1
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Sachs S, Reinhard S, Eilts J, Sauer M, Werner C. Visualizing the trans-synaptic arrangement of synaptic proteins by expansion microscopy. Front Cell Neurosci 2024; 18:1328726. [PMID: 38486709 PMCID: PMC10937466 DOI: 10.3389/fncel.2024.1328726] [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: 10/27/2023] [Accepted: 02/13/2024] [Indexed: 03/17/2024] Open
Abstract
High fidelity synaptic neurotransmission in the millisecond range is provided by a defined structural arrangement of synaptic proteins. At the presynapse multi-epitope scaffolding proteins are organized spatially at release sites to guarantee optimal binding of neurotransmitters at receptor clusters. The organization of pre- and postsynaptic proteins in trans-synaptic nanocolumns would thus intuitively support efficient information transfer at the synapse. Visualization of these protein-dense regions as well as the minute size of protein-packed synaptic clefts remains, however, challenging. To enable efficient labeling of these protein complexes, we developed post-gelation immunolabeling expansion microscopy combined with Airyscan super-resolution microscopy. Using ~8-fold expanded samples, Airyscan enables multicolor fluorescence imaging with 20-40 nm spatial resolution. Post-immunolabeling of decrowded (expanded) samples provides increased labeling efficiency and allows the visualization of trans-synaptic nanocolumns. Our approach is ideally suited to investigate the pathological impact on nanocolumn arrangement e.g., in limbic encephalitis with autoantibodies targeting trans-synaptic leucine-rich glioma inactivated 1 protein (LGI1).
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Affiliation(s)
| | | | | | | | - Christian Werner
- Department of Biotechnology and Biophysics, Biocenter, University of Würzburg, Würzburg, Germany
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2
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Wu LG, Chan CY. Membrane transformations of fusion and budding. Nat Commun 2024; 15:21. [PMID: 38167896 PMCID: PMC10761761 DOI: 10.1038/s41467-023-44539-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2023] [Accepted: 12/15/2023] [Indexed: 01/05/2024] Open
Abstract
Membrane fusion and budding mediate fundamental processes like intracellular trafficking, exocytosis, and endocytosis. Fusion is thought to open a nanometer-range pore that may subsequently close or dilate irreversibly, whereas budding transforms flat membranes into vesicles. Reviewing recent breakthroughs in real-time visualization of membrane transformations well exceeding this classical view, we synthesize a new model and describe its underlying mechanistic principles and functions. Fusion involves hemi-to-full fusion, pore expansion, constriction and/or closure while fusing vesicles may shrink, enlarge, or receive another vesicle fusion; endocytosis follows exocytosis primarily by closing Ω-shaped profiles pre-formed through the flat-to-Λ-to-Ω-shape transition or formed via fusion. Calcium/SNARE-dependent fusion machinery, cytoskeleton-dependent membrane tension, osmotic pressure, calcium/dynamin-dependent fission machinery, and actin/dynamin-dependent force machinery work together to generate fusion and budding modes differing in pore status, vesicle size, speed and quantity, controls release probability, synchronization and content release rates/amounts, and underlies exo-endocytosis coupling to maintain membrane homeostasis. These transformations, underlying mechanisms, and functions may be conserved for fusion and budding in general.
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Affiliation(s)
- Ling-Gang Wu
- National Institute of Neurological Disorders and Stroke, Bethesda, MD, USA.
