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Wong MY, Zhou C, Shakiryanova D, Lloyd TE, Deitcher DL, Levitan ES. Neuropeptide delivery to synapses by long-range vesicle circulation and sporadic capture. Cell 2012; 148:1029-38. [PMID: 22385966 DOI: 10.1016/j.cell.2011.12.036] [Citation(s) in RCA: 112] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Revised: 10/13/2011] [Accepted: 12/16/2011] [Indexed: 12/11/2022]
Abstract
Neurotransmission requires anterograde axonal transport of dense core vesicles (DCVs) containing neuropeptides and active zone components from the soma to nerve terminals. However, it is puzzling how one-way traffic could uniformly supply sequential release sites called en passant boutons. Here, Drosophila neuropeptide-containing DCVs are tracked in vivo for minutes with a new method called simultaneous photobleaching and imaging (SPAIM). Surprisingly, anterograde DCVs typically bypass proximal boutons to accumulate initially in the most distal bouton. Then, excess distal DCVs undergo dynactin-dependent retrograde transport back through proximal boutons into the axon. Just before re-entering the soma, DCVs again reverse for another round of anterograde axonal transport. While circulating over long distances, both anterograde and retrograde DCVs are captured sporadically in en passant boutons. Therefore, vesicle circulation, which includes long-range retrograde transport and inefficient bidirectional capture, overcomes the limitations of one-way anterograde transport to uniformly supply release sites with DCVs.
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Affiliation(s)
- Man Yan Wong
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
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Levitan ES, Shakiryanova D. Imaging neuropeptide release in the Drosophila neuromuscular junction (NMJ). Cold Spring Harb Protoc 2010; 2010:pdb.prot5529. [PMID: 21123416 DOI: 10.1101/pdb.prot5529] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Electrophysiological studies of synaptic function cannot directly reveal the internal workings of the nerve terminal and do not robustly report release of neuropeptides and neurotrophins. These limitations can now be overcome with the presynaptic expression of green fluorescent protein (GFP) indicators of vesicle motion, release, and signaling. This protocol describes how to image single wavelength and ratiometric fluorescence resonance energy transfer (FRET)-based GFP indicators with fluorescence microscopy in living synaptic boutons of the Drosophila neuromuscular junction (NMJ). The steps for setting up the imaging equipment for epifluorescence microscopy are given, followed by special considerations for preparing the larval NMJ for peptide release studies.
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Levitan ES, Shakiryanova D. Imaging the Drosophila neuromuscular junction (NMJ): basic optical principles and equipment. Cold Spring Harb Protoc 2010; 2010:pdb.top92. [PMID: 21123433 DOI: 10.1101/pdb.top92] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Electrophysiological studies of synaptic function cannot directly reveal the internal workings of the nerve terminal and do not robustly report release of neuropeptides and neurotrophins. These limitations can now be overcome with the presynaptic expression of green fluorescent protein (GFP) indicators of vesicle motion, release, and signaling. This article describes how to image single wavelength and ratiometric fluorescence resonance energy transfer (FRET)-based GFP indicators with fluorescence microscopy in living synaptic boutons of the Drosophila neuromuscular junction (NMJ). The basic optical principles and equipment required for epifluorescence microscopy are described in detail.
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Wong MY, Shakiryanova D, Levitan ES. Presynaptic ryanodine receptor-CamKII signaling is required for activity-dependent capture of transiting vesicles. J Mol Neurosci 2008; 37:146-50. [PMID: 18592416 DOI: 10.1007/s12031-008-9080-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Accepted: 03/24/2008] [Indexed: 11/24/2022]
Abstract
Activity elicits capture of dense-core vesicles (DCVs) that transit through resting Drosophila synaptic boutons to produce a rebound in presynaptic neuropeptide content following release. The onset of capture overlaps with an increase in the mobility of DCVs already present in synaptic boutons. Vesicle mobilization requires Ca(2+)-induced Ca2+ release by presynaptic endoplasmic reticulum (ER) ryanodine receptors (RyRs) that in turn stimulates Ca2+/calmodulin-dependent kinase II (CamKII). Here we show that the same signaling is required for activity-dependent capture of transiting DCVs. Specifically, the CamKII inhibitor KN-93, but not its inactive analog KN-92, eliminated the rebound replacement of neuropeptidergic DCVs in synaptic boutons. Furthermore, pharmacologically or genetically inhibiting neuronal sarco-endoplasmic reticulum calcium ATPase to deplete presynaptic ER Ca2+ stores or directly inhibiting RyRs prevented the capture response. These results show that the presynaptic RyR-CamKII pathway, which triggers mobilization of resident synaptic DCVs to facilitate exocytosis, also mediates activity-dependent capture of transiting DCVs to replenish neuropeptide stores.
