Synaptotagmin-7 places dense-core vesicles at the cell membrane to promote Munc13-2- and Ca2+-dependent priming
- University of Copenhagen, Denmark
- Max Planck Institute of Experimental Medicine, Germany
Abstract
Synaptotagmins confer calcium-dependence to the exocytosis of secretory vesicles, but how coexpressed synaptotagmins interact remains unclear. We find that synaptotagmin-1 and synaptotagmin-7 when present alone act as standalone fast and slow Ca2+-sensors for vesicle fusion in mouse chromaffin cells. When present together, synaptotagmin-1 and synaptotagmin-7 are found in largely non-overlapping clusters on dense-core vesicles. Synaptotagmin-7 stimulates Ca2+-dependent vesicle priming and inhibits depriming, and it promotes ubMunc13-2- and phorbolester-dependent priming, especially at low resting calcium concentrations. The priming effect of synaptotagmin-7 increases the number of vesicles fusing via synaptotagmin-1, while negatively affecting their fusion speed, indicating both synergistic and competitive interactions between synaptotagmins. Synaptotagmin-7 places vesicles in close membrane apposition (<6 nm); without it, vesicles accumulate out of reach of the fusion complex (20-40 nm). We suggest that a synaptotagmin-7-dependent movement toward the membrane is involved in Munc13-2/phorbolester/Ca2+-dependent priming as a prelude to fast and slow exocytosis triggering.
Data availability
All data generated or analysed during this study are or will be included in the manuscript and supporting files.
Article and author information
Author details
Jakob Balslev Sørensen
Funding
University of Copenhagen 2016 excellence program (KU2016)
- Jakob Balslev Sørensen
Novo Nordisk Foundation (NNF19OC0058298)
- Jakob Balslev Sørensen
Lundbeckfonden (R221-2016-1202)
- Jakob Balslev Sørensen
Independent Research Fund Denmark (0134-00141A)
- Jakob Balslev Sørensen
Lundbeckfonden (R34-A3740)
- Paulo S Pinheiro
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: Mice were kept in an AAALAC-accredited stable at the University of Copenhagen operating a 12h/12h light/dark cycle with access to water and food ad libitum. Permission to keep and breed KO mice were obtained from the Danish Animal Experiments Inspectorate (permissions 2006/562-43 and 2018-15-0202-00157).
Reviewing Editor
- Axel T Brunger, Stanford University, United States
Publication history
- Received: November 2, 2020
- Accepted: March 19, 2021
- Accepted Manuscript published: March 22, 2021 (version 1)
- Version of Record published: March 31, 2021 (version 2)
Copyright
© 2021, Tawfik et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Synaptotagmin-7 places dense-core vesicles at the cell membrane to promote Munc13-2- and Ca2+-dependent priming
eLife 10:e64527.
https://doi.org/10.7554/eLife.64527
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