1
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Xia X, Li Y. A new GRAB sensor reveals differences in the dynamics and molecular regulation between neuropeptide and neurotransmitter release. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.22.595424. [PMID: 38826473 PMCID: PMC11142204 DOI: 10.1101/2024.05.22.595424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2024]
Abstract
The co-existence and co-transmission of neuropeptides and small molecule neurotransmitters in the same neuron is a fundamental aspect of almost all neurons across various species. However, the differences regarding their in vivo spatiotemporal dynamics and underlying molecular regulation remain poorly understood. Here, we developed a GPCR-activation-based (GRAB) sensor for detecting short neuropeptide F (sNPF) with high sensitivity and spatiotemporal resolution. Furthermore, we explore the differences of in vivo dynamics and molecular regulation between sNPF and acetylcholine (ACh) from the same neurons. Interestingly, the release of sNPF and ACh shows different spatiotemporal dynamics. Notably, we found that distinct synaptotagmins (Syt) are involved in these two processes, as Syt7 and Sytα for sNPF release, while Syt1 for ACh release. Thus, this new GRAB sensor provides a powerful tool for studying neuropeptide release and providing new insights into the distinct release dynamics and molecular regulation between neuropeptides and small molecule neurotransmitters.
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Affiliation(s)
- Xiju Xia
- State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing 100871, China
- PKU-IDG/McGovern Institute for Brain Research, Beijing 100871, China
- Academy for Advanced Interdisciplinary Studies (AAIS), and Peking University–Tsinghua University–National Institute of Biological Sciences Joint Graduate Program (PTN), Peking University, Beijing, 100871, China
| | - Yulong Li
- State Key Laboratory of Membrane Biology, School of Life Sciences, Peking University, Beijing 100871, China
- PKU-IDG/McGovern Institute for Brain Research, Beijing 100871, China
- Academy for Advanced Interdisciplinary Studies (AAIS), and Peking University–Tsinghua University–National Institute of Biological Sciences Joint Graduate Program (PTN), Peking University, Beijing, 100871, China
- Chinese Institute for Brain Research, Beijing 102206, China
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2
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Ortiz EA, Campbell PD, Nelson JC, Granato M. A single base pair substitution in zebrafish distinguishes between innate and acute startle behavior regulation. PLoS One 2024; 19:e0300529. [PMID: 38498506 PMCID: PMC10947677 DOI: 10.1371/journal.pone.0300529] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Accepted: 02/26/2024] [Indexed: 03/20/2024] Open
Abstract
Behavioral thresholds define the lowest stimulus intensities sufficient to elicit a behavioral response. Establishment of baseline behavioral thresholds during development is critical for proper responses throughout the animal's life. Despite the relevance of such innate thresholds, the molecular mechanisms critical to establishing behavioral thresholds during development are not well understood. The acoustic startle response is a conserved behavior whose threshold is established during development yet is subsequently acutely regulated. We have previously identified a zebrafish mutant line (escapist) that displays a decreased baseline or innate acoustic startle threshold. Here, we identify a single base pair substitution on Chromosome 25 located within the coding sequence of the synaptotagmin 7a (syt7a) gene that is tightly linked to the escapist acoustic hypersensitivity phenotype. By generating animals in which we deleted the syt7a open reading frame, and subsequent complementation testing with the escapist line, we demonstrate that loss of syt7a function is not the cause of the escapist behavioral phenotype. Nonetheless, escapist mutants provide a powerful tool to decipher the overlap between acute and developmental regulation of behavioral thresholds. Extensive behavioral analyses reveal that in escapist mutants the establishment of the innate acoustic startle threshold is impaired, while regulation of its acute threshold remains intact. Moreover, our behavioral analyses reveal a deficit in baseline responses to visual stimuli, but not in the acute regulation of responses to visual stimuli. Together, this work eliminates loss of syt7a as causative for the escapist phenotype and suggests that mechanisms that regulate the establishment of behavioral thresholds in escapist larvae can operate independently from those regulating acute threshold regulation.
