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Queiroz Zetune Villa Real K, Mougios N, Rehm R, Sograte-Idrissi S, Albert L, Rahimi AM, Maidorn M, Hentze J, Martínez-Carranza M, Hosseini H, Saal KA, Oleksiievets N, Prigge M, Tsukanov R, Stenmark P, Fornasiero EF, Opazo F. A Versatile Synaptotagmin-1 Nanobody Provides Perturbation-Free Live Synaptic Imaging And Low Linkage-Error in Super-Resolution Microscopy. SMALL METHODS 2023; 7:e2300218. [PMID: 37421204 DOI: 10.1002/smtd.202300218] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Revised: 06/09/2023] [Indexed: 07/10/2023]
Abstract
Imaging of living synapses has relied for over two decades on the overexpression of synaptic proteins fused to fluorescent reporters. This strategy alters the stoichiometry of synaptic components and ultimately affects synapse physiology. To overcome these limitations, here a nanobody is presented that binds the calcium sensor synaptotagmin-1 (NbSyt1). This nanobody functions as an intrabody (iNbSyt1) in living neurons and is minimally invasive, leaving synaptic transmission almost unaffected, as suggested by the crystal structure of the NbSyt1 bound to Synaptotagmin-1 and by the physiological data. Its single-domain nature enables the generation of protein-based fluorescent reporters, as showcased here by measuring spatially localized presynaptic Ca2+ with a NbSyt1- jGCaMP8 chimera. Moreover, the small size of NbSyt1 makes it ideal for various super-resolution imaging methods. Overall, NbSyt1 is a versatile binder that will enable imaging in cellular and molecular neuroscience with unprecedented precision across multiple spatiotemporal scales.
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Affiliation(s)
- Karine Queiroz Zetune Villa Real
- Institute of Neuro- and Sensory Physiology, University Medical Center Göttingen, 37073, Göttingen, Germany
- Center for Biostructural Imaging of Neurodegeneration (BIN), University Medical Center Göttingen, 37075, Göttingen, Germany
| | - Nikolaos Mougios
- Institute of Neuro- and Sensory Physiology, University Medical Center Göttingen, 37073, Göttingen, Germany
- Center for Biostructural Imaging of Neurodegeneration (BIN), University Medical Center Göttingen, 37075, Göttingen, Germany
| | - Ronja Rehm
- Institute of Neuro- and Sensory Physiology, University Medical Center Göttingen, 37073, Göttingen, Germany
| | - Shama Sograte-Idrissi
- Institute of Neuro- and Sensory Physiology, University Medical Center Göttingen, 37073, Göttingen, Germany
- Center for Biostructural Imaging of Neurodegeneration (BIN), University Medical Center Göttingen, 37075, Göttingen, Germany
| | - László Albert
- Institute of Neuro- and Sensory Physiology, University Medical Center Göttingen, 37073, Göttingen, Germany
- Center for Biostructural Imaging of Neurodegeneration (BIN), University Medical Center Göttingen, 37075, Göttingen, Germany
| | - Amir Mohammad Rahimi
- Institute of Neuro- and Sensory Physiology, University Medical Center Göttingen, 37073, Göttingen, Germany
- Center for Biostructural Imaging of Neurodegeneration (BIN), University Medical Center Göttingen, 37075, Göttingen, Germany
| | - Manuel Maidorn
- Institute of Neuro- and Sensory Physiology, University Medical Center Göttingen, 37073, Göttingen, Germany
- Center for Biostructural Imaging of Neurodegeneration (BIN), University Medical Center Göttingen, 37075, Göttingen, Germany
| | - Jannik Hentze
- Institute of Neuro- and Sensory Physiology, University Medical Center Göttingen, 37073, Göttingen, Germany
- Center for Biostructural Imaging of Neurodegeneration (BIN), University Medical Center Göttingen, 37075, Göttingen, Germany
| | - Markel Martínez-Carranza
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Stockholm, SE-10691, Sweden
| | - Hassan Hosseini
- Research Group Neuromodulatory Networks, Leibniz Institute for Neurobiology, 39118, Magdeburg, Germany
| | - Kim-Ann Saal
- Institute of Neuro- and Sensory Physiology, University Medical Center Göttingen, 37073, Göttingen, Germany
| | - Nazar Oleksiievets
- III. Institute of Physics - Biophysics, Georg August University, 37077, Göttingen, Germany
| | - Matthias Prigge
- Research Group Neuromodulatory Networks, Leibniz Institute for Neurobiology, 39118, Magdeburg, Germany
- Center for Behavioral Brain Sciences, 39118, Magdeburg, Germany
| | - Roman Tsukanov
- III. Institute of Physics - Biophysics, Georg August University, 37077, Göttingen, Germany
| | - Pål Stenmark
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Stockholm, SE-10691, Sweden
| | - Eugenio F Fornasiero
- Institute of Neuro- and Sensory Physiology, University Medical Center Göttingen, 37073, Göttingen, Germany
| | - Felipe Opazo
- Institute of Neuro- and Sensory Physiology, University Medical Center Göttingen, 37073, Göttingen, Germany
- Center for Biostructural Imaging of Neurodegeneration (BIN), University Medical Center Göttingen, 37075, Göttingen, Germany
- NanoTag Biotechnologies GmbH, 37079, Göttingen, Germany
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2
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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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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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Endocytic Adaptor Proteins in Health and Disease: Lessons from Model Organisms and Human Mutations. Cells 2019; 8:cells8111345. [PMID: 31671891 PMCID: PMC6912373 DOI: 10.3390/cells8111345] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Revised: 10/24/2019] [Accepted: 10/25/2019] [Indexed: 12/11/2022] Open
Abstract
Cells need to exchange material and information with their environment. This is largely achieved via cell-surface receptors which mediate processes ranging from nutrient uptake to signaling responses. Consequently, their surface levels have to be dynamically controlled. Endocytosis constitutes a powerful mechanism to regulate the surface proteome and to recycle vesicular transmembrane proteins that strand at the plasma membrane after exocytosis. For efficient internalization, the cargo proteins need to be linked to the endocytic machinery via adaptor proteins such as the heterotetrameric endocytic adaptor complex AP-2 and a variety of mostly monomeric endocytic adaptors. In line with the importance of endocytosis for nutrient uptake, cell signaling and neurotransmission, animal models and human mutations have revealed that defects in these adaptors are associated with several diseases ranging from metabolic disorders to encephalopathies. This review will discuss the physiological functions of the so far known adaptor proteins and will provide a comprehensive overview of their links to human diseases.
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Flavonoid-Rich Ethanol Extract from the Leaves of Diospyros kaki Attenuates D-Galactose-Induced Oxidative Stress and Neuroinflammation-Mediated Brain Aging in Mice. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2018; 2018:8938207. [PMID: 30671176 PMCID: PMC6323539 DOI: 10.1155/2018/8938207] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Revised: 07/04/2018] [Accepted: 07/30/2018] [Indexed: 12/21/2022]
Abstract
Aging is a major factor that contributes to neurological impairment and neuropathological changes, such as inflammation, oxidative stress, neuronal apoptosis, and synaptic dysfunction. Flavonoids act as protective antioxidant and anti-inflammatory agents against various age-related neurodegenerative diseases. Here, we investigated the protective effect and mechanisms of the flavonoid-rich ethanol extract from the leaves of Diospyros kaki (FELDK) in the cortex and hippocampus of D-galactose- (gal-) aged mice. Our results showed that FELDK treatment restored memory impairment in mice as determined by the Y-maze and Morris water maze tests. FELDK decreased oxidative stress levels via inhibiting reactive oxygen species (ROS) and malondialdehyde (MDA) production and elevating antioxidative enzymes. FELDK also alleviated D-gal-induced neuroinflammation via suppressing the expression of advanced glycation end products (AGEs) and receptor for AGEs (RAGE) and activating microgliosis and astrocytosis, nuclear factor kappa B (NF-κB) nuclear translocation, and downstream inflammatory mediators. Moreover, FELDK inhibited the phosphatidylinositol 3-kinase (PI3K)/Akt and C-jun N-terminal kinase (JNK) apoptotic signaling pathways and ameliorated the impairment of synapse-related proteins. Hence, these results indicate that FELDK exerts neuroprotective effects on D-gal-induced brain aging. Thus, FELDK may be a potential therapeutic strategy for preventing and treating age-related neurodegenerative diseases such as Alzheimer's disease.
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Kuznetsova KG, Kliuchnikova AA, Ilina IU, Chernobrovkin AL, Novikova SE, Farafonova TE, Karpov DS, Ivanov MV, Goncharov AO, Ilgisonis EV, Voronko OE, Nasaev SS, Zgoda VG, Zubarev RA, Gorshkov MV, Moshkovskii SA. Proteogenomics of Adenosine-to-Inosine RNA Editing in the Fruit Fly. J Proteome Res 2018; 17:3889-3903. [DOI: 10.1021/acs.jproteome.8b00553] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
| | - Anna A. Kliuchnikova
- Institute of Biomedical Chemistry, Moscow, Russia
- Pirogov Russian National Research Medical University (RNRMU), Moscow, Russia
| | | | | | | | | | - Dmitry S. Karpov
- Institute of Biomedical Chemistry, Moscow, Russia
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, Russia
| | - Mark V. Ivanov
- Institute of Energy Problems of Chemical Physics, Russian Academy of Sciences, Moscow, Russia
- Moscow Institute of Physics and Technology (State University), Dolgoprudny, Moscow Region, Russia
| | - Anton O. Goncharov
- Institute of Biomedical Chemistry, Moscow, Russia
- Pirogov Russian National Research Medical University (RNRMU), Moscow, Russia
| | | | | | - Shamsudin S. Nasaev
- Pirogov Russian National Research Medical University (RNRMU), Moscow, Russia
| | | | - Roman A. Zubarev
- Karolinska Institutet, Stockholm, Sweden
- I.M. Sechenov First Moscow State Medical University, Moscow, Russia
| | - Mikhail V. Gorshkov
- Institute of Energy Problems of Chemical Physics, Russian Academy of Sciences, Moscow, Russia
- Moscow Institute of Physics and Technology (State University), Dolgoprudny, Moscow Region, Russia
| | - Sergei A. Moshkovskii
- Institute of Biomedical Chemistry, Moscow, Russia
- Pirogov Russian National Research Medical University (RNRMU), Moscow, Russia
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7
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Kaempf N, Maritzen T. Safeguards of Neurotransmission: Endocytic Adaptors as Regulators of Synaptic Vesicle Composition and Function. Front Cell Neurosci 2017; 11:320. [PMID: 29085282 PMCID: PMC5649181 DOI: 10.3389/fncel.2017.00320] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Accepted: 09/26/2017] [Indexed: 11/13/2022] Open
Abstract
Communication between neurons relies on neurotransmitters which are released from synaptic vesicles (SVs) upon Ca2+ stimuli. To efficiently load neurotransmitters, sense the rise in intracellular Ca2+ and fuse with the presynaptic membrane, SVs need to be equipped with a stringently controlled set of transmembrane proteins. In fact, changes in SV protein composition quickly compromise neurotransmission and most prominently give rise to epileptic seizures. During exocytosis SVs fully collapse into the presynaptic membrane and consequently have to be replenished to sustain neurotransmission. Therefore, surface-stranded SV proteins have to be efficiently retrieved post-fusion to be used for the generation of a new set of fully functional SVs, a process in which dedicated endocytic sorting adaptors play a crucial role. The question of how the precise reformation of SVs is achieved is intimately linked to how SV membranes are retrieved. For a long time both processes were believed to be two sides of the same coin since Clathrin-mediated endocytosis (CME), the proposed predominant SV recycling mode, will jointly retrieve SV membranes and proteins. However, with the recent proposal of Clathrin-independent SV recycling pathways SV membrane retrieval and SV reformation turn into separable events. This review highlights the progress made in unraveling the molecular mechanisms mediating the high-fidelity retrieval of SV proteins and discusses how the gathered knowledge about SV protein recycling fits in with the new notions of SV membrane endocytosis.