| | - Chung Yu Chan
- National Institute of Neurological Disorders and Stroke, Bethesda, MD, USA
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3
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Samhan-Arias AK, Poejo J, Marques-da-Silva D, Martínez-Costa OH, Gutierrez-Merino C. Are There Lipid Membrane-Domain Subtypes in Neurons with Different Roles in Calcium Signaling? Molecules 2023; 28:7909. [PMID: 38067638 PMCID: PMC10708093 DOI: 10.3390/molecules28237909] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Revised: 11/24/2023] [Accepted: 11/29/2023] [Indexed: 12/18/2023] Open
Abstract
Lipid membrane nanodomains or lipid rafts are 10-200 nm diameter size cholesterol- and sphingolipid-enriched domains of the plasma membrane, gathering many proteins with different roles. Isolation and characterization of plasma membrane proteins by differential centrifugation and proteomic studies have revealed a remarkable diversity of proteins in these domains. The limited size of the lipid membrane nanodomain challenges the simple possibility that all of them can coexist within the same lipid membrane domain. As caveolin-1, flotillin isoforms and gangliosides are currently used as neuronal lipid membrane nanodomain markers, we first analyzed the structural features of these components forming nanodomains at the plasma membrane since they are relevant for building supramolecular complexes constituted by these molecular signatures. Among the proteins associated with neuronal lipid membrane nanodomains, there are a large number of proteins that play major roles in calcium signaling, such as ionotropic and metabotropic receptors for neurotransmitters, calcium channels, and calcium pumps. This review highlights a large variation between the calcium signaling proteins that have been reported to be associated with isolated caveolin-1 and flotillin-lipid membrane nanodomains. Since these calcium signaling proteins are scattered in different locations of the neuronal plasma membrane, i.e., in presynapses, postsynapses, axonal or dendritic trees, or in the neuronal soma, our analysis suggests that different lipid membrane-domain subtypes should exist in neurons. Furthermore, we conclude that classification of lipid membrane domains by their content in calcium signaling proteins sheds light on the roles of these domains for neuronal activities that are dependent upon the intracellular calcium concentration. Some examples described in this review include the synaptic and metabolic activity, secretion of neurotransmitters and neuromodulators, neuronal excitability (long-term potentiation and long-term depression), axonal and dendritic growth but also neuronal cell survival and death.
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Affiliation(s)
- Alejandro K. Samhan-Arias
- Departamento de Bioquímica, Universidad Autónoma de Madrid (UAM), C/Arturo Duperier 4, 28029 Madrid, Spain;
- Instituto de Investigaciones Biomédicas ‘Sols-Morreale’ (CSIC-UAM), C/Arturo Duperier 4, 28029 Madrid, Spain
| | - Joana Poejo
- Instituto de Biomarcadores de Patologías Moleculares, Universidad de Extremadura, 06006 Badajoz, Spain;
| | - Dorinda Marques-da-Silva
- LSRE—Laboratory of Separation and Reaction Engineering and LCM—Laboratory of Catalysis and Materials, School of Management and Technology, Polytechnic Institute of Leiria, Morro do Lena-Alto do Vieiro, 2411-901 Leiria, Portugal;
- ALiCE—Associate Laboratory in Chemical Engineering, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
- School of Technology and Management, Polytechnic Institute of Leiria, Morro do Lena-Alto do Vieiro, 2411-901 Leiria, Portugal
| | - Oscar H. Martínez-Costa
- Departamento de Bioquímica, Universidad Autónoma de Madrid (UAM), C/Arturo Duperier 4, 28029 Madrid, Spain;
- Instituto de Investigaciones Biomédicas ‘Sols-Morreale’ (CSIC-UAM), C/Arturo Duperier 4, 28029 Madrid, Spain
| | - Carlos Gutierrez-Merino
- Instituto de Biomarcadores de Patologías Moleculares, Universidad de Extremadura, 06006 Badajoz, Spain;
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4
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Bingham D, Jakobs CE, Wernert F, Boroni-Rueda F, Jullien N, Schentarra EM, Friedl K, Da Costa Moura J, van Bommel DM, Caillol G, Ogawa Y, Papandréou MJ, Leterrier C. Presynapses contain distinct actin nanostructures. J Cell Biol 2023; 222:e202208110. [PMID: 37578754 PMCID: PMC10424573 DOI: 10.1083/jcb.202208110] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2022] [Revised: 06/07/2023] [Accepted: 07/25/2023] [Indexed: 08/15/2023] Open
Abstract
The architecture of the actin cytoskeleton that concentrates at presynapses remains poorly known, hindering our understanding of its roles in synaptic physiology. In this work, we measure and visualize presynaptic actin by diffraction-limited and super-resolution microscopy, thanks to a validated model of bead-induced presynapses in cultured neurons. We identify a major population of actin-enriched presynapses that concentrates more presynaptic components and shows higher synaptic vesicle cycling than their non-enriched counterparts. Pharmacological perturbations point to an optimal actin amount and the presence of distinct actin structures within presynapses. We directly visualize these nanostructures using Single Molecule Localization Microscopy (SMLM), defining three distinct types: an actin mesh at the active zone, actin rails between the active zone and deeper reserve pools, and actin corrals around the whole presynaptic compartment. Finally, CRISPR-tagging of endogenous actin allows us to validate our results in natural synapses between cultured neurons, confirming the role of actin enrichment and the presence of three types of presynaptic actin nanostructures.
