Endophilin A and B join forces with clathrin to mediate synaptic vesicle recycling in Caenorhabditis elegans

  • Synaptic vesicle (SV) recycling enables ongoing transmitter release, even during prolonged activity. SV membrane and proteins are retrieved by ultrafast endocytosis and new SVs are formed from synaptic endosomes (large vesicles—LVs). Many proteins contribute to SV recycling, e.g., endophilin, synaptojanin, dynamin and clathrin, while the site of action of these proteins (at the plasma membrane (PM) vs. at the endosomal membrane) is only partially understood. Here, we investigated the roles of endophilin A (UNC-57), endophilin-related protein (ERP-1, homologous to human endophilin B1) and of clathrin, in SV recycling at the cholinergic neuromuscular junction (NMJ) of C. elegans. erp-1 mutants exhibited reduced transmission and a progressive reduction in optogenetically evoked muscle contraction, indicative of impaired SV recycling. This was confirmed by electrophysiology, where particularly endophilin A (UNC-57), but also endophilin B (ERP-1) mutants exhibited reduced transmission. By optogenetic and electrophysiological analysis, phenotypes in the unc-57; erp-1 double mutant are largely dominated by the unc-57 mutation, arguing for partially redundant functions of endophilins A and B, but also hinting at a back-up mechanism for neuronal endocytosis. By electron microscopy (EM), we observed that unc-57 and erp-1; unc-57 double mutants showed increased numbers of synaptic endosomes of large size, assigning a role for both proteins at the endosome, because endosomal disintegration into new SVs, but not formation of endosomes were hampered. Accordingly, only low amounts of SVs were present. Also erp-1 mutants show reduced SV numbers (but no increase in LVs), thus ERP-1 contributes to SV formation. We analyzed temperature-sensitive mutants of clathrin heavy chain (chc-1), as well as erp-1; chc-1 and unc-57; chc-1 double mutants. SV recycling phenotypes were obvious from optogenetic stimulation experiments. By EM, chc-1 mutants showed formation of numerous and large endosomes, arguing that clathrin, as shown for mammalian synapses, acts at the endosome in formation of new SVs. Without endophilins, clathrin formed endosomes at the PM, while endophilins A and B compensated for the loss of clathrin at the PM, under conditions of high SV turnover.

Download full text files

Export metadata

Author:Szi-chieh Yu, Barbara Jánosi, Jana F. LiewaldORCiDGND, Sebastian Wabnig, Alexander GottschalkORCiDGND
Pubmed Id:https://pubmed.ncbi.nlm.nih.gov/29962934
Parent Title (English):Frontiers in molecular neuroscience
Publisher:Frontiers Research Foundation
Place of publication:Lausanne
Contributor(s):Shigeki Watanabe
Document Type:Article
Year of Completion:2018
Date of first Publication:2018/06/14
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2018/08/16
Tag:clathrin heavy chains; electron microscopy; electrophysiology; endophilin; genetic analysis; optogenetic stimulation; recycling pathway; synaptic vesicles
Issue:Art. 196
Page Number:17
First Page:1
Last Page:17
Copyright © 2018 Yu, Jánosi, Liewald, Wabnig and Gottschalk. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Institutes:Biochemie, Chemie und Pharmazie / Biochemie und Chemie
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 54 Chemie / 540 Chemie und zugeordnete Wissenschaften
5 Naturwissenschaften und Mathematik / 59 Tiere (Zoologie) / 590 Tiere (Zoologie)
Open-Access-Publikationsfonds:Biochemie, Chemie und Pharmazie
Licence (German):License LogoCreative Commons - Namensnennung 4.0