The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Vann Bennett - One of the best experts on this subject based on the ideXlab platform.
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βii Spectrin promotes mouse brain connectivity through stabilizing axonal plasma membranes and enabling axonal organelle transport
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Damaris N Lorenzo, Alexandra Badea, Ruobo Zhou, Peter J Mohler, Xiaowei Zhuang, Vann BennettAbstract:βII-Spectrin is the generally expressed member of the β-Spectrin family of elongated polypeptides that form micrometer-scale networks associated with plasma membranes. We addressed in vivo functions of βII-Spectrin in neurons by knockout of βII-Spectrin in mouse neural progenitors. βII-Spectrin deficiency caused severe defects in long-range axonal connectivity and axonal degeneration. βII-Spectrin–null neurons exhibited reduced axon growth, loss of actin–Spectrin-based periodic membrane skeleton, and impaired bidirectional axonal transport of synaptic cargo. We found that βII-Spectrin associates with KIF3A, KIF5B, KIF1A, and dynactin, implicating Spectrin in the coupling of motors and synaptic cargo. βII-Spectrin required phosphoinositide lipid binding to promote axonal transport and restore axon growth. Knockout of ankyrin-B (AnkB), a βII-Spectrin partner, primarily impaired retrograde organelle transport, while double knockout of βII-Spectrin and AnkB nearly eliminated transport. Thus, βII-Spectrin promotes both axon growth and axon stability through establishing the actin–Spectrin-based membrane-associated periodic skeleton as well as enabling axonal transport of synaptic cargo.
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an adaptable Spectrin ankyrin based mechanism for long range organization of plasma membranes in vertebrate tissues
Current Topics in Membranes, 2016Co-Authors: Vann Bennett, Damaris N LorenzoAbstract:Ankyrins are membrane-associated proteins that together with their Spectrin partners are responsible for micron-scale organization of vertebrate plasma membranes, including those of erythrocytes, excitable membranes of neurons and heart, lateral membrane domains of columnar epithelial cells, and striated muscle. Ankyrins coordinate functionally related membrane transporters and cell adhesion proteins (15 protein families identified so far) within plasma membrane compartments through independently evolved interactions of intrinsically disordered sequences with a highly conserved peptide-binding groove formed by the ANK repeat solenoid. Ankyrins are coupled to Spectrins, which are elongated organelle-sized proteins that form mechanically resilient arrays through cross-linking by specialized actin filaments. In addition to protein interactions, cellular targeting and assembly of Spectrin/ankyrin domains also critically depend on palmitoylation of ankyrin-G by aspartate-histidine-histidine-cysteine 5/8 palmitoyltransferases, as well as interaction of beta-2 Spectrin with phosphoinositide lipids. These lipid-dependent Spectrin/ankyrin domains are not static but are locally dynamic and determine membrane identity through opposing endocytosis of bulk lipids as well as specific proteins. A partnership between Spectrin, ankyrin, and cell adhesion molecules first emerged in bilaterians over 500 million years ago. Ankyrin and Spectrin may have been recruited to plasma membranes from more ancient roles in organelle transport. The basic bilaterian Spectrin-ankyrin toolkit markedly expanded in vertebrates through gene duplications combined with variation in unstructured intramolecular regulatory sequences as well as independent evolution of ankyrin-binding activity by ion transporters involved in action potentials and calcium homeostasis. In addition, giant vertebrate ankyrins with specialized roles in axons acquired new coding sequences by exon shuffling. We speculate that early axon initial segments and epithelial lateral membranes initially were based on Spectrin-ankyrin-cell adhesion molecule assemblies and subsequently served as "incubators," where ion transporters independently acquired ankyrin-binding activity through positive selection.
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membrane domains based on ankyrin and Spectrin associated with cell cell interactions
Cold Spring Harbor Perspectives in Biology, 2009Co-Authors: Vann Bennett, Jane HealyAbstract:Nodes of Ranvier and axon initial segments of myelinated nerves, sites of cell-cell contact in early embryos and epithelial cells, and neuromuscular junctions of skeletal muscle all perform physiological functions that depend on clustering of functionally related but structurally diverse ion transporters and cell adhesion molecules within microdomains of the plasma membrane. These specialized cell surface domains appeared at different times in metazoan evolution, involve a variety of cell types, and are populated by distinct membrane-spanning proteins. Nevertheless, recent work has shown that these domains all share on their cytoplasmic surfaces a membrane skeleton comprised of members of the ankyrin and Spectrin families. This review will summarize basic features of ankyrins and Spectrins, and will discuss emerging evidence that these proteins are key players in a conserved mechanism responsible for assembly and maintenance of physiologically important domains on the surfaces of diverse cells.
