Sparse force-bearing bridges between neighboring synaptic vesicles

Abstract Most vesicles in the interior of synaptic terminals are clustered in clouds close to active zone regions of the plasma membrane where exocytosis occurs. Electron-dense structures, termed bridges, have been reported between a small minority of pairs of neighboring vesicles within the clouds. Synapsin proteins have been implicated previously, but the existence of the bridges as stable structures in vivo has been questioned. Here we use electron tomography to show that the bridges are present but less frequent in synapsin knockouts compared to wildtype. An analysis of distances between neighbors in wildtype tomograms indicated that the bridges are strong enough to resist centrifugal forces likely induced by fixation with aldehydes. The results confirm that the bridges are stable structures and that synapsin proteins are involved in formation or stabilization.

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Carboxypeptidase E cytoplasmic tail mediates localization of synaptic vesicles to the pre-active zone in hypothalamic pre-synaptic terminals

Journal of Neurochemistry ◽

10.1111/j.1471-4159.2010.06820.x ◽

2010 ◽

Vol 114 (3) ◽

pp. 886-896 ◽

Cited By ~ 15

Author(s):

Hong Lou ◽

Joshua J. Park ◽

Niamh X. Cawley ◽

Annahita Sarcon ◽

Lei Sun ◽

...

Keyword(s):

Active Zone ◽

Synaptic Vesicles ◽

Cytoplasmic Tail ◽

Carboxypeptidase E ◽

Synaptic Terminals

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Complexin cooperates with Bruchpilot to tether synaptic vesicles to the active zone cytomatrix

The Journal of Cell Biology ◽

10.1083/jcb.201806155 ◽

2019 ◽

Vol 218 (3) ◽

pp. 1011-1026 ◽

Cited By ~ 6

Author(s):

Nicole Scholz ◽

Nadine Ehmann ◽

Divya Sachidanandan ◽

Cordelia Imig ◽

Benjamin H. Cooper ◽

...

Keyword(s):

Protein Interactions ◽

Active Zone ◽

Synaptic Vesicles ◽

Snare Complex ◽

C Terminus ◽

Unknown Protein ◽

Transmission Part ◽

Molecular Components ◽

In Vivo Screen

Information processing by the nervous system depends on neurotransmitter release from synaptic vesicles (SVs) at the presynaptic active zone. Molecular components of the cytomatrix at the active zone (CAZ) regulate the final stages of the SV cycle preceding exocytosis and thereby shape the efficacy and plasticity of synaptic transmission. Part of this regulation is reflected by a physical association of SVs with filamentous CAZ structures via largely unknown protein interactions. The very C-terminal region of Bruchpilot (Brp), a key component of the Drosophila melanogaster CAZ, participates in SV tethering. Here, we identify the conserved SNARE regulator Complexin (Cpx) in an in vivo screen for molecules that link the Brp C terminus to SVs. Brp and Cpx interact genetically and functionally. Both proteins promote SV recruitment to the Drosophila CAZ and counteract short-term synaptic depression. Analyzing SV tethering to active zone ribbons of cpx3 knockout mice supports an evolutionarily conserved role of Cpx upstream of SNARE complex assembly.

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Neurotransmitter Release

10.1093/med/9780190237493.003.0011 ◽

2017 ◽

Author(s):

Peggy Mason

Keyword(s):

Plasma Membrane ◽

Synaptic Vesicle ◽

Active Zone ◽

Neurotransmitter Release ◽

Synaptic Vesicles ◽

Synaptic Cleft ◽

Fusion Pore ◽

Synaptic Membrane ◽

Specialized Region ◽

Synaptic Vesicle Fusion

The biochemical and physiological processes of neurotransmitter release from an active zone, a specialized region of synaptic membrane, are examined. Synaptic vesicles containing neurotransmitters are docked at the active zone and then primed for release by SNARE complexes that bring them into extreme proximity to the plasma membrane. Entry of calcium ions through voltage-gated calcium channels triggers synaptic vesicle fusion with the synaptic terminal membrane and the consequent diffusion of neurotransmitter into the synaptic cleft. Release results when the fusion pore bridging the synaptic vesicle and plasma membrane widens and neurotransmitter from the inside of the synaptic vesicle diffuses into the synaptic cleft. Membrane from the active zone membrane is endocytosed, and synaptic vesicle proteins are then reassembled into recycled synaptic vesicles, allowing for more rounds of neurotransmitter release.

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Synaptic vesicles transiently dock to refill release sites

10.1101/509216 ◽

2018 ◽

Cited By ~ 6

Author(s):

Grant F Kusick ◽

Morven Chin ◽

Sumana Raychaudhuri ◽

Kristina Lippmann ◽

Kadidia P Adula ◽

...

Keyword(s):

Plasma Membrane ◽

Active Zone ◽

Synaptic Vesicles ◽

Electrical Field Stimulation ◽

Dependent Manner ◽

Single Action ◽

Calcium Dependent ◽

Synaptic Vesicle Exocytosis ◽

Vesicle Exocytosis ◽

Asynchronous Release

AbstractSynaptic vesicles fuse with the plasma membrane to release neurotransmitter following an action potential, after which new vesicles must ‘dock’ to refill vacated release sites. To capture synaptic vesicle exocytosis at cultured mouse hippocampal synapses, we induced single action potentials by electrical field stimulation then subjected neurons to high-pressure freezing to examine their morphology by electron microscopy. During synchronous release, multiple vesicles can fuse at a single active zone; this multivesicular release is augmented by increasing extracellular calcium. Fusions during synchronous release are distributed throughout the active zone, whereas fusions during asynchronous release are biased toward the center of the active zone. Immediately after stimulation, the total number of docked vesicles across all synapses decreases by ∼40%. Between 8 and 14 ms, new vesicles are recruited to the plasma membrane and fully replenish the docked pool in a calcium-dependent manner, but docking of these vesicles is transient and they either undock or fuse within 100 ms. These results demonstrate that recruitment of synaptic vesicles to release sites is rapid and reversible.