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Affiliation(s)
- Dominic Bingham
- CNRS, INP UMR7051, NeuroCyto, Aix Marseille Université, Marseille, France
| | | | - Florian Wernert
- CNRS, INP UMR7051, NeuroCyto, Aix Marseille Université, Marseille, France
| | - Fanny Boroni-Rueda
- CNRS, INP UMR7051, NeuroCyto, Aix Marseille Université, Marseille, France
| | - Nicolas Jullien
- CNRS, INP UMR7051, NeuroCyto, Aix Marseille Université, Marseille, France
| | | | - Karoline Friedl
- CNRS, INP UMR7051, NeuroCyto, Aix Marseille Université, Marseille, France
- Abbelight, Cachan, France
| | | | | | - Ghislaine Caillol
- CNRS, INP UMR7051, NeuroCyto, Aix Marseille Université, Marseille, France
| | - Yuki Ogawa
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
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5
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Chang HF, Schirra C, Pattu V, Krause E, Becherer U. Lytic granule exocytosis at immune synapses: lessons from neuronal synapses. Front Immunol 2023; 14:1177670. [PMID: 37275872 PMCID: PMC10233144 DOI: 10.3389/fimmu.2023.1177670] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Accepted: 05/09/2023] [Indexed: 06/07/2023] Open
Abstract
Regulated exocytosis is a central mechanism of cellular communication. It is not only the basis for neurotransmission and hormone release, but also plays an important role in the immune system for the release of cytokines and cytotoxic molecules. In cytotoxic T lymphocytes (CTLs), the formation of the immunological synapse is required for the delivery of the cytotoxic substances such as granzymes and perforin, which are stored in lytic granules and released via exocytosis. The molecular mechanisms of their fusion with the plasma membrane are only partially understood. In this review, we discuss the molecular players involved in the regulated exocytosis of CTL, highlighting the parallels and differences to neuronal synaptic transmission. Additionally, we examine the strengths and weaknesses of both systems to study exocytosis.
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6
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Bademosi AT, Meunier FA. Unveiling the Nanoscale Dynamics of the Exocytic Machinery in Chromaffin Cells with Single-Molecule Imaging. Methods Mol Biol 2023; 2565:311-327. [PMID: 36205903 DOI: 10.1007/978-1-0716-2671-9_21] [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] [Indexed: 06/16/2023]
Abstract
Neuronal and hormonal communication relies on the exocytic fusion of vesicles containing neurotransmitters and hormones with the plasma membrane. This process is tightly regulated by key protein-protein and protein-lipid interactions and culminates in the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex formation and zippering that promotes vesicular fusion. Located on both sides of the vesicle and the plasma membrane, the zippering of the SNARE complex acts to overcome the energy barrier afforded by the repulsive electrostatic force stemming from apposing two negatively charged phospholipid membranes. Another component opposing the timely organization of the fusion machinery is thermal Brownian energy that tends to homogenize all cellular molecules by constantly switching their motions and directions through short-lived molecular interactions. Much less is known of the mechanisms counteracting these chaotic forces, allowing seamless cellular functions such as exocytic fusion. Super-resolution microscopy techniques such as single-molecule imaging have proven useful to start uncovering these nanoscale mechanisms. Here, we used single-particle tracking photoactivatable localization microscopy (sptPALM) to track syntaxin-1-mEos, a SNARE protein located on the plasma membrane of cultured bovine chromaffin cells. We demonstrate that syntaxin-1-mEos undergoes dramatic change in its mobility in response to secretagogue stimulation leading to increased nanoclustering. These nanoclusters are transient in nature and likely to provide docked vesicles with a molecular environment conducive to exocytic fusion.
