Biophysical Society Conference | Estes Park 2023

Membrane Fusion and Budding

Sunday Speaker Abstracts

REVISITING ELECTRON MICROSCOPY’S “GOLDEN DECADE” OF IMAGING SYNAPTIC VESICLE DYNAMICS: THE 1970’S John Heuser 1 ; 1 Washington University in St. Louis, St. Louis, MO, USA No Abstract

SYNAPTOTAGMIN 7 DOCKS SYNAPTIC VESICLES FOR DOC2Α -TRIGGERED ASYNCHRONOUS NEUROTRANSMITTER RELEASE Edwin R. Chapman 1 ; Zhenyong Wu 2 ; Grant F. Kusick 3 ; Shigeki Watanabe 3 ; 1 HHMI & University of Wisconsin-Madison, Neuroscience, Madison, WI, USA 2 Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China 3 Johns Hopkins University, School of Medicine, Baltimore, MD, USA The molecular basis of asynchronous neurotransmitter release remains enigmatic despite decades of intense study. Synaptotagmin (syt) 7 and Doc2 have both been proposed as Ca 2+ sensors that trigger this mode of exocytosis, but conflicting findings have led to controversy. Here, we demonstrate that at excitatory mouse hippocampal synapses from cultured neurons and acute slices, Doc2α is the major Ca 2+ sensor for asynchronous release, while syt7 supports this process through activity-dependent docking of synap tic vesicles. In synapses lacking Doc2α, asynchronous release after single action potentials is strongly reduced, while deleting syt7 has no effect. However, in the absence of syt7, docked vesicles cannot recover on millisecond timescales. Consequently, both synchronous and asynchronous release depress from the second pulse on during repetitive activity. By contrast, synapses lacking Doc2α have normal activity dependent docking, but continue to exhibit decreased asynchronous release after multiple stimuli. Moreover, disruption of both Ca 2+ sensors is non-additive. These findings result in a new model whereby syt7 drives activity-dependent docking, thus ‘feeding’ synaptic vesicles to Doc2 for asynchronous release during ongoing transmission.

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