A stochastic model of active zone material mediated synaptic vesicle docking and priming at resting active zones

Active zones are molecular machines that control neurotransmitter release through synaptic vesicle docking and priming, and through coupling of these vesicles to Ca2+ entry. The complexity of active zone machinery has made it challenging to determine which mechanisms drive these roles in release. Here, we induce RIM+ELKS knockout to eliminate active zone scaffolding networks, and then reconstruct each active zone function. Re-expression of RIM1-Zn fingers positioned Munc13 on undocked vesicles and rendered them release-competent. Reconstitution of release-triggering required docking of these vesicles to Ca2+ channels. Fusing RIM1-Zn to CaVbeta4-subunits sufficed to restore docking, priming and release-triggering without reinstating active zone scaffolds. Hence, exocytotic activities of the 80 kDa CaVbeta4-Zn fusion protein bypassed the need for megadalton-sized secretory machines. These data define key mechanisms of active zone function, establish that fusion competence and docking are mechanistically separable, and reveal that active zone scaffolding networks are not required for release.

Download Full-text

Alignment of Synaptic Vesicle Macromolecules with the Macromolecules in Active Zone Material that Direct Vesicle Docking

PLoS ONE ◽

10.1371/journal.pone.0069410 ◽

2013 ◽

Vol 8 (7) ◽

pp. e69410 ◽

Cited By ~ 28

Author(s):

Mark L. Harlow ◽

Joseph A. Szule ◽

Jing Xu ◽

Jae Hoon Jung ◽

Robert M. Marshall ◽

...

Keyword(s):

Synaptic Vesicle ◽

Active Zone ◽

Vesicle Docking

Download Full-text

Hypothesis Relating the Structure, Biochemistry and Function of Active Zone Material Macromolecules at a Neuromuscular Junction

Frontiers in Synaptic Neuroscience ◽

10.3389/fnsyn.2021.798225 ◽

2022 ◽

Vol 13 ◽

Author(s):

Joseph A. Szule

Keyword(s):

Membrane Fusion ◽

Synaptic Vesicle ◽

Active Zone ◽

Structural Integrity ◽

Neuromuscular Junctions ◽

Vesicle Trafficking ◽

Material Structure ◽

Neurotransmitter Secretion ◽

Active Zones ◽

And Function

This report integrates knowledge of in situ macromolecular structures and synaptic protein biochemistry to propose a unified hypothesis for the regulation of certain vesicle trafficking events (i.e., docking, priming, Ca2+-triggering, and membrane fusion) that lead to neurotransmitter secretion from specialized “active zones” of presynaptic axon terminals. Advancements in electron tomography, to image tissue sections in 3D at nanometer scale resolution, have led to structural characterizations of a network of different classes of macromolecules at the active zone, called “Active Zone Material’. At frog neuromuscular junctions, the classes of Active Zone Material macromolecules “top-masts”, “booms”, “spars”, “ribs” and “pins” direct synaptic vesicle docking while “pins”, “ribs” and “pegs” regulate priming to influence Ca2+-triggering and membrane fusion. Other classes, “beams”, “steps”, “masts”, and “synaptic vesicle luminal filaments’ likely help organize and maintain the structural integrity of active zones. Extensive studies on the biochemistry that regulates secretion have led to comprehensive characterizations of the many conserved proteins universally involved in these trafficking events. Here, a hypothesis including a partial proteomic atlas of Active Zone Material is presented which considers the common roles, binding partners, physical features/structure, and relative positioning in the axon terminal of both the proteins and classes of macromolecules involved in the vesicle trafficking events. The hypothesis designates voltage-gated Ca2+ channels and Ca2+-gated K+ channels to ribs and pegs that are connected to macromolecules that span the presynaptic membrane at the active zone. SNARE proteins (Syntaxin, SNAP25, and Synaptobrevin), SNARE-interacting proteins Synaptotagmin, Munc13, Munc18, Complexin, and NSF are designated to ribs and/or pins. Rab3A and Rabphillin-3A are designated to top-masts and/or booms and/or spars. RIM, Bassoon, and Piccolo are designated to beams, steps, masts, ribs, spars, booms, and top-masts. Spectrin is designated to beams. Lastly, the luminal portions of SV2 are thought to form the bulk of the observed synaptic vesicle luminal filaments. The goal here is to help direct future studies that aim to bridge Active Zone Material structure, biochemistry, and function to ultimately determine how it regulates the trafficking events in vivo that lead to neurotransmitter secretion.

Download Full-text

A novel region in the CaV2.1 α1 subunit C-terminus regulates fast synaptic vesicle fusion and vesicle docking at the mammalian presynaptic active zone

eLife ◽

10.7554/elife.28412 ◽

2017 ◽

Vol 6 ◽

Cited By ~ 19

Author(s):

Matthias Lübbert ◽

R Oliver Goral ◽

Rachel Satterfield ◽

Travis Putzke ◽

Arn MJM van den Maagdenberg ◽

...