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Affiliation(s)
- Natalie Kaempf
- Molecular Physiology and Cell Biology Section, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany
| | - Tanja Maritzen
- Molecular Physiology and Cell Biology Section, Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany
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8
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Tang X, Xie C, Wang Y, Wang X. Localization of Rab3A-binding site on C2A domain of synaptotagmin I to reveal its regulatory mechanism. Int J Biol Macromol 2017; 96:736-742. [DOI: 10.1016/j.ijbiomac.2016.12.074] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2016] [Revised: 12/22/2016] [Accepted: 12/29/2016] [Indexed: 10/20/2022]
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9
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Li L, Wu X, Yue HY, Zhu YC, Xu J. Myosin light chain kinase facilitates endocytosis of synaptic vesicles at hippocampal boutons. J Neurochem 2016; 138:60-73. [PMID: 27062289 DOI: 10.1111/jnc.13635] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Revised: 03/27/2016] [Accepted: 04/05/2016] [Indexed: 02/07/2023]
Abstract
At nerve terminals, endocytosis efficiently recycles vesicle membrane to maintain synaptic transmission under different levels of neuronal activity. Ca(2+) and its downstream signal pathways are critical for the activity-dependent regulation of endocytosis. An activity- and Ca(2+) -dependent kinase, myosin light chain kinase (MLCK) has been reported to regulate vesicle mobilization, vesicle cycling, and motility in different synapses, but whether it has a general contribution to regulation of endocytosis at nerve terminals remains unknown. We investigated this issue at rat hippocampal boutons by imaging vesicle endocytosis as the real-time retrieval of vesicular synaptophysin tagged with a pH-sensitive green fluorescence protein. We found that endocytosis induced by 200 action potentials (5-40 Hz) was slowed by acute inhibition of MLCK and down-regulation of MLCK with RNA interference, while the total amount of vesicle exocytosis and somatic Ca(2+) channel current did not change with MLCK down-regulation. Acute inhibition of myosin II similarly impaired endocytosis. Furthermore, down-regulation of MLCK prevented depolarization-induced phosphorylation of myosin light chain, an effect shared by blockers of Ca(2+) channels and calmodulin. These results suggest that MLCK facilitates vesicle endocytosis through activity-dependent phosphorylation of myosin downstream of Ca(2+) /calmodulin, probably as a widely existing mechanism among synapses. Our study suggests that MLCK is an important activity-dependent regulator of vesicle recycling in hippocampal neurons, which are critical for learning and memory. The kinetics of vesicle membrane endocytosis at nerve terminals has long been known to depend on activity and Ca(2+) . This study provides evidence suggesting that myosin light chain kinase increases endocytosis efficiency at hippocampal neurons by mediating Ca(2+) /calmodulin-dependent phosphorylation of myosin. The authors propose that this signal cascade may serve as a common pathway contributing to the activity-dependent regulation of vesicle endocytosis at synapses.
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Affiliation(s)
- Lin Li
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Augusta, Georgia, USA
| | - Xiaomei Wu
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Augusta, Georgia, USA.,Department of Neurochemistry, Institute of Nautical Medicine, Nantong University, Nantong, Jiangsu, China
| | - Hai-Yuan Yue
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Augusta, Georgia, USA
| | - Yong-Chuan Zhu
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Augusta, Georgia, USA
| | - Jianhua Xu
- Department of Neuroscience and Regenerative Medicine, Medical College of Georgia, Augusta, Georgia, USA.,Department of Neurology, Medical College of Georgia, Augusta, Georgia, USA
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10
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Overlapping functions of stonin 2 and SV2 in sorting of the calcium sensor synaptotagmin 1 to synaptic vesicles. Proc Natl Acad Sci U S A 2015; 112:7297-302. [PMID: 26015569 PMCID: PMC4466747 DOI: 10.1073/pnas.1501627112] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Brain function depends on neurotransmission, and alterations in this process are linked to neurological disorders. Neurotransmitter release requires the rapid recycling of synaptic vesicles (SVs) by endocytosis. How synapses maintain the molecular composition of SVs during recycling is poorly understood. We demonstrate that overlapping functions of two completely distinct proteins, the vesicle protein SV2A/B and the adaptor stonin 2, mediate endocytic sorting of the vesicular calcium sensor synaptotagmin 1. As SV2A is the target of the commonly used antiepileptic drug levetiracetam and is linked to late onset Alzheimer’s disease, our findings bear implications for the treatment of neurological and neurodegenerative disorders. Neurotransmission involves the calcium-regulated exocytic fusion of synaptic vesicles (SVs) and the subsequent retrieval of SV membranes followed by reformation of properly sized and shaped SVs. An unresolved question is whether each SV protein is sorted by its own dedicated adaptor or whether sorting is facilitated by association between different SV proteins. We demonstrate that endocytic sorting of the calcium sensor synaptotagmin 1 (Syt1) is mediated by the overlapping activities of the Syt1-associated SV glycoprotein SV2A/B and the endocytic Syt1-adaptor stonin 2 (Stn2). Deletion or knockdown of either SV2A/B or Stn2 results in partial Syt1 loss and missorting of Syt1 to the neuronal surface, whereas deletion of both SV2A/B and Stn2 dramatically exacerbates this phenotype. Selective missorting and degradation of Syt1 in the absence of SV2A/B and Stn2 impairs the efficacy of neurotransmission at hippocampal synapses. These results indicate that endocytic sorting of Syt1 to SVs is mediated by the overlapping activities of SV2A/B and Stn2 and favor a model according to which SV protein sorting is guarded by both cargo-specific mechanisms as well as association between SV proteins.
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11
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Kononenko N, Haucke V. Molecular Mechanisms of Presynaptic Membrane Retrieval and Synaptic Vesicle Reformation. Neuron 2015; 85:484-96. [DOI: 10.1016/j.neuron.2014.12.016] [Citation(s) in RCA: 123] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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12
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Podufall J, Tian R, Knoche E, Puchkov D, Walter AM, Rosa S, Quentin C, Vukoja A, Jung N, Lampe A, Wichmann C, Böhme M, Depner H, Zhang YQ, Schmoranzer J, Sigrist SJ, Haucke V. A presynaptic role for the cytomatrix protein GIT in synaptic vesicle recycling. Cell Rep 2014; 7:1417-1425. [PMID: 24882013 DOI: 10.1016/j.celrep.2014.04.051] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Revised: 04/09/2014] [Accepted: 04/23/2014] [Indexed: 01/06/2023] Open
Abstract
Neurotransmission involves the exo-endocytic cycling of synaptic vesicles (SVs) within nerve terminals. Exocytosis is facilitated by a cytomatrix assembled at the active zone (AZ). The precise spatial and functional relationship between exocytic fusion of SVs at AZ membranes and endocytic SV retrieval is unknown. Here, we identify the scaffold G protein coupled receptor kinase 2 interacting (GIT) protein as a component of the AZ-associated cytomatrix and as a regulator of SV endocytosis. GIT1 and its D. melanogaster ortholog, dGIT, are shown to directly associate with the endocytic adaptor stonin 2/stoned B. In Drosophila dgit mutants, stoned B and synaptotagmin levels are reduced and stoned B is partially mislocalized. Moreover, dgit mutants show morphological and functional defects in SV recycling. These data establish a presynaptic role for GIT in SV recycling and suggest a connection between the AZ cytomatrix and the endocytic machinery.
