Synaptotagmin-1 functions as the Ca2+-sensor for spontaneous release

Spontaneous 'mini' release occurs at all synapses, but its nature remains enigmatic. We found that >95% of spontaneous release in murine cortical neurons was induced by Ca2+-binding to synaptotagmin-1 (Syt1), the Ca2+ sensor for fast synchronous neurotransmitter release. Thus, spontaneous and evoked release used the same Ca2+-dependent release mechanism. As a consequence, Syt1 mutations that altered its Ca2+ affinity altered spontaneous and evoked release correspondingly. Paradoxically, Syt1 deletions (as opposed to point mutations) massively increased spontaneous release. This increased spontaneous release remained Ca2+ dependent but was activated at lower Ca2+ concentrations and with a lower Ca2+ cooperativity than synaptotagmin-driven spontaneous release. Thus, in addition to serving as a Ca2+ sensor for spontaneous and evoked release, Syt1 clamped a second, more sensitive Ca2+ sensor for spontaneous release that resembles the Ca2+ sensor for evoked asynchronous release. These data suggest that Syt1 controls both evoked and spontaneous release at a synapse as a simultaneous Ca2+-dependent activator and clamp of exocytosis.

[1]  S. Prestwich,et al.  Adenosine antagonists increase spontaneous and evoked transmitter release from neuronal cells in culture , 1987, Brain Research.

[2]  D. Elmqvist,et al.  Calcium dependence of spontaneous acetylcholine release at mammalian motor nerve terminals. , 1965, The Journal of physiology.

[3]  T. Südhof,et al.  Synaptic assembly of the brain in the absence of neurotransmitter secretion. , 2000, Science.

[4]  J. Littleton,et al.  Calcium dependence of neurotransmitter release and rate of spontaneous vesicle fusions are altered in Drosophila synaptotagmin mutants. , 1994, Proceedings of the National Academy of Sciences of the United States of America.

[5]  T. Südhof,et al.  Autonomous Function of Synaptotagmin 1 in Triggering Synchronous Release Independent of Asynchronous Release , 2005, Neuron.

[6]  David Baltimore,et al.  Germline Transmission and Tissue-Specific Expression of Transgenes Delivered by Lentiviral Vectors , 2002, Science.

[7]  K. Moulder,et al.  Spontaneous and Evoked Glutamate Release Activates Two Populations of NMDA Receptors with Limited Overlap , 2008, The Journal of Neuroscience.

[8]  J. Littleton,et al.  Is synaptotagmin the calcium sensor? , 2003, Current Opinion in Neurobiology.

[9]  T. Südhof,et al.  Synaptotagmin I functions as a calcium regulator of release probability , 2001, Nature.

[10]  T. Südhof,et al.  Synaptotagmin-1, -2, and -9: Ca2+ Sensors for Fast Release that Specify Distinct Presynaptic Properties in Subsets of Neurons , 2007, Neuron.

[11]  Ralf Schneggenburger,et al.  Intracellular calcium dependence of transmitter release rates at a fast central synapse , 2000, Nature.

[12]  R. Nehring,et al.  Differential Abilities of SNAP-25 Homologs to Support Neuronal Function , 2007, The Journal of Neuroscience.

[13]  B Sakmann,et al.  Calcium sensitivity of glutamate release in a calyx-type terminal. , 2000, Science.

[14]  Marco Capogna,et al.  Miniature synaptic events maintain dendritic spines via AMPA receptor activation , 1999, Nature Neuroscience.

[15]  E. Lambe,et al.  Nicotine Induces Glutamate Release from Thalamocortical Terminals in Prefrontal Cortex , 2003, Neuropsychopharmacology.

[16]  T. Südhof,et al.  A Gain-of-Function Mutation in Synaptotagmin-1 Reveals a Critical Role of Ca2+-Dependent Soluble N-Ethylmaleimide-Sensitive Factor Attachment Protein Receptor Complex Binding in Synaptic Exocytosis , 2006, The Journal of Neuroscience.

[17]  I. Robinson,et al.  The C2B Ca2+-binding motif of synaptotagmin is required for synaptic transmission in vivo , 2002, Nature.

[18]  Alan Fine,et al.  Calcium Stores in Hippocampal Synaptic Boutons Mediate Short-Term Plasticity, Store-Operated Ca2+ Entry, and Spontaneous Transmitter Release , 2001, Neuron.

[19]  M. Glitsch.  Spontaneous neurotransmitter release and Ca2+--how spontaneous is spontaneous neurotransmitter release? , 2008, Cell calcium.

