The Experts below are selected from a list of 105 Experts worldwide ranked by ideXlab platform
Tobias Moser - One of the best experts on this subject based on the ideXlab platform.
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Exocytosis at the hair cell ribbon synapse apparently operates without neuronal SNARE proteins
Nature Neuroscience, 2011Co-Authors: Régis Nouvian, Thomas Binz, Jakob Neef, Anna V. Bulankina, Ellen Reisinger, Tina Pangršič, Thomas Frank, Stefan Sikorra, Nils Brose, Tobias MoserAbstract:In addition to the morphological difference, inner hair cell (IHC) synapses do not have the full complement of neuronal SNARE proteins found in other types of synapses. Here, Nouvian et al . provide a series of empirical evidence that shows that exocytosis in IHCs occurs independently of neuronal SNARE proteins. SNARE proteins mediate membrane fusion. Neurosecretion depends on neuronal soluble NSF attachment protein receptors (SNAREs; SNAP-25, syntaxin-1, and Synaptobrevin-1 or Synaptobrevin-2) and is blocked by neurotoxin-mediated cleavage or genetic ablation. We found that exocytosis in mouse inner hair cells (IHCs) was insensitive to neurotoxins and genetic ablation of neuronal SNAREs. mRNA, but no synaptically localized protein, of neuronal SNAREs was present in IHCs. Thus, IHC exocytosis is unconventional and may operate independently of neuronal SNAREs.
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Exocytosis at the hair cell ribbon synapse apparently operates without neuronal SNARE proteins
Nature Neuroscience, 2011Co-Authors: Régis Nouvian, Thomas Binz, Jakob Neef, Anna V. Bulankina, Ellen Reisinger, Tina Pangršič, Thomas Frank, Stefan Sikorra, Nils Brose, Tobias MoserAbstract:SNARE proteins mediate membrane fusion. Neurosecretion depends on neuronal soluble NSF attachment protein receptors (SNAREs; SNAP-25, syntaxin-1, and Synaptobrevin-1 or Synaptobrevin-2) and is blocked by neurotoxin-mediated cleavage or genetic ablation. We found that exocytosis in mouse inner hair cells (IHCs) was insensitive to neurotoxins and genetic ablation of neuronal SNAREs. mRNA, but no synaptically localized protein, of neuronal SNAREs was present in IHCs. Thus, IHC exocytosis is unconventional and may operate independently of neuronal SNAREs.
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Maturation of Ribbon Synapses in Hair Cells Is Driven by Thyroid Hormone
The Journal of Neuroscience, 2007Co-Authors: Gaston Sendin, Anna V. Bulankina, Dietmar Riedel, Tobias MoserAbstract:Ribbon synapses of inner hair cells (IHCs) undergo developmental maturation until after the onset of hearing. Here, we studied whether IHC synaptogenesis is regulated by thyroid hormone (TH). We performed perforated patch-clamp recordings of Ca2+ currents and exocytic membrane capacitance changes in IHCs of athyroid and TH-substituted Pax8−/− mice during postnatal development. Ca2+ currents remained elevated in athyroid IHCs at the end of the second postnatal week, when it had developmentally declined in wild-type and TH-rescued mutant IHCs. The efficiency of Ca2+ influx in triggering exocytosis of the readily releasable vesicle pool was reduced in athyroid IHCs. Ribbon synapses were formed despite the TH deficiency. However, different from wild type, in which synapse elimination takes place at approximately the onset of hearing, the number of ribbon synapses remained elevated in 2-week-old athyroid IHCs. Moreover, the ultrastructure of these synapses appeared immature. Using quantitative reverse transcription-PCR, we found a TH-dependent developmental upregulation of the mRNAs for the neuronal SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins, SNAP25 (synaptosomal-associated protein of 25 kDa) and Synaptobrevin 1, in the organ of Corti. These molecular changes probably contribute to the improvement of exocytosis efficiency in mature IHCs. IHCs of 2-week-old athyroid Pax8−/− mice maintained the normally temporary efferent innervation. Moreover, they lacked large-conductance Ca2+-activated K+ channels and KCNQ4 channels. This together with the persistently increased Ca2+ influx permitted continued action potential generation. We conclude that TH regulates IHC differentiation and is essential for morphological and functional maturation of their ribbon synapses. We suggest that presynaptic dysfunction of IHCs is a mechanism in congenital hypothyroid deafness.