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Ankyrin-B Targets β2-Spectrin to an Intracellular Compartment in Neonatal Cardiomyocytes
The Journal of biological chemistry, 2004Co-Authors: Peter J Mohler, Woohyun Yoon, Vann BennettAbstract:Abstract Ankyrin-B is a Spectrin-binding protein that is required for localization of inositol 1,4,5-trisphosphate receptor and ryanodine receptor in neonatal cardiomyocytes. This work addresses the interaction between ankyrin-B and β2-Spectrin in these cells. Ankyrin-B and β2-Spectrin are colocalized in an intracellular striated compartment overlying the M-line and distinct from T-tubules, sarcoplasmic reticulum, Golgi, endoplasmic reticulum, lysosomes, and endosomes. β2-Spectrin is absent in ankyrin-B-null cardiomyocytes and is restored to a normal striated pattern by rescue with green fluorescent protein-220-kDa ankyrin-B. We identified two mutants (A1000P and DAR976AAA) located in the ZU5 domain which eliminate Spectrin binding activity of ankyrin-B. Ankyrin-B mutants lacking Spectrin binding activity are normally targeted but do not reestablish β2-Spectrin in ankyrin-B+/- cardiomyocytes. However, both mutant forms of ankyrin-B are still capable of restoring inositol 1,4,5-trisphosphate receptor localization and normal contraction frequency of cardiomyocytes. Therefore, direct binding of β2-Spectrin to ankyrin-B is required for the normal targeting of β2-Spectrin in neonatal cardiomyocytes. In contrast, ankyrin-B localization and function are independent of β2-Spectrin. In summary, this work demonstrates that interaction between members of the ankyrin and β-Spectrin families previously established in erythrocytes and axon initial segments also occurs in neonatal cardiomyocytes with ankyrin-B and β2-Spectrin. This work also establishes a functional hierarchy in which ankyrin-B determines the localization of β2-Spectrin and operates independently of β2-Spectrin in its role in organizing membrane-spanning proteins.
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α-Adducin dissociates from F-actin and Spectrin during platelet activation
The Journal of cell biology, 2003Co-Authors: Kurt L. Barkalow, Vann Bennett, Joseph E. Italiano, Denise E. Chou, Yoichiro Matsuoka, John H. HartwigAbstract:ASpectrin-based skeleton uniformly underlies and supports the plasma membrane of the resting platelet, but remodels and centralizes in the activated platelet. α-Adducin, a phosphoprotein that forms a ternary complex with F-actin and Spectrin, is dephosphorylated and mostly bound to Spectrin in the membrane skeleton of the resting platelet at sites where actin filaments attach to the ends of Spectrin molecules. Platelets activated through protease-activated receptor 1, FcγRIIA, or by treatment with PMA phosphorylate adducin at Ser726. Phosphoadducin releases from the membrane skeleton concomitant with its dissociation from Spectrin and actin. Inhibition of PKC blunts adducin phosphorylation and release from Spectrin and actin, preventing the centralization of Spectrin that normally follows cell activation. We conclude that adducin targets actin filament ends to Spectrin to complete the assembly of the resting membrane skeleton. Dissociation of phosphoadducin releases Spectrin from actin, facilitating centralization of Spectrin, and leads to the exposure of barbed actin filament ends that may then participate in converting the resting platelet's disc shape into its active form.
Matthew N Rasband - One of the best experts on this subject based on the ideXlab platform.
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β Spectrin dependent and domain specific mechanisms for na channel clustering
eLife, 2020Co-Authors: Chenghsin Liu, Jeffrey L Noebels, Peter J Mohler, Ryan Seo, Michael C Stankewich, Thomas J Hund, Matthew N RasbandAbstract:Previously, we showed that a hierarchy of Spectrin cytoskeletal proteins maintains nodal Na+ channels (Liu et al., 2020). Here, using mice lacking β1, β4, or β1/β4 Spectrins, we show this hierarchy does not function at axon initial segments (AIS). Although β1 Spectrin, together with AnkyrinR (AnkR), compensates for loss of nodal β4 Spectrin, it cannot compensate at AIS. We show AnkR lacks the domain necessary for AIS localization. Whereas loss of β4 Spectrin causes motor impairment and disrupts AIS, loss of β1 Spectrin has no discernable effect on central nervous system structure or function. However, mice lacking both neuronal β1 and β4 Spectrin show exacerbated nervous system dysfunction compared to mice lacking β1 or β4 Spectrin alone, including profound disruption of AIS Na+ channel clustering, progressive loss of nodal Na+ channels, and seizures. These results further define the important role of AIS and nodal Spectrins for nervous system function.
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αii Spectrin forms a periodic cytoskeleton at the axon initial segment and is required for nervous system function
The Journal of Neuroscience, 2017Co-Authors: Claire Yumei Huang, Chuansheng Zhang, Tammy Szuyu Ho, Juan A Osesprieto, Joshua Lalonde, Jeffrey L Noebels, Christophe Leterrier, Alma L Burlingame, Matthew N RasbandAbstract:Spectrins form a submembranous cytoskeleton proposed to confer strength and flexibility to neurons and to participate in ion channel clustering at axon initial segments (AIS) and nodes of Ranvier. Neuronal Spectrin cytoskeletons consist of diverse β subunits and αII Spectrin. Although αII Spectrin is found in neurons in both axonal and somatodendritic domains, using proteomics, biochemistry, and super-resolution microscopy we show that αII and βIV Spectrin interact and form a periodic AIS cytoskeleton. To determine the role of Spectrins in the nervous system, we generated Sptan1 f/f mice for deletion of CNS αII Spectrin. We analyzed αII Spectrin-deficient mice of both sexes and found that loss of αII Spectrin causes profound reductions in all β Spectrins. αII Spectrin-deficient mice die before one month of age, have disrupted AIS and many other neurological impairments including seizures, disrupted cortical lamination, and widespread neurodegeneration. These results demonstrate the importance of the Spectrin cytoskeleton both at the AIS and throughout the nervous system. SIGNIFICANCE STATEMENT Spectrin cytoskeletons play diverse roles in neurons including assembly of excitable domains like the axon initial segment and nodes of Ranvier. However, the molecular composition and structure of these cytoskeletons remain poorly understood. Here, we show αII Spectrin partners with βIV Spectrin to form a periodic cytoskeleton at axon initial segments and nodes of Ranvier. Using a new αII Spectrin conditional knockout mouse we show that αII Spectrin is required for axon initial segment assembly, neuronal excitability, cortical lamination, and to protect against neurodegeneration. These results demonstrate the broad importance of Spectrin cytoskeletons for nervous system function and development, and have important implications for nervous system injuries and diseases because disruption of the Spectrin cytoskeleton is a common molecular pathology.
