Variable Priming of a Docked Synaptic Vesicle PNAS PLUS
Variable priming of a docked synaptic vesicle PNAS PLUS Jae Hoon Junga,b,c, Joseph A. Szulea,c, Robert M. Marshalla,c, and Uel J. McMahana,c,1 aDepartment of Neurobiology, Stanford University School of Medicine, Stanford, CA 94305; bDepartment of Physics, Stanford University School of Humanities and Sciences, Stanford, CA 94305; and cDepartment of Biology, Texas A&M University, College Station, TX 77845 Edited by Thomas S. Reese, National Institutes of Health, Bethesda, MD, and approved January 12, 2016 (received for review November 30, 2015) The priming of a docked synaptic vesicle determines the proba- transition. Biochemical and electrophysiological approaches have bility of its membrane (VM) fusing with the presynaptic membrane provided evidence that priming is mediated by interactions be- (PM) when a nerve impulse arrives. To gain insight into the nature tween the SNARE proteins and their regulators (7, 12–14, 24) and of priming, we searched by electron tomography for structural can involve differences in positioning of docked SVs relative to + relationships correlated with fusion probability at active zones of Ca2 channels (25). Biochemistry has also led to the suggestion axon terminals at frog neuromuscular junctions. For terminals that primed SVs may become deprimed (26). fixed at rest, the contact area between the VM of docked vesicles We have previously shown by electron tomography on frog and PM varied >10-fold with a normal distribution. There was no neuromuscular junctions (NMJs) fixed at rest that there are, for merging of the membranes. For terminals fixed during repetitive docked SVs, variations in the extent of the VM–PM contact area evoked synaptic transmission, the normal distribution of contact and in the length of the several AZM macromolecules linking areas was shifted to the left, due in part to a decreased number of the VM to the PM, the so-called ribs, pegs, and pins (2, 27).
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