Andrew G Engel - One of the best experts on this subject based on the ideXlab platform.
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Congenital Myasthenic Syndromes in 2018
Current Neurology and Neuroscience Reports, 2018Co-Authors: Andrew G EngelAbstract:Purpose of Review Summarize features of the currently recognized congenital myasthenic syndromes (CMS) with emphasis on novel findings identified in the past 6 years. Recent Findings Since the last review of the CMS in this journal in 2012, several novel CMS were identified. The identified disease proteins are SNAP25B, synaptotagmin 2, Munc13-1, Synaptobrevin-1, GFPT1, DPAGT1, ALG2, ALG14, Agrin, GMPPB, LRP4, myosin 9A, collagen 13A1, the mitochondrial citrate carrier, PREPL, LAMA5, the vesicular ACh transporter, and the high-affinity presynaptic choline transporter. Summary Exome sequencing has provided a powerful tool for identifying novel CMS. Identifying the disease genes is essential for determining optimal therapy. The landscape of the CMS is still unfolding.
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novel Synaptobrevin 1 mutation causes fatal congenital myasthenic syndrome
Annals of clinical and translational neurology, 2017Co-Authors: Xin Ming Shen, Rosana Herminia Scola, Paulo Jose Lorenzoni, Lineu Cesar Werneck, Joan M Brengman, Duygu Selcen, Andrew G EngelAbstract:OBJECTIVE: To identify the molecular basis and elucidate the pathogenesis of a fatal congenital myasthenic syndrome. METHODS: We performed clinical electrophysiology studies, exome and Sanger sequencing, and analyzed functional consequences of the identified mutation. RESULTS: Clinical electrophysiology studies of the patient revealed several-fold potentiation of the evoked muscle action potential by high frequency nerve stimulation pointing to a presynaptic defect. Exome sequencing identified a homozygous c.340delA frameshift mutation in Synaptobrevin 1 (SYB1), one of the three SNARE proteins essential for synaptic vesicle exocytosis. Analysis of both human spinal cord gray matter and normal human muscle revealed expression of the SYB1A and SYB1D isoforms, predicting expression of one or both isoforms in the motor nerve terminal. The identified mutation elongates the intravesicular C-terminus of the A isoform from 5 to 71, and of the D isoform from 4 to 31 residues. Transfection of either mutant isoform into bovine chromaffin cells markedly reduces depolarization-evoked exocytosis, and transfection of either mutant isoform into HEK cells significantly decreases expression of either mutant compared to wild type. INTERPRETATION: The mutation is pathogenic because elongation of the intravesicular C-terminus of the A and D isoforms increases the energy required to move their C-terminus into the synaptic vesicle membrane, a key step for fusion of the synaptic vesicle with the presynaptic membrane, and because it is predicted to reduce expression of either isoform in the nerve terminal.
Thomas Binz - One of the best experts on this subject based on the ideXlab platform.
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Exocytosis at the hair cell ribbon synapse apparently operates without neuronal SNARE proteins
Nature Neuroscience, 2011Co-Authors: Régis Nouvian, Thomas Binz, Jakob Neef, Anna V. Bulankina, Ellen Reisinger, Tina Pangršič, Thomas Frank, Stefan Sikorra, Nils Brose, Tobias MoserAbstract:In addition to the morphological difference, inner hair cell (IHC) synapses do not have the full complement of neuronal SNARE proteins found in other types of synapses. Here, Nouvian et al . provide a series of empirical evidence that shows that exocytosis in IHCs occurs independently of neuronal SNARE proteins. SNARE proteins mediate membrane fusion. Neurosecretion depends on neuronal soluble NSF attachment protein receptors (SNAREs; SNAP-25, syntaxin-1, and Synaptobrevin-1 or Synaptobrevin-2) and is blocked by neurotoxin-mediated cleavage or genetic ablation. We found that exocytosis in mouse inner hair cells (IHCs) was insensitive to neurotoxins and genetic ablation of neuronal SNAREs. mRNA, but no synaptically localized protein, of neuronal SNAREs was present in IHCs. Thus, IHC exocytosis is unconventional and may operate independently of neuronal SNAREs.