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Affiliation(s)
- Man Yan Wong
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, PA , 15261, USA
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Abstract
Recently, it has become possible to directly detect changes in neuropeptide vesicle dynamics in nerve terminals in vivo and to measure the release of neuropeptides induced experimentally or evoked by normal behavior. These results were obtained with the use of transgenic fruit flies that express a neuropeptide tagged with green fluorescent protein. Here, we describe how vesicle movement and neuropeptide release can be studied in the larval Drosophila neuromuscular junction using fluorescence microscopy. Analysis methods are described for quantifying movement based on time lapse and fluorescence recovery after photobleaching data. Specific approaches that can be applied to nerve terminals include single particle tracking, correlation and Fourier analysis. Utilization of these methods led to the first detection of vesicle mobilization in nerve terminals and the discoveries of activity-dependent capture of transiting vesicles and post-tetanic potentiation of neuropeptide release. Overall, this protocol can be carried out in an hour with ready Drosophila.
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Affiliation(s)
- Edwin S Levitan
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
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Shakiryanova D, Klose MK, Zhou Y, Gu T, Deitcher DL, Atwood HL, Hewes RS, Levitan ES. Presynaptic ryanodine receptor-activated calmodulin kinase II increases vesicle mobility and potentiates neuropeptide release. J Neurosci 2007; 27:7799-806. [PMID: 17634373 PMCID: PMC6672873 DOI: 10.1523/jneurosci.1879-07.2007] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Although it has been postulated that vesicle mobility is increased to enhance release of transmitters and neuropeptides, the mechanism responsible for increasing vesicle motion in nerve terminals and the effect of perturbing this mobilization on synaptic plasticity are unknown. Here, green fluorescent protein-tagged dense-core vesicles (DCVs) are imaged in Drosophila motor neuron terminals, where DCV mobility is increased for minutes after seconds of activity. Ca2+-induced Ca2+ release from presynaptic endoplasmic reticulum (ER) is shown to be necessary and sufficient for sustained DCV mobilization. However, this ryanodine receptor (RyR)-mediated effect is short-lived and only initiates signaling. Calmodulin kinase II (CaMKII), which is not activated directly by external Ca2+ influx, then acts as a downstream effector of released ER Ca2+. RyR and CaMKII are essential for post-tetanic potentiation of neuropeptide secretion. Therefore, the presynaptic signaling pathway for increasing DCV mobility is identified and shown to be required for synaptic plasticity.
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Affiliation(s)
- Dinara Shakiryanova
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Markus K. Klose
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Yi Zhou
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
| | - Tingting Gu
- Departments of Zoology and Cell Biology, University of Oklahoma, Norman, Oklahoma 73019, and
| | - David L. Deitcher
- Department of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853
| | - Harold L. Atwood
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
| | - Randall S. Hewes
- Departments of Zoology and Cell Biology, University of Oklahoma, Norman, Oklahoma 73019, and
| | - Edwin S. Levitan
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261
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Shakiryanova D, Tully A, Levitan ES. Activity-dependent synaptic capture of transiting peptidergic vesicles. Nat Neurosci 2006; 9:896-900. [PMID: 16767091 DOI: 10.1038/nn1719] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2006] [Accepted: 05/18/2006] [Indexed: 12/23/2022]
Abstract
Synapses require resources synthesized in the neuronal soma, but there are no known mechanisms to overcome delays associated with the synthesis and axonal transport of new proteins generated in response to activity, or to direct resources specifically to active synapses. Here, in vivo imaging of the Drosophila melanogaster neuromuscular junction reveals a cell-biological strategy that addresses these constraints. Peptidergic vesicles continually transit through resting terminals, but retrograde peptidergic vesicle flux is accessed following activity to rapidly boost neuropeptide content in synaptic boutons. The presence of excess transiting vesicles implies that synaptic neuropeptide stores are limited by the capture of peptidergic vesicles at the terminal, rather than by synthesis in the soma or delivery via the axon. Furthermore, activity-dependent capture from a pool of transiting vesicles provides a nerve terminal-based mechanism for directing distally and slowly generated resources quickly to active synapses. Finally, retrograde transport in the nerve terminal is regulated by activity.
