorder characterized by a loss of brain surface convolutions caused by genetic variants that disrupt neuronal migration. However, the genetic origins of the disorder remain unidentified in nearly one-fifth of people with lissencephaly. Using whole-exome sequencing, we identified a de novo BAIAP2 variant, p.Arg29Trp, in an individual with lissencephaly with a posterior more severe than anterior (P>A) gradient, implicating BAIAP2 as a potential lissencephaly gene. Spatial transcriptome analysis in the developing mouse cortex revealed that Baiap2 is expressed in the cortical plate and intermediate zone in an anterior low to posterior high gradient. We next used in utero electroporation to explore the effects of the Baiap2 variant in the developing mouse cortex. We found that Baiap2 knockdown caused abnormalities in neuronal migration, morphogenesis and differentiation. Expression of the p.Arg29Trp variant failed to rescue the migration defect, suggesting a loss-of-function effect. Mechanistically, the variant interfered with the ability of BAIAP2 to localize to the cell membrane. These results suggest that the functions of BAIAP2 in the cytoskeleton, cell morphogenesis and migration are important for cortical development and for the pathogenesis of lissencephaly in humans.
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Affiliation(s)
- Meng-Han Tsai
- Department of Neurology & Department of Medical Research, Kaohsiung Chang Gung Memorial Hospital, Kaohsiung 833, Taiwan
- School of Medicine, Chang Gung University, Taoyuan 333, Taiwan
| | - Wan-Cian Lin
- Institute of Brain Science, College of Medicine, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
- Faculty of Medicine, College of Medicine, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
| | - Shih-Ying Chen
- Department of Neurology & Department of Medical Research, Kaohsiung Chang Gung Memorial Hospital, Kaohsiung 833, Taiwan
| | - Meng-Ying Hsieh
- Division of Pediatric Neurology, Department of Pediatrics, Chang Gung Memorial Hospital, Taipei 105, Taiwan
| | - Fang-Shin Nian
- Institute of Brain Science, College of Medicine, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
- Institute of Clinical Medicine, College of Medicine, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
| | - Haw-Yuan Cheng
- Institute of Brain Science, College of Medicine, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
| | - Hong-Jun Zhao
- Institute of Brain Science, College of Medicine, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
| | - Shih-Shun Hung
- Institute of Anatomy and Cell Biology, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
| | - Chi-Hsin Hsu
- Genomics Center for Clinical and Biotechnological Applications, Cancer Progression Research Center, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
| | - Pei-Shan Hou
- Institute of Anatomy and Cell Biology, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
| | - Chien-Yi Tung
- Genomics Center for Clinical and Biotechnological Applications, Cancer Progression Research Center, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
| | - Mei-Hsuan Lee
- Institute of Clinical Medicine, College of Medicine, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
- Advanced Therapeutics Research Center, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
| | - Jin-Wu Tsai
- Institute of Brain Science, College of Medicine, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
- Advanced Therapeutics Research Center, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
- Brain Research Center, National Yang Ming Chiao Tung University, Taipei 112, Taiwan
- Department of Biological Science and Technology, College of Biological Science and Technology, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
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Tao-Cheng JH, Moreira SL, Winters CA, Reese TS, Dosemeci A. Modification of the synaptic cleft under excitatory conditions. Front Synaptic Neurosci 2023; 15:1239098. [PMID: 37840571 PMCID: PMC10568020 DOI: 10.3389/fnsyn.2023.1239098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Accepted: 09/14/2023] [Indexed: 10/17/2023] Open
Abstract
The synaptic cleft is the extracellular part of the synapse, bridging the pre- and postsynaptic membranes. The geometry and molecular organization of the cleft is gaining increased attention as an important determinant of synaptic efficacy. The present study by electron microscopy focuses on short-term morphological changes at the synaptic cleft under excitatory conditions. Depolarization of cultured hippocampal neurons with high K+ results in an increased frequency of synaptic profiles with clefts widened at the periphery (open clefts), typically exhibiting patches of membranes lined by postsynaptic density, but lacking associated presynaptic membranes (18.0% open clefts in high K+ compared to 1.8% in controls). Similarly, higher frequencies of open clefts were observed in adult brain upon a delay of perfusion fixation to promote excitatory/ischemic conditions. Inhibition of basal activity in cultured neurons through the application of TTX results in the disappearance of open clefts whereas application of NMDA increases their frequency (19.0% in NMDA vs. 5.3% in control and 2.6% in APV). Depletion of extracellular Ca2+ with EGTA also promotes an increase in the frequency of open clefts (16.6% in EGTA vs. 4.0% in controls), comparable to that by depolarization or NMDA, implicating dissociation of Ca2+-dependent trans-synaptic bridges. Dissociation of transsynaptic bridges under excitatory conditions may allow perisynaptic mobile elements, such as AMPA receptors to enter the cleft. In addition, peripheral opening of the cleft would facilitate neurotransmitter clearance and thus may have a homeostatic and/or protective function.