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Exocytosis at the hair cell ribbon synapse apparently operates without neuronal SNARE proteins
Nature Neuroscience, 2011Co-Authors: Régis Nouvian, Thomas Binz, Jakob Neef, Anna V. Bulankina, Ellen Reisinger, Tina Pangršič, Thomas Frank, Stefan Sikorra, Nils Brose, Tobias MoserAbstract:SNARE proteins mediate membrane fusion. Neurosecretion depends on neuronal soluble NSF attachment protein receptors (SNAREs; SNAP-25, syntaxin-1, and Synaptobrevin-1 or Synaptobrevin-2) and is blocked by neurotoxin-mediated cleavage or genetic ablation. We found that exocytosis in mouse inner hair cells (IHCs) was insensitive to neurotoxins and genetic ablation of neuronal SNAREs. mRNA, but no synaptically localized protein, of neuronal SNAREs was present in IHCs. Thus, IHC exocytosis is unconventional and may operate independently of neuronal SNAREs.
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Exploring the functional domain and the target of the tetanus toxin light chain in neurohypophysial terminals.
Neuroscience, 1994Co-Authors: G. Dayanithi, S. Yamasaki, Thomas Binz, Brigitte Stecher, Barbara Höhne-zell, Ulrich Weller, Heiner Niemann, Manfred GratzlAbstract:Abstract The tetanus toxin light chain blocks calcium induced vasopressin release from neurohypophysial nerve terminals. Here we show that histidine residue 233 within the putative zinc binding motif of the tetanus toxin light chain is essential for the inhibition of exocytosis, in the rat. The zinc chelating agent dipicolinic acid as well as captopril, an inhibitor of zinc-dependent peptidases, counteract the effect of the neurotoxin. Synthetic peptides, the sequences of which correspond to motifs present in the cytoplasmic domain of the synaptic vesicle membrane protein Synaptobrevin 1 and 2, prevent the effect of the tetanus toxin light chain. Our results indicate that zinc bound to the zinc binding motif constitutes the active site of the tetanus toxin light chain. Moreover they suggest that cleavage of Synaptobrevin by the neurotoxin causes the inhibition of exocytotic release of vasopressin from secretory granules.
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Cleavage of members of the Synaptobrevin/VAMP family by types D and F botulinal neurotoxins and tetanus toxin
Journal of Biological Chemistry, 1994Co-Authors: S. Yamasaki, Juan Blasi, A Baumeister, Thomas Binz, E Link, F Cornille, B Roques, E M Fykse, T C Südhof, Reinhard JahnAbstract:Tetanus toxin (TeTx) and the various forms of botulinal neurotoxins (BoNT/A to BoNT/G) potently inhibit neurotransmission by means of their L chains which selectively proteolyze synaptic proteins such as Synaptobrevin (TeTx, BoNT/B, BoNT/F), SNAP-25 (BoNT/A), and syntaxin (BoNT/C1). Here we show that BoNT/D cleaves rat Synaptobrevin 1 and 2 in toxified synaptosomes and in isolated vesicles. In contrast, Synaptobrevin 1, as generated by in vitro translation, is only a poor substrate for BoNT/D, whereas this species is cleaved by BoNT/F with similar potency. Cleavage by BoNT/D occurs at the peptide bond Lys59-Leu60 which is adjacent to the BoNT/F cleavage site (Gln58-Lys59) and again differs from the site hydrolyzed by TeTx and BoNT/B (Gln76-Phe77). Cellubrevin, a recently discovered isoform expressed outside the nervous system, is efficiently cleaved by all three toxins examined. For further characterization of the substrate requirements of BoNT/D, we tested amino- and carboxyl-terminal deletion mutants of Synaptobrevin 2 as well as synthetic peptides. Shorter peptides containing up to 15 amino acids on either side of the cleavage site were not cleaved, and a peptide extending from Arg47 to Thr116 was a poor substrate for all three toxins tested. However, cleavability was restored when the peptide is further extended at the NH2 terminus (Thr27-Thr116) demonstrating that NH2 terminally located sequences of Synaptobrevin which are distal from the respective cleavage sites are required for proteolysis. To further examine the isoform specificity, several mutants of rat Synaptobrevin 2 were generated in which individual amino acids were replaced with those found in rat Synaptobrevin 1. We show that a Met46 to Ile46 substitution drastically diminishes cleavability by BoNT/D and that the presence of Val76 instead of Gln76 dictates the reduced cleavability of Synaptobrevin isoforms by TeTx.