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Affiliation(s)
- Jasmin Podufall
- Leibniz Institute for Molecular Pharmacology, Robert Rössle Strasse 10, 13125 Berlin, Germany; Membrane Biochemistry, Institute of Chemistry & Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany
| | - Rui Tian
- Genetics, Institute for Biology, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany; Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
| | - Elena Knoche
- NeuroCure Cluster of Excellence, Charité Universitätsmedizin Berlin, Virchowweg 6, 10117 Berlin, Germany
| | - Dmytro Puchkov
- Leibniz Institute for Molecular Pharmacology, Robert Rössle Strasse 10, 13125 Berlin, Germany; Membrane Biochemistry, Institute of Chemistry & Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany
| | - Alexander M Walter
- Leibniz Institute for Molecular Pharmacology, Robert Rössle Strasse 10, 13125 Berlin, Germany; Genetics, Institute for Biology, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany; NeuroCure Cluster of Excellence, Charité Universitätsmedizin Berlin, Virchowweg 6, 10117 Berlin, Germany
| | - Stefanie Rosa
- Leibniz Institute for Molecular Pharmacology, Robert Rössle Strasse 10, 13125 Berlin, Germany; Genetics, Institute for Biology, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany
| | - Christine Quentin
- Genetics, Institute for Biology, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany
| | - Anela Vukoja
- Leibniz Institute for Molecular Pharmacology, Robert Rössle Strasse 10, 13125 Berlin, Germany; Membrane Biochemistry, Institute of Chemistry & Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany
| | - Nadja Jung
- Membrane Biochemistry, Institute of Chemistry & Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany
| | - Andre Lampe
- Leibniz Institute for Molecular Pharmacology, Robert Rössle Strasse 10, 13125 Berlin, Germany; Membrane Biochemistry, Institute of Chemistry & Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany
| | - Carolin Wichmann
- Genetics, Institute for Biology, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany
| | - Mathias Böhme
- Genetics, Institute for Biology, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany
| | - Harald Depner
- Genetics, Institute for Biology, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany
| | - Yong Q Zhang
- Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
| | - Jan Schmoranzer
- Leibniz Institute for Molecular Pharmacology, Robert Rössle Strasse 10, 13125 Berlin, Germany; Membrane Biochemistry, Institute of Chemistry & Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany
| | - Stephan J Sigrist
- Genetics, Institute for Biology, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany; NeuroCure Cluster of Excellence, Charité Universitätsmedizin Berlin, Virchowweg 6, 10117 Berlin, Germany.
| | - Volker Haucke
- Leibniz Institute for Molecular Pharmacology, Robert Rössle Strasse 10, 13125 Berlin, Germany; NeuroCure Cluster of Excellence, Charité Universitätsmedizin Berlin, Virchowweg 6, 10117 Berlin, Germany; Membrane Biochemistry, Institute of Chemistry & Biochemistry, Freie Universität Berlin, Takustraße 6, 14195 Berlin, Germany.
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Vanlandingham PA, Barmchi MP, Royer S, Green R, Bao H, Reist N, Zhang B. AP180 couples protein retrieval to clathrin-mediated endocytosis of synaptic vesicles. Traffic 2014; 15:433-50. [PMID: 24456281 PMCID: PMC4320755 DOI: 10.1111/tra.12153] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2013] [Revised: 01/16/2014] [Accepted: 01/26/2014] [Indexed: 01/01/2023]
Abstract
How clathrin-mediated endocytosis (CME) retrieves vesicle proteins into newly formed synaptic vesicles (SVs) remains a major puzzle. Besides its roles in stimulating clathrin-coated vesicle formation and regulating SV size, the clathrin assembly protein AP180 has been identified as a key player in retrieving SV proteins. The mechanisms by which AP180 recruits SV proteins are not fully understood. Here, we show that following acute inactivation of AP180 in Drosophila, SV recycling is severely impaired at the larval neuromuscular synapse based on analyses of FM 1-43 uptake and synaptic ultrastructure. More dramatically, AP180 activity is important to maintain the integrity of SV protein complexes at the plasma membrane during endocytosis. These observations suggest that AP180 normally clusters SV proteins together during recycling. Consistent with this notion, SV protein composition and distribution are altered in AP180 mutant flies. Finally, AP180 co-immunoprecipitates with SV proteins, including the vesicular glutamate transporter and neuronal synaptobrevin. These results reveal a new mode by which AP180 couples protein retrieval to CME of SVs. AP180 is also genetically linked to Alzheimer's disease. Hence, the findings of this study may provide new mechanistic insight into the role of AP180 dysfunction in Alzheimer's disease.
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Confocal imaging of fluorescently labeled proteins in the Drosophila larval neuromuscular junction. Methods Mol Biol 2014; 1075:201-12. [PMID: 24052353 DOI: 10.1007/978-1-60761-847-8_9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The Drosophila larval neuromuscular junction (NMJ) consists of a presynaptic motor neuron terminal and a postsynaptic muscle cell that offer an accessible and popular model system for the analysis of synaptic growth and function. I describe techniques for visualizing fluorescently labeled proteins within dissected, formaldehyde-fixed second to third instar larval NMJs. In addition, I present two strategies using confocal microscopy to solve a particular problem in NMJ analysis: distinguishing fluorescence in the presynaptic nerve terminal from that in the adjacent postsynaptic muscle cell. This problem arises from the fact that the membrane of the muscle cell envelops the motor neuron terminal with a convoluted process called the subsynaptic reticulum, obscuring the boundary between muscle and nerve. A first strategy entails taking thin optical sections through synaptic boutons to capture a cross section of the nerve terminal, and a second strategy involves visualizing epitope-tagged isoforms of particular proteins that have been transgenically expressed in either the nerve or the muscle.
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Poudel KR, Bai J. Synaptic vesicle morphology: a case of protein sorting? Curr Opin Cell Biol 2013; 26:28-33. [PMID: 24529243 DOI: 10.1016/j.ceb.2013.09.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Revised: 09/03/2013] [Accepted: 09/04/2013] [Indexed: 10/26/2022]
Abstract
Synaptic vesicles (SVs) are the repositories of neurotransmitters. They are locally recycled at nerve terminals following exocytosis. A unique feature of these vesicles is the uniformity of their morphology, which is well maintained even after rounds of exocytosis and endocytosis. Several studies suggest that disruption of clathrin adaptor proteins leads to defects in sorting cargoes and alterations in SV morphology. Here, we review the links between adaptor proteins and SV size, and highlight how protein sorting may impact SV architecture. Molecular players such as clathrin, adaptor proteins, accessory proteins, SV cargoes and lipid composition may act together to establish a stable regulatory network to maintain SV morphology.
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Affiliation(s)
- Kumud R Poudel
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA, USA; Department of Biochemistry, University of Washington, Seattle, WA, USA
| | - Jihong Bai
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA, USA; Department of Biochemistry, University of Washington, Seattle, WA, USA.
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16
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Wise A, Schatoff E, Flores J, Hua SY, Ueda A, Wu CF, Venkatesh T. Drosophila-Cdh1 (Rap/Fzr) a regulatory subunit of APC/C is required for synaptic morphology, synaptic transmission and locomotion. Int J Dev Neurosci 2013; 31:624-33. [PMID: 23933137 DOI: 10.1016/j.ijdevneu.2013.07.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Revised: 06/24/2013] [Accepted: 07/17/2013] [Indexed: 01/12/2023] Open
Abstract
The assembly of functional synapses requires the orchestration of the synthesis and degradation of a multitude of proteins. Protein degradation and modification by the conserved ubiquitination pathway has emerged as a key cellular regulatory mechanism during nervous system development and function (Kwabe and Brose, 2011). The anaphase promoting complex/cyclosome (APC/C) is a multi-subunit ubiquitin ligase complex primarily characterized for its role in the regulation of mitosis (Peters, 2002). In recent years, a role for APC/C in nervous system development and function has been rapidly emerging (Stegmuller and Bonni, 2005; Li et al., 2008). In the mammalian central nervous system the activator subunit, APC/C-Cdh1, has been shown to be a regulator of axon growth and dendrite morphogenesis (Konishi et al., 2004). In the Drosophila peripheral nervous system (PNS), APC2, a ligase subunit of the APC/C complex has been shown to regulate synaptic bouton size and activity (van Roessel et al., 2004). To investigate the role of APC/C-Cdh1 at the synapse we examined loss-of-function mutants of Rap/Fzr (Retina aberrant in pattern/Fizzy related), a Drosophila homolog of the mammalian Cdh1 during the development of the larval neuromuscular junction in Drosophila. Our cell biological, ultrastructural, electrophysiological, and behavioral data showed that rap/fzr loss-of-function mutations lead to changes in synaptic structure and function as well as locomotion defects. Data presented here show changes in size and morphology of synaptic boutons, and, muscle tissue organization. Electrophysiological experiments show that loss-of-function mutants exhibit increased frequency of spontaneous miniature synaptic potentials, indicating a higher rate of spontaneous synaptic vesicle fusion events. In addition, larval locomotion and peristaltic movement were also impaired. These findings suggest a role for Drosophila APC/C-Cdh1 mediated ubiquitination in regulating synaptic morphology, function and integrity of muscle structure in the peripheral nervous system.
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Affiliation(s)
- Alexandria Wise
- Department of Biology, City College of New York, and The Graduate Center of CUNY, New York, NY 10031, United States; Department of Pathology and Cell Biology, Columbia University, 630 West 168th Street, New York, NY 10032, United States
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Cortical surface area correlates with STON2 gene Ser307Pro polymorphism in first-episode treatment-naïve patients with schizophrenia. PLoS One 2013; 8:e64090. [PMID: 23785397 PMCID: PMC3681785 DOI: 10.1371/journal.pone.0064090] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Accepted: 04/09/2013] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND Evidence shows that STON2 gene is associated with synaptic function and schizophrenia. This study aims to explore the relationship between two functional polymorphisms (Ser307Pro and Ala851Ser) of STON2 gene and the cortical surface area in first-episode treatment-naïve patients with schizophrenia and healthy controls. METHODOLOGY/PRINCIPAL FINDINGS Magnetic resonance imaging of the whole cortical surface area, which was computed by an automated surface-based technique (FreeSurfer), was obtained from 74 first-episode treatment-naïve patients with schizophrenia and 55 healthy controls. Multiple regression analysis was performed to investigate the effect of genotype subgroups on the cortical surface area. A significant genotype-by-diagnosis effect on the cortical surface area was observed. Pro-allele carriers of Ser307Pro polymorphism had larger right inferior temporal surface area than Ser/Ser carriers in the patients with schizophrenia; however, no significant difference was found in the same area in the healthy controls. The Ala851Ser polymorphism of STON2 gene was not significantly associated with the cortical surface area in patients with schizophrenia and healthy controls. CONCLUSIONS/SIGNIFICANCE The present study demonstrated that the functional variant of the STON2 gene could alter cortical surface area on the right inferior temporal and contribute to the pathogenesis of schizophrenia.
