Drosophila Synaptotagmin 7 negatively regulates synaptic vesicle release and replenishment in a dosage-dependent manner

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Abstract

Synchronous neurotransmitter release is triggered by Ca²⁺ binding to the synaptic vesicle protein Synaptotagmin 1, while asynchronous fusion and short-term facilitation is hypothesized to be mediated by plasma membrane-localized Synaptotagmin 7 (SYT7). We generated mutations in Drosophila Syt7 to determine if it plays a conserved role as the Ca²⁺ sensor for these processes. Electrophysiology and quantal imaging revealed evoked release was elevated 2-fold. Syt7 mutants also had a larger pool of readily-releasable vesicles, faster recovery following stimulation, and intact facilitation. Syt1/Syt7 double mutants displayed more release than Syt1 mutants alone, indicating SYT7 does not mediate the residual asynchronous release remaining in the absence of SYT1. SYT7 localizes to an internal membrane tubular network within the peri-active zone, but does not enrich at active zones. These findings indicate the two Ca²⁺ sensor model of SYT1 and SYT7 mediating all phases of neurotransmitter release and facilitation is not applicable at Drosophila synapses.

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All data generated during this study are included in the manuscript and supporting files.

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Zhuo Guan

Department of Biology, Massachusetts Institute of Technology, Cambridge, United States

Competing interests
The authors declare that no competing interests exist.
Monica C Quiñones-Frías

The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, United States

Competing interests
The authors declare that no competing interests exist.
Yulia Akbergenova

The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, United States

Competing interests
The authors declare that no competing interests exist.
J Troy Littleton

The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, United States

For correspondence
troy@mit.edu

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0001-5576-2887

Funding

National Institutes of Health (NS40296)

J Troy Littleton

National Institutes of Health (MH104536)

J Troy Littleton

National Institutes of Health (T32GM007287)

Monica C Quiñones-Frías

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

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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.