Neurotransmitter Release: Priming at Presynaptic Active Zones

Presynaptic glutamate receptors (GluRs) modulate neurotransmitter release and are physiological targets for regulation during various forms of plasticity. Although much is known about the auxiliary subunits associated with postsynaptic GluRs, far less is understood about presynaptic auxiliary GluR subunits and their functions. At theDrosophilaneuromuscular junction, a presynaptic GluR,DKaiR1D, localizes near active zones and operates as an autoreceptor to tune baseline transmission and enhance presynaptic neurotransmitter release in response to diminished postsynaptic GluR functionality, a process referred to as presynaptic homeostatic potentiation (PHP). Here, we identify an auxiliary subunit that collaborates with DKaiR1D to promote these synaptic functions. This subunit, dSol-1, is the homolog of theCaenorhabditis elegansCUB (Complement C1r/C1s, Uegf, Bmp1) domain protein Sol-1. We find thatdSol-1functions in neurons to facilitate baseline neurotransmission and to enable PHP expression, properties shared withDKaiR1D. Intriguingly, presynaptic overexpression ofdSol-1is sufficient to enhance neurotransmitter release through aDKaiR1D-dependent mechanism. Furthermore,dSol-1is necessary to rapidly increase the abundance of DKaiR1D receptors near active zones during homeostatic signaling. Together with recent work showing the CUB domain protein Neto2 is necessary for the homeostatic modulation of postsynaptic GluRs in mammals, our data demonstrate that dSol-1 is required for the homeostatic regulation of presynaptic GluRs. Thus, we propose that CUB domain proteins are fundamental homeostatic modulators of GluRs on both sides of the synapse.

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Separation of presynaptic Cav2 and Cav1 channel function in synaptic vesicle exo- and endocytosis by the membrane anchored Ca2+ pump PMCA

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2106621118 ◽

2021 ◽

Vol 118 (28) ◽

pp. e2106621118

Author(s):

Niklas Krick ◽

Stefanie Ryglewski ◽

Aylin Pichler ◽

Arthur Bikbaev ◽

Torsten Götz ◽

...

Keyword(s):

Synaptic Vesicle ◽

Neurotransmitter Release ◽

Calcium Currents ◽

Short Term ◽

Triggered Release ◽

Presynaptic Terminals ◽

Dynamic Regulation ◽

Short Term Plasticity ◽

Separate Control ◽

Active Zones

Synaptic vesicle (SV) release, recycling, and plastic changes of release probability co-occur side by side within nerve terminals and rely on local Ca2+ signals with different temporal and spatial profiles. The mechanisms that guarantee separate regulation of these vital presynaptic functions during action potential (AP)–triggered presynaptic Ca2+ entry remain unclear. Combining Drosophila genetics with electrophysiology and imaging reveals the localization of two different voltage-gated calcium channels at the presynaptic terminals of glutamatergic neuromuscular synapses (the Drosophila Cav2 homolog, Dmca1A or cacophony, and the Cav1 homolog, Dmca1D) but with spatial and functional separation. Cav2 within active zones is required for AP-triggered neurotransmitter release. By contrast, Cav1 localizes predominantly around active zones and contributes substantially to AP-evoked Ca2+ influx but has a small impact on release. Instead, L-type calcium currents through Cav1 fine-tune short-term plasticity and facilitate SV recycling. Separate control of SV exo- and endocytosis by AP-triggered presynaptic Ca2+ influx through different channels demands efficient measures to protect the neurotransmitter release machinery against Cav1-mediated Ca2+ influx. We show that the plasma membrane Ca2+ ATPase (PMCA) resides in between active zones and isolates Cav2-triggered release from Cav1-mediated dynamic regulation of recycling and short-term plasticity, two processes which Cav2 may also contribute to. As L-type Cav1 channels also localize next to PQ-type Cav2 channels within axon terminals of some central mammalian synapses, we propose that Cav2, Cav1, and PMCA act as a conserved functional triad that enables separate control of SV release and recycling rates in presynaptic terminals.