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An αII Spectrin-Based Cytoskeleton Protects Large-Diameter Myelinated Axons from Degeneration
Journal of Neuroscience, 2017Co-Authors: Claire Yumei Huang, Chuansheng Zhang, Christophe Leterrier, Daniel Zollinger, Matthew N RasbandAbstract:Axons must withstand mechanical forces, including tension, torsion, and compression. Spectrins and actin form a periodic cytoskeleton proposed to protect axons against these forces. However, because Spectrins also participate in assembly of axon initial segments (AISs) and nodes of Ranvier, it is difficult to uncouple their roles in maintaining axon integrity from their functions at AIS and nodes. To overcome this problem and to determine the importance of Spectrin cytoskeletons for axon integrity, we generated mice with II Spectrin-deficient peripheral sensory neurons. The axons of these neurons are very long and exposed to the mechanical forces associated with limb movement; most lack an AIS, and some are unmyelinated and have no nodes. We analyzed II Spectrin-deficient mice of both sexes and found that, in myelinated axons, II Spectrin forms a periodic cytoskeleton with IV and II Spectrin at nodes of Ranvier and paranodes, respectively, but that loss of II Spectrin disrupts this organization. Avil-cre;Sptan1 f/f mice have reduced numbers of nodes, disrupted paranodal junctions, and mislocalized Kv1 K channels. We show that the density of nodal IV Spectrin is constant among axons, but the density of nodal II Spectrin increases with axon diameter. Remarkably, Avil-cre;Sptan1 f/f mice have intact nociception and small-diameter axons, but severe ataxia due to preferential degeneration of large-diameter myelinated axons. Our results suggest that nodal II Spectrin helps resist the mechanical forces experienced by large-diameter axons, and that II Spectrin-dependent cytoskel-etons are also required for assembly of nodes of Ranvier.
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an αii Spectrin based cytoskeleton protects large diameter myelinated axons from degeneration
The Journal of Neuroscience, 2017Co-Authors: Claire Yumei Huang, Chuansheng Zhang, Christophe Leterrier, Daniel R Zollinger, Matthew N RasbandAbstract:Axons must withstand mechanical forces, including tension, torsion, and compression. Spectrins and actin form a periodic cytoskeleton proposed to protect axons against these forces. However, because Spectrins also participate in assembly of axon initial segments (AISs) and nodes of Ranvier, it is difficult to uncouple their roles in maintaining axon integrity from their functions at AIS and nodes. To overcome this problem and to determine the importance of Spectrin cytoskeletons for axon integrity, we generated mice with αII Spectrin-deficient peripheral sensory neurons. The axons of these neurons are very long and exposed to the mechanical forces associated with limb movement; most lack an AIS, and some are unmyelinated and have no nodes. We analyzed αII Spectrin-deficient mice of both sexes and found that, in myelinated axons, αII Spectrin forms a periodic cytoskeleton with βIV and βII Spectrin at nodes of Ranvier and paranodes, respectively, but that loss of αII Spectrin disrupts this organization. Avil-cre;Sptan1f/f mice have reduced numbers of nodes, disrupted paranodal junctions, and mislocalized Kv1 K+ channels. We show that the density of nodal βIV Spectrin is constant among axons, but the density of nodal αII Spectrin increases with axon diameter. Remarkably, Avil-cre;Sptan1f/f mice have intact nociception and small-diameter axons, but severe ataxia due to preferential degeneration of large-diameter myelinated axons. Our results suggest that nodal αII Spectrin helps resist the mechanical forces experienced by large-diameter axons, and that αII Spectrin-dependent cytoskeletons are also required for assembly of nodes of Ranvier.SIGNIFICANCE STATEMENT A periodic axonal cytoskeleton consisting of actin and Spectrin has been proposed to help axons resist the mechanical forces to which they are exposed (e.g., compression, torsion, and stretch). However, until now, no vertebrate animal model has tested the requirement of the Spectrin cytoskeleton in maintenance of axon integrity. We demonstrate the role of the periodic Spectrin-dependent cytoskeleton in axons and show that loss of αII Spectrin from PNS axons causes preferential degeneration of large-diameter myelinated axons. We show that nodal αII Spectrin is found at greater densities in large-diameter myelinated axons, suggesting that nodes are particularly vulnerable domains requiring a specialized cytoskeleton to protect against axon degeneration.