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Maldonado C, Alicea D, Gonzalez M, Bykhovskaia M, Marie B. Adar is essential for optimal presynaptic function. Mol Cell Neurosci 2012; 52:173-80. [PMID: 23127996 DOI: 10.1016/j.mcn.2012.10.009] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Revised: 09/20/2012] [Accepted: 10/23/2012] [Indexed: 12/31/2022] Open
Abstract
RNA editing is a powerful way to recode genetic information. Because it potentially affects RNA targets that are predominantly present in neurons, it is widely hypothesized to affect neuronal structure and physiology. Across phyla, loss of the enzyme responsible for RNA editing, Adar, leads to behavioral changes, impaired locomotion, neurodegeneration and death. However, the consequences of a loss of Adar activity on neuronal structure and function have not been studied in detail. In particular, the role of RNA editing on synaptic development and physiology has not been investigated. Here we test the physiological and morphological consequences of the lack of Adar activity on the Drosophila neuromuscular junction (NMJ). Our detailed examination of synaptic transmission showed that loss of Adar increases quantal size, reduces the number of quanta of neurotransmitter released and perturbs the calcium dependence of synaptic release. In addition, we find that staining for several synaptic vesicle proteins is abnormally intense at Adar deficient synapses. Consistent with this finding, Adar mutants showed a major alteration in synaptic ultrastructure. Finally, we present evidence of compensatory changes in muscle membrane properties in response to the changes in presynaptic activity within the Adar mutant NMJs.
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Affiliation(s)
- Carolina Maldonado
- Institute of Neurobiology, Medical Sciences Campus, University of Puerto Rico, PR
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Mate SE, Van Der Meulen JH, Arya P, Bhattacharyya S, Band H, Hoffman EP. Eps homology domain endosomal transport proteins differentially localize to the neuromuscular junction. Skelet Muscle 2012; 2:19. [PMID: 22974368 PMCID: PMC3541266 DOI: 10.1186/2044-5040-2-19] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Accepted: 07/10/2012] [Indexed: 01/19/2023] Open
Abstract
Background Recycling of endosomes is important for trafficking and maintenance of proteins at the neuromuscular junction (NMJ). We have previously shown high expression of the endocytic recycling regulator Eps15 homology domain-containing (EHD)1 proteinin the Torpedo californica electric organ, a model tissue for investigating a cholinergic synapse. In this study, we investigated the localization of EHD1 and its paralogs EHD2, EHD3, and EHD4 in mouse skeletal muscle, and assessed the morphological changes in EHD1−/− NMJs. Methods Localization of the candidate NMJ protein EHD1 was assessed by confocal microscopy analysis of whole-mount mouse skeletal muscle fibers after direct gene transfer and immunolabeling. The potential function of EHD1 was assessed by specific force measurement and α-bungarotoxin-based endplate morphology mapping in EHD1−/− mouse skeletal muscle. Results Endogenous EHD1 localized to primary synaptic clefts of murine NMJ, and this localization was confirmed by expression of recombinant green fluorescent protein labeled-EHD1 in murine skeletal muscle in vivo. EHD1−/− mouse skeletal muscle had normal histology and NMJ morphology, and normal specific force generation during muscle contraction. The EHD 1–4 proteins showed differential localization in skeletal muscle: EHD2 to muscle vasculature, EHD3 to perisynaptic regions, and EHD4 to perinuclear regions and to primary synaptic clefts, but at lower levels than EHD1. Additionally, specific antibodies raised against mammalian EHD1-4 recognized proteins of the expected mass in the T. californica electric organ. Finally, we found that EHD4 expression was more abundant in EHD1−/− mouse skeletal muscle than in wild-type skeletal muscle. Conclusion EHD1 and EHD4 localize to the primary synaptic clefts of the NMJ. Lack of obvious defects in NMJ structure and muscle function in EHD1−/− muscle may be due to functional compensation by other EHD paralogs.
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Affiliation(s)
- Suzanne E Mate
- Research Center for Genetic Medicine, Children's National Medical Center, Washington, DC, USA.
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Mullen GP, Grundahl KM, Gu M, Watanabe S, Hobson RJ, Crowell JA, McManus JR, Mathews EA, Jorgensen EM, Rand JB. UNC-41/stonin functions with AP2 to recycle synaptic vesicles in Caenorhabditis elegans. PLoS One 2012; 7:e40095. [PMID: 22808098 PMCID: PMC3393740 DOI: 10.1371/journal.pone.0040095] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2012] [Accepted: 05/31/2012] [Indexed: 11/20/2022] Open
Abstract
The recycling of synaptic vesicles requires the recovery of vesicle proteins and membrane. Members of the stonin protein family (Drosophila Stoned B, mammalian stonin 2) have been shown to link the synaptic vesicle protein synaptotagmin to the endocytic machinery. Here we characterize the unc-41 gene, which encodes the stonin ortholog in the nematode Caenorhabditis elegans. Transgenic expression of Drosophila stonedB rescues unc-41 mutant phenotypes, demonstrating that UNC-41 is a bona fide member of the stonin family. In unc-41 mutants, synaptotagmin is present in axons, but is mislocalized and diffuse. In contrast, UNC-41 is localized normally in synaptotagmin mutants, demonstrating a unidirectional relationship for localization. The phenotype of snt-1 unc-41 double mutants is stronger than snt-1 mutants, suggesting that UNC-41 may have additional, synaptotagmin-independent functions. We also show that unc-41 mutants have defects in synaptic vesicle membrane endocytosis, including a ∼50% reduction of vesicles in both acetylcholine and GABA motor neurons. These endocytic defects are similar to those observed in apm-2 mutants, which lack the µ2 subunit of the AP2 adaptor complex. However, no further reduction in synaptic vesicles was observed in unc-41 apm-2 double mutants, suggesting that UNC-41 acts in the same endocytic pathway as µ2 adaptin.
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Affiliation(s)
- Gregory P. Mullen
- Genetic Models of Disease Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, United States of America
| | - Kiely M. Grundahl
- Genetic Models of Disease Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, United States of America
| | - Mingyu Gu
- Howard Hughes Medical Institute and Department of Biology, University of Utah, Salt Lake City, Utah, United States of America
| | - Shigeki Watanabe
- Howard Hughes Medical Institute and Department of Biology, University of Utah, Salt Lake City, Utah, United States of America
| | - Robert J. Hobson
- Howard Hughes Medical Institute and Department of Biology, University of Utah, Salt Lake City, Utah, United States of America
| | - John A. Crowell
- Genetic Models of Disease Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, United States of America
| | - John R. McManus
- Genetic Models of Disease Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, United States of America
| | - Eleanor A. Mathews
- Genetic Models of Disease Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, United States of America
| | - Erik M. Jorgensen
- Howard Hughes Medical Institute and Department of Biology, University of Utah, Salt Lake City, Utah, United States of America
| | - James B. Rand
- Genetic Models of Disease Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, United States of America
- * E-mail:
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Soekmadji C, Angkawidjaja C, Kelly LE. Ca2+ regulates the Drosophila Stoned-A and Stoned-B proteins interaction with the C2B domain of Synaptotagmin-1. PLoS One 2012; 7:e38822. [PMID: 22701718 PMCID: PMC3373503 DOI: 10.1371/journal.pone.0038822] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2012] [Accepted: 05/11/2012] [Indexed: 02/02/2023] Open
Abstract
The dicistronic Drosophila stoned gene is involved in exocytosis and/or endocytosis of synaptic vesicles. Mutations in either stonedA or stonedB cause a severe disruption of neurotransmission in fruit flies. Previous studies have shown that the coiled-coil domain of the Stoned-A and the µ-homology domain of the Stoned-B protein can interact with the C2B domain of Synaptotagmin-1. However, very little is known about the mechanism of interaction between the Stoned proteins and the C2B domain of Synaptotagmin-1. Here we report that these interactions are increased in the presence of Ca(2+). The Ca(2+)-dependent interaction between the µ-homology domain of Stoned-B and C2B domain of Synaptotagmin-1 is affected by phospholipids. The C-terminal region of the C2B domain, including the tryptophan-containing motif, and the Ca(2+) binding loop region that modulate the Ca(2+)-dependent oligomerization, regulates the binding of the Stoned-A and Stoned-B proteins to the C2B domain. Stoned-B, but not Stoned-A, interacts with the Ca(2+)-binding loop region of C2B domain. The results indicate that Ca(2+)-induced self-association of the C2B domain regulates the binding of both Stoned-A and Stoned-B proteins to Synaptotagmin-1. The Stoned proteins may regulate sustainable neurotransmission in vivo by binding to Ca(2+)-bound Synaptotagmin-1 associated synaptic vesicles.
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Affiliation(s)
- Carolina Soekmadji
- Department of Genetics, The University of Melbourne, Parkville, Victoria, Australia.
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Maritzen T, Koo SJ, Haucke V. Turning CALM into excitement: AP180 and CALM in endocytosis and disease. Biol Cell 2012; 104:588-602. [DOI: 10.1111/boc.201200008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Accepted: 05/23/2012] [Indexed: 11/28/2022]
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Abstract
We review mainly the work from our research group here. Our focus has been on the use of genetic methods to delineate the mechanisms of synaptic vesicle recycling and cellular trafficking. Acute temperature-sensitive paralytic mutants have been of particular value in this approach. We have primarily used screens for suppressor and enhancer mutations to identify genetic loci coding for proteins that interact with Dynamin in Drosophila. In addition, we have used reverse genetic approaches to investigate few other candidate molecules that may play a role in synaptic vesicle endocytosis. We have in particular discussed at some length the role of endocytic accessory proteins Stoned and Eps15 in vesicle recycling.
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Affiliation(s)
- Riddhi Majumder
- National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India
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Habets RLP, Verstreken P. FlAsH-FALI inactivation of a protein at the third-instar neuromuscular junction. Cold Spring Harb Protoc 2011; 2011:pdb.prot5597. [PMID: 21460046 DOI: 10.1101/pdb.prot5597] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
INTRODUCTIONFluorescein-assisted light inactivation (FALI) is a powerful method for studying acute loss of protein function, even if the corresponding mutations lead to early lethality. In this protocol, FALI is mediated by the membrane-permeable FlAsH (4′,5′-bis(1,3,2-dithioarsolan-2-yl)fluorescein) compound that binds with high specificity to the genetically encoded tetracysteine tag and thus allows the inactivation of protein function in vivo with exquisite spatial (<40 Å) and temporal (<30 sec) resolution. It also enables the analysis of kinetically distinct processes such as synaptic vesicle exocytosis and endocytosis. This protocol describes efficient inactivation of a protein using FlAsH-FALI at the neuromuscular junction (NMJ) of third-instar larvae. Note that FlAsH-FALI in other tissues is also theoretically possible with minor adaptations to the protocol described here. We explain controls for positional effects, for unspecific FlAsH binding to endogenous proteins, and for phototoxicity. Following FlAsH-FALI, protein function can be studied using a number of secondary assays, including electrophysiology, immunohistochemistry, and electron microscopy or FM1-43 labeling of synaptic vesicle pools.