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Affiliation(s)
- Adekunle T Bademosi
- Clem Jones Centre for Ageing Dementia Research (CJCADR), Queensland Brain Institute (QBI), The University of Queensland, St Lucia Campus, Brisbane, QLD, Australia.
| | - Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research (CJCADR), Queensland Brain Institute (QBI), The University of Queensland, St Lucia Campus, Brisbane, QLD, Australia.
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7
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Lamanna J, Ferro M, Spadini S, Malgaroli A. Exploiting the molecular diversity of the synapse to investigate neuronal communication: A guide through the current toolkit. Eur J Neurosci 2022; 56:6141-6161. [PMID: 36239030 PMCID: PMC10100385 DOI: 10.1111/ejn.15848] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Revised: 07/15/2022] [Accepted: 10/10/2022] [Indexed: 12/29/2022]
Abstract
Chemical synapses are tiny and overcrowded environments, deeply embedded inside brain tissue and enriched with thousands of protein species. Many efforts have been devoted to developing custom approaches for evaluating and modifying synaptic activity. Most of these methods are based on the engineering of one or more synaptic protein scaffolds used to target active moieties to the synaptic compartment or to manipulate synaptic functioning. In this review, we summarize the most recent methodological advances and provide a description of the involved proteins as well as the operation principle. Furthermore, we highlight their advantages and limitations in relation to studies of synaptic transmission in vitro and in vivo. Concerning the labelling methods, the most important challenge is how to extend the available approaches to the in vivo setting. On the other hand, for those methods that allow manipulation of synaptic function, this limit has been overcome using optogenetic approaches that can be more easily applied to the living brain. Finally, future applications of these methods to neuroscience, as well as new potential routes for development, are discussed.
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Affiliation(s)
- Jacopo Lamanna
- Center for Behavioral Neuroscience and Communication (BNC), Vita-Salute San Raffaele University, Milan, Italy.,Faculty of Psychology, Vita-Salute San Raffaele University, Milan, Italy
| | - Mattia Ferro
- Center for Behavioral Neuroscience and Communication (BNC), Vita-Salute San Raffaele University, Milan, Italy.,Department of Psychology, Sigmund Freud University, Milan, Italy
| | - Sara Spadini
- Center for Behavioral Neuroscience and Communication (BNC), Vita-Salute San Raffaele University, Milan, Italy.,Faculty of Psychology, Vita-Salute San Raffaele University, Milan, Italy
| | - Antonio Malgaroli
- Center for Behavioral Neuroscience and Communication (BNC), Vita-Salute San Raffaele University, Milan, Italy.,Faculty of Psychology, Vita-Salute San Raffaele University, Milan, Italy.,San Raffaele Turro, IRCCS Ospedale San Raffaele, Milan, Italy
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8
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Dissection of the long-range projections of specific neurons at the synaptic level in the whole mouse brain. Proc Natl Acad Sci U S A 2022; 119:e2202536119. [PMID: 36161898 PMCID: PMC9546530 DOI: 10.1073/pnas.2202536119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Through synaptic connections, long-range circuits transmit information among neurons and connect different brain regions to form functional motifs and execute specific functions. Tracing the synaptic distribution of specific neurons requires submicron-level resolution information. However, it is a great challenge to map the synaptic terminals completely because these fine structures span multiple regions, even in the whole brain. Here, we develop a pipeline including viral tracing, sample embedding, fluorescent micro-optical sectional tomography, and big data processing. We mapped the whole-brain distribution and architecture of long projections of the parvalbumin neurons in the basal forebrain at the synaptic level. These neurons send massive projections to multiple downstream regions with subregional preference. With three-dimensional reconstruction in the targeted areas, we found that synaptic degeneration was inconsistent with the accumulation of amyloid-β plaques but was preferred in memory-related circuits, such as hippocampal formation and thalamus, but not in most hypothalamic nuclei in 8-month-old mice with five familial Alzheimer's disease mutations. Our pipeline provides a platform for generating a whole-brain atlas of cell-type-specific synaptic terminals in the physiological and pathological brain, which can provide an important resource for the study of the organizational logic of specific neural circuits and the circuitry changes in pathological conditions.