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Affiliation(s)
- Jung-Hwa Tao-Cheng
- NINDS Electron Microscopy Facility, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, MD, United States
| | - Sandra L. Moreira
- NINDS Electron Microscopy Facility, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, MD, United States
| | - Christine A. Winters
- Laboratory of Neurobiology, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, MD, United States
| | - Thomas S. Reese
- Laboratory of Neurobiology, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, MD, United States
| | - Ayse Dosemeci
- Laboratory of Neurobiology, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, MD, United States
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Guo X, Zhu K, Zhu X, Zhao W, Miao Y. Two-dimensional molecular condensation in cell signaling and mechanosensing. Acta Biochim Biophys Sin (Shanghai) 2023; 55:1064-1074. [PMID: 37475548 PMCID: PMC10423693 DOI: 10.3724/abbs.2023132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2023] [Accepted: 05/21/2023] [Indexed: 07/22/2023] Open
Abstract
Membraneless organelles (MLO) regulate diverse biological processes in a spatiotemporally controlled manner spanning from inside to outside of the cells. The plasma membrane (PM) at the cell surface serves as a central platform for forming multi-component signaling hubs that sense mechanical and chemical cues during physiological and pathological conditions. During signal transduction, the assembly and formation of membrane-bound MLO are dynamically tunable depending on the physicochemical properties of the surrounding environment and partitioning biomolecules. Biomechanical properties of MLO-associated membrane structures can control the microenvironment for biomolecular interactions and assembly. Lipid-protein complex interactions determine the catalytic region's assembly pattern and assembly rate and, thereby, the amplitude of activities. In this review, we will focus on how cell surface microenvironments, including membrane curvature, surface topology and tension, lipid-phase separation, and adhesion force, guide the assembly of PM-associated MLO for cell signal transductions.
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Affiliation(s)
- Xiangfu Guo
- School of ChemistryChemical Engineering and BiotechnologyNanyang Technological UniversitySingapore637457Singapore
| | - Kexin Zhu
- School of Biological SciencesNanyang Technological UniversitySingapore637551Singapore
| | - Xinlu Zhu
- School of Biological SciencesNanyang Technological UniversitySingapore637551Singapore
| | - Wenting Zhao
- School of ChemistryChemical Engineering and BiotechnologyNanyang Technological UniversitySingapore637457Singapore
- Institute for Digital Molecular Analytics and ScienceNanyang Technological UniversitySingapore636921Singapore
| | - Yansong Miao
- School of Biological SciencesNanyang Technological UniversitySingapore637551Singapore
- Institute for Digital Molecular Analytics and ScienceNanyang Technological UniversitySingapore636921Singapore
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Feng Z, Lee S, Jia B, Jian T, Kim E, Zhang M. IRSp53 promotes postsynaptic density formation and actin filament bundling. J Cell Biol 2022; 221:213346. [PMID: 35819332 PMCID: PMC9280192 DOI: 10.1083/jcb.202105035] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 11/04/2021] [Accepted: 06/13/2022] [Indexed: 01/14/2023] Open
Abstract
IRSp53 (aka BAIAP2) is a scaffold protein that couples membranes with the cytoskeleton in actin-filled protrusions such as filopodia and lamellipodia. The protein is abundantly expressed in excitatory synapses and is essential for synapse development and synaptic plasticity, although with poorly understood mechanisms. Here we show that specific multivalent interactions between IRSp53 and its binding partners PSD-95 or Shank3 drive phase separation of the complexes in solution. IRSp53 can be enriched to the reconstituted excitatory PSD (ePSD) condensates via bridging to the core and deeper layers of ePSD. Overexpression of a mutant defective in the IRSp53/PSD-95 interaction perturbs synaptic enrichment of IRSp53 in mouse cortical neurons. The reconstituted PSD condensates promote bundled actin filament formation both in solution and on membranes, via IRSp53-mediated actin binding and bundling. Overexpression of mutants that perturb IRSp53-actin interaction leads to defects in synaptic maturation of cortical neurons. Together, our studies provide potential mechanistic insights into the physiological roles of IRSp53 in synapse formation and function.