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Habets RLP, Verstreken P. Construction and expression of tetracysteine-tagged proteins for FlAsH-FALI. Cold Spring Harb Protoc 2011; 2011:pdb.prot5596. [PMID: 21460045 DOI: 10.1101/pdb.prot5596] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Vijayakrishnan N, Phillips SE, Broadie K. Drosophila rolling blackout displays lipase domain-dependent and -independent endocytic functions downstream of dynamin. Traffic 2010; 11:1567-78. [PMID: 21029287 DOI: 10.1111/j.1600-0854.2010.01117.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Drosophila temperature-sensitive rolling blackout (rbo(ts) ) mutants display a total block of endocytosis in non-neuronal cells and a weaker, partial defect at neuronal synapses. RBO is an integral plasma membrane protein and is predicted to be a serine esterase. To determine if lipase activity is required for RBO function, we mutated the catalytic serine 358 to alanine in the G-X-S-X-G active site, and assayed genomic rescue of rbo mutant non-neuronal and neuronal phenotypes. The rbo(S358A) mutant is unable to rescue rbo null 100% embryonic lethality, indicating that the lipase domain is critical for RBO essential function. Likewise, the rbo(S358A) mutant cannot provide any rescue of endocytic blockade in rbo(ts) Garland cells, showing that the lipase domain is indispensable for non-neuronal endocytosis. In contrast, rbo(ts) conditional paralysis, synaptic transmission block and synapse endocytic defects are all fully rescued by the rbo(S358A) mutant, showing that the RBO lipase domain is dispensable in neuronal contexts. We identified a synthetic lethal interaction between rbo(ts) and the well-characterized dynamin GTPase conditional shibire (shi(ts1)) mutant. In both non-neuronal cells and neuronal synapses, shi(ts1); rbo(ts) phenocopies shi(ts1) endocytic defects, indicating that dynamin and RBO act in the same pathway, with dynamin functioning upstream of RBO. We conclude that RBO possesses both lipase domain-dependent and scaffolding functions with differential requirements in non-neuronal versus neuronal endocytosis mechanisms downstream of dynamin GTPase activity.
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Affiliation(s)
- Niranjana Vijayakrishnan
- Department of Biological Sciences, Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37235-1634, USA
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Abstract
The stoned proteins, stoned A (STNA) and stoned B (STNB), are essential for normal vesicle trafficking in Drosophila melanogaster neurons, and deletion of the stoned locus is lethal. Although there is a growing body of research aimed at defining the roles of these proteins, particularly for STNB where homologues have now been identified in all multicellular species, their functions and mechanisms of action are not yet established. The two proteins are structurally unrelated, consistent with two distinct cellular functions. The evidence suggests a critical requirement for stoned proteins in recycling/regulation or specification of a competent synaptic vesicle pool. As stoned proteins may be specific to a particular pathway of endocytosis, studies of their function are likely to be valuable in distinguishing between the different mechanisms of membrane retrieval and their respective contributions to synaptic vesicle recycling, a subject of considerable scientific debate. In this review, we examine the published literature on stoned and comment on the available data, conclusions from these analyses and how they may relate to alternative models of vesicle cycling.
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Affiliation(s)
- A Marie Phillips
- Department of Genetics, The University of Melbourne, Parkville 3010, Australia.
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Thompson CJ, Schilling T, Howard MR, Genever PG. SNARE-dependent glutamate release in megakaryocytes. Exp Hematol 2010; 38:504-15. [PMID: 20347926 PMCID: PMC2877886 DOI: 10.1016/j.exphem.2010.03.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2009] [Revised: 03/12/2010] [Accepted: 03/17/2010] [Indexed: 02/06/2023]
Abstract
Objective The identification of signaling pathways involved in megakaryocytopoiesis is essential for development of novel therapeutics to treat hematological disorders. Following our previous findings that megakaryocytes express functional channel-forming N-methyl-D-aspartate-type glutamate receptors, here we aimed to determine the glutamate release capacity in undifferentiated and differentiated megakaryocytes and the role of soluble N-ethyl maleimide-sensitive factor attachment protein receptor (SNARE) proteins that are known to be associated with vesicular exocytosis. Materials and Methods Using the megakaryocytic cell line MEG-01, primary megakaryocytes, and tissue sections of bone marrow, reverse transcription polymerase chain reaction, Western blot analysis, and immunolocalization were employed to detect factors required for vesicular glutamate release. Vesicle recycling was monitored by acridine orange and FM1-43 staining and glutamate release activity was assessed by an enzyme-linked fluorimetric assay. Genetically modified MEG-01 cells, with deletion or overexpression of SNARE and vesicular proteins, were also examined for glutamate release activity. Results We demonstrated that megakaryocytes express numerous proteins required for vesicular glutamate release, including core SNARE proteins, vesicle-associated membrane protein, soluble N-ethyl maleimide-sensitive factor attachment protein−23, and syntaxin, as well as specific glutamate-loading vesicle proteins, VGLUT1 and VGLUT2. Moreover, active vesicle recycling and differentiation-dependent glutamate release were observed in megakaryocytes. Vesicle-associated membrane protein−deficient MEG-01 cells, which are impaired in vesicle recycling, showed a 30% decrease in released glutamate, whereas overexpression of VGLUT1 exhibited up to a 2.2-fold increase in glutamate release. Conclusion These data show that glutamate release from megakaryocytes occurs in a SNARE-dependent, exocytotic manner and is increased during differentiation, suggesting that manipulation of glutamate signaling could influence megakaryocytopoiesis and, therefore, offer a suitable target for the treatment of thrombosis and other hematological disorders.
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Affiliation(s)
- Jeremy Dittman
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065; ,
| | - Timothy A. Ryan
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065; ,
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Kelly L, Phillips A. Molecular and genetic characterization of the interactions between the Drosophila stoned-B protein and DAP-160 (intersectin). Biochem J 2009; 388:195-204. [PMID: 15631619 PMCID: PMC1186708 DOI: 10.1042/bj20041797] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The stoned locus of Drosophila produces a dicistronic transcript and encodes two proteins, stoned-A (STNA) and stoned-B (STNB). Both proteins are located at synaptic terminals. The STNB protein contains a domain that has homology with the mu-subunit of the AP (adaptor protein) complex, as well as a number of NPF (Asp-Pro-Phe) motifs known to bind EH (Eps15 homology) domains. Mutations at the stoned locus interact synergistically with mutations at the shibire (dynamin) locus and alter synaptic vesicle endocytosis. The STNB protein has also been shown to interact with synaptic vesicles via synaptogamin-I. We initiated an investigation of the possible interaction of DAP-160 (dynamin-associated protein of 160 kDa), a Drosophila member of the intersectin family, with the STNB protein. We show here that both of the viable stoned alleles interacted with a genetic construct that reduces DAP-160 levels to 25% of normal. One of these stoned alleles contains a substitution resulting in a stop codon in the open reading frame encoding STNB. This allele also shows markedly reduced levels of both DAP-160 and dynamin. As anticipated, the NPF motifs in STNB are found to be high-affinity binding motifs for the EH domains of DAP-160. One of the SH3 (Src homology 3) domains of DAP-160 also interacts with STNB. Finally, we show that immunoprecipitation of STNB from fly head extracts co-precipitates with DAP-160, and we conclude that the interaction of the STNB protein with both synaptotagmin I and DAP-160 may regulate synaptic vesicle recycling by recruiting dynamin to a pre-fission complex.
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Affiliation(s)
- Leonard E. Kelly
- Department of Genetics, University of Melbourne, Parkville, Victoria, Australia 3010
- To whom correspondence should be addressed (email )
| | - A. Marie Phillips
- Department of Genetics, University of Melbourne, Parkville, Victoria, Australia 3010
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31
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Maritzen T, Podufall J, Haucke V. Stonins-Specialized Adaptors for Synaptic Vesicle Recycling and Beyond? Traffic 2009; 11:8-15. [DOI: 10.1111/j.1600-0854.2009.00971.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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32
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Gu M, Schuske K, Watanabe S, Liu Q, Baum P, Garriga G, Jorgensen EM. Mu2 adaptin facilitates but is not essential for synaptic vesicle recycling in Caenorhabditis elegans. ACTA ACUST UNITED AC 2008; 183:881-92. [PMID: 19047463 PMCID: PMC2592831 DOI: 10.1083/jcb.200806088] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Synaptic vesicles must be recycled to sustain neurotransmission, in large part via clathrin-mediated endocytosis. Clathrin is recruited to endocytic sites on the plasma membrane by the AP2 adaptor complex. The medium subunit (μ2) of AP2 binds to cargo proteins and phosphatidylinositol-4,5-bisphosphate on the cell surface. Here, we characterize the apm-2 gene (also called dpy-23), which encodes the only μ2 subunit in the nematode Caenorhabditis elegans. APM-2 is highly expressed in the nervous system and is localized to synapses; yet specific loss of APM-2 in neurons does not affect locomotion. In apm-2 mutants, clathrin is mislocalized at synapses, and synaptic vesicle numbers and evoked responses are reduced to 60 and 65%, respectively. Collectively, these data suggest AP2 μ2 facilitates but is not essential for synaptic vesicle recycling.