[20]  T. Südhof,et al.  SNARE Function Analyzed in Synaptobrevin/VAMP Knockout Mice , 2001, Science.

[21]  T. Söllner,et al.  Regulated exocytosis and SNARE function (Review) , 2003, Molecular membrane biology.

[22]  J. Rizo,et al.  Synaptic vesicle fusion , 2008, Nature Structural &Molecular Biology.

[23]  R. Gray,et al.  Nicotinic Modulation of Glutamate and GABA Synaptic Transmission in Hippocampal Neurons , 1999, Annals of the New York Academy of Sciences.

[24]  N. Barazangi,et al.  Nicotine-induced enhancement of glutamatergic and GABAergic synaptic transmission in the mouse amygdala. , 2001, Journal of neurophysiology.

[25]  S. Stojilkovic.  Ca2+-regulated exocytosis and SNARE function , 2005, Trends in Endocrinology & Metabolism.

[26]  Xinran Liu,et al.  An Isolated Pool of Vesicles Recycles at Rest and Drives Spontaneous Neurotransmission , 2005, Neuron.

[27]  Wade G. Regehr,et al.  Quantal events shape cerebellar interneuron firing , 2002, Nature Neuroscience.

[28]  E. Kavalali,et al.  Seeking a function for spontaneous neurotransmission , 2006, Nature Neuroscience.

[29]  G. Bernardi,et al.  Muscarinic receptors depress GABAergic synaptic transmission in rat midbrain dopamine neurons , 2000, Neuroscience.

[30]  T. Südhof,et al.  N-Glycosylation Is Essential for Vesicular Targeting of Synaptotagmin 1 , 2004, Neuron.

[31]  E. Schuman,et al.  Miniature Neurotransmission Stabilizes Synaptic Function via Tonic Suppression of Local Dendritic Protein Synthesis , 2006, Cell.

[32]  T. Südhof,et al.  Genetic analysis of synaptotagmin 2 in spontaneous and Ca2+‐triggered neurotransmitter release , 2006, The EMBO journal.

[33]  T. Südhof,et al.  Ca2+ binding to synaptotagmin: how many Ca2+ ions bind to the tip of a C2‐domain? , 1998, The EMBO journal.

[34]  T. Südhof,et al.  Synaptotagmin I: A major Ca2+ sensor for transmitter release at a central synapse , 1994, Cell.

[35]  Christian Rosenmund,et al.  Definition of the Readily Releasable Pool of Vesicles at Hippocampal Synapses , 1996, Neuron.

[36]  B. Katz,et al.  Spontaneous subthreshold activity at motor nerve endings , 1952, The Journal of physiology.

[37]  T. Südhof,et al.  A dual-Ca2+-sensor model for neurotransmitter release in a central synapse , 2007, Nature.

[38]  Zhiping P. Pang,et al.  Monitoring synaptic transmission in primary neuronal cultures using local extracellular stimulation , 2007, Journal of Neuroscience Methods.

[39]  R. Burgess,et al.  Distinct Requirements for Evoked and Spontaneous Release of Neurotransmitter Are Revealed by Mutations in theDrosophila Gene neuronal-synaptobrevin , 1998, The Journal of Neuroscience.

[40]  A. Marty,et al.  Presynaptic calcium stores underlie large-amplitude miniature IPSCs and spontaneous calcium transients , 2000, Nature Neuroscience.

[41]  T. Südhof,et al.  Three-Dimensional Structure of the Synaptotagmin 1 C2B-Domain Synaptotagmin 1 as a Phospholipid Binding Machine , 2001, Neuron.

[42]  C. Stricker,et al.  The contribution of intracellular calcium stores to mEPSCs recorded in layer II neurones of rat barrel cortex , 2002, The Journal of physiology.

[43]  C. Mulle,et al.  Evidence for "preterminal" nicotinic receptors on GABAergic axons in the rat interpeduncular nucleus , 1993, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[44]  D. Hagler,et al.  Properties of synchronous and asynchronous release during pulse train depression in cultured hippocampal neurons. , 2001, Journal of neurophysiology.

[45]  G. Augustine,et al.  Dual Roles of the C2B Domain of Synaptotagmin I in Synchronizing Ca2+-Dependent Neurotransmitter Release , 2004, The Journal of Neuroscience.

[46]  C. Stevens,et al.  The Synaptotagmin C2A Domain Is Part of the Calcium Sensor Controlling Fast Synaptic Transmission , 2003, Neuron.

[47]  V. Shahrezaei,et al.  Competition between Phasic and Asynchronous Release for Recovered Synaptic Vesicles at Developing Hippocampal Autaptic Synapses , 2022 .