Calcium-Independent Exo-endocytosis Coupling at Small Central Synapses

Marta Orlando,Dietmar Schmitz,Christian Rosenmund,Melissa A Herman

doi:10.1016/j.celrep.2019.11.060

Abstract

At presynaptic terminals, neurotransmitters are released by synaptic vesicle exocytosis at the active zone. In order to maintain efficient neurotransmission and proper synaptic structure, sites of vesicle fusion must be cleared rapidly by endocytosis. Therefore, the coupling of exo- and endocytosis is crucial. Despite many years of research, the exact molecular and biophysical requirements for the coupling of exo- and endocytosis remain unclear. We investigate whether endocytosis can be triggered in a calcium-independent fashion by evoking calcium-independent exocytosis using a hypertonic sucrose solution. We demonstrate that endocytosis can be triggered, in the absence of calcium influx, in a clathrin-independent manner that relies on actin polymerization. Our findings point to a central role of membrane tension dependent on actin for efficient coupling of exo- and endocytosis.

Highlights

At chemical synapses, a presynaptic electrical signal is converted into a chemical secretory response through the fusion of neurotransmitter-filled synaptic vesicles (SVs) with the plasma membrane
We investigate whether endocytosis can be triggered in a calcium-independent fashion by evoking calcium-independent exocytosis using a hypertonic sucrose solution
We demonstrate that endocytosis can be triggered, in the absence of calcium influx, in a clathrin-independent manner that relies on actin polymerization

Summary

Introduction

A presynaptic electrical signal is converted into a chemical secretory response through the fusion of neurotransmitter-filled synaptic vesicles (SVs) with the plasma membrane. After spontaneous and evoked SV fusion, membranes and proteins are recycled by endocytosis, a process that retrieves vesicular components from the plasma membrane (Sudhof, 2004). A triskelion vesicle coat protein, has long been proposed to be a fundamental component of the retrieval of SV components from the plasma membrane (Royle and Lagnado, 2010; Saheki and De Camilli, 2012); recent findings suggest that the reuptake pathway for SV material after evoked fusion is clathrin independent (Soykan et al, 2017; Watanabe et al, 2014; Wu et al, 2014c). Clathrin is proposed to be required for SV reformation from endosomal structures (Kononenko and Haucke, 2015; Watanabe et al, 2014)

Results

Discussion

Conclusion