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Affiliation(s)
- Mingyu Gu
- Howard Hughes Medical Institute and Department of Biology, University of Utah, Salt Lake City, UT 84112, USA
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33
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Venkatachalam K, Long AA, Elsaesser R, Nikolaeva D, Broadie K, Montell C. Motor deficit in a Drosophila model of mucolipidosis type IV due to defective clearance of apoptotic cells. Cell 2008; 135:838-51. [PMID: 19041749 DOI: 10.1016/j.cell.2008.09.041] [Citation(s) in RCA: 162] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Revised: 07/25/2008] [Accepted: 09/17/2008] [Indexed: 11/27/2022]
Abstract
Disruption of the Transient Receptor Potential (TRP) mucolipin 1 (TRPML1) channel results in the neurodegenerative disorder mucolipidosis type IV (MLIV), a lysosomal storage disease with severe motor impairments. The mechanisms underlying MLIV are poorly understood and there is no treatment. Here, we report a Drosophila MLIV model, which recapitulates the key disease features, including abnormal intracellular accumulation of macromolecules, motor defects, and neurodegeneration. The basis for the buildup of macromolecules was defective autophagy, which resulted in oxidative stress and impaired synaptic transmission. Late-apoptotic cells accumulated in trpml mutant brains, suggesting diminished cell clearance. The accumulation of late-apoptotic cells and motor deficits were suppressed by expression of trpml(+) in neurons, glia, or hematopoietic cells. We conclude that the neurodegeneration and motor defects result primarily from decreased clearance of apoptotic cells. Since hematopoietic cells in humans are involved in clearance of apoptotic cells, our results raise the possibility that bone marrow transplantation may limit the progression of MLIV.
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Affiliation(s)
- Kartik Venkatachalam
- Departments of Biological Chemistry and Neuroscience, Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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34
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Vijayakrishnan N, Woodruff EA, Broadie K. Rolling blackout is required for bulk endocytosis in non-neuronal cells and neuronal synapses. J Cell Sci 2008; 122:114-25. [PMID: 19066280 DOI: 10.1242/jcs.036673] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rolling blackout (RBO) is a Drosophila EFR3 integral membrane lipase. A conditional temperature-sensitive (TS) mutant (rbo(ts)) displays paralysis within minutes following a temperature shift from 25 degrees C to 37 degrees C, an impairment previously attributed solely to blocked synaptic-vesicle exocytosis. However, we found that rbo(ts) displays a strong synergistic interaction with the Syntaxin-1A TS allele syx(3-69), recently shown to be a dominant positive mutant that increases Syntaxin-1A function. At neuromuscular synapses, rbo(ts) showed a strong defect in styryl-FM-dye (FM) endocytosis, and rbo(ts);syx(3-69) double mutants displayed a synergistic, more severe, endocytosis impairment. Similarly, central rbo(ts) synapses in primary brain culture showed severely defective FM endocytosis. Non-neuronal nephrocyte Garland cells showed the same endocytosis defect in tracer-uptake assays. Ultrastructurally, rbo(ts) displayed a specific defect in tracer uptake into endosomes in both neuronal and non-neuronal cells. At the rbo(ts) synapse, there was a total blockade of endosome formation via activity-dependent bulk endocytosis. Clathrin-mediated endocytosis was not affected; indeed, there was a significant increase in direct vesicle formation. Together, these results demonstrate that RBO is required for constitutive and/or bulk endocytosis and/or macropinocytosis in both neuronal and non-neuronal cells, and that, at the synapse, this mechanism is responsive to the rate of Syntaxin-1A-dependent exocytosis.
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Affiliation(s)
- Niranjana Vijayakrishnan
- Department of Biological Sciences, Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37235, USA
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35
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Gatto CL, Broadie K. Temporal requirements of the fragile X mental retardation protein in the regulation of synaptic structure. Development 2008; 135:2637-48. [PMID: 18579676 DOI: 10.1242/dev.022244] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Fragile X syndrome (FraX), caused by the loss-of-function of one gene (FMR1), is the most common inherited form of both mental retardation and autism spectrum disorders. The FMR1 product (FMRP) is an mRNA-binding translation regulator that mediates activity-dependent control of synaptic structure and function. To develop any FraX intervention strategy, it is essential to define when and where FMRP loss causes the manifestation of synaptic defects, and whether the reintroduction of FMRP can restore normal synapse properties. In the Drosophila FraX model, dFMRP loss causes neuromuscular junction (NMJ) synapse over-elaboration (overgrowth, overbranching, excess synaptic boutons), accumulation of development-arrested satellite boutons, and altered neurotransmission. We used the Gene-Switch method to conditionally drive dFMRP expression to define the spatiotemporal requirements in synaptic mechanisms. Constitutive induction of targeted neuronal dFMRP at wild-type levels rescues all synaptic architectural defects in Drosophila Fmr1 (dfmr1)-null mutants, demonstrating a presynaptic requirement for synapse structuring. By contrast, presynaptic dFMRP expression does not ameliorate functional neurotransmission defects, indicating a postsynaptic dFMRP requirement. Strikingly, targeted early induction of dFMRP effects nearly complete rescue of synaptic structure defects, showing a primarily early-development role. In addition, acute dFMRP expression at maturity partially alleviates dfmr1-null defects, although rescue is not as complete as either early or constitutive dFMRP expression, showing a modest capacity for late-stage structural plasticity. We conclude that dFMRP predominantly acts early in synaptogenesis to modulate architecture, but that late dFMRP introduction at maturity can weakly compensate for early absence of dFMRP function.
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Affiliation(s)
- Cheryl L Gatto
- Department of Biological Sciences, Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37232, USA
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36
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Mohrmann R, Matthies HJ, Woodruff E, Broadie K. Stoned B mediates sorting of integral synaptic vesicle proteins. Neuroscience 2008; 153:1048-63. [PMID: 18436388 DOI: 10.1016/j.neuroscience.2008.02.060] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2007] [Revised: 02/01/2008] [Accepted: 02/01/2008] [Indexed: 10/22/2022]
Abstract
A continuous supply of fusion-competent synaptic vesicles is essential for sustainable neurotransmission. Drosophila mutations of the dicistronic stoned locus disrupt normal vesicle cycling and cause functional deficits in synaptic transmission. Although both Stoned A and B proteins putatively participate in reconstituting synaptic vesicles, their precise function is still unclear. Here we investigate the effects of progressive depletion of Stoned B protein (STNB) on the release properties of neuromuscular synapses using a novel set of synthetic stnB hypomorphic alleles. Decreasing neuronal STNB expression to < or =35% of wild-type level causes a strong reduction in excitatory junctional current amplitude at low stimulation frequencies and a marked slowing in synaptic depression during high-frequency stimulation, suggesting vesicle depletion is attenuated by decreased release probability. Recovery from synaptic depression after prolonged stimulation is also decelerated in mutants, indicating a delayed recovery of fusion-ready vesicles. These phenotypes appear not to be due to a diminished vesicle population, since the docked vesicle pool is ultrastructurally unaffected, and the total number of vesicles is only slightly reduced in these hypomorphs, unlike lethal stoned mutants. Therefore, we conclude that STNB not only functions as an essential component of the endocytic complex for vesicle reconstitution, as previously proposed, but also regulates the competence of recycled vesicles to undergo fusion. In support of such role of STNB, synaptic levels of the vesicular glutamate transporter (vGLUT) and synaptotagmin-1 are strongly reduced with diminishing STNB function, while other synaptic proteins are largely unaffected. We conclude that STNB organizes the endocytic sorting of a subset of integral synaptic vesicle proteins thereby regulating the fusion-competence of the recycled vesicle.
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Affiliation(s)
- R Mohrmann
- Department of Biological Sciences, Vanderbilt University, 1210 Medical Research Building III, , Nashville, TN 37235-1634, USA
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37
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Jung N, Wienisch M, Gu M, Rand JB, Müller SL, Krause G, Jorgensen EM, Klingauf J, Haucke V. Molecular basis of synaptic vesicle cargo recognition by the endocytic sorting adaptor stonin 2. ACTA ACUST UNITED AC 2008; 179:1497-510. [PMID: 18166656 PMCID: PMC2373488 DOI: 10.1083/jcb.200708107] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
Synaptic transmission depends on clathrin-mediated recycling of synaptic vesicles (SVs). How select SV proteins are targeted for internalization has remained elusive. Stonins are evolutionarily conserved adaptors dedicated to endocytic sorting of the SV protein synaptotagmin. Our data identify the molecular determinants for recognition of synaptotagmin by stonin 2 or its Caenorhabditis elegans orthologue UNC-41B. The interaction involves the direct association of clusters of basic residues on the surface of the cytoplasmic domain of synaptotagmin 1 and a β strand within the μ–homology domain of stonin 2. Mutation of K783, Y784, and E785 to alanine within this stonin 2 β strand results in failure of the mutant stonin protein to associate with synaptotagmin, to accumulate at synapses, and to facilitate synaptotagmin internalization. Synaptotagmin-binding–defective UNC-41B is unable to rescue paralysis in C. elegans stonin mutant animals, suggesting that the mechanism of stonin-mediated SV cargo recognition is conserved from worms to mammals.
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Affiliation(s)
- Nadja Jung
- Department of Membrane Biochemistry, Institute of Chemistry and Biochemistry, Freie Universität Berlin, 14195 Berlin, Germany
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38
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Rodemer C, Haucke V. Clathrin/AP-2-dependent endocytosis: a novel playground for the pharmacological toolbox? Handb Exp Pharmacol 2008:105-122. [PMID: 18491050 DOI: 10.1007/978-3-540-72843-6_5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Endocytosis is a vital process for mammalian cells by which they communicate with their environment, internalize nutrients, hormones, or growth factors, or take up extracellular fluids and particles. The best studied among the various pathways to ingest material from the extracellular side is clathrin/AP-2-mediated endocytosis. The past several years have allowed us to gain unprecedented molecular insights into the role of the heterotetrameric AP-2 adaptor complex as a central protein-protein and protein-lipid interaction hub at the plasmalemma. During the initial stages of clathrin-coated pit formation, AP-2 interacts with phosphoinositides and cargo membrane proteins as well as with a variety of accessory proteins and clathrin to coordinate clathrin coat polymerization with membrane deformation and cargo recruitment. In addition, a growing list of alternative adaptors provides opportunity for clathrin-dependent cargo selective pathways of internalization and endosomal sorting. Many of these interactions are now understood in structural detail and are thus amenable to pharmacological interference. In this review we will summarize our present state of knowledge about AP-2 and its partners in endocytosis and delineate potential strategies for pharmacological manipulations.
