title: Uncoupling the roles of synaptotagmin I during endo- and exocytosis of synaptic vesicles.
abstract: Synaptotagmin I (syt1) is required for normal rates of synaptic vesicle endo- and exocytosis. However, whether the kinetic defects observed during endocytosis in Syt1 knockout neurons are secondary to defective exocytosis or whether syt1 directly regulates the rate of vesicle retrieval remains unknown. To address this question, we sought to dissociate these two activities. We uncoupled the function of syt1 in exo- and endocytosis in mouse neurons either by re-targeting the protein or via mutagenesis of its tandem C2 domains. The effect of these manipulations on exo- and endocytosis were analyzed using electrophysiology, in conjunction with optical imaging of the vesicle cycle. Our results indicate that syt1 is directly involved in endocytosis. Notably, either of the C2 domains of syt1, C2A or C2B, was able to function as a Ca(2+) sensor for endocytosis. Thus, syt1 functions as a dual Ca(2+) sensor for both endo- and exocytosis, potentially coupling these two components of the vesicle cycle.
authors.affiliation: Howard Hughes Medical Institute and Department of Neuroscience, University of Wisconsin, Madison, Wisconsin, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Yao
authors.forename: Sung E
authors.initials: SE
authors.lastname: Kwon
authors.forename: Jon D
authors.initials: JD
authors.lastname: Gaffaney
authors.forename: F Mark
authors.initials: FM
authors.lastname: Dunning
authors.forename: Edwin R
authors.initials: ER
authors.lastname: Chapman
mesh_terms: D000200:Action Potentials / Q000235:genetics; D000818:Animals; D000831:Animals, Newborn; D001703:Biophysics; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D019439:Chromaffin Cells; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D004558:Electric Stimulation; D004705:Endocytosis / Q000235:genetics / Q000502:physiology*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000235:genetics; D005089:Exocytosis / Q000235:genetics / Q000502:physiology*; D019922:GAP-43 Protein / Q000737:chemistry / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics; D006624:Hippocampus / Q000166:cytology; D051379:Mice; D008954:Models, Biological; D016296:Mutagenesis / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000502:physiology; D018408:Patch-Clamp Techniques; D017434:Protein Structure, Tertiary / Q000235:genetics; D013569:Synapses / Q000235:genetics / Q000502:physiology*; D013572:Synaptic Vesicles / Q000235:genetics / Q000502:physiology*; D050863:Synaptotagmin I / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D019922:GAP-43 Protein; D050863:Synaptotagmin I; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D049452:Green Fluorescent Proteins; D004533:Egtazic Acid; D002118:Calcium