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Affiliation(s)
- Zhe Feng
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Hong Kong, China,State Key Laboratory of Genetic Engineering, School of Life Sciences, Fudan University, Shanghai, China
| | - Suho Lee
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science (IBS), Daejeon, Korea
| | - Bowen Jia
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Hong Kong, China
| | - Tao Jian
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Hong Kong, China
| | - Eunjoon Kim
- Center for Synaptic Brain Dysfunctions, Institute for Basic Science (IBS), Daejeon, Korea,Department of Biological Sciences, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea,Correspondence to Eunjoon Kim:
| | - Mingjie Zhang
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Hong Kong, China,School of Life Sciences, Southern University of Science and Technology, Shenzhen, China
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Chatzi C, Westbrook GL. Revisiting I-BAR Proteins at Central Synapses. Front Neural Circuits 2022; 15:787436. [PMID: 34975417 PMCID: PMC8716821 DOI: 10.3389/fncir.2021.787436] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Accepted: 11/08/2021] [Indexed: 01/30/2023] Open
Abstract
Dendritic spines, the distinctive postsynaptic feature of central nervous system (CNS) excitatory synapses, have been studied extensively as electrical and chemical compartments, as well as scaffolds for receptor cycling and positioning of signaling molecules. The dynamics of the shape, number, and molecular composition of spines, and how they are regulated by neural activity, are critically important in synaptic efficacy, synaptic plasticity, and ultimately learning and memory. Dendritic spines originate as outward protrusions of the cell membrane, but this aspect of spine formation and stabilization has not been a major focus of investigation compared to studies of membrane protrusions in non-neuronal cells. We review here one family of proteins involved in membrane curvature at synapses, the BAR (Bin-Amphiphysin-Rvs) domain proteins. The subfamily of inverse BAR (I-BAR) proteins sense and introduce outward membrane curvature, and serve as bridges between the cell membrane and the cytoskeleton. We focus on three I-BAR domain proteins that are expressed in the central nervous system: Mtss2, MIM, and IRSp53 that promote negative, concave curvature based on their ability to self-associate. Recent studies suggest that each has distinct functions in synapse formation and synaptic plasticity. The action of I-BARs is also shaped by crosstalk with other signaling components, forming signaling platforms that can function in a circuit-dependent manner. We discuss another potentially important feature-the ability of some BAR domain proteins to impact the function of other family members by heterooligomerization. Understanding the spatiotemporal resolution of synaptic I-BAR protein expression and their interactions should provide insights into the interplay between activity-dependent neural plasticity and network rewiring in the CNS.
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Affiliation(s)
- Christina Chatzi
- Vollum Institute, Oregon Health and Science University, Portland, OR, United States
| | - Gary L Westbrook
- Vollum Institute, Oregon Health and Science University, Portland, OR, United States
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Abstract
Neurons are highly specialized cells equipped with a sophisticated molecular machinery for the reception, integration, conduction and distribution of information. The evolutionary origin of neurons remains unsolved. How did novel and pre-existing proteins assemble into the complex machinery of the synapse and of the apparatus conducting current along the neuron? In this review, the step-wise assembly of functional modules in neuron evolution serves as a paradigm for the emergence and modification of molecular machinery in the evolution of cell types in multicellular organisms. The pre-synaptic machinery emerged through modification of calcium-regulated large vesicle release, while the postsynaptic machinery has different origins: the glutamatergic postsynapse originated through the fusion of a sensory signaling module and a module for filopodial outgrowth, while the GABAergic postsynapse incorporated an ancient actin regulatory module. The synaptic junction, in turn, is built around two adhesion modules controlled by phosphorylation, which resemble septate and adherens junctions. Finally, neuronal action potentials emerged via a series of duplications and modifications of voltage-gated ion channels. Based on these origins, key molecular innovations are identified that led to the birth of the first neuron in animal evolution.
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Tao-Cheng JH, Crocker V, Moreira SL, Azzam R. Optimization of protocols for pre-embedding immunogold electron microscopy of neurons in cell cultures and brains. Mol Brain 2021; 14:86. [PMID: 34082785 PMCID: PMC8173732 DOI: 10.1186/s13041-021-00799-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Accepted: 05/27/2021] [Indexed: 02/08/2023] Open
Abstract
Immunogold labeling allows localization of proteins at the electron microscopy (EM) level of resolution, and quantification of signals. The present paper summarizes methodological issues and experiences gained from studies on the distribution of synaptic and other neuron-specific proteins in cell cultures and brain tissues via a pre-embedding method. An optimal protocol includes careful determination of a fixation condition for any particular antibody, a well-planned tissue processing procedure, and a strict evaluation of the credibility of the labeling. Here, tips and caveats on different steps of the sample preparation protocol are illustrated with examples. A good starting condition for EM-compatible fixation and permeabilization is 4% paraformaldehyde in PBS for 30 min at room temperature, followed by 30 min incubation with 0.1% saponin. An optimal condition can then be readjusted for each particular antibody. Each lot of the secondary antibody (conjugated with a 1.4 nm small gold particle) needs to be evaluated against known standards for labeling efficiency. Silver enhancement is required to make the small gold visible, and quality of the silver-enhanced signals can be affected by subsequent steps of osmium tetroxide treatment, uranyl acetate en bloc staining, and by detergent or ethanol used to clean the diamond knife for cutting thin sections. Most importantly, verification of signals requires understanding of the protein of interest in order to validate for correct localization of antibodies at expected epitopes on particular organelles, and quantification of signals needs to take into consideration the penetration gradient of reagents and clumping of secondary antibodies.