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Macromolecular complexes at active zones: integrated nano-machineries for neurotransmitter release

Cellular and Molecular Life Sciences ◽

10.1007/s00018-014-1657-5 ◽

2014 ◽

Vol 71 (20) ◽

pp. 3903-3916 ◽

Cited By ~ 7

Author(s):

John Jia En Chua

Keyword(s):

Neurotransmitter Release ◽

Macromolecular Complexes ◽

Active Zones

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Reconstructing essential active zone functions within a synapse

10.1101/2021.11.21.469466 ◽

2021 ◽

Author(s):

Chao Tan ◽

Shan Shan H Wang ◽

Giovanni de Nola ◽

Pascal S Kaeser

Keyword(s):

Fusion Protein ◽

Synaptic Vesicle ◽

Active Zone ◽

Neurotransmitter Release ◽

Molecular Machines ◽

Vesicle Docking ◽

Active Zones ◽

Ca2 Channels

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.

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Neurotransmitter Release: Priming at Presynaptic Active Zones

10.1007/springerreference_117503 ◽

2012 ◽

Keyword(s):

Neurotransmitter Release ◽

Active Zones

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Endogenous tagging reveals differential regulation of Ca2+ channels at single AZs during presynaptic homeostatic potentiation and depression

10.1101/240051 ◽

2017 ◽

Cited By ~ 4

Author(s):

Scott J. Gratz ◽

Pragya Goel ◽

Joseph J. Bruckner ◽

Roberto X. Hernandez ◽

Karam Khateeb ◽

...

Keyword(s):

Information Flow ◽

Neurotransmitter Release ◽

Synaptic Strength ◽

Live Imaging ◽

Differential Regulation ◽

Synaptic Function ◽

Homeostatic Plasticity ◽

Multiple Forms ◽

Active Zones ◽

Ca2 Channels

AbstractNeurons communicate through Ca2+-dependent neurotransmitter release at presynaptic active zones (AZs). Neurotransmitter release properties play a key role in defining information flow in circuits and are tuned during multiple forms of plasticity. Despite their central role in determining neurotransmitter release properties, little is known about how Ca2+ channel levels are modulated to calibrate synaptic function. We used CRISPR to tag the Drosophila CaV2 Ca2+ channel Cacophony (Cac) and investigated the regulation of endogenous Ca2+ channels during homeostatic plasticity in males in which all endogenous Cac channels are tagged. We found that heterogeneously distributed Cac is highly predictive of neurotransmitter release probability at individual AZs and differentially regulated during opposing forms of presynaptic homeostatic plasticity. Specifically, Cac levels at AZ are increased during chronic and acute presynaptic homeostatic potentiation (PHP), and live imaging during acute expression of PHP reveals proportional Ca2+ channel accumulation across heterogeneous AZs. In contrast, endogenous Cac levels do not change during presynaptic homeostatic depression (PHD), implying that the reported reduction in Ca2+ influx during PHD is achieved through functional adaptions to pre-existing Ca2+ channels. Thus, distinct mechanisms bi-directionally modulate presynaptic Ca2+ levels to maintain stable synaptic strength in response to diverse challenges, with Ca2+ channel abundance providing a rapidly tunable substrate for potentiating neurotransmitter release over both acute and chronic timescales.

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A presynaptic spectrin network controls active zone assembly and neurotransmitter release

10.1101/812032 ◽

2019 ◽

Author(s):

Qi Wang ◽

Lindsey Friend ◽

Rosario Vicidomini ◽

Tae Hee Han ◽

Peter Nguyen ◽

...