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αII Spectrin forms a periodic cytoskeleton at the axon initial segment and is required for nervous system function
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2017Co-Authors: Claire Yumei Huang, Chuansheng Zhang, Joshua Lalonde, Jeffrey L Noebels, Christophe Leterrier, Alma L Burlingame, Juan A. Oses-prieto, Matthew N RasbandAbstract:Spectrins form a submembranous cytoskeleton proposed to confer strength and flexibility to neurons and to participate in ion channel clustering at axon initial segments (AIS) and nodes of Ranvier. Neuronal Spectrin cytoskeletons consist of diverse β subunits and αII Spectrin. Although αII Spectrin is found in neurons in both axonal and somatodendritic domains, using proteomics, biochemistry, and superresolution microscopy, we show that αII and βIV Spectrin interact and form a periodic AIS cytoskeleton. To determine the role of Spectrins in the nervous system, we generated Sptan1f/f mice for deletion of CNS αII Spectrin. We analyzed αII Spectrin-deficient mice of both sexes and found that loss of αII Spectrin causes profound reductions in all β Spectrins. αII Spectrin-deficient mice die before 1 month of age and have disrupted AIS and many other neurological impairments including seizures, disrupted cortical lamination, and widespread neurodegeneration. These results demonstrate the importance of the Spectrin cytoskeleton both at the AIS and throughout the nervous system.SIGNIFICANCE STATEMENT Spectrin cytoskeletons play diverse roles in neurons, including assembly of excitable domains such as the axon initial segment (AIS) and nodes of Ranvier. However, the molecular composition and structure of these cytoskeletons remain poorly understood. Here, we show that αII Spectrin partners with βIV Spectrin to form a periodic cytoskeleton at the AIS. Using a new αII Spectrin conditional knock-out mouse, we show that αII Spectrin is required for AIS assembly, neuronal excitability, cortical lamination, and to protect against neurodegeneration. These results demonstrate the broad importance of Spectrin cytoskeletons for nervous system function and development and have important implications for nervous system injuries and diseases because disruption of the Spectrin cytoskeleton is a common molecular pathology.
Christophe Leterrier - One of the best experts on this subject based on the ideXlab platform.
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Ultrastructure of the axonal periodic scaffold reveals a braid-like organization of actin rings
Nature Communications, 2019Co-Authors: Stéphane Vassilopoulos, Solène Gibaud, Angélique Jimenez, Ghislaine Caillol, Christophe LeterrierAbstract:The ultrastructural details of the periodic scaffold of actin rings under the plasma membrane of axons remain unknown. Here, the authors combine platinum-replica electron and optical super-resolution microscopy and resolve actin rings as braids made of two long, intertwined actin filaments connected by a dense mesh of aligned Spectrins. Recent super-resolution microscopy studies have unveiled a periodic scaffold of actin rings regularly spaced by Spectrins under the plasma membrane of axons. However, ultrastructural details are unknown, limiting a molecular and mechanistic understanding of these enigmatic structures. Here, we combine platinum-replica electron and optical super-resolution microscopy to investigate the cortical cytoskeleton of axons at the ultrastructural level. Immunogold labeling and correlative super-resolution/electron microscopy allow us to unambiguously resolve actin rings as braids made of two long, intertwined actin filaments connected by a dense mesh of aligned Spectrins. This molecular arrangement contrasts with the currently assumed model of actin rings made of short, capped actin filaments. Along the proximal axon, we resolved the presence of phospho-myosin light chain and the scaffold connection with microtubules via ankyrin G. We propose that braided rings explain the observed stability of the actin-Spectrin scaffold and ultimately participate in preserving the axon integrity.
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Ultrastructure of the axonal periodic scaffold reveals a braid-like organization of actin rings
Nature Communications, 2019Co-Authors: Stéphane Vassilopoulos, Solène Gibaud, Angélique Jimenez, Ghislaine Caillol, Christophe LeterrierAbstract:Recent super-resolution microscopy studies have unveiled a periodic scaffold of actin rings regularly spaced by Spectrins under the plasma membrane of axons. However, ultrastructural details are unknown, limiting a molecular and mechanistic understanding of these enigmatic structures. Here, we combine platinum-replica electron and optical super-resolution micro-scopy to investigate the cortical cytoskeleton of axons at the ultrastructural level. Immunogold labeling and correlative super-resolution/electron microscopy allow us to unambiguously resolve actin rings as braids made of two long, intertwined actin filaments connected by a dense mesh of aligned Spectrins. This molecular arrangement contrasts with the currently assumed model of actin rings made of short, capped actin filaments. Along the proximal axon, we resolved the presence of phospho-myosin light chain and the scaffold connection with microtubules via ankyrin G. We propose that braided rings explain the observed stability of the actin-Spectrin scaffold and ultimately participate in preserving the axon integrity.