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Affiliation(s)
- Elelbin A. Ortiz
- Department of Neuroscience, University of Pennsylvania, Pennsylvania, PA, United States of America
- Department of Cell and Developmental Biology, University of Pennsylvania, Pennsylvania, PA, United States of America
| | - Philip D. Campbell
- Department of Cell and Developmental Biology, University of Pennsylvania, Pennsylvania, PA, United States of America
- Department of Psychiatry, University of Pennsylvania, Pennsylvania, PA, United States of America
| | - Jessica C. Nelson
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO, United States of America
| | - Michael Granato
- Department of Cell and Developmental Biology, University of Pennsylvania, Pennsylvania, PA, United States of America
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3
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Saldarriaga CA, Alatout MH, Khurram OU, Gransee HM, Sieck GC, Mantilla CB. Chloroquine impairs maximal transdiaphragmatic pressure generation in old mice. J Appl Physiol (1985) 2023; 135:1126-1134. [PMID: 37823202 PMCID: PMC10979802 DOI: 10.1152/japplphysiol.00365.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Revised: 09/19/2023] [Accepted: 10/07/2023] [Indexed: 10/13/2023] Open
Abstract
Aging results in increased neuromuscular transmission failure and denervation of the diaphragm muscle, as well as decreased force generation across a range of motor behaviors. Increased risk for respiratory complications in old age is a major health problem. Aging impairs autophagy, a tightly regulated multistep process responsible for clearing misfolded or aggregated proteins and damaged organelles. In motor neurons, aging-related autophagy impairment may contribute to deficits in neurotransmission, subsequent muscle atrophy, and loss of muscle force. Chloroquine is commonly used to inhibit autophagy. We hypothesized that chloroquine decreases transdiaphragmatic pressure (Pdi) in mice. Old mice (16-28 mo old; n = 26) were randomly allocated to receive intraperitoneal chloroquine (50 mg/kg) or vehicle 4 h before measuring Pdi during eupnea, hypoxia (10% O2)-hypercapnia (5% CO2) exposure, spontaneous deep breaths ("sighs"), and maximal activation elicited by bilateral phrenic nerve stimulation (Pdimax). Pdi amplitude and ventilatory parameters across experimental groups and behaviors were evaluated using a mixed linear model. There were no differences in Pdi amplitude across treatments during eupnea (∼8 cm H2O), hypoxia-hypercapnia (∼10 cm H2O), or sigh (∼36 cm H2O), consistent with prior studies documenting a lack of aging effects on ventilatory behaviors. In vehicle and chloroquine-treated mice, average Pdimax was 61 and 46 cm H2O, respectively. Chloroquine decreased Pdimax by 24% compared to vehicle (P < 0.05). There were no sex or age effects on Pdi in older mice. The observed decrease in Pdimax suggests aging-related susceptibility to impairments in autophagy, consistent with the effects of chloroquine on this important homeostatic process.NEW & NOTEWORTHY Recent findings suggest that autophagy plays a role in the development of aging-related neuromuscular dysfunction; however, the contribution of autophagy impairment to the maintenance of diaphragm force generation in old age is unknown. This study shows that in old mice, chloroquine administration decreases maximal transdiaphragmatic pressure generation. These chloroquine effects suggest a susceptibility to impairments in autophagy in old age.
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Affiliation(s)
- Carlos A Saldarriaga
- Department of Anesthesiology and Perioperative Medicine, College of Medicine and Science, Mayo Clinic, Rochester, Minnesota, United States
| | - Mayar H Alatout
- Department of Anesthesiology and Perioperative Medicine, College of Medicine and Science, Mayo Clinic, Rochester, Minnesota, United States
| | - Obaid U Khurram
- Department of Physiology and Biomedical Engineering, College of Medicine and Science, Mayo Clinic, Rochester, Minnesota, United States
| | - Heather M Gransee
- Department of Anesthesiology and Perioperative Medicine, College of Medicine and Science, Mayo Clinic, Rochester, Minnesota, United States
| | - Gary C Sieck
- Department of Anesthesiology and Perioperative Medicine, College of Medicine and Science, Mayo Clinic, Rochester, Minnesota, United States
- Department of Physiology and Biomedical Engineering, College of Medicine and Science, Mayo Clinic, Rochester, Minnesota, United States
| | - Carlos B Mantilla
- Department of Anesthesiology and Perioperative Medicine, College of Medicine and Science, Mayo Clinic, Rochester, Minnesota, United States
- Department of Physiology and Biomedical Engineering, College of Medicine and Science, Mayo Clinic, Rochester, Minnesota, United States
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4
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Ortiz EA, Campbell PD, Nelson JC, Granato M. A single base pair substitution on Chromosome 25 in zebrafish distinguishes between development and acute regulation of behavioral thresholds. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.25.554673. [PMID: 37662318 PMCID: PMC10473726 DOI: 10.1101/2023.08.25.554673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/05/2023]
Abstract
Behavioral thresholds define the lowest stimulus intensities sufficient to elicit a behavioral response. Establishment of baseline behavioral thresholds during development is critical for proper responses throughout the animal's life. Despite the relevance of such innate thresholds, the molecular mechanisms critical to establishing behavioral thresholds during development are not well understood. The acoustic startle response is a conserved behavior whose threshold is established during development yet is subsequently acutely regulated. We have previously identified a zebrafish mutant line ( escapist ) that displays a decreased baseline or innate acoustic startle threshold. Here, we identify a single base pair substitution on Chromosome 25 located within the coding sequence of the synaptotagmin 7a ( syt7a ) gene that is tightly linked to the escapist acoustic hypersensitivity phenotype. By generating animals in which we deleted the syt7a open reading frame, and subsequent complementation testing with the escapist line, we demonstrate that loss of syt7a function is not the cause of the escapist behavioral phenotype. Nonetheless, escapist mutants provide a powerful tool to decipher the overlap between acute and developmental regulation of behavioral thresholds. Extensive behavioral analyses reveal that in escapist mutants the establishment of the innate acoustic startle threshold is impaired, while regulation of its acute threshold remains intact. Moreover, our behavioral analyses reveal a deficit in baseline responses to visual stimuli, but not in the acute regulation of responses to visual stimuli. Together, this work eliminates loss of syt7a as causative for the escapist phenotype and suggests that mechanisms that regulate the establishment of behavioral thresholds in escapist larvae can operate largely independently from those regulating acute threshold regulation.