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9
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Gormal RS, Meunier FA. Nanoscale organization of the pre-synapse: Tracking the neurotransmitter release machinery. Curr Opin Neurobiol 2022; 75:102576. [PMID: 35716557 DOI: 10.1016/j.conb.2022.102576] [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: 02/16/2022] [Revised: 05/02/2022] [Accepted: 05/11/2022] [Indexed: 11/18/2022]
Abstract
Chemical communication is underpinned by the fusion of neurotransmitter-containing synaptic vesicles with the plasma membrane at active zones. With the advent of super-resolution microscopy, the door is now opened to unravel the dynamic remodeling of synapses underpinning learning and memory. Imaging proteins with conventional light microscopy cannot provide submicron information vital to determining the nanoscale organization of the synapse. We will first review the current super-resolution microscopy techniques available to investigate the localization and movement of synaptic proteins and how they have been applied to visualize the synapse. We discuss the new techniques and analytical approaches have provided comprehensive insights into synaptic organization in various model systems. Finally, this review provides a brief update on how these super-resolution techniques and analyses have opened the way to a much greater understanding of the synapse, the fusion and compensatory endocytosis machinery.
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Affiliation(s)
- Rachel S Gormal
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Queensland, 4072, Australia. https://twitter.com/rachelgormal
| | - Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Queensland, 4072, Australia.
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10
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Kwon J, Elgawish MS, Shim S. Bleaching-Resistant Super-Resolution Fluorescence Microscopy. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2022; 9:e2101817. [PMID: 35088584 PMCID: PMC8948665 DOI: 10.1002/advs.202101817] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2021] [Revised: 01/07/2022] [Indexed: 05/08/2023]
Abstract
Photobleaching is the permanent loss of fluorescence after extended exposure to light and is a major limiting factor in super-resolution microscopy (SRM) that restricts spatiotemporal resolution and observation time. Strategies for preventing or overcoming photobleaching in SRM are reviewed developing new probes and chemical environments. Photostabilization strategies are introduced first, which are borrowed from conventional fluorescence microscopy, that are employed in SRM. SRM-specific strategies are then highlighted that exploit the on-off transitions of fluorescence, which is the key mechanism for achieving super-resolution, which are becoming new routes to address photobleaching in SRM. Off states can serve as a shelter from excitation by light or an exit to release a damaged probe and replace it with a fresh one. Such efforts in overcoming the photobleaching limits are anticipated to enhance resolution to molecular scales and to extend the observation time to physiological lifespans.
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Affiliation(s)
- Jiwoong Kwon
- Department of Biophysics and Biophysical ChemistryJohns Hopkins UniversityBaltimoreMD21205USA
| | - Mohamed Saleh Elgawish
- Department of ChemistryKorea UniversitySeoul02841Republic of Korea
- Medicinal Chemistry DepartmentFaculty of PharmacySuez Canal UniversityIsmailia41522Egypt
| | - Sang‐Hee Shim
- Department of ChemistryKorea UniversitySeoul02841Republic of Korea
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11
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Gagliano G, Nelson T, Saliba N, Vargas-Hernández S, Gustavsson AK. Light Sheet Illumination for 3D Single-Molecule Super-Resolution Imaging of Neuronal Synapses. Front Synaptic Neurosci 2021; 13:761530. [PMID: 34899261 PMCID: PMC8651567 DOI: 10.3389/fnsyn.2021.761530] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Accepted: 10/27/2021] [Indexed: 01/02/2023] Open
Abstract
The function of the neuronal synapse depends on the dynamics and interactions of individual molecules at the nanoscale. With the development of single-molecule super-resolution microscopy over the last decades, researchers now have a powerful and versatile imaging tool for mapping the molecular mechanisms behind the biological function. However, imaging of thicker samples, such as mammalian cells and tissue, in all three dimensions is still challenging due to increased fluorescence background and imaging volumes. The combination of single-molecule imaging with light sheet illumination is an emerging approach that allows for imaging of biological samples with reduced fluorescence background, photobleaching, and photodamage. In this review, we first present a brief overview of light sheet illumination and previous super-resolution techniques used for imaging of neurons and synapses. We then provide an in-depth technical review of the fundamental concepts and the current state of the art in the fields of three-dimensional single-molecule tracking and super-resolution imaging with light sheet illumination. We review how light sheet illumination can improve single-molecule tracking and super-resolution imaging in individual neurons and synapses, and we discuss emerging perspectives and new innovations that have the potential to enable and improve single-molecule imaging in brain tissue.