Keyword(s):

Synaptic Vesicle ◽

Active Zone ◽

Neurotransmitter Release ◽

Physical Distance ◽

Subunit C ◽

Vesicle Docking ◽

C Terminus ◽

Synaptic Vesicle Release ◽

Synaptic Vesicle Fusion ◽

Α1 Subunit

In central nervous system (CNS) synapses, action potential-evoked neurotransmitter release is principally mediated by CaV2.1 calcium channels (CaV2.1) and is highly dependent on the physical distance between CaV2.1 and synaptic vesicles (coupling). Although various active zone proteins are proposed to control coupling and abundance of CaV2.1 through direct interactions with the CaV2.1 α1 subunit C-terminus at the active zone, the role of these interaction partners is controversial. To define the intrinsic motifs that regulate coupling, we expressed mutant CaV2.1 α1 subunits on a CaV2.1 null background at the calyx of Held presynaptic terminal. Our results identified a region that directly controlled fast synaptic vesicle release and vesicle docking at the active zone independent of CaV2.1 abundance. In addition, proposed individual direct interactions with active zone proteins are insufficient for CaV2.1 abundance and coupling. Therefore, our work advances our molecular understanding of CaV2.1 regulation of neurotransmitter release in mammalian CNS synapses.

Download Full-text

(M)Unc13s in Active Zone Diversity: A Drosophila Perspective

Frontiers in Synaptic Neuroscience ◽

10.3389/fnsyn.2021.798204 ◽

2022 ◽

Vol 13 ◽

Author(s):

Chengji Piao ◽

Stephan J. Sigrist

Keyword(s):

Synaptic Vesicle ◽

Active Zone ◽

Stoichiometric Composition ◽

Release Site ◽

Homeostatic Plasticity ◽

Release Factor ◽

Loosely Coupled ◽

Action Potential Frequency ◽

Active Zones ◽

Potential Frequency

The so-called active zones at pre-synaptic terminals are the ultimate filtering devices, which couple between action potential frequency and shape, and the information transferred to the post-synaptic neurons, finally tuning behaviors. Within active zones, the release of the synaptic vesicle operates from specialized “release sites.” The (M)Unc13 class of proteins is meant to define release sites topologically and biochemically, and diversity between Unc13-type release factor isoforms is suspected to steer diversity at active zones. The two major Unc13-type isoforms, namely, Unc13A and Unc13B, have recently been described from the molecular to the behavioral level, exploiting Drosophila being uniquely suited to causally link between these levels. The exact nanoscale distribution of voltage-gated Ca2+ channels relative to release sites (“coupling”) at pre-synaptic active zones fundamentally steers the release of the synaptic vesicle. Unc13A and B were found to be either tightly or loosely coupled across Drosophila synapses. In this review, we reported recent findings on diverse aspects of Drosophila Unc13A and B, importantly, their nano-topological distribution at active zones and their roles in release site generation, active zone assembly, and pre-synaptic homeostatic plasticity. We compared their stoichiometric composition at different synapse types, reviewing the correlation between nanoscale distribution of these two isoforms and release physiology and, finally, discuss how isoform-specific release components might drive the functional heterogeneity of synapses and encode discrete behavior.

Download Full-text

Faculty Opinions recommendation of A novel region in the CaV2.1 α1 subunit C-terminus regulates fast synaptic vesicle fusion and vesicle docking at the mammalian presynaptic active zone.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.727964942.793539677 ◽

2017 ◽

Author(s):

Jens Rettig ◽

David Stevens

Keyword(s):

Synaptic Vesicle ◽

Active Zone ◽

Vesicle Fusion ◽

Subunit C ◽

Vesicle Docking ◽

C Terminus ◽

Presynaptic Active Zone ◽

Synaptic Vesicle Fusion ◽

Α1 Subunit

Download Full-text

Liprin-α3 controls vesicle docking and exocytosis at the active zone of hippocampal synapses

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1719012115 ◽

2018 ◽

Vol 115 (9) ◽

pp. 2234-2239 ◽

Cited By ~ 22

Author(s):

Man Yan Wong ◽

Changliang Liu ◽

Shan Shan H. Wang ◽

Aram C. F. Roquas ◽

Stephen C. Fowler ◽

...

Keyword(s):

Synaptic Vesicle ◽

Active Zone ◽

Hippocampal Neurons ◽

Stimulated Emission ◽

Loss Of Function ◽

Zone Structure ◽

Vesicle Docking ◽

Synaptic Vesicle Exocytosis ◽

Vesicle Exocytosis ◽

And Function

The presynaptic active zone provides sites for vesicle docking and release at central nervous synapses and is essential for speed and accuracy of synaptic transmission. Liprin-α binds to several active zone proteins, and loss-of-function studies in invertebrates established important roles for Liprin-α in neurodevelopment and active zone assembly. However, Liprin-α localization and functions in vertebrates have remained unclear. We used stimulated emission depletion superresolution microscopy to systematically determine the localization of Liprin-α2 and Liprin-α3, the two predominant Liprin-α proteins in the vertebrate brain, relative to other active-zone proteins. Both proteins were widely distributed in hippocampal nerve terminals, and Liprin-α3, but not Liprin-α2, had a prominent component that colocalized with the active-zone proteins Bassoon, RIM, Munc13, RIM-BP, and ELKS. To assess Liprin-α3 functions, we generated Liprin-α3–KO mice by using CRISPR/Cas9 gene editing. We found reduced synaptic vesicle tethering and docking in hippocampal neurons of Liprin-α3–KO mice, and synaptic vesicle exocytosis was impaired. Liprin-α3 KO also led to mild alterations in active zone structure, accompanied by translocation of Liprin-α2 to active zones. These findings establish important roles for Liprin-α3 in active-zone assembly and function, and suggest that interplay between various Liprin-α proteins controls their active-zone localization.

Download Full-text