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5
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Guss EJ, Akbergenova Y, Cunningham KL, Littleton JT. Loss of the extracellular matrix protein Perlecan disrupts axonal and synaptic stability during Drosophila development. eLife 2023; 12:RP88273. [PMID: 37368474 PMCID: PMC10328508 DOI: 10.7554/elife.88273] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/28/2023] Open
Abstract
Heparan sulfate proteoglycans (HSPGs) form essential components of the extracellular matrix (ECM) and basement membrane (BM) and have both structural and signaling roles. Perlecan is a secreted ECM-localized HSPG that contributes to tissue integrity and cell-cell communication. Although a core component of the ECM, the role of Perlecan in neuronal structure and function is less understood. Here, we identify a role for Drosophila Perlecan in the maintenance of larval motoneuron axonal and synaptic stability. Loss of Perlecan causes alterations in the axonal cytoskeleton, followed by axonal breakage and synaptic retraction of neuromuscular junctions. These phenotypes are not prevented by blocking Wallerian degeneration and are independent of Perlecan's role in Wingless signaling. Expression of Perlecan solely in motoneurons cannot rescue synaptic retraction phenotypes. Similarly, removing Perlecan specifically from neurons, glia, or muscle does not cause synaptic retraction, indicating the protein is secreted from multiple cell types and functions non-cell autonomously. Within the peripheral nervous system, Perlecan predominantly localizes to the neural lamella, a specialized ECM surrounding nerve bundles. Indeed, the neural lamella is disrupted in the absence of Perlecan, with axons occasionally exiting their usual boundary in the nerve bundle. In addition, entire nerve bundles degenerate in a temporally coordinated manner across individual hemi-segments throughout larval development. These observations indicate disruption of neural lamella ECM function triggers axonal destabilization and synaptic retraction of motoneurons, revealing a role for Perlecan in axonal and synaptic integrity during nervous system development.
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Affiliation(s)
- Ellen J Guss
- The Picower Institute for Learning and Memory, Department of Biology, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - Yulia Akbergenova
- The Picower Institute for Learning and Memory, Department of Biology, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - Karen L Cunningham
- The Picower Institute for Learning and Memory, Department of Biology, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Biology, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, United States
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Jusyte M, Blaum N, Böhme MA, Berns MMM, Bonard AE, Vámosi ÁB, Pushpalatha KV, Kobbersmed JRL, Walter AM. Unc13A dynamically stabilizes vesicle priming at synaptic release sites for short-term facilitation and homeostatic potentiation. Cell Rep 2023; 42:112541. [PMID: 37243591 DOI: 10.1016/j.celrep.2023.112541] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Revised: 03/10/2023] [Accepted: 05/03/2023] [Indexed: 05/29/2023] Open
Abstract
Presynaptic plasticity adjusts neurotransmitter (NT) liberation. Short-term facilitation (STF) tunes synapses to millisecond repetitive activation, while presynaptic homeostatic potentiation (PHP) of NT release stabilizes transmission over minutes. Despite different timescales of STF and PHP, our analysis of Drosophila neuromuscular junctions reveals functional overlap and shared molecular dependence on the release-site protein Unc13A. Mutating Unc13A's calmodulin binding domain (CaM-domain) increases baseline transmission while blocking STF and PHP. Mathematical modeling suggests that Ca2+/calmodulin/Unc13A interaction plastically stabilizes vesicle priming at release sites and that CaM-domain mutation causes constitutive stabilization, thereby blocking plasticity. Labeling the functionally essential Unc13A MUN domain reveals higher STED microscopy signals closer to release sites following CaM-domain mutation. Acute phorbol ester treatment similarly enhances NT release and blocks STF/PHP in synapses expressing wild-type Unc13A, while CaM-domain mutation occludes this, indicating common downstream effects. Thus, Unc13A regulatory domains integrate signals across timescales to switch release-site participation for synaptic plasticity.
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Affiliation(s)
- Meida Jusyte
- Molecular and Theoretical Neuroscience, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany; Einstein Center for Neurosciences Berlin, Charité Universitätsmedizin Berlin, Berlin, Germany
| | - Natalie Blaum
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Mathias A Böhme
- Molecular and Theoretical Neuroscience, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany; Rudolf Schönheimer Institute of Biochemistry, Division of General Biochemistry, Medical Faculty, Leipzig University, Leipzig, Germany
| | - Manon M M Berns
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Alix E Bonard
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Ábel B Vámosi
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | | | - Janus R L Kobbersmed
- Department of Mathematical Sciences, University of Copenhagen, Copenhagen, Denmark; Center of Functionally Integrative Neuroscience, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Alexander M Walter
- Molecular and Theoretical Neuroscience, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany; Einstein Center for Neurosciences Berlin, Charité Universitätsmedizin Berlin, Berlin, Germany; Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark.
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7
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Akefe IO, Osborne SL, Matthews B, Wallis TP, Meunier FA. Lipids and Secretory Vesicle Exocytosis. ADVANCES IN NEUROBIOLOGY 2023; 33:357-397. [PMID: 37615874 DOI: 10.1007/978-3-031-34229-5_14] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
In recent years, the number of studies implicating lipids in the regulation of synaptic vesicle exocytosis has risen considerably. It has become increasingly clear that lipids such as phosphoinositides, lysophospholipids, cholesterol, arachidonic acid and myristic acid play critical regulatory roles in the processes leading up to exocytosis. Lipids may affect membrane fusion reactions by altering the physical properties of the membrane, recruiting key regulatory proteins, concentrating proteins into exocytic "hotspots" or by modulating protein functions allosterically. Discrete changes in phosphoinositides concentration are involved in multiple trafficking events including exocytosis and endocytosis. Lipid-modifying enzymes such as the DDHD2 isoform of phospholipase A1 were recently shown to contribute to memory acquisition via dynamic modifications of the brain lipid landscape. Considering the increasing reports on neurodegenerative disorders associated with aberrant intracellular trafficking, an improved understanding of the control of lipid pathways is physiologically and clinically significant and will afford unique insights into mechanisms and therapeutic methods for neurodegenerative diseases. Consequently, this chapter will discuss the different classes of lipids, phospholipase enzymes, the evidence linking them to synaptic neurotransmitter release and how they act to regulate key steps in the multi-step process leading to neuronal communication and memory acquisition.