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Affiliation(s)
- C Rodemer
- Department of Membrane Biochemistry, Robert-Rossle-Str.10, Berlin
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39
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Renden R, von Gersdorff H. Synaptic vesicle endocytosis at a CNS nerve terminal: faster kinetics at physiological temperatures and increased endocytotic capacity during maturation. J Neurophysiol 2007; 98:3349-59. [PMID: 17942618 DOI: 10.1152/jn.00898.2007] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Synaptic vesicle membrane must be quickly retrieved and recycled after copious exocytosis to limit the depletion of vesicle pools. The rate of endocytosis at the calyx of Held nerve terminal has been measured directly using membrane capacitance measurements from immature postnatal day P7-P10 rat pups at room temperature (RT: 23-24 degrees C). This rate has an average time constant of tens of seconds and becomes slower when the amount of exocytosis (measured as capacitance jump) increases. Such slow rates seem paradoxical for a synapse that can operate continuously at high-input frequencies. Here we perform time-resolved membrane capacitance measurements from the mouse calyx of Held in brain stem slices at physiological temperature (PT: 35-37 degrees C), and also from more mature calyces after the onset of hearing (P14-P18). Our results show that the rate of endocytosis is strongly temperature dependent, whereas the endocytotic capacity of a nerve terminal is dependent on developmental stage. At PT we find that endocytosis accelerates due to the addition of a kinetically fast component (time constant: tau = 1-2 s) immediately after exocytosis. Surprisingly, we find that at RT the rate of endocytosis triggered by short (1- to 5-ms) or long (> or =10-ms) depolarizing pulses in P14-P18 mice are similar (tau approximately 15 s). Furthermore, this rate is greatly accelerated at PT (tau approximately 2 s). Thus endocytosis becomes faster and less saturable during synaptic maturation, making the calyceal terminal more capable of sustaining prolonged high-frequency transmitter release.
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Affiliation(s)
- Robert Renden
- The Vollum Institute, L-474, Oregon Health and Science University, Portland, OR 97239, USA
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40
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Akbergenova Y, Bykhovskaia M. Synapsin maintains the reserve vesicle pool and spatial segregation of the recycling pool in Drosophila presynaptic boutons. Brain Res 2007; 1178:52-64. [PMID: 17904536 DOI: 10.1016/j.brainres.2007.08.042] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2007] [Revised: 08/09/2007] [Accepted: 08/13/2007] [Indexed: 10/22/2022]
Abstract
We employed optical detection of the lipophylic dye FM1-43 and focal recordings of quantal release to investigate how synapsin affects vesicle cycling at the neuromuscular junction of synapsin knockout (Syn KO) Drosophila. Loading the dye employing high K+ stimulation, which presumably involves the recycling pool of vesicles in exo/endocytosis, stained the periphery of wild type (WT) boutons, while in Syn KO the dye was redistributed towards the center of the bouton. When endocytosis was promoted by cyclosporin A pretreatment, the dye uptake was significantly enhanced in WT boutons, and the entire boutons were stained, suggesting staining of the reserve vesicle pool. In Syn KO boutons, the same loading paradigm produced fainter staining and significantly faster destaining. When the axon was stimulated electrically, a distinct difference in dye loading patterns was observed in WT boutons at different stimulation frequencies: a low stimulation frequency (3 Hz) produced a ring-shaped staining pattern, while at a higher frequency (10 Hz) the dye was redistributed towards the center of the bouton and the fluorescence intensity was significantly increased. This difference in staining patterns was essentially disrupted in Syn KO boutons, although synapsin did not affect the rate of quantal release. Stimulation of the nerve in the presence of bafilomycin, the blocker of the transmitter uptake, produced significantly stronger depression in Syn KO boutons. These results, taken together, suggest that synapsin maintains the reserve pool of vesicles and segregation between the recycling and reserve pools, and that it mediates mobilization of the reserve pool during intense stimulation.
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Affiliation(s)
- Yulia Akbergenova
- Department of Biological Sciences, Lehigh University, 111 Research Dr., Bethlehem, PA 18015, USA
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41
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Koh TW, Korolchuk VI, Wairkar YP, Jiao W, Evergren E, Pan H, Zhou Y, Venken KJT, Shupliakov O, Robinson IM, O'Kane CJ, Bellen HJ. Eps15 and Dap160 control synaptic vesicle membrane retrieval and synapse development. ACTA ACUST UNITED AC 2007; 178:309-22. [PMID: 17620409 PMCID: PMC2064449 DOI: 10.1083/jcb.200701030] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Epidermal growth factor receptor pathway substrate clone 15 (Eps15) is a protein implicated in endocytosis, endosomal protein sorting, and cytoskeletal organization. Its role is, however, still unclear, because of reasons including limitations of dominant-negative experiments and apparent redundancy with other endocytic proteins. We generated Drosophila eps15-null mutants and show that Eps15 is required for proper synaptic bouton development and normal levels of synaptic vesicle (SV) endocytosis. Consistent with a role in SV endocytosis, Eps15 moves from the center of synaptic boutons to the periphery in response to synaptic activity. The endocytic protein, Dap160/intersectin, is a major binding partner of Eps15, and eps15 mutants phenotypically resemble dap160 mutants. Analyses of eps15 dap160 double mutants suggest that Eps15 functions in concert with Dap160 during SV endocytosis. Based on these data, we hypothesize that Eps15 and Dap160 promote the efficiency of endocytosis from the plasma membrane by maintaining high concentrations of multiple endocytic proteins, including dynamin, at synapses.
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Affiliation(s)
- Tong-Wey Koh
- Graduate Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA
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42
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Grise F, Taib N, Monterrat C, Lagrée V, Lang J. Distinct roles of the C2A and the C2B domain of the vesicular Ca2+ sensor synaptotagmin 9 in endocrine beta-cells. Biochem J 2007; 403:483-92. [PMID: 17263688 PMCID: PMC1876385 DOI: 10.1042/bj20061182] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Synaptotagmins form a family of calcium-sensor proteins implicated in exocytosis, and these vesicular transmembrane proteins are endowed with two cytosolic calcium-binding C2 domains, C2A and C2B. Whereas the isoforms syt1 and syt2 have been studied in detail, less is known about syt9, the calcium sensor involved in endocrine secretion such as insulin release from large dense core vesicles in pancreatic beta-cells. Using cell-based assays to closely mimic physiological conditions, we observed SNARE (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor)-independent translocation of syt9C2AB to the plasma membrane at calcium levels corresponding to endocrine exocytosis, followed by internalization to endosomes. The use of point mutants and truncations revealed that initial translocation required only the C2A domain, whereas the C2B domain ensured partial pre-binding of syt9C2AB to the membrane and post-stimulatory localization to endosomes. In contrast with the known properties of neuronal and neuroendocrine syt1 or syt2, the C2B domain of syt9 did not undergo calcium-dependent membrane binding despite a high degree of structural homology as observed through molecular modelling. The present study demonstrates distinct intracellular properties of syt9 with different roles for each C2 domain in endocrine cells.
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Affiliation(s)
- Florence Grise
- *Jeune Equipe 2390, Institut Européen de Chimie et Biologie, Université de Bordeaux 1, 2 Av. Robert Escarpit, F-33607 Pessac, France
| | - Nada Taib
- †UMR 5144 CNRS Mobios, Institut Européen de Chimie et Biologie, Université de Bordeaux 1, 2 Av. Robert Escarpit, F-33607 Pessac, France
| | - Carole Monterrat
- *Jeune Equipe 2390, Institut Européen de Chimie et Biologie, Université de Bordeaux 1, 2 Av. Robert Escarpit, F-33607 Pessac, France
| | - Valérie Lagrée
- *Jeune Equipe 2390, Institut Européen de Chimie et Biologie, Université de Bordeaux 1, 2 Av. Robert Escarpit, F-33607 Pessac, France
| | - Jochen Lang
- *Jeune Equipe 2390, Institut Européen de Chimie et Biologie, Université de Bordeaux 1, 2 Av. Robert Escarpit, F-33607 Pessac, France
- To whom correspondence should be addressed (email )
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43
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Megighian A, Rigoni M, Caccin P, Zordan MA, Montecucco C. A lysolecithin/fatty acid mixture promotes and then blocks neurotransmitter release at the Drosophila melanogaster larval neuromuscular junction. Neurosci Lett 2007; 416:6-11. [PMID: 17293048 DOI: 10.1016/j.neulet.2007.01.040] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2006] [Revised: 01/15/2007] [Accepted: 01/19/2007] [Indexed: 11/17/2022]
Abstract
The study of the effect of snake presynaptic neurotoxins with phospholipase A2 activity on nerve terminals has recently unveiled the inhibitory action of a lysophosphatidylcholine (LysoPC)/fatty acid mixture. We report here that these neurotoxins have no activity on Drosophila melanogaster nerve terminals. However, a 1:1 mixture of LysoPC and oleic acid induces an early increase, followed by an inhibition of both evoked and spontaneous neurotransmitter release. This effect is also induced by LysoPC alone. The present findings provide an indirect evidence that the lipid hemifusion-to-pore transition is a key event in neuroexocytosis in Drosophila. Moreover, these findings substantiate the use of LysoPC as a general agonist of membrane fusion at nerve terminals. This novel tool could contribute to the unraveling of the molecular steps involved in neuroexocytosis, particularly in Drosophila, where it is straightforward to combine it with electrophysiology and genetics.
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Affiliation(s)
- Aram Megighian
- Department of Human Anatomy and Physiology, Section of Physiology, University of Padova, Via Marzolo 3, Padova, Italy.
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44
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Bonanomi D, Benfenati F, Valtorta F. Protein sorting in the synaptic vesicle life cycle. Prog Neurobiol 2006; 80:177-217. [PMID: 17074429 DOI: 10.1016/j.pneurobio.2006.09.002] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2006] [Revised: 09/14/2006] [Accepted: 09/18/2006] [Indexed: 01/06/2023]
Abstract
At early stages of differentiation neurons already contain many of the components necessary for synaptic transmission. However, in order to establish fully functional synapses, both the pre- and postsynaptic partners must undergo a process of maturation. At the presynaptic level, synaptic vesicles (SVs) must acquire the highly specialized complement of proteins, which make them competent for efficient neurotransmitter release. Although several of these proteins have been characterized and linked to precise functions in the regulation of the SV life cycle, a systematic and unifying view of the mechanisms underlying selective protein sorting during SV biogenesis remains elusive. Since SV components do not share common sorting motifs, their targeting to SVs likely relies on a complex network of protein-protein and protein-lipid interactions, as well as on post-translational modifications. Pleiomorphic carriers containing SV proteins travel and recycle along the axon in developing neurons. Nevertheless, SV components appear to eventually undertake separate trafficking routes including recycling through the neuronal endomembrane system and the plasmalemma. Importantly, SV biogenesis does not appear to be limited to a precise stage during neuronal differentiation, but it rather continues throughout the entire neuronal lifespan and within synapses. At nerve terminals, remodeling of the SV membrane results from the use of alternative exocytotic pathways and possible passage through as yet poorly characterized vacuolar/endosomal compartments. As a result of both processes, SVs with heterogeneous molecular make-up, and hence displaying variable competence for exocytosis, may be generated and coexist within the same nerve terminal.
