title: RIM1 and RIM2 redundantly determine Ca2+ channel density and readily releasable pool size at a large hindbrain synapse.
abstract: The localization and density of voltage-gated Ca(2+) channels at active zones are essential for the amount and kinetics of transmitter release at synapses. RIM proteins are scaffolding proteins at the active zone that bind to several other presynaptic proteins, including voltage-gated Ca(2+) channel α-subunits. The long isoforms of RIM proteins, which contain NH2-terminal Rab3- and Munc13-interacting domains, as well as a central PDZ domain and two COOH-terminal C2 domains, are encoded by two genes, Rim1 and Rim2. Here, we used the ideal accessibility of the large calyx of Held synapse for direct presynaptic electrophysiology to investigate whether the two Rim genes have redundant, or separate, functions in determining the presynaptic Ca(2+) channel density, and the size of a readily releasable vesicle pool (RRP). Quantitative PCR showed that cochlear nucleus neurons, which include calyx of Held generating neurons, express both RIM1 and RIM2. Conditional genetic inactivation of RIM2 at the calyx of Held led to a subtle reduction in presynaptic Ca(2+) current density, whereas deletion of RIM1 was ineffective. The release efficiency of brief presynaptic Ca(2+) "tail" currents and the RRP were unaffected in conditional single RIM1 and RIM2 knockout (KO) mice, whereas both parameters were strongly reduced in RIM1/2 double KO mice. Thus, despite a somewhat more decisive role for RIM2 in determining presynaptic Ca(2+) channel density, RIM1 and RIM2 can overall replace each other's presynaptic functions at a large relay synapse in the hindbrain, the calyx of Held.
authors.affiliation: Laboratory of Synaptic Mechanisms, Brain-Mind Institute, School of Life Sciences, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; and.
authors.forename: Yunyun
authors.initials: Y
authors.lastname: Han
authors.affiliation: Laboratory of Synaptic Mechanisms, Brain-Mind Institute, School of Life Sciences, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; and.
authors.forename: Norbert
authors.initials: N
authors.lastname: Babai
authors.affiliation: Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California.
authors.forename: Pascal
authors.initials: P
authors.lastname: Kaeser
authors.affiliation: Department of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California.
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Südhof
authors.affiliation: Laboratory of Synaptic Mechanisms, Brain-Mind Institute, School of Life Sciences, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; and ralf.schneggenburger@epfl.ch.
authors.forename: Ralf
authors.initials: R
authors.lastname: Schneggenburger
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D017626:Cochlear Nucleus / Q000187:drug effects / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D018345:Mice, Knockout; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013572:Synaptic Vesicles / Q000187:drug effects / Q000502:physiology*; D046509:Tissue Culture Techniques; D020692:rab3 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D015220:Calcium Channels; C491490:Rims1 protein, mouse; D018698:Glutamic Acid; D019204:GTP-Binding Proteins; C475524:Rim2 protein, mouse; D020692:rab3 GTP-Binding Proteins; D002118:Calcium
keywords: active zone; auditory brainstem; calyx of Held; presynaptic proteins; protein domains; protein isoforms