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Affiliation(s)
- Isaac O Akefe
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, Australia
| | - Shona L Osborne
- ARC Training Centre for Innovation in Biomedical Imaging Technology (CIBIT), The University of Queensland, St Lucia, QLD, Australia
| | - Benjamin Matthews
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, Australia
| | - Tristan P Wallis
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, Australia
| | - Frédéric A Meunier
- Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, St Lucia, QLD, Australia.
- School of Biomedical Sciences, The University of Queensland, St Lucia, QLD, Australia.
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8
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MacLeod KM, Pandya S. Expression and Neurotransmitter Association of the Synaptic Calcium Sensor Synaptotagmin in the Avian Auditory Brain Stem. J Assoc Res Otolaryngol 2022; 23:701-720. [PMID: 35999323 PMCID: PMC9789253 DOI: 10.1007/s10162-022-00863-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2021] [Accepted: 07/12/2022] [Indexed: 01/31/2023] Open
Abstract
In the avian auditory brain stem, acoustic timing and intensity cues are processed in separate, parallel pathways via the two divisions of the cochlear nucleus, nucleus angularis (NA) and nucleus magnocellularis (NM). Differences in excitatory and inhibitory synaptic properties, such as release probability and short-term plasticity, contribute to differential processing of the auditory nerve inputs. We investigated the distribution of synaptotagmin, a putative calcium sensor for exocytosis, via immunohistochemistry and double immunofluorescence in the embryonic and hatchling chick brain stem (Gallus gallus). We found that the two major isoforms, synaptotagmin 1 (Syt1) and synaptotagmin 2 (Syt2), showed differential expression. In the NM, anti-Syt2 label was strong and resembled the endbulb terminals of the auditory nerve inputs, while anti-Syt1 label was weaker and more punctate. In NA, both isoforms were intensely expressed throughout the neuropil. A third isoform, synaptotagmin 7 (Syt7), was largely absent from the cochlear nuclei. In nucleus laminaris (NL, the target nucleus of NM), anti-Syt2 and anti-Syt7 strongly labeled the dendritic lamina. These patterns were established by embryonic day 18 and persisted to postnatal day 7. Double-labeling immunofluorescence showed that Syt1 and Syt2 were associated with vesicular glutamate transporter 2 (VGluT2), but not vesicular GABA transporter (VGAT), suggesting that these Syt isoforms were localized to excitatory, but not inhibitory, terminals. These results suggest that Syt2 is the major calcium binding protein underlying excitatory neurotransmission in the timing pathway comprising NM and NL, while Syt2 and Syt1 regulate excitatory transmission in the parallel intensity pathway via cochlear nucleus NA.
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Affiliation(s)
- Katrina M MacLeod
- Department of Biology, University of Maryland, College Park, MD, 20742, USA.
| | - Sangeeta Pandya
- Department of Biology, University of Maryland, College Park, MD, 20742, USA
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9
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Weingarten DJ, Shrestha A, Juda-Nelson K, Kissiwaa SA, Spruston E, Jackman SL. Fast resupply of synaptic vesicles requires synaptotagmin-3. Nature 2022; 611:320-325. [PMID: 36261524 DOI: 10.1038/s41586-022-05337-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Accepted: 09/12/2022] [Indexed: 01/09/2023]
Abstract
Sustained neuronal activity demands a rapid resupply of synaptic vesicles to maintain reliable synaptic transmission. Such vesicle replenishment is accelerated by submicromolar presynaptic Ca2+ signals by an as-yet unidentified high-affinity Ca2+ sensor1,2. Here we identify synaptotagmin-3 (SYT3)3,4 as that presynaptic high-affinity Ca2+ sensor, which drives vesicle replenishment and short-term synaptic plasticity. Synapses in Syt3 knockout mice exhibited enhanced short-term depression, and recovery from depression was slower and insensitive to presynaptic residual Ca2+. During sustained neuronal firing, SYT3 accelerated vesicle replenishment and increased the size of the readily releasable pool. SYT3 also mediated short-term facilitation under conditions of low release probability and promoted synaptic enhancement together with another high-affinity synaptotagmin, SYT7 (ref. 5). Biophysical modelling predicted that SYT3 mediates both replenishment and facilitation by promoting the transition of loosely docked vesicles to tightly docked, primed states. Our results reveal a crucial role for presynaptic SYT3 in the maintenance of reliable high-frequency synaptic transmission. Moreover, multiple forms of short-term plasticity may converge on a mechanism of reversible, Ca2+-dependent vesicle docking.
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Affiliation(s)
| | - Amita Shrestha
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
| | - Kessa Juda-Nelson
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
| | - Sarah A Kissiwaa
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
| | - Evan Spruston
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
| | - Skyler L Jackman
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA.