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A dual role for βII-Spectrin in axons
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Christophe LeterrierAbstract:Spectrins have been known for a long time as submembrane structural proteins, but a study from Lorenzo et al. (1) demonstrates an unexpected role for a neuronal Spectrin in axonal transport. Actin and Spectrins form specialized submembrane scaffolds important for the morphogenesis, compartmentation, and mechanical properties in a range of differentiated cell types (2, 3). Spectrin assembles the submembrane scaffold that shapes red blood cells—in fact, it was named from the membranous ghosts (specter) of erythrocytes where it was first discovered (4). In these cells, Spectrins arrange in a hexagonal pattern, connecting short actin nodes (5⇓–7), generating the toroidal shape of erythrocytes. Spectrins are tetramers made of 2 α- and 2 β-Spectrin subunits (αI and βI in erythrocytes) that can stretch between 60 and 200 nm in length (8). The actin/Spectrin scaffold thus provides flexibility and mechanical resistance to the large deformations that erythrocytes undergo along small capillaries (9). In neurons, a protein resembling Spectrin had been identified and initially named fodrin (10). Fodrin was later found to be the general Spectrin present in most cells (11), and later shown to consist of αII- and βII-Spectrin tetramers (12). These Spectrins assemble under the plasma membrane in cultured cells (10, 13) and in neurons (10, 14), but their precise arrangement remained unknown until recently. In 2013, superresolution optical microscopy images showed that Spectrins assemble axially along the axon and parts of dendrites, with tetramers forming a succession of cylinders connecting actin rings (15). Due to the 190-nm length of the neuronal Spectrin tetramer (16, 17), this results in a scaffold containing submembrane actin rings regularly spaced every 190 nm along the axon … [↵][1]1Email: christophe.leterrier{at}univ-amu.fr. [1]: #xref-corresp-1-1
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A dual role for βII-Spectrin in axons
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Christophe LeterrierAbstract:Spectrins have been known for a long time as submembrane structural proteins, but a study from Lorenzo et al. (1) demonstrates an unexpected role for a neuronal Spectrin in axonal transport. Actin and Spectrins form specialized submembrane scaffolds important for the morphogenesis, compartmentation, and mechanical properties in a range of differentiated cell types (2, 3). Spectrin assembles the submembrane scaffold that shapes red blood cells—in fact, it was named from the membranous ghosts (specter) of erythrocytes where it was first discovered (4). In these cells, Spectrins arrange in a hexagonal pattern, connecting short actin nodes (5⇓–7), generating the toroidal shape of erythrocytes. Spectrins are tetramers made of 2 α- and 2 β-Spectrin subunits (αI and βI in erythrocytes) that can stretch between 60 and 200 nm in length (8). The actin/Spectrin scaffold thus provides flexibility and mechanical resistance to the large deformations that erythrocytes undergo along small capillaries (9).
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αii Spectrin forms a periodic cytoskeleton at the axon initial segment and is required for nervous system function
The Journal of Neuroscience, 2017Co-Authors: Claire Yumei Huang, Chuansheng Zhang, Tammy Szuyu Ho, Juan A Osesprieto, Joshua Lalonde, Jeffrey L Noebels, Christophe Leterrier, Alma L Burlingame, Matthew N RasbandAbstract:Spectrins form a submembranous cytoskeleton proposed to confer strength and flexibility to neurons and to participate in ion channel clustering at axon initial segments (AIS) and nodes of Ranvier. Neuronal Spectrin cytoskeletons consist of diverse β subunits and αII Spectrin. Although αII Spectrin is found in neurons in both axonal and somatodendritic domains, using proteomics, biochemistry, and super-resolution microscopy we show that αII and βIV Spectrin interact and form a periodic AIS cytoskeleton. To determine the role of Spectrins in the nervous system, we generated Sptan1 f/f mice for deletion of CNS αII Spectrin. We analyzed αII Spectrin-deficient mice of both sexes and found that loss of αII Spectrin causes profound reductions in all β Spectrins. αII Spectrin-deficient mice die before one month of age, have disrupted AIS and many other neurological impairments including seizures, disrupted cortical lamination, and widespread neurodegeneration. These results demonstrate the importance of the Spectrin cytoskeleton both at the AIS and throughout the nervous system. SIGNIFICANCE STATEMENT Spectrin cytoskeletons play diverse roles in neurons including assembly of excitable domains like the axon initial segment and nodes of Ranvier. However, the molecular composition and structure of these cytoskeletons remain poorly understood. Here, we show αII Spectrin partners with βIV Spectrin to form a periodic cytoskeleton at axon initial segments and nodes of Ranvier. Using a new αII Spectrin conditional knockout mouse we show that αII Spectrin is required for axon initial segment assembly, neuronal excitability, cortical lamination, and to protect against neurodegeneration. These results demonstrate the broad importance of Spectrin cytoskeletons for nervous system function and development, and have important implications for nervous system injuries and diseases because disruption of the Spectrin cytoskeleton is a common molecular pathology.
Peter J Mohler - One of the best experts on this subject based on the ideXlab platform.
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β Spectrin dependent and domain specific mechanisms for na channel clustering
eLife, 2020Co-Authors: Chenghsin Liu, Jeffrey L Noebels, Peter J Mohler, Ryan Seo, Michael C Stankewich, Thomas J Hund, Matthew N RasbandAbstract:Previously, we showed that a hierarchy of Spectrin cytoskeletal proteins maintains nodal Na+ channels (Liu et al., 2020). Here, using mice lacking β1, β4, or β1/β4 Spectrins, we show this hierarchy does not function at axon initial segments (AIS). Although β1 Spectrin, together with AnkyrinR (AnkR), compensates for loss of nodal β4 Spectrin, it cannot compensate at AIS. We show AnkR lacks the domain necessary for AIS localization. Whereas loss of β4 Spectrin causes motor impairment and disrupts AIS, loss of β1 Spectrin has no discernable effect on central nervous system structure or function. However, mice lacking both neuronal β1 and β4 Spectrin show exacerbated nervous system dysfunction compared to mice lacking β1 or β4 Spectrin alone, including profound disruption of AIS Na+ channel clustering, progressive loss of nodal Na+ channels, and seizures. These results further define the important role of AIS and nodal Spectrins for nervous system function.
