RT Journal Article
SR Electronic
T1 TRIM67 Regulates Exocytic Mode and Neuronal Morphogenesis via SNAP47
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2020.02.01.930404
DO 10.1101/2020.02.01.930404
A1 Fabio L. Urbina
A1 Shalini Menon
A1 Dennis Goldfarb
A1 M. Ben Major
A1 Patrick Brennwald
A1 Stephanie L. Gupton
YR 2020
UL http://biorxiv.org/content/early/2020/02/02/2020.02.01.930404.abstract
AB Morphogenesis in developing neurons involves dramatic plasma membrane expansion, which classic hypotheses suggest is fueled by SNARE-mediated exocytosis. Distinct modes of fusion have been described; during full vesicle fusion (FVF) the entirety of vesicle contents are secreted and the vesicle membrane incorporates into the plasma membrane. In contrast, a transient fusion pore secretes lumenal cargo, but closes without membrane addition in kiss and run fusion (KNR). If exocytosis provides material for neuronal morphogenesis, this would suggest FVF predominates, although this has not been examined. Fortuitously in developing neurons, exocytic events are spatially and temporally discrete, unlike exocytic events at the neuronal synapse, allowing resolution of single vesicle fusion events although they are diffraction-limited. Here, we resolve individual exocytic events in developing murine cortical neurons, and use a newly developed classification tool to differentiate and quantify different modes of fusion. We identify four distinct modes of fusion: two FVF-like modes that insert membrane material and two KNR-like modes that do not. Within the FVF-like and KNR-like modes, discrete fluorescence profiles suggest distinct behavior of the fusion pore. Consistent with our hypothesis, FVF-like exocytosis predominates. Simulations and experimental manipulations agree that exocytosis provides sufficient amounts of membrane material for neuronal morphogenesis. Mechanistically we identify that the E3 ubiquitin ligase TRIM67 promotes FVF-like exocytosis by limiting incorporation of the Qb/Qc SNARE SNAP47 into SNARE complexes and thus, SNAP47 involvement in exocytosis. Our data suggest that SNAP47 regulates behavior of the fusion pore between the vesicle and plasma membrane, temporarily arresting the pore in an open state.