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Affiliation(s)
- Jung-Hwa Tao-Cheng
- NINDS Electron Microscopy Facility, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA.
| | - Virginia Crocker
- NINDS Electron Microscopy Facility, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Sandra Lara Moreira
- NINDS Electron Microscopy Facility, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Rita Azzam
- NINDS Electron Microscopy Facility, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA
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Tao-Cheng JH. Activity-dependent redistribution of CaMKII in the postsynaptic compartment of hippocampal neurons. Mol Brain 2020; 13:53. [PMID: 32238193 PMCID: PMC7110642 DOI: 10.1186/s13041-020-00594-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Accepted: 03/23/2020] [Indexed: 11/10/2022] Open
Abstract
Calcium/calmodulin-dependent protein kinase II (CaMKII), an abundant protein in neurons, is involved in synaptic plasticity and learning. CaMKII associates with multiple proteins located at or near the postsynaptic density (PSD), and CaMKII is known to translocate from cytoplasm to PSD under excitatory conditions. The present study examined the laminar distribution of CaMKII at the PSD by immunogold labeling in dissociated hippocampal cultures under low calcium (EGTA or APV), control, and stimulated (depolarization with high K+ or NMDA) conditions. The patterns of CaMKII distribution are classified with particular reference to the two layers of the PSD: (1) the PSD core, a layer within ~ 30-40 nm to the postsynaptic membrane, and (2) the PSD pallium, a deeper layer beyond the PSD core, ~ 100-120 nm from the postsynaptic membrane. Under low calcium conditions, a subpopulation (40%) of synapses stood out with no CaMKII labeling at the PSD, indicating that localization of CaMKII at the PSD is sensitive to calcium levels. Under control conditions, the majority (~ 60-70%) of synapses had label for CaMKII dispersed evenly in the spine, including the PSD and the nearby cytoplasm. Upon stimulation, the majority (60-75%) of synapses had label for CaMKII concentrated at the PSD, delineating the PSD pallium from the cytoplasm. Median distance of label for CaMKII to postsynaptic membrane was higher in low calcium samples (68-77 nm), than in control (59-63 nm) and stimulated samples (49-53 nm). Thus, upon stimulation, not only more CaMKII translocated to the PSD, but they also were closer to the postsynaptic membrane. Additionally, there were two relatively infrequent labeling patterns that may represent intermediate stages of CaMKII distribution between basal and stimulated conditions: (1) one type showed label preferentially localized near the PSD core where CaMKII may be binding to NR2B, an NMDA receptor concentrated at the PSD core, and (2) the second type showed label preferentially in the PSD pallium, where CaMKII may be binding to Shank, a PSD scaffold protein located in the PSD pallium. Both of these distribution patterns may portray the initial stages of CaMKII translocation upon synaptic activation. In addition to binding to PSD proteins, the concentrated CaMKII labeling at the PSD under heightened excitatory conditions could also be formed by self-clustering of CaMKII molecules recruited to the PSD. Most importantly, these accumulated CaMKII molecules do not extend beyond the border of the PSD pallium, and are likely held in the pallium by binding to Shank under these conditions.
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Affiliation(s)
- Jung-Hwa Tao-Cheng
- NINDS Electron Microscopy Facility, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA.
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Tao-Cheng JH. Stimulation induces gradual increases in the thickness and curvature of postsynaptic density of hippocampal CA1 neurons in slice cultures. Mol Brain 2019; 12:44. [PMID: 31053145 PMCID: PMC6499976 DOI: 10.1186/s13041-019-0468-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2019] [Accepted: 04/25/2019] [Indexed: 11/10/2022] Open
Abstract
Activity can induce structural changes in glutamatergic excitatory synapses, including increase in thickness and curvature of the postsynaptic density (PSD); these structural changes can only be documented by electron microscopy. Here in organotypic hippocampal slice cultures where experimental conditions can be easily manipulated, increases in thickness and curvature of PSDs were noticeable within 30 s of stimulation and progressed with time up to 3 min. These structural changes were reversible upon returning the samples to control medium for 5-10 min. Thus, the postsynaptic density is a very dynamic structure that undergoes rapid reorganization of its components upon stimulation, and recovery upon cessation of stimulation. The gradual increase in thickness of PSD could result from a gradual translocation of some PSD proteins to the PSD, and the increase in curvature of the PSD is likely led by postsynaptic elements.
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Affiliation(s)
- Jung-Hwa Tao-Cheng
- NINDS Electron Microscopy Facility, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892, USA.
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