Keyword(s):

Active Zone ◽

Neurotransmitter Release ◽

Synaptic Cleft ◽

Structure And Function ◽

Dynamic Changes ◽

Synaptic Structure ◽

Synaptic Boutons ◽

Active Zones ◽

And Function ◽

Spectrin Network

ABSTRACTWe have previously reported that Drosophila Tenectin (Tnc) recruits αPS2/βPS integrin to ensure structural and functional integrity at larval NMJs (Wang et al., 2018). In muscles, Tnc/integrin engages the spectrin network to regulate the size and architecture of synaptic boutons. In neurons, Tnc/integrin controls neurotransmitter release. Here we show that presynaptic Tnc/integrin modulates the synaptic accumulation of key active zone components, including the Ca2+ channel Cac and the active zone scaffold Brp. Presynaptic α-Spectrin appears to be both required and sufficient for the recruitment of Cac and Brp. We visualized the endogenous α-Spectrin and found that Tnc controls spectrin recruitment at synaptic terminals. Thus, Tnc/integrin anchors the presynaptic spectrin network and ensures the proper assembly and function of the active zones. Since pre- and postsynaptic Tnc/integrin limit each other, we hypothesize that this pathway links dynamic changes within the synaptic cleft to changes in synaptic structure and function.

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Reduced endogenous Ca2+ buffering speeds active zone Ca2+ signaling

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1508419112 ◽

2015 ◽

Vol 112 (23) ◽

pp. E3075-E3084 ◽

Cited By ~ 27

Author(s):

Igor Delvendahl ◽

Lukasz Jablonski ◽

Carolin Baade ◽

Victor Matveev ◽

Erwin Neher ◽

...

Keyword(s):

High Resolution ◽

Synaptic Transmission ◽

Active Zone ◽

Neurotransmitter Release ◽

Mossy Fiber ◽

Repetitive Firing ◽

Two Photon ◽

High Affinity ◽

Model Predictions ◽

Active Zones

Fast synchronous neurotransmitter release at the presynaptic active zone is triggered by local Ca2+ signals, which are confined in their spatiotemporal extent by endogenous Ca2+ buffers. However, it remains elusive how rapid and reliable Ca2+ signaling can be sustained during repetitive release. Here, we established quantitative two-photon Ca2+ imaging in cerebellar mossy fiber boutons, which fire at exceptionally high rates. We show that endogenous fixed buffers have a surprisingly low Ca2+-binding ratio (∼15) and low affinity, whereas mobile buffers have high affinity. Experimentally constrained modeling revealed that the low endogenous buffering promotes fast clearance of Ca2+ from the active zone during repetitive firing. Measuring Ca2+ signals at different distances from active zones with ultra-high-resolution confirmed our model predictions. Our results lead to the concept that reduced Ca2+ buffering enables fast active zone Ca2+ signaling, suggesting that the strength of endogenous Ca2+ buffering limits the rate of synchronous synaptic transmission.

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Neurotransmitter release mechanisms and microtubules

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1983.0038 ◽

1983 ◽

Vol 218 (1211) ◽

pp. 253-258 ◽

Cited By ~ 15

Keyword(s):

Neurotransmitter Release ◽

Synaptic Vesicles ◽

Ordered Structure ◽

Presynaptic Membrane ◽

Vesicle Membrane ◽

Ordered Arrays ◽

The Central Nervous System ◽

Active Zones ◽

Dense Projections ◽

Regular Arrays

The morphological mechanisms involved in translocation of the synaptic vesicle to the presynaptic membrane, release of transmitter from the vesicle and recycling of the vesicle membrane are still far from understood. However, there is strong evidence that vesicles move along the surfaces of a specific set of highly labile presynaptic microtubules that direct the vesicles to the active zones. These microtubules are focused in a precise geometrical array, which is in register with and in contact with presynaptic dense projections of the central nervous system synapse or presynaptic dense bars of the motor endplate. These dense complexes constitute the presynaptic grid or active zones. The regular arrays of dense projections or bars are in turn coincident with rings or chains of synaptic vesicles mobilized at release sites on the presynaptic membrane (having arrived at these precise points by microtubule translocation). Thus it is suggested that the presynaptic microtubules not only translocate synaptic vesicles, but because of their ordered arrays determine, in ontogeny, the ordered structure of the presynaptic grid.

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