title: Doc2 supports spontaneous synaptic transmission by a Ca(2+)-independent mechanism.
abstract: Two families of Ca(2+)-binding proteins have been proposed as Ca(2+) sensors for spontaneous release: synaptotagmins and Doc2s, with the intriguing possibility that Doc2s may represent high-affinity Ca(2+) sensors that are activated by deletion of synaptotagmins, thereby accounting for the increased spontaneous release in synaptotagmin-deficient synapses. Here, we use an shRNA-dependent quadruple knockdown of all four Ca(2+)-binding proteins of the Doc2 family to confirm that Doc2-deficient synapses exhibit a marked decrease in the frequency of spontaneous release events. Knockdown of Doc2s in synaptotagmin-1-deficient synapses, however, failed to reduce either the increased spontaneous release or the decreased evoked release of these synapses, suggesting that Doc2s do not constitute Ca(2+) sensors for asynchronous release. Moreover, rescue experiments revealed that the decrease in spontaneous release induced by the Doc2 knockdown in wild-type synapses is fully reversed by mutant Doc2B lacking Ca(2+)-binding sites. Thus, our data suggest that Doc2s are modulators of spontaneous synaptic transmission that act by a Ca(2+)-independent mechanism.
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University, 265 Campus Drive, Stanford, CA 94305-5453, USA.
authors.forename: Zhiping P
authors.initials: ZP
authors.lastname: Pang
authors.forename: Taulant
authors.initials: T
authors.lastname: Bacaj
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Yang
authors.forename: Peng
authors.initials: P
authors.lastname: Zhou
authors.forename: Wei
authors.initials: W
authors.lastname: Xu
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Südhof
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001703:Biophysics; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D006801:Humans; D008565:Membrane Proteins / Q000172:deficiency; D051379:Mice; D018345:Mice, Knockout; D016297:Mutagenesis, Site-Directed / Q000379:methods; D009154:Mutation / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques / Q000379:methods; D034622:RNA Interference / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D014162:Transfection; D033921:Vesicular Transport Proteins
chemical_list: D002135:Calcium-Binding Proteins; C490421:Doc2b protein, mouse; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C424133:Sytl1 protein, mouse; D033921:Vesicular Transport Proteins; C519993:rabphilin protein, mouse; D002118:Calcium