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Affiliation(s)
- Gabriella Gagliano
- Department of Chemistry, Rice University, Houston, TX, United States
- Applied Physics Program, Rice University, Houston, TX, United States
- Smalley-Curl Institute, Rice University, Houston, TX, United States
| | - Tyler Nelson
- Department of Chemistry, Rice University, Houston, TX, United States
- Applied Physics Program, Rice University, Houston, TX, United States
- Smalley-Curl Institute, Rice University, Houston, TX, United States
| | - Nahima Saliba
- Department of Chemistry, Rice University, Houston, TX, United States
| | - Sofía Vargas-Hernández
- Department of Chemistry, Rice University, Houston, TX, United States
- Systems, Synthetic, and Physical Biology Program, Rice University, Houston, TX, United States
- Institute of Biosciences & Bioengineering, Rice University, Houston, TX, United States
| | - Anna-Karin Gustavsson
- Department of Chemistry, Rice University, Houston, TX, United States
- Smalley-Curl Institute, Rice University, Houston, TX, United States
- Institute of Biosciences & Bioengineering, Rice University, Houston, TX, United States
- Department of Biosciences, Rice University, Houston, TX, United States
- Laboratory for Nanophotonics, Rice University, Houston, TX, United States
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12
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Moreno Manrique JF, Voit PR, Windsor KE, Karla AR, Rodriguez SR, Beaudoin GMJ. SynapseJ: An Automated, Synapse Identification Macro for ImageJ. Front Neural Circuits 2021; 15:731333. [PMID: 34675779 PMCID: PMC8524137 DOI: 10.3389/fncir.2021.731333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2021] [Accepted: 08/25/2021] [Indexed: 12/03/2022] Open
Abstract
While electron microscopy represents the gold standard for detection of synapses, a number of limitations prevent its broad applicability. A key method for detecting synapses is immunostaining for markers of pre- and post-synaptic proteins, which can infer a synapse based upon the apposition of the two markers. While immunostaining and imaging techniques have improved to allow for identification of synapses in tissue, analysis and identification of these appositions are not facile, and there has been a lack of tools to accurately identify these appositions. Here, we delineate a macro that uses open-source and freely available ImageJ or FIJI for analysis of multichannel, z-stack confocal images. With use of a high magnification with a high NA objective, we outline two methods to identify puncta in either sparsely or densely labeled images. Puncta from each channel are used to eliminate non-apposed puncta and are subsequently linked with their cognate from the other channel. These methods are applied to analysis of a pre-synaptic marker, bassoon, with two different post-synaptic markers, gephyrin and N-methyl-d-aspartate (NMDA) receptor subunit 1 (NR1). Using gephyrin as an inhibitory, post-synaptic scaffolding protein, we identify inhibitory synapses in basolateral amygdala, central amygdala, arcuate and the ventromedial hypothalamus. Systematic variation of the settings identify the parameters most critical for this analysis. Identification of specifically overlapping puncta allows for correlation of morphometry data between each channel. Finally, we extend the analysis to only examine puncta overlapping with a cytoplasmic marker of specific cell types, a distinct advantage beyond electron microscopy. Bassoon puncta are restricted to virally transduced, pedunculopontine tegmental nucleus (PPN) axons expressing yellow fluorescent protein. NR1 puncta are restricted to tyrosine hydroxylase labeled dopaminergic neurons of the substantia nigra pars compacta (SNc). The macro identifies bassoon-NR1 overlap throughout the image, or those only restricted to the PPN-SNc connections. Thus, we have extended the available analysis tools that can be used to study synapses in situ. Our analysis code is freely available and open-source allowing for further innovation.