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10
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AP2 Regulates Thickveins Trafficking to Attenuate NMJ Growth Signaling in Drosophila. eNeuro 2022; 9:ENEURO.0044-22.2022. [PMID: 36180220 PMCID: PMC9581581 DOI: 10.1523/eneuro.0044-22.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Revised: 09/09/2022] [Accepted: 09/23/2022] [Indexed: 12/15/2022] Open
Abstract
Compromised endocytosis in neurons leads to synapse overgrowth and altered organization of synaptic proteins. However, the molecular players and the signaling pathways which regulate the process remain poorly understood. Here, we show that σ2-adaptin, one of the subunits of the AP2-complex, genetically interacts with Mad, Medea and Dad (components of BMP signaling) to control neuromuscular junction (NMJ) growth in Drosophila Ultrastructural analysis of σ2-adaptin mutants show an accumulation of large vesicles and membranous structures akin to endosomes at the synapse. We found that mutations in σ2-adaptin lead to an accumulation of Tkv receptors at the presynaptic membrane. Interestingly, the level of small GTPase Rab11 was significantly reduced in the σ2-adaptin mutant synapses. However, expression of Rab11 does not restore the synaptic defects of σ2-adaptin mutations. We propose a model in which AP2 regulates Tkv internalization and endosomal recycling to control synaptic growth.
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11
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Riggs E, Shakkour Z, Anderson CL, Carney PR. SYT1-Associated Neurodevelopmental Disorder: A Narrative Review. CHILDREN 2022; 9:children9101439. [PMID: 36291375 PMCID: PMC9601251 DOI: 10.3390/children9101439] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 09/13/2022] [Accepted: 09/15/2022] [Indexed: 11/16/2022]
Abstract
Synaptic dysregulations often result in damaging effects on the central nervous system, resulting in a wide range of brain and neurodevelopment disorders that are caused by mutations disrupting synaptic proteins. SYT1, an identified synaptotagmin protein, plays an essential role in mediating the release of calcium-triggered neurotransmitters (NT) involved in regular synaptic vesicle exocytosis. Considering the significant role of SYT1 in the physiology of synaptic neurotransmission, dysfunction and degeneration of this protein can result in a severe neurological impairment. Genetic variants lead to a newly discovered rare disorder, known as SYT1-associated neurodevelopment disorder. In this review, we will discuss in depth the function of SYT1 in synapse and the underlying molecular mechanisms. We will highlight the genetic basis of SYT1-associated neurodevelopmental disorder along with known phenotypes, with possible interventions and direction of research.
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Affiliation(s)
- Edith Riggs
- College of Osteopathic Medicine, Kansas City University School of Medicine, Kansas City, MO 64106, USA
| | - Zaynab Shakkour
- School of Medicine, University of Missouri Child Health, Columbia, MO 65201, USA
| | - Christopher L. Anderson
- School of Medicine, University of Missouri Child Health, Columbia, MO 65201, USA
- Correspondence:
| | - Paul R. Carney
- School of Medicine, University of Missouri Child Health, Columbia, MO 65201, USA
- Department of Engineering, University of Missouri Biomedical Engineering, Columbia, MO 65201, USA
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12
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Anqueira-González A, Acevedo-Gonzalez JP, Montes-Mercado A, Irizarry-Hernández C, Fuenzalida-Uribe NL, Ghezzi A. Transcriptional Correlates of Chronic Alcohol Neuroadaptation in Drosophila Larvae. Front Behav Neurosci 2021; 15:768694. [PMID: 34803626 PMCID: PMC8599819 DOI: 10.3389/fnbeh.2021.768694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Accepted: 10/15/2021] [Indexed: 11/24/2022] Open
Abstract
When presented with the choice, Drosophila melanogaster females will often prefer to lay eggs on food containing a significant amount of alcohol. While, in some cases, this behavioral decision can provide a survival advantage to the developing larvae, it can also lead to developmental and cognitive problems. Alcohol consumption can affect executive functions, episodic memory, and other brain function capacities. However, in the fruit fly, the initial cognitive effects of alcohol consumption have been shown to reverse upon persistent exposure to alcohol. Using an olfactory conditioning assay where an odorant is implemented as a conditioned stimulus and paired with a heat shock as an unconditioned stimulus, a previous study has shown that when exposed to a short acute dose of alcohol, Drosophila larvae can no longer learn this association. Interestingly, upon prolonged chronic alcohol exposure, larvae seem to successfully avoid the conditioned stimulus just as well as control alcohol-naive larvae, suggestive of alcohol-induced neuroadaptations. However, the mechanisms by which Drosophila adapt to the presence of alcohol remains unknown. In this study, we explore the transcriptional correlates of neuroadaptation in Drosophila larvae exposed to chronic alcohol to understand the genetic and cellular components responsible for this adaptation. For this, we employed RNA sequencing technology to evaluate differences in gene expression in the brain of larvae chronically exposed to alcohol. Our results suggest that alcohol-induced neuroadaptations are modulated by a diverse array of synaptic genes within the larval brain through a series of epigenetic modulators.