Régis Nouvian - One of the best experts on this subject based on the ideXlab platform.
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Exocytosis at the hair cell ribbon synapse apparently operates without neuronal SNARE proteins
Nature Neuroscience, 2011Co-Authors: Régis Nouvian, Thomas Binz, Jakob Neef, Anna V. Bulankina, Ellen Reisinger, Tina Pangršič, Thomas Frank, Stefan Sikorra, Nils Brose, Tobias MoserAbstract:In addition to the morphological difference, inner hair cell (IHC) synapses do not have the full complement of neuronal SNARE proteins found in other types of synapses. Here, Nouvian et al . provide a series of empirical evidence that shows that exocytosis in IHCs occurs independently of neuronal SNARE proteins. SNARE proteins mediate membrane fusion. Neurosecretion depends on neuronal soluble NSF attachment protein receptors (SNAREs; SNAP-25, syntaxin-1, and Synaptobrevin-1 or Synaptobrevin-2) and is blocked by neurotoxin-mediated cleavage or genetic ablation. We found that exocytosis in mouse inner hair cells (IHCs) was insensitive to neurotoxins and genetic ablation of neuronal SNAREs. mRNA, but no synaptically localized protein, of neuronal SNAREs was present in IHCs. Thus, IHC exocytosis is unconventional and may operate independently of neuronal SNAREs.
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Exocytosis at the hair cell ribbon synapse apparently operates without neuronal SNARE proteins
Nature Neuroscience, 2011Co-Authors: Régis Nouvian, Thomas Binz, Jakob Neef, Anna V. Bulankina, Ellen Reisinger, Tina Pangršič, Thomas Frank, Stefan Sikorra, Nils Brose, Tobias MoserAbstract:SNARE proteins mediate membrane fusion. Neurosecretion depends on neuronal soluble NSF attachment protein receptors (SNAREs; SNAP-25, syntaxin-1, and Synaptobrevin-1 or Synaptobrevin-2) and is blocked by neurotoxin-mediated cleavage or genetic ablation. We found that exocytosis in mouse inner hair cells (IHCs) was insensitive to neurotoxins and genetic ablation of neuronal SNAREs. mRNA, but no synaptically localized protein, of neuronal SNAREs was present in IHCs. Thus, IHC exocytosis is unconventional and may operate independently of neuronal SNAREs.
Cesare Montecucco - One of the best experts on this subject based on the ideXlab platform.
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SNAREcomplexesandneuroexocytosis: how many, how close?
2020Co-Authors: Cesare Montecucco, Giampietro Schiavo, Sergio PantanoAbstract:Regulated secretion is an essential process in alleukaryotic cells. The release of molecules containedinside exocytic granules and synaptic vesicles ismediated by the assembly of a SNARE complex formedby the coil-coiling of three proteins: SNAP-25, syntaxinand VAMP/Synaptobrevin. It seems that SNAREcomplexes assemble together in rosette-shaped super-complexes but there is controversy on the actualnumber (N) of copies of SNARE complexes that arenecessary to mediate exocytosis. We discuss attemptsto determine the value of N and suggest that N varieswith the type of exocytic vesicles. In addition, wepropose that the N value in neuroexocytosis can beestimated by the comparative use of different types ofbotulinum neurotoxins.IntroductionNeuroexocytosis is the fundamental physiological processthat leads a nai¨ve cytosolic synaptic vesicle (SV) to bind toand fuse with the presynaptic membrane, therebydischarging its neurotransmitter contents into the syn-aptic cleft. Our interest in neuroexocytosis arose some20 years ago when we began to study the mechanism ofaction of the clostridial neurotoxins causing tetanus andbotulism. Meanwhile, an unprecedented wealth of infor-mation brought the field from the static, low-resolutionpicture provided by electron microscopy to the tantalizingmolecular and biophysical puzzle that is currentlyavailable. At present, many scientists are trying topinpoint the right place and time of action for the manymolecules that are suggested to be linked, in one way oranother, to neuroexocytosis.The three synaptic SNARE proteins SNAP-25, VAMP/Synaptobrevin and syntaxin occupy a central position inthis process by forming a heterotrimeric complex, whichbinds N-ethylmaleimide sensitive fusion ATPase (NSF)and soluble NSF attachment protein [a-SNAP; hence theacronym