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A unique C2 domain at the C terminus of Munc13 promotes synaptic vesicle priming

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2016276118 ◽

2021 ◽

Vol 118 (11) ◽

pp. e2016276118

Author(s):

Murugesh Padmanarayana ◽

Haowen Liu ◽

Francesco Michelassi ◽

Lei Li ◽

Daniel Betensky ◽

...

Keyword(s):

Plasma Membrane ◽

Synaptic Vesicle ◽

Neurotransmitter Release ◽

Synaptic Vesicles ◽

Genetic Screen ◽

C2 Domain ◽

Forward Genetic Screen ◽

Molecular Events ◽

C Terminus

Neurotransmitter release during synaptic transmission comprises a tightly orchestrated sequence of molecular events, and Munc13-1 is a cornerstone of the fusion machinery. A forward genetic screen for defects in neurotransmitter release in Caenorhabditis elegans identified a mutation in the Munc13-1 ortholog UNC-13 that eliminated its unique and deeply conserved C-terminal module (referred to as HC2M) containing a Ca2+-insensitive C2 domain flanked by membrane-binding helices. The HC2M module could be functionally replaced in vivo by protein domains that localize to synaptic vesicles but not to the plasma membrane. HC2M is broadly conserved in other Unc13 family members and is required for efficient synaptic vesicle priming. We propose that the HC2M domain evolved as a vesicle/endosome adaptor and acquired synaptic vesicle specificity in the Unc13ABC protein family.

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The structure and function of ‘active zone material’ at synapses

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2014.0189 ◽

2015 ◽

Vol 370 (1672) ◽

pp. 20140189 ◽

Cited By ~ 13

Author(s):

Joseph A. Szule ◽

Jae Hoon Jung ◽

Uel J. McMahan

Keyword(s):

Spatial Resolution ◽

Active Zone ◽

Synaptic Vesicles ◽

Neuromuscular Junctions ◽

Electron Tomography ◽

Structure And Function ◽

Presynaptic Membrane ◽

Axon Terminals ◽

Active Zones ◽

And Function

The docking of synaptic vesicles on the presynaptic membrane and their priming for fusion with it to mediate synaptic transmission of nerve impulses typically occur at structurally specialized regions on the membrane called active zones. Stable components of active zones include aggregates of macromolecules, ‘active zone material’ (AZM), attached to the presynaptic membrane, and aggregates of Ca 2+ -channels in the membrane, through which Ca 2+ enters the cytosol to trigger impulse-evoked vesicle fusion with the presynaptic membrane by interacting with Ca 2+ -sensors on the vesicles. This laboratory has used electron tomography to study, at macromolecular spatial resolution, the structure and function of AZM at the simply arranged active zones of axon terminals at frog neuromuscular junctions. The results support the conclusion that AZM directs the docking and priming of synaptic vesicles and essential positioning of Ca 2+ -channels relative to the vesicles' Ca 2+ -sensors. Here we review the findings and comment on their applicability to understanding mechanisms of docking, priming and Ca 2+ -triggering at other synapses, where the arrangement of active zone components differs.

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Complexin cooperates with Bruchpilot to tether synaptic vesicles to the active zone cytomatrix

10.1101/350207 ◽

2018 ◽

Author(s):

Nicole Scholz ◽

Nadine Ehmann ◽

Divya Sachidanandan ◽

Cordelia Imig ◽

Benjamin H. Cooper ◽

...

Keyword(s):

Protein Interactions ◽

Active Zone ◽

Synaptic Vesicles ◽

Bipolar Cells ◽

Snare Complex ◽

Protein Receptor ◽

C Terminus ◽

Transmission Part ◽

Molecular Components

ABSTRACTInformation processing by the nervous system depends on the release of neurotransmitter from synaptic vesicles (SVs) at the presynaptic active zone. Molecular components of the cytomatrix at the active zone (CAZ) regulate the final stages of the SV cycle preceding exocytosis and thereby shape the efficacy and plasticity of synaptic transmission. Part of this regulation is reflected by a physical association of SVs with filamentous CAZ structures. However, our understanding of the protein interactions underlying SV tethering by the CAZ is far from complete. The very C-terminal region of Bruchpilot (Brp), a key component of the Drosophila CAZ, participates in SV tethering. Yet so far, no vesicular or cytoplasmic molecules have been reported to engage in an interaction with Brp’s C-terminus. Here, we carried out an in vivo screen for molecules that link the Brp C-terminus to SVs. This strategy identified the conserved SNARE (soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptor) regulator Complexin (Cpx) as a vesicular interaction partner of Brp. We show that Brp and Cpx interact genetically and functionally. Interfering with Cpx targeting to SVs mirrored distinctive features of a C-terminal Brp truncation: impaired SV recruitment to the CAZ and enhanced short-term synaptic depression. Extending the study beyond Drosophila synapses, we interrogated active zones of mouse rod bipolar cells. Here, too, we collected evidence for an evolutionarily conserved role of Cpx upstream of SNARE complex assembly where it participates in SV tethering to the CAZ.

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