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Affiliation(s)
- Amanda Anqueira-González
- Department of Biology, University of Puerto Rico-Río Piedras Campus, San Juan, PR, United States
| | - Jenny P Acevedo-Gonzalez
- Department of Biology, University of Puerto Rico-Río Piedras Campus, San Juan, PR, United States
| | - Airined Montes-Mercado
- Department of Biology, University of Puerto Rico-Río Piedras Campus, San Juan, PR, United States
| | | | | | - Alfredo Ghezzi
- Department of Biology, University of Puerto Rico-Río Piedras Campus, San Juan, PR, United States
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13
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Sauvola CW, Akbergenova Y, Cunningham KL, Aponte-Santiago NA, Littleton JT. The decoy SNARE Tomosyn sets tonic versus phasic release properties and is required for homeostatic synaptic plasticity. eLife 2021; 10:e72841. [PMID: 34713802 PMCID: PMC8612732 DOI: 10.7554/elife.72841] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Accepted: 10/27/2021] [Indexed: 12/14/2022] Open
Abstract
Synaptic vesicle (SV) release probability (Pr) is a key presynaptic determinant of synaptic strength established by cell-intrinsic properties and further refined by plasticity. To characterize mechanisms that generate Pr heterogeneity between distinct neuronal populations, we examined glutamatergic tonic (Ib) and phasic (Is) motoneurons in Drosophila with stereotyped differences in Pr and synaptic plasticity. We found the decoy soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) Tomosyn is differentially expressed between these motoneuron subclasses and contributes to intrinsic differences in their synaptic output. Tomosyn expression enables tonic release in Ib motoneurons by reducing SNARE complex formation and suppressing Pr to generate decreased levels of SV fusion and enhanced resistance to synaptic fatigue. In contrast, phasic release dominates when Tomosyn expression is low, enabling high intrinsic Pr at Is terminals at the expense of sustained release and robust presynaptic potentiation. In addition, loss of Tomosyn disrupts the ability of tonic synapses to undergo presynaptic homeostatic potentiation.
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Affiliation(s)
- Chad W Sauvola
- Department of Brain and Cognitive Sciences, The Picower Institute of Learning and Memory, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Yulia Akbergenova
- Department of Brain and Cognitive Sciences, The Picower Institute of Learning and Memory, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Karen L Cunningham
- Department of Biology, Massachusetts Institute of TechnologyCambridgeUnited States
| | | | - J Troy Littleton
- Department of Brain and Cognitive Sciences, The Picower Institute of Learning and Memory, Massachusetts Institute of TechnologyCambridgeUnited States
- Department of Biology, Massachusetts Institute of TechnologyCambridgeUnited States
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14
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Weyrer C, Turecek J, Harrison B, Regehr WG. Introduction of synaptotagmin 7 promotes facilitation at the climbing fiber to Purkinje cell synapse. Cell Rep 2021; 36:109719. [PMID: 34551307 PMCID: PMC9152841 DOI: 10.1016/j.celrep.2021.109719] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 06/29/2021] [Accepted: 08/25/2021] [Indexed: 11/15/2022] Open
Abstract
Synaptotagmin 7 (Syt7) is a high-affinity calcium sensor that is implicated in multiple aspects of synaptic transmission. Here, we study the influence of Syt7 on the climbing fiber (CF) to Purkinje cell (PC) synapse. We find that small facilitation and prominent calcium-dependent recovery from depression at this synapse do not rely on Syt7 and that Syt7 is not normally present in CFs. We expressed Syt7 in CFs to assess the consequences of introducing Syt7 to a synapse that normally lacks Syt7. Syt7 expression does not promote asynchronous release or accelerate recovery from depression. Syt7 decreases the excitatory postsynaptic current (EPSC) magnitude, consistent with a decrease in the initial probability of release (PR). Syt7 also increases synaptic facilitation to such a large extent that it could not arise solely as an indirect consequence of decreased PR. Thus, the primary consequence of Syt7 expression in CFs, which normally lack Syt7, is to promote synaptic facilitation.
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Affiliation(s)
- Christopher Weyrer
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA; Department of Physiology, Development, and Neuroscience, University of Cambridge, Cambridge CB2 3EG, UK
| | - Josef Turecek
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Bailey Harrison
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
| | - Wade G Regehr
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
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15
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Li L, Liu H, Krout M, Richmond JE, Wang Y, Bai J, Weeratunga S, Collins BM, Ventimiglia D, Yu Y, Xia J, Tang J, Liu J, Hu Z. A novel dual Ca2+ sensor system regulates Ca2+-dependent neurotransmitter release. J Cell Biol 2021; 220:211787. [PMID: 33570571 PMCID: PMC7883739 DOI: 10.1083/jcb.202008121] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2020] [Revised: 12/19/2020] [Accepted: 01/15/2021] [Indexed: 02/08/2023] Open
Abstract
Ca2+-dependent neurotransmitter release requires synaptotagmins as Ca2+ sensors to trigger synaptic vesicle (SV) exocytosis via binding of their tandem C2 domains—C2A and C2B—to Ca2+. We have previously demonstrated that SNT-1, a mouse synaptotagmin-1 (Syt1) homologue, functions as the fast Ca2+ sensor in Caenorhabditis elegans. Here, we report a new Ca2+ sensor, SNT-3, which triggers delayed Ca2+-dependent neurotransmitter release. snt-1;snt-3 double mutants abolish evoked synaptic transmission, demonstrating that C. elegans NMJs use a dual Ca2+ sensor system. SNT-3 possesses canonical aspartate residues in both C2 domains, but lacks an N-terminal transmembrane (TM) domain. Biochemical evidence demonstrates that SNT-3 binds both Ca2+ and the plasma membrane. Functional analysis shows that SNT-3 is activated when SNT-1 function is impaired, triggering SV release that is loosely coupled to Ca2+ entry. Compared with SNT-1, which is tethered to SVs, SNT-3 is not associated with SV. Eliminating the SV tethering of SNT-1 by removing the TM domain or the whole N terminus rescues fast release kinetics, demonstrating that cytoplasmic SNT-1 is still functional and triggers fast neurotransmitter release, but also exhibits decreased evoked amplitude and release probability. These results suggest that the fast and slow properties of SV release are determined by the intrinsically different C2 domains in SNT-1 and SNT-3, rather than their N-termini–mediated membrane tethering. Our findings therefore reveal a novel dual Ca2+ sensor system in C. elegans and provide significant insights into Ca2+-regulated exocytosis.