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βii Spectrin promotes mouse brain connectivity through stabilizing axonal plasma membranes and enabling axonal organelle transport
Proceedings of the National Academy of Sciences of the United States of America, 2019Co-Authors: Damaris N Lorenzo, Alexandra Badea, Ruobo Zhou, Peter J Mohler, Xiaowei Zhuang, Vann BennettAbstract:βII-Spectrin is the generally expressed member of the β-Spectrin family of elongated polypeptides that form micrometer-scale networks associated with plasma membranes. We addressed in vivo functions of βII-Spectrin in neurons by knockout of βII-Spectrin in mouse neural progenitors. βII-Spectrin deficiency caused severe defects in long-range axonal connectivity and axonal degeneration. βII-Spectrin–null neurons exhibited reduced axon growth, loss of actin–Spectrin-based periodic membrane skeleton, and impaired bidirectional axonal transport of synaptic cargo. We found that βII-Spectrin associates with KIF3A, KIF5B, KIF1A, and dynactin, implicating Spectrin in the coupling of motors and synaptic cargo. βII-Spectrin required phosphoinositide lipid binding to promote axonal transport and restore axon growth. Knockout of ankyrin-B (AnkB), a βII-Spectrin partner, primarily impaired retrograde organelle transport, while double knockout of βII-Spectrin and AnkB nearly eliminated transport. Thus, βII-Spectrin promotes both axon growth and axon stability through establishing the actin–Spectrin-based membrane-associated periodic skeleton as well as enabling axonal transport of synaptic cargo.
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The role of βII Spectrin in cardiac health and disease.
Life sciences, 2017Co-Authors: Mohamed H. Derbala, Peter J Mohler, Aaron Guo, Sakima A. SmithAbstract:Abstract Spectrins are large, flexible proteins comprised of α-β dimers that are connected head-to-head to form the canonical heterotetrameric Spectrin structure. Spectrins were initially believed to be exclusively found in human erythrocytic membrane and are highly conserved among different species. βII Spectrin, the most common isoform of non-erythrocytic Spectrin, is found in all nucleated cells and forms larger macromolecular complexes with ankyrins and actins. Not only is βII Spectrin a central cytoskeletal scaffolding protein involved in preserving cell structure but it has also emerged as a critical protein required for distinct physiologic functions such as posttranslational localization of crucial membrane proteins and signal transduction. In the heart, βII Spectrin plays a vital role in maintaining normal cardiac membrane excitability and proper cardiac development during embryogenesis. Mutations in βII Spectrin genes have been strongly linked with the development of serious cardiac disorders such as congenital arrhythmias, heart failure, and possibly sudden cardiac death. This review focuses on our current knowledge of the role βII Spectrin plays in the cardiovascular system in health and disease and the potential future clinical implications.
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Ankyrins and Spectrins in Cardiovascular Biology and Disease.
Frontiers in physiology, 2017Co-Authors: Mona El Refaey, Peter J MohlerAbstract:Ankyrins are adaptor proteins critical for the expression and targeting of cardiac membrane proteins, signaling molecules, and cytoskeletal elements. Findings in humans and animal models have highlighted the in vivo roles for ankyrins in normal physiology and in cardiovascular disease, most notably in cardiac arrhythmia. For example, human ANK2 loss-of-function variants are associated with a complex array of electrical and structural phenotypes now termed "ankyrin-B syndrome," whereas alterations in the ankyrin-G pathway for Nav channel targeting are associated with human Brugada syndrome. Further, both ankyrin-G and -B are now linked with acquired forms of cardiovascular disease including myocardial infarction and atrial fibrillation. Spectrins are ankyrin-associated proteins and recent studies support the critical role of ankyrin-Spectrin interactions in normal cardiac physiology as well as regulation of key ion channel and signaling complexes. This review will highlight the roles of ankyrins and Spectrins in cardiovascular physiology as well as illustrate the link between the dysfunction in ankyrin- and Spectrin-based pathways and disease.
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Ankyrins and Spectrins in Cardiovascular Biology and Disease.
Frontiers in Physiology, 2017Co-Authors: Mona El Refaey, Peter J MohlerAbstract:Ankyrins are adaptor proteins critical for the expression and targeting of cardiac membrane proteins, signaling molecules, and cytoskeletal elements. Findings in humans and animal models have highlighted the in vivo roles for ankyrins in normal physiology and in cardiovascular disease, most notably in cardiac arrhythmia. For example, human ANK2 loss-of-function variants are associated with a complex array of electrical and structural phenotypes now termed “ankyrin-B syndrome”, whereas alterations in the ankyrin-G pathway for Nav channel targeting are associated with human Brugada syndrome. Further, both ankyrin-G and -B are now linked with acquired forms of cardiovascular disease including myocardial infarction and atrial fibrillation. Spectrins are ankyrin-associated proteins and recent studies support the critical role of ankyrin-Spectrin interactions in normal cardiac physiology as well as regulation of key ion channel and signaling complexes. This review will highlight the roles of ankyrins and Spectrins in cardiovascular physiology as well as illustrate the link between dysfunction in ankyrin- and Spectrin-based pathways and disease.