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Affiliation(s)
- Dario Bonanomi
- Department of Neuroscience, San Raffaele Scientific Institute and Vita-Salute University, Milan, Italy
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45
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Ryan TA. A pre-synaptic to-do list for coupling exocytosis to endocytosis. Curr Opin Cell Biol 2006; 18:416-21. [PMID: 16806881 DOI: 10.1016/j.ceb.2006.06.013] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2006] [Accepted: 06/08/2006] [Indexed: 02/06/2023]
Abstract
Synaptic vesicles are made locally in the nerve terminal during recycling of membrane. Synaptic vesicle proteins must be sorted and concentrated on the plasma membrane, packaged into a budding vesicle of precise size and cut away from the synaptic surface. Adaptors, scaffolds, BAR-domain and ENTH-domain proteins all must be coordinated to carry out this sequence of events prior to the action of dynamin. Details of how this is orchestrated at nerve terminals are just beginning to emerge.
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Affiliation(s)
- Timothy A Ryan
- Department of Biochemistry, Weill Medical College of Cornell University, 1300 York Ave, New York NY 10021 USA.
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46
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Majumdar A, Ramagiri S, Rikhy R. Drosophila homologue of Eps15 is essential for synaptic vesicle recycling. Exp Cell Res 2006; 312:2288-98. [PMID: 16709407 DOI: 10.1016/j.yexcr.2006.03.030] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2006] [Revised: 03/15/2006] [Accepted: 03/23/2006] [Indexed: 10/24/2022]
Abstract
The mammalian protein Eps15 is phosphorylated by EGF receptor tyrosine kinase and has been shown to interact with several components of the endocytic machinery. We have identified a hypomorphic Eps15 mutant in Drosophila which shows reversible paralysis and an altered physiology at restrictive temperatures. In addition, the temperature-sensitive paralytic defect of shibire mutant is enhanced by this mutant. Eps15 is enriched in the larval neuromuscular junction in endocytic 'hot spots' in a pattern similar to Dynamin. Eps15 mutants show a decrease in the alpha-Adaptin levels at the larval neuromuscular junction synapse. Genetic and biochemical studies of interactions with components of the endocytic machinery suggest that Eps15 has an important role in synaptic vesicle recycling and regulates recruitment of alpha-Adaptin.
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Affiliation(s)
- Amitabha Majumdar
- Department of Biological Sciences, Tata Institute of Fundamental Research, Colaba Mumbai 400005, India.
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47
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Diril MK, Wienisch M, Jung N, Klingauf J, Haucke V. Stonin 2 Is an AP-2-Dependent Endocytic Sorting Adaptor for Synaptotagmin Internalization and Recycling. Dev Cell 2006; 10:233-44. [PMID: 16459302 DOI: 10.1016/j.devcel.2005.12.011] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2005] [Revised: 11/12/2005] [Accepted: 12/08/2005] [Indexed: 11/17/2022]
Abstract
Clathrin-mediated endocytosis is involved in the internalization, recycling, and degradation of cycling membrane receptors as well as in the biogenesis of synaptic vesicle proteins. While many constitutively internalized cargo proteins are recognized directly by the clathrin adaptor complex AP-2, stimulation-dependent endocytosis of membrane proteins is often facilitated by specialized sorting adaptors. Although clathrin-mediated endocytosis appears to be a major pathway for presynaptic vesicle cycling, no sorting adaptor dedicated to synaptic vesicle membrane protein endocytosis has been indentified in mammals. Here, we show that stonin 2, a mammalian ortholog of Drosophila stoned B, facilitates clathrin/AP-2-dependent internalization of synaptotagmin and targets it to a recycling vesicle pool in living neurons. The ability of stonin 2 to facilitate endocytosis of synaptotagmin is dependent on its association with AP-2, an intact mu-homology domain, and functional AP-2 heterotetramers. Our data identify stonin 2 as an AP-2-dependent endocytic sorting adaptor for synaptotagmin internalization and recycling.
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Affiliation(s)
- M Kasim Diril
- Freie Universität Berlin, Institute of Chemistry and Biochemistry, Department of Membrane Biochemistry, Takustrasse 6, D-14195 Berlin, Germany
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Bao H, Daniels RW, MacLeod GT, Charlton MP, Atwood HL, Zhang B. AP180 maintains the distribution of synaptic and vesicle proteins in the nerve terminal and indirectly regulates the efficacy of Ca2+-triggered exocytosis. J Neurophysiol 2005; 94:1888-903. [PMID: 15888532 DOI: 10.1152/jn.00080.2005] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
AP180 plays an important role in clathrin-mediated endocytosis of synaptic vesicles (SVs) and has also been implicated in retrieving SV proteins. In Drosophila, deletion of its homologue, Like-AP180 (LAP), has been shown to increase the size of SVs but decrease the number of SVs and transmitter release. However, it remains elusive whether a reduction in the total vesicle pool directly affects transmitter release. Further, it is unknown whether the lap mutation also affects vesicle protein retrieval and synaptic protein localization and, if so, how it might affect exocytosis. Using a combination of electrophysiology, optical imaging, electron microscopy, and immunocytochemistry, we have further characterized the lap mutant and hereby show that LAP plays additional roles in maintaining both normal synaptic transmission and protein distribution at synapses. While increasing the rate of spontaneous vesicle fusion, the lap mutation dramatically reduces impulse-evoked transmitter release at steps downstream of calcium entry and vesicle docking. Notably, lap mutations disrupt calcium coupling to exocytosis and reduce calcium cooperativity. These results suggest a primary defect in calcium sensors on the vesicles or on the release machinery. Consistent with this hypothesis, three vesicle proteins critical for calcium-mediated exocytosis, synaptotagmin I, cysteine-string protein, and neuronal synaptobrevin, are all mislocalized to the extrasynaptic axonal regions along with Dap160, an active zone marker (nc82), and glutamate receptors in the mutant. These results suggest that AP180 is required for either recycling vesicle proteins and/or maintaining the distribution of both vesicle and synaptic proteins in the nerve terminal.
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Affiliation(s)
- Hong Bao
- Section of Neurobiology, Institute for Neuroscience, 1 University Station, The University of Texas at Austin, Austin, Texas 78712, USA
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van Roessel P, Elliott DA, Robinson IM, Prokop A, Brand AH. Independent regulation of synaptic size and activity by the anaphase-promoting complex. Cell 2005; 119:707-18. [PMID: 15550251 DOI: 10.1016/j.cell.2004.11.028] [Citation(s) in RCA: 170] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2004] [Revised: 10/04/2004] [Accepted: 11/05/2004] [Indexed: 10/26/2022]
Abstract
Neuronal plasticity relies on tightly regulated control of protein levels at synapses. One mechanism to control protein abundance is the ubiquitin-proteasome degradation system. Recent studies have implicated ubiquitin-mediated protein degradation in synaptic development, function, and plasticity, but little is known about the regulatory mechanisms controlling ubiquitylation in neurons. In contrast, ubiquitylation has long been studied as a central regulator of the eukaryotic cell cycle. A critical mediator of cell-cycle transitions, the anaphase-promoting complex/cyclosome (APC/C), is an E3 ubiquitin ligase. Although the APC/C has been detected in several differentiated cell types, a functional role for the complex in postmitotic cells has been elusive. We describe a novel postmitotic role for the APC/C at Drosophila neuromuscular synapses: independent regulation of synaptic growth and synaptic transmission. In neurons, the APC/C controls synaptic size via a downstream effector Liprin-alpha; in muscles, the APC/C regulates synaptic transmission, controlling the concentration of a postsynaptic glutamate receptor.
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Affiliation(s)
- Peter van Roessel
- Wellcome Trust/Cancer Research UK Gurdon Institute and Department of Anatomy, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, United Kingdom
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Sherry DM, Heidelberger R. Distribution of proteins associated with synaptic vesicle endocytosis in the mouse and goldfish retina. J Comp Neurol 2005; 484:440-57. [PMID: 15770653 DOI: 10.1002/cne.20504] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Current models of synaptic transmission require retrieval of membrane from the presynaptic terminal following neurotransmitter exocytosis. Dynamin, a GTPase, is thought to be critical for this retrieval process. At ribbon synapses of retinal bipolar neurons, however, compensatory endocytosis does not require GTP hydrolysis, suggesting that endocytosis mechanisms may differ among synapses. To understand better the synaptic vesicle recycling at conventional and ribbon synapses, the distributions of dynamin and two associated proteins, amphiphysin and clathrin, were examined in the retinas of goldfish and mouse by using immunocytochemical methods. Labeling for dynamin, clathrin, and amphiphysin was distributed differentially among conventional and ribbon synapses in retinas of both species. Ribbon synapses of photoreceptors and most bipolar cells labeled only weakly for dynamin relative to conventional synapses. Amphyiphysin labeling was strong at many ribbon synapses, and labeling in rod terminals was stronger than in cone terminals in the mouse retina. Clathrin labeling was heterogeneous among ribbon synapses. Similarly to the case with amphiphysin, mouse rod terminals showed stronger clathrin labeling than cone terminals. Among conventional synapses, there was heterogeneous labeling for all three endocytic proteins. Some labeling for each protein might have been associated with postsynaptic terminals. The differential distribution of labeling for these proteins among identified synapses in the retina suggests considerable heterogeneity in the molecular mechanisms underlying synaptic membrane retrieval, even among synapses with similar active zone ultrastructure. Thus, as with exocytosis, mechanisms of synaptic membrane retrieval may be tuned by the precise complement of proteins expressed within the synaptic terminal.
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Affiliation(s)
- David M Sherry
- University of Houston College of Optometry, Houston, Texas 77204-2020, USA.
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