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Affiliation(s)
| | - Parker R Voit
- Department of Biology, Trinity University, San Antonio, TX, United States
| | - Kathryn E Windsor
- Department of Biology, Trinity University, San Antonio, TX, United States
| | - Aamuktha R Karla
- Department of Biology, Trinity University, San Antonio, TX, United States
| | - Sierra R Rodriguez
- Department of Biology, Trinity University, San Antonio, TX, United States
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13
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Abstract
Fluorescence imaging techniques play a pivotal role in our understanding of the nervous system. The emergence of various super-resolution microscopy methods and specialized fluorescent probes enables direct insight into neuronal structure and protein arrangements in cellular subcompartments with so far unmatched resolution. Super-resolving visualization techniques in neurons unveil a novel understanding of cytoskeletal composition, distribution, motility, and signaling of membrane proteins, subsynaptic structure and function, and neuron-glia interaction. Well-defined molecular targets in autoimmune and neurodegenerative disease models provide excellent starting points for in-depth investigation of disease pathophysiology using novel and innovative imaging methodology. Application of super-resolution microscopy in human brain samples and for testing clinical biomarkers is still in its infancy but opens new opportunities for translational research in neurology and neuroscience. In this review, we describe how super-resolving microscopy has improved our understanding of neuronal and brain function and dysfunction in the last two decades.
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Affiliation(s)
- Christian Werner
- Department of Biotechnology & Biophysics, Biocenter, University of Würzburg, 97074 Würzburg, Germany
| | - Markus Sauer
- Department of Biotechnology & Biophysics, Biocenter, University of Würzburg, 97074 Würzburg, Germany
| | - Christian Geis
- Section Translational Neuroimmunology, Department of Neurology, Jena University Hospital, Am Klinikum 1, 07747 Jena, Germany
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14
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Winters BL, Vaughan CW. Mechanisms of endocannabinoid control of synaptic plasticity. Neuropharmacology 2021; 197:108736. [PMID: 34343612 DOI: 10.1016/j.neuropharm.2021.108736] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Revised: 07/27/2021] [Accepted: 07/28/2021] [Indexed: 01/13/2023]
Abstract
The endogenous cannabinoid transmitter system regulates synaptic transmission throughout the nervous system. Unlike conventional transmitters, specific stimuli induce synthesis of endocannabinoids (eCBs) in the postsynaptic neuron, and these travel backwards to modulate presynaptic inputs. In doing so, eCBs can induce short-term changes in synaptic strength and longer-term plasticity. While this eCB regulation is near ubiquitous, it displays major regional and synapse specific variations with different synapse specific forms of short-versus long-term plasticity throughout the brain. These differences are due to the plethora of pre- and postsynaptic mechanisms which have been implicated in eCB signalling, the intricacies of which are only just being realised. In this review, we shall describe the current understanding and highlight new advances in this area, with a focus on the retrograde action of eCBs at CB1 receptors (CB1Rs).
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Affiliation(s)
- Bryony Laura Winters
- Pain Management Research Institute, Kolling Institute of Medical Research, Northern Clinical School, University of Sydney at Royal North Shore Hospital, NSW, Australia.
| | - Christopher Walter Vaughan
- Pain Management Research Institute, Kolling Institute of Medical Research, Northern Clinical School, University of Sydney at Royal North Shore Hospital, NSW, Australia
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15
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León A, Aparicio GI, Scorticati C. Neuronal Glycoprotein M6a: An Emerging Molecule in Chemical Synapse Formation and Dysfunction. Front Synaptic Neurosci 2021; 13:661681. [PMID: 34017241 PMCID: PMC8129562 DOI: 10.3389/fnsyn.2021.661681] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2021] [Accepted: 04/07/2021] [Indexed: 12/27/2022] Open
Abstract
The cellular and molecular mechanisms underlying neuropsychiatric and neurodevelopmental disorders show that most of them can be categorized as synaptopathies-or damage of synaptic function and plasticity. Synaptic formation and maintenance are orchestrated by protein complexes that are in turn regulated in space and time during neuronal development allowing synaptic plasticity. However, the exact mechanisms by which these processes are managed remain unknown. Large-scale genomic and proteomic projects led to the discovery of new molecules and their associated variants as disease risk factors. Neuronal glycoprotein M6a, encoded by the GPM6A gene is emerging as one of these molecules. M6a has been involved in neuron development and synapse formation and plasticity, and was also recently proposed as a gene-target in various neuropsychiatric disorders where it could also be used as a biomarker. In this review, we provide an overview of the structure and molecular mechanisms by which glycoprotein M6a participates in synapse formation and maintenance. We also review evidence collected from patients carrying mutations in the GPM6A gene; animal models, and in vitro studies that together emphasize the relevance of M6a, particularly in synapses and in neurological conditions.