Claire Yumei Huang - One of the best experts on this subject based on the ideXlab platform.
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defining new mechanistic roles for αii Spectrin in cardiac function
Journal of Biological Chemistry, 2019Co-Authors: Ellen R Lubbers, Claire Yumei Huang, Nathaniel P Murphy, Hassan Hussein Musa, Rohan Gupta, Morgan V Price, Mei Han, Georges Daoud, Daniel Gratz, Mona El RefaeyAbstract:Spectrins are cytoskeletal proteins essential for membrane biogenesis and regulation and serve critical roles in protein targeting and cellular signaling. αII Spectrin (SPTAN1) is one of two α Spectrin genes and αII Spectrin dysfunction is linked to alterations in axon initial segment formation, cortical lamination, and neuronal excitability. Furthermore, human αII Spectrin loss-of-function variants cause neurological disease. As global αII Spectrin knockout mice are embryonic lethal, the in vivo roles of αII Spectrin in adult heart are unknown and untested. Here, based on pronounced alterations in αII Spectrin regulation in human heart failure we tested the in vivo roles of αII Spectrin in the vertebrate heart. We created a mouse model of cardiomyocyte-selective αII Spectrin-deficiency (cKO) and used this model to define the roles of αII Spectrin in cardiac function. αII Spectrin cKO mice displayed significant structural, cellular, and electrical phenotypes that resulted in accelerated structural remodeling, fibrosis, arrhythmia, and mortality in response to stress. At the molecular level, we demonstrate that αII Spectrin plays a nodal role for global cardiac Spectrin regulation, as αII Spectrin cKO hearts exhibited remodeling of αI Spectrin and altered β-Spectrin expression and localization. At the cellular level, αII Spectrin deficiency resulted in altered expression, targeting, and regulation of cardiac ion channels NaV1.5 and KV4.3. In summary, our findings define critical and unexpected roles for the multifunctional αII Spectrin protein in the heart. Furthermore, our work provides a new in vivo animal model to study the roles of αII Spectrin in the cardiomyocyte.
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αii Spectrin forms a periodic cytoskeleton at the axon initial segment and is required for nervous system function
The Journal of Neuroscience, 2017Co-Authors: Claire Yumei Huang, Chuansheng Zhang, Tammy Szuyu Ho, Juan A Osesprieto, Joshua Lalonde, Jeffrey L Noebels, Christophe Leterrier, Alma L Burlingame, Matthew N RasbandAbstract:Spectrins form a submembranous cytoskeleton proposed to confer strength and flexibility to neurons and to participate in ion channel clustering at axon initial segments (AIS) and nodes of Ranvier. Neuronal Spectrin cytoskeletons consist of diverse β subunits and αII Spectrin. Although αII Spectrin is found in neurons in both axonal and somatodendritic domains, using proteomics, biochemistry, and super-resolution microscopy we show that αII and βIV Spectrin interact and form a periodic AIS cytoskeleton. To determine the role of Spectrins in the nervous system, we generated Sptan1 f/f mice for deletion of CNS αII Spectrin. We analyzed αII Spectrin-deficient mice of both sexes and found that loss of αII Spectrin causes profound reductions in all β Spectrins. αII Spectrin-deficient mice die before one month of age, have disrupted AIS and many other neurological impairments including seizures, disrupted cortical lamination, and widespread neurodegeneration. These results demonstrate the importance of the Spectrin cytoskeleton both at the AIS and throughout the nervous system. SIGNIFICANCE STATEMENT Spectrin cytoskeletons play diverse roles in neurons including assembly of excitable domains like the axon initial segment and nodes of Ranvier. However, the molecular composition and structure of these cytoskeletons remain poorly understood. Here, we show αII Spectrin partners with βIV Spectrin to form a periodic cytoskeleton at axon initial segments and nodes of Ranvier. Using a new αII Spectrin conditional knockout mouse we show that αII Spectrin is required for axon initial segment assembly, neuronal excitability, cortical lamination, and to protect against neurodegeneration. These results demonstrate the broad importance of Spectrin cytoskeletons for nervous system function and development, and have important implications for nervous system injuries and diseases because disruption of the Spectrin cytoskeleton is a common molecular pathology.
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An αII Spectrin-Based Cytoskeleton Protects Large-Diameter Myelinated Axons from Degeneration
Journal of Neuroscience, 2017Co-Authors: Claire Yumei Huang, Chuansheng Zhang, Christophe Leterrier, Daniel Zollinger, Matthew N RasbandAbstract:Axons must withstand mechanical forces, including tension, torsion, and compression. Spectrins and actin form a periodic cytoskeleton proposed to protect axons against these forces. However, because Spectrins also participate in assembly of axon initial segments (AISs) and nodes of Ranvier, it is difficult to uncouple their roles in maintaining axon integrity from their functions at AIS and nodes. To overcome this problem and to determine the importance of Spectrin cytoskeletons for axon integrity, we generated mice with II Spectrin-deficient peripheral sensory neurons. The axons of these neurons are very long and exposed to the mechanical forces associated with limb movement; most lack an AIS, and some are unmyelinated and have no nodes. We analyzed II Spectrin-deficient mice of both sexes and found that, in myelinated axons, II Spectrin forms a periodic cytoskeleton with IV and II Spectrin at nodes of Ranvier and paranodes, respectively, but that loss of II Spectrin disrupts this organization. Avil-cre;Sptan1 f/f mice have reduced numbers of nodes, disrupted paranodal junctions, and mislocalized Kv1 K channels. We show that the density of nodal IV Spectrin is constant among axons, but the density of nodal II Spectrin increases with axon diameter. Remarkably, Avil-cre;Sptan1 f/f mice have intact nociception and small-diameter axons, but severe ataxia due to preferential degeneration of large-diameter myelinated axons. Our results suggest that nodal II Spectrin helps resist the mechanical forces experienced by large-diameter axons, and that II Spectrin-dependent cytoskel-etons are also required for assembly of nodes of Ranvier.
