title: Synaptotagmin-1 and -7 Are Redundantly Essential for Maintaining the Capacity of the Readily-Releasable Pool of Synaptic Vesicles.
abstract: In forebrain neurons, Ca(2+) triggers exocytosis of readily releasable vesicles by binding to synaptotagmin-1 and -7, thereby inducing fast and slow vesicle exocytosis, respectively. Loss-of-function of synaptotagmin-1 or -7 selectively impairs the fast and slow phase of release, respectively, but does not change the size of the readily-releasable pool (RRP) of vesicles as measured by stimulation of release with hypertonic sucrose, or alter the rate of vesicle priming into the RRP. Here we show, however, that simultaneous loss-of-function of both synaptotagmin-1 and -7 dramatically decreased the capacity of the RRP, again without altering the rate of vesicle priming into the RRP. Either synaptotagmin-1 or -7 was sufficient to rescue the RRP size in neurons lacking both synaptotagmin-1 and -7. Although maintenance of RRP size was Ca(2+)-independent, mutations in Ca(2+)-binding sequences of synaptotagmin-1 or synaptotagmin-7--which are contained in flexible top-loop sequences of their C2 domains--blocked the ability of these synaptotagmins to maintain the RRP size. Both synaptotagmins bound to SNARE complexes; SNARE complex binding was reduced by the top-loop mutations that impaired RRP maintenance. Thus, synaptotagmin-1 and -7 perform redundant functions in maintaining the capacity of the RRP in addition to nonredundant functions in the Ca(2+) triggering of different phases of release.
authors.affiliation: Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University, Stanford, California, United States of America.
authors.forename: Taulant
authors.initials: T
authors.lastname: Bacaj
authors.affiliation: Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University, Stanford, California, United States of America; Nancy Pritzker Laboratory, Department of Psychiatry and Behavioral Sciences, Stanford University Medical School, Stanford, California, United States of America.
authors.forename: Dick
authors.initials: D
authors.lastname: Wu
authors.affiliation: Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University, Stanford, California, United States of America.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Burré
authors.affiliation: Nancy Pritzker Laboratory, Department of Psychiatry and Behavioral Sciences, Stanford University Medical School, Stanford, California, United States of America.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Malenka
authors.affiliation: Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut, United States of America.
authors.forename: Xinran
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University, Stanford, California, United States of America.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Südhof
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001665:Binding Sites; D020013:Calcium Signaling; D002478:Cells, Cultured; D019706:Excitatory Postsynaptic Potentials; D057809:HEK293 Cells; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D053444:Inhibitory Postsynaptic Potentials; D018345:Mice, Knockout; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D034622:RNA Interference; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D050600:SNARE Proteins / Q000378:metabolism; D013572:Synaptic Vesicles / Q000378:metabolism* / Q000648:ultrastructure; D050863:Synaptotagmin I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050857:Synaptotagmins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D009419:Nerve Tissue Proteins; D011994:Recombinant Proteins; D050600:SNARE Proteins; D050863:Synaptotagmin I; C494311:Syt1 protein, mouse; C494303:Syt7 protein, mouse; D050857:Synaptotagmins