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Affiliation(s)
| | | | - Camila Scorticati
- Instituto de Investigaciones Biotecnológicas “Rodolfo A. Ugalde”, Universidad Nacional de San Martín and Consejo Nacional de Investigaciones Científicas y Técnicas (IIBio-UNSAM-CONICET), Buenos Aires, Argentina
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16
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Yang X, Annaert W. The Nanoscopic Organization of Synapse Structures: A Common Basis for Cell Communication. MEMBRANES 2021; 11:248. [PMID: 33808285 PMCID: PMC8065904 DOI: 10.3390/membranes11040248] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Revised: 03/26/2021] [Accepted: 03/27/2021] [Indexed: 11/16/2022]
Abstract
Synapse structures, including neuronal and immunological synapses, can be seen as the plasma membrane contact sites between two individual cells where information is transmitted from one cell to the other. The distance between the two plasma membranes is only a few tens of nanometers, but these areas are densely populated with functionally different proteins, including adhesion proteins, receptors, and transporters. The narrow space between the two plasma membranes has been a barrier for resolving the synaptic architecture due to the diffraction limit in conventional microscopy (~250 nm). Various advanced super-resolution microscopy techniques, such as stimulated emission depletion (STED), structured illumination microscopy (SIM), and single-molecule localization microscopy (SMLM), bypass the diffraction limit and provide a sub-diffraction-limit resolving power, ranging from 10 to 100 nm. The studies using super-resolution microscopy have revealed unprecedented details of the nanoscopic organization and dynamics of synaptic molecules. In general, most synaptic proteins appear to be heterogeneously distributed and form nanodomains at the membranes. These nanodomains are dynamic functional units, playing important roles in mediating signal transmission through synapses. Herein, we discuss our current knowledge on the super-resolution nanoscopic architecture of synapses and their functional implications, with a particular focus on the neuronal synapses and immune synapses.
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Affiliation(s)
| | - Wim Annaert
- VIB Center for Brain and Disease Research and KU Leuven, Department of Neurosciences, Gasthuisberg, B-3000 Leuven, Belgium;
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17
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Minehart JA, Speer CM. A Picture Worth a Thousand Molecules-Integrative Technologies for Mapping Subcellular Molecular Organization and Plasticity in Developing Circuits. Front Synaptic Neurosci 2021; 12:615059. [PMID: 33469427 PMCID: PMC7813761 DOI: 10.3389/fnsyn.2020.615059] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Accepted: 12/07/2020] [Indexed: 12/23/2022] Open
Abstract
A key challenge in developmental neuroscience is identifying the local regulatory mechanisms that control neurite and synaptic refinement over large brain volumes. Innovative molecular techniques and high-resolution imaging tools are beginning to reshape our view of how local protein translation in subcellular compartments drives axonal, dendritic, and synaptic development and plasticity. Here we review recent progress in three areas of neurite and synaptic study in situ-compartment-specific transcriptomics/translatomics, targeted proteomics, and super-resolution imaging analysis of synaptic organization and development. We discuss synergies between sequencing and imaging techniques for the discovery and validation of local molecular signaling mechanisms regulating synaptic development, plasticity, and maintenance in circuits.
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Affiliation(s)
| | - Colenso M. Speer
- Department of Biology, University of Maryland, College Park, MD, United States
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