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Affiliation(s)
- Lei Li
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland, Australia
| | - Haowen Liu
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland, Australia
| | - Mia Krout
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL
| | - Janet E Richmond
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL
| | - Yu Wang
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA
| | - Jihong Bai
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA
| | - Saroja Weeratunga
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
| | - Brett M Collins
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland, Australia
| | - Donovan Ventimiglia
- Lulu and Anthony Wang Laboratory of Neural Circuits and Behavior, The Rockefeller University, New York, NY
| | - Yi Yu
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland, Australia
| | - Jingyao Xia
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland, Australia
| | - Jing Tang
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland, Australia
| | - Jie Liu
- Neuroscience Program, Monash Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash University, Melbourne, Victoria, Australia
| | - Zhitao Hu
- Queensland Brain Institute, Clem Jones Centre for Ageing Dementia Research, The University of Queensland, Brisbane, Queensland, Australia
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16
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Sauvola CW, Littleton JT. SNARE Regulatory Proteins in Synaptic Vesicle Fusion and Recycling. Front Mol Neurosci 2021; 14:733138. [PMID: 34421538 PMCID: PMC8377282 DOI: 10.3389/fnmol.2021.733138] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 07/20/2021] [Indexed: 01/01/2023] Open
Abstract
Membrane fusion is a universal feature of eukaryotic protein trafficking and is mediated by the soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) family. SNARE proteins embedded in opposing membranes spontaneously assemble to drive membrane fusion and cargo exchange in vitro. Evolution has generated a diverse complement of SNARE regulatory proteins (SRPs) that ensure membrane fusion occurs at the right time and place in vivo. While a core set of SNAREs and SRPs are common to all eukaryotic cells, a specialized set of SRPs within neurons confer additional regulation to synaptic vesicle (SV) fusion. Neuronal communication is characterized by precise spatial and temporal control of SNARE dynamics within presynaptic subdomains specialized for neurotransmitter release. Action potential-elicited Ca2+ influx at these release sites triggers zippering of SNAREs embedded in the SV and plasma membrane to drive bilayer fusion and release of neurotransmitters that activate downstream targets. Here we discuss current models for how SRPs regulate SNARE dynamics and presynaptic output, emphasizing invertebrate genetic findings that advanced our understanding of SRP regulation of SV cycling.
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Affiliation(s)
- Chad W Sauvola
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States.,Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, United States
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17
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Weiss JT, Donlea JM. Sleep deprivation results in diverse patterns of synaptic scaling across the Drosophila mushroom bodies. Curr Biol 2021; 31:3248-3261.e3. [PMID: 34107302 PMCID: PMC8355077 DOI: 10.1016/j.cub.2021.05.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 03/22/2021] [Accepted: 05/11/2021] [Indexed: 11/19/2022]
Abstract
Sleep is essential for a variety of plastic processes, including learning and memory. However, the consequences of insufficient sleep on circuit connectivity remain poorly understood. To better appreciate the effects of sleep loss on synaptic connectivity across a memory-encoding circuit, we examined changes in the distribution of synaptic markers in the Drosophila mushroom body (MB). Protein-trap tags for active zone components indicate that recent sleep time is inversely correlated with Bruchpilot (BRP) abundance in the MB lobes; sleep loss elevates BRP while sleep induction reduces BRP across the MB. Overnight sleep deprivation also elevated levels of dSyd-1 and Cacophony, but not other pre-synaptic proteins. Cell-type-specific genetic reporters show that MB-intrinsic Kenyon cells (KCs) exhibit increased pre-synaptic BRP throughout the axonal lobes after sleep deprivation; similar increases were not detected in projections from large interneurons or dopaminergic neurons that innervate the MB. These results indicate that pre-synaptic plasticity in KCs is responsible for elevated levels of BRP in the MB lobes of sleep-deprived flies. Because KCs provide synaptic inputs to several classes of post-synaptic partners, we next used a fluorescent reporter for synaptic contacts to test whether each class of KC output connections is scaled uniformly by sleep loss. The KC output synapses that we observed here can be divided into three classes: KCs to MB interneurons; KCs to dopaminergic neurons; and KCs to MB output neurons. No single class showed uniform scaling across each constituent member, indicating that different rules may govern plasticity during sleep loss across cell types.
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Affiliation(s)
- Jacqueline T Weiss
- Department of Neurobiology, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, CA 90095, USA; Neuroscience Interdepartmental Program, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Jeffrey M Donlea
- Department of Neurobiology, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, CA 90095, USA.
