Imaging data for "Beyond the MUN domain, Munc13 controls priming and depriming of synaptic vesicles"

Synaptic vesicle docking and priming are dynamic processes. At the molecular level, SNAREs, synaptotagmins, Munc18, Munc13, and other factors are critical for Ca2+-triggered synaptic vesicle fusion with the plasma membrane, while disassembly factors, including the AAA+ ATPase N-ethylmalemide sensitive factor (NSF) and -SNAP disassemble and recycle SNAREs, but also antagonize fusion under some conditions. Here, we isolated synaptic vesicles from mouse brains and combined them with synthetic plasma membrane-mimicking vesicles in a new hybrid fusion assay. We included Munc18, Munc13, complexin, NSF, α-SNAP, and an ATP regeneration system and maintained their continuous presence—as in the neuron—to investigate how these opposing processes yield fusogenic synaptic vesicles. In this setting, synaptic vesicle association is reversible, and the ATP-regeneration system produces the most synchronous Ca2+-triggered fusion, suggesting that disassembly factors perform quality control at the early stages of synaptic vesicle association and establish a highly fusogenic state of the system. We uncovered a new functional role for Munc13 ancillary to the MUN domain that alleviates an α-SNAP-dependent inhibition of Ca2+-triggered fusion.