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an αii Spectrin based cytoskeleton protects large diameter myelinated axons from degeneration
The Journal of Neuroscience, 2017Co-Authors: Claire Yumei Huang, Chuansheng Zhang, Christophe Leterrier, Daniel R Zollinger, Matthew N RasbandAbstract:Axons must withstand mechanical forces, including tension, torsion, and compression. Spectrins and actin form a periodic cytoskeleton proposed to protect axons against these forces. However, because Spectrins also participate in assembly of axon initial segments (AISs) and nodes of Ranvier, it is difficult to uncouple their roles in maintaining axon integrity from their functions at AIS and nodes. To overcome this problem and to determine the importance of Spectrin cytoskeletons for axon integrity, we generated mice with αII Spectrin-deficient peripheral sensory neurons. The axons of these neurons are very long and exposed to the mechanical forces associated with limb movement; most lack an AIS, and some are unmyelinated and have no nodes. We analyzed αII Spectrin-deficient mice of both sexes and found that, in myelinated axons, αII Spectrin forms a periodic cytoskeleton with βIV and βII Spectrin at nodes of Ranvier and paranodes, respectively, but that loss of αII Spectrin disrupts this organization. Avil-cre;Sptan1f/f mice have reduced numbers of nodes, disrupted paranodal junctions, and mislocalized Kv1 K+ channels. We show that the density of nodal βIV Spectrin is constant among axons, but the density of nodal αII Spectrin increases with axon diameter. Remarkably, Avil-cre;Sptan1f/f mice have intact nociception and small-diameter axons, but severe ataxia due to preferential degeneration of large-diameter myelinated axons. Our results suggest that nodal αII Spectrin helps resist the mechanical forces experienced by large-diameter axons, and that αII Spectrin-dependent cytoskeletons are also required for assembly of nodes of Ranvier.SIGNIFICANCE STATEMENT A periodic axonal cytoskeleton consisting of actin and Spectrin has been proposed to help axons resist the mechanical forces to which they are exposed (e.g., compression, torsion, and stretch). However, until now, no vertebrate animal model has tested the requirement of the Spectrin cytoskeleton in maintenance of axon integrity. We demonstrate the role of the periodic Spectrin-dependent cytoskeleton in axons and show that loss of αII Spectrin from PNS axons causes preferential degeneration of large-diameter myelinated axons. We show that nodal αII Spectrin is found at greater densities in large-diameter myelinated axons, suggesting that nodes are particularly vulnerable domains requiring a specialized cytoskeleton to protect against axon degeneration.
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αII Spectrin forms a periodic cytoskeleton at the axon initial segment and is required for nervous system function
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2017Co-Authors: Claire Yumei Huang, Chuansheng Zhang, Joshua Lalonde, Jeffrey L Noebels, Christophe Leterrier, Alma L Burlingame, Juan A. Oses-prieto, Matthew N RasbandAbstract:Spectrins form a submembranous cytoskeleton proposed to confer strength and flexibility to neurons and to participate in ion channel clustering at axon initial segments (AIS) and nodes of Ranvier. Neuronal Spectrin cytoskeletons consist of diverse β subunits and αII Spectrin. Although αII Spectrin is found in neurons in both axonal and somatodendritic domains, using proteomics, biochemistry, and superresolution microscopy, we show that αII and βIV Spectrin interact and form a periodic AIS cytoskeleton. To determine the role of Spectrins in the nervous system, we generated Sptan1f/f mice for deletion of CNS αII Spectrin. We analyzed αII Spectrin-deficient mice of both sexes and found that loss of αII Spectrin causes profound reductions in all β Spectrins. αII Spectrin-deficient mice die before 1 month of age and have disrupted AIS and many other neurological impairments including seizures, disrupted cortical lamination, and widespread neurodegeneration. These results demonstrate the importance of the Spectrin cytoskeleton both at the AIS and throughout the nervous system.SIGNIFICANCE STATEMENT Spectrin cytoskeletons play diverse roles in neurons, including assembly of excitable domains such as the axon initial segment (AIS) and nodes of Ranvier. However, the molecular composition and structure of these cytoskeletons remain poorly understood. Here, we show that αII Spectrin partners with βIV Spectrin to form a periodic cytoskeleton at the AIS. Using a new αII Spectrin conditional knock-out mouse, we show that αII Spectrin is required for AIS assembly, neuronal excitability, cortical lamination, and to protect against neurodegeneration. These results demonstrate the broad importance of Spectrin cytoskeletons for nervous system function and development and have important implications for nervous system injuries and diseases because disruption of the Spectrin cytoskeleton is a common molecular pathology.