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18
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Tawfik B, Martins JS, Houy S, Imig C, Pinheiro PS, Wojcik SM, Brose N, Cooper BH, Sørensen JB. Synaptotagmin-7 places dense-core vesicles at the cell membrane to promote Munc13-2- and Ca 2+-dependent priming. eLife 2021; 10:64527. [PMID: 33749593 PMCID: PMC8012061 DOI: 10.7554/elife.64527] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Accepted: 03/19/2021] [Indexed: 12/17/2022] Open
Abstract
Synaptotagmins confer calcium-dependence to the exocytosis of secretory vesicles, but how coexpressed synaptotagmins interact remains unclear. We find that synaptotagmin-1 and synaptotagmin-7 when present alone act as standalone fast and slow Ca2+-sensors for vesicle fusion in mouse chromaffin cells. When present together, synaptotagmin-1 and synaptotagmin-7 are found in largely non-overlapping clusters on dense-core vesicles. Synaptotagmin-7 stimulates Ca2+-dependent vesicle priming and inhibits depriming, and it promotes ubMunc13-2- and phorbolester-dependent priming, especially at low resting calcium concentrations. The priming effect of synaptotagmin-7 increases the number of vesicles fusing via synaptotagmin-1, while negatively affecting their fusion speed, indicating both synergistic and competitive interactions between synaptotagmins. Synaptotagmin-7 places vesicles in close membrane apposition (<6 nm); without it, vesicles accumulate out of reach of the fusion complex (20-40 nm). We suggest that a synaptotagmin-7-dependent movement toward the membrane is involved in Munc13-2/phorbolester/Ca2+-dependent priming as a prelude to fast and slow exocytosis triggering.
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Affiliation(s)
- Bassam Tawfik
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Joana S Martins
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Sébastien Houy
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Cordelia Imig
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Paulo S Pinheiro
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark.,Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal
| | - Sonja M Wojcik
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Nils Brose
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
| | - Benjamin H Cooper
- Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany
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19
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Function of Drosophila Synaptotagmins in membrane trafficking at synapses. Cell Mol Life Sci 2021; 78:4335-4364. [PMID: 33619613 PMCID: PMC8164606 DOI: 10.1007/s00018-021-03788-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 01/29/2021] [Accepted: 02/09/2021] [Indexed: 12/13/2022]
Abstract
The Synaptotagmin (SYT) family of proteins play key roles in regulating membrane trafficking at neuronal synapses. Using both Ca2+-dependent and Ca2+-independent interactions, several SYT isoforms participate in synchronous and asynchronous fusion of synaptic vesicles (SVs) while preventing spontaneous release that occurs in the absence of stimulation. Changes in the function or abundance of the SYT1 and SYT7 isoforms alter the number and route by which SVs fuse at nerve terminals. Several SYT family members also regulate trafficking of other subcellular organelles at synapses, including dense core vesicles (DCV), exosomes, and postsynaptic vesicles. Although SYTs are linked to trafficking of multiple classes of synaptic membrane compartments, how and when they interact with lipids, the SNARE machinery and other release effectors are still being elucidated. Given mutations in the SYT family cause disorders in both the central and peripheral nervous system in humans, ongoing efforts are defining how these proteins regulate vesicle trafficking within distinct neuronal compartments. Here, we review the Drosophila SYT family and examine their role in synaptic communication. Studies in this invertebrate model have revealed key similarities and several differences with the predicted activity of their mammalian counterparts. In addition, we highlight the remaining areas of uncertainty in the field and describe outstanding questions on how the SYT family regulates membrane trafficking at nerve terminals.
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20
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Fujii T, Sakurai A, Littleton JT, Yoshihara M. Synaptotagmin 7 switches short-term synaptic plasticity from depression to facilitation by suppressing synaptic transmission. Sci Rep 2021; 11:4059. [PMID: 33603074 PMCID: PMC7892890 DOI: 10.1038/s41598-021-83397-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Accepted: 01/22/2021] [Indexed: 01/25/2023] Open
Abstract
Short-term synaptic plasticity is a fast and robust modification in neuronal presynaptic output that can enhance release strength to drive facilitation or diminish it to promote depression. The mechanisms that determine whether neurons display short-term facilitation or depression are still unclear. Here we show that the Ca2+-binding protein Synaptotagmin 7 (Syt7) determines the sign of short-term synaptic plasticity by controlling the initial probability of synaptic vesicle (SV) fusion. Electrophysiological analysis of Syt7 null mutants at Drosophila embryonic neuromuscular junctions demonstrate loss of the protein converts the normally observed synaptic facilitation response during repetitive stimulation into synaptic depression. In contrast, overexpression of Syt7 dramatically enhanced the magnitude of short-term facilitation. These changes in short-term plasticity were mirrored by corresponding alterations in the initial evoked response, with SV release probability enhanced in Syt7 mutants and suppressed following Syt7 overexpression. Indeed, Syt7 mutants were able to display facilitation in lower [Ca2+] where release was reduced. These data suggest Syt7 does not act by directly sensing residual Ca2+ and argues for the existence of a distinct Ca2+ sensor beyond Syt7 that mediates facilitation. Instead, Syt7 normally suppresses synaptic transmission to maintain an output range where facilitation is available to the neuron.
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Affiliation(s)
- Takaaki Fujii
- Memory Neurobiology Project, National Institute of Information and Communications Technology, Kobe, Japan
| | - Akira Sakurai
- Memory Neurobiology Project, National Institute of Information and Communications Technology, Kobe, Japan
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Department of Biology, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Motojiro Yoshihara
- Memory Neurobiology Project, National Institute of Information and Communications Technology, Kobe, Japan.
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