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Affiliation(s)
- Dinara Shakiryanova
- Department of Pharmacology, University of Pittburgh, Pittsburgh, Pennsylvania 15261, USA
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Abstract
The acidity of mammalian secretory vesicles drives concentration and processing of their contents. Here, pH-sensitive green fluorescent protein (GFP) variants show that the > or =30-fold (H+) difference between secretory vesicles (pH < or = 5.7) and the cytoplasm (pH = 7.2) in mammalian cells is not present in peptidergic and small synaptic vesicles of the Drosophila neuromuscular junction. First, we find that fluorescence from Topaz-tagged atrial natriuretic factor, a peptidergic vesicle pH indicator, is only modestly affected by collapsing the H+ gradient in type III synaptic boutons. Quantitation shows that peptidergic vesicles are nearly neutral (pH = 6.74 +/- 0.05), even when temperature is elevated. Furthermore, small synaptic vesicles in glutamatergic synaptic boutons, studied with synaptophluorin, are as alkaline as peptidergic vesicles. Finally, yellow fluorescent protein measurements show that cytoplasmic pH is only slightly different than in mammals (pH = 7.4). Thus, the marked acidity of mammalian secretory vesicles is not conserved in evolution, and a modest vesicular H+ gradient is sufficient for supporting neurotransmission.
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Affiliation(s)
- David A Sturman
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
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Shakiryanova D, Tully A, Hewes RS, Deitcher DL, Levitan ES. Activity-dependent liberation of synaptic neuropeptide vesicles. Nat Neurosci 2005; 8:173-8. [PMID: 15643430 DOI: 10.1038/nn1377] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2004] [Accepted: 10/26/2004] [Indexed: 11/08/2022]
Abstract
Despite the importance of neuropeptide release, which is evoked by long bouts of action potential activity and which regulates behavior, peptidergic vesicle movement has not been examined in living nerve terminals. Previous in vitro studies have found that secretory vesicle motion at many sites of release is constitutive: Ca(2+) does not affect the movement of small synaptic vesicles in nerve terminals or the movement of large dense core vesicles in growth cones and endocrine cells. However, in vivo imaging of a neuropeptide, atrial natriuretic factor, tagged with green fluorescent protein in larval Drosophila melanogaster neuromuscular junctions shows that peptidergic vesicle behavior in nerve terminals is sensitive to activity-induced Ca(2+) influx. Specifically, peptidergic vesicles are immobile in resting synaptic boutons but become mobile after seconds of stimulation. Vesicle movement is undirected, occurs without the use of axonal transport motors or F-actin, and aids in the depletion of undocked neuropeptide vesicles. Peptidergic vesicle mobilization and post-tetanic potentiation of neuropeptide release are sustained for minutes.
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Affiliation(s)
- Dinara Shakiryanova
- Department of Pharmacology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA
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Ma Y, Shakiryanova D, Vardya I, Popov SV. Quantitative Analysis of Microtubule Transport in Growing Nerve Processes. Curr Biol 2004; 14:725-30. [PMID: 15084289 DOI: 10.1016/j.cub.2004.03.061] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2003] [Revised: 01/19/2004] [Accepted: 03/02/2004] [Indexed: 11/24/2022]
Abstract
In neurons, tubulin is synthesized primarily in the cell body, whereas the molecular machinery for neurite extension and elaboration of microtubule (MT) array is localized to the growth cone region. This unique functional and biochemical compartmentalization of neuronal cells requires transport mechanisms for the delivery of newly synthesized tubulin and other cytoplasmic components from the cell body to the growing axon. According to the polymer transport model, tubulin is transported along the axon as a polymer. Because the majority of axonal MTs are stationary at any given moment, it has been assumed that only a small fraction of MTs translocates along the axon by saltatory movement reminiscent of the fast axonal transport. Such intermittent "stop and go" MT transport has been difficult to detect or to exclude by using direct video microscopy methods. In this study, we measured the translocation of MT plus ends in the axonal shaft by expressing GFP-EB1 in Xenopus embryo neurons in culture. Formal quantitative analysis of MT assembly/disassembly indicated that none of the MTs in the axonal shaft were rapidly transported. Our results suggest that transport of axonal MTs is not required for delivery of newly synthesized tubulin to the growing nerve processes.
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Affiliation(s)
- Yitao Ma
- Department of Physiology and Biophysics, M/C 901, University of Illinois at Chicago, 835 South Wolcott Avenue, Chicago, IL 60612, USA
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