SNARE (SNAP receptor)] [1]. The synapticSNARE proteins are the specific substrates of the eightclostridial neurotoxins (one tetanus neurotoxin, TeNT,and seven botulinum neurotoxins: BoNT/A–G) [2,3].These neurotoxins specifically bind to nerve terminalsand deliver their zinc-endopeptidase N-terminal domaininside the cytosol, where it specifically cleaves a SNAREprotein at a single site within its cytosolic portion. Suchspecific cleavage leads to a prolonged, but eventuallyreversible, inhibition of neuroexocytosis, which in vivoresults in the paralytic syndromes of botulism andtetanus. Despite the availability of several pieces ofexperimental evidence demonstrating the involvement ofSNAREproteinsinneuroexocytosis,andinthemajorityofmembrane traffic events within eukaryotic cells [4,5], thisremains the most impressive proof of their central role inneuroexocytosis; and a badly unwanted one, if oneconsiders the hundreds of thousands of newborn babiesthattheWHOreportstodieeachyearbytetanusneonatorum in the non tetanus-vaccinated areas of theworld [6].There is evidence that SNARE complexes assembletogether in rosette super-complexes around the site ofmembrane fusion. Additional proteins, including thecalcium sensor synaptotagmin I and the syntaxin-inter-acting protein Munc-18 [5,7,8], cooperate with SNAREs toaccomplish neuroexocytosis, although their completenumber and precise mode- and time-of-action has not yetbeen established [5,7,8]. In addition, the number of copiesof SNARE complexes, termed N, that are necessary tomediate exocytosis is not known. Different methodsprovide different estimates and we discuss here someattempts at determining the value of N and the possibilitythat N varies with the type of exocytosis event. We willconcludebyproposingtheuseofdifferenttypesofBoNTtoestimate the N value in neuroexocytosis.The neuronal SNARE complexDespitethelargerepertoireofSNAREsthatarepresentina typical mammalian cell (up to 26 have been identified inbudding yeast) [9], only a few of them are involved in therapid, highly controlled release of the neurotransmitter-containing vesicles, which follows nerve membranedepolarization. This event enables the influx of calciumthrough calcium channels located near the ‘active zones’,which are the preferred sites of neuroexocytosis [5,7].VAMP/Synaptobrevin 1 and 2 (here abbreviated asVAMP) are 13 kDa integral membrane proteins of SVandof large dense-core granules. They consist of four parts
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Tetanus and botulinum-B neurotoxins block neurotransmitter release by proteolytic cleavage of Synaptobrevin
Nature, 1992Co-Authors: Giampietro G. Schiavo, Fabio Benfenati, Bernard Poulain, Ornella Rossetto, Patrizia Polverino De Laureto, Bibhuti R. Dasgupta, Cesare MontecuccoAbstract:CLOSTRIDIAL neurotoxins, including tetanus toxin and the seven serotypes of botulinum toxin (A–G), are produced as single chains and cleaved to generate toxins with two chains joined by a single disulphide bond (Fig. 1). The heavy chain (M_r 100,000 (100K)) is responsible for specific binding to neuronal cells and cell penetration of the light chain (50K), which blocks neurotransmitter release^1–9. Several lines of evidence have recently suggested that clostridial neurotoxins could be zinc endopeptidases^2,10–14. Here we show that tetanus and botulinum toxins serotype B are zinc endopeptidases, the activation of which requires reduction of the interchain disulphide bond. The protease activity is localized on the light chain and is specific for Synaptobrevin, an integral membrane protein of small synaptic vesicles. The rat Synaptobrevin-2 isoform is cleaved by both neurotoxins at the same single site, the peptide bond Gln76-Phe77, but the isoform Synaptobrevin-1, which has a valine at the corresponding position, is not cleaved. The blocking of neurotransmitter release of Aplysia neurons injected with tetanus toxin or botulinum toxin serotype B is substantially delayed by peptides containing the Synaptobrevin-2 cleavage site. These results indicate that tetanus and botulinum B neurotoxins block neurotransmitter release by cleaving Synaptobrevin-2, a protein that, on the basis of our results, seems to play a key part in neurotransmitter release.
