title: The Munc13 proteins differentially regulate readily releasable pool dynamics and calcium-dependent recovery at a central synapse.
abstract: The Munc13 gene family encodes molecules located at the synaptic active zone that regulate the reliability of synapses to encode information over a wide range of frequencies in response to action potentials. In the CNS, proteins of the Munc13 family are critical in regulating neurotransmitter release and synaptic plasticity. Although Munc13-1 is essential for synaptic transmission, it is paradoxical that Munc13-2 and Munc13-3 are functionally dispensable at some synapses, although their loss in other synapses leads to increases in frequency-dependent facilitation. We addressed this issue at the calyx of Held synapse, a giant glutamatergic synapse that we found to express all these Munc13 isoforms. We studied their roles in the regulation of synaptic transmission and their impact on the reliability of information transfer. Through detailed electrophysiological analyses of Munc13-2, Munc13-3, and Munc13-2-3 knock-out and wild-type mice, we report that the combined loss of Munc13-2 and Munc13-3 led to an increase in the rate of calcium-dependent recovery and a change in kinetics of release of the readily releasable pool. Furthermore, viral-mediated overexpression of a dominant-negative form of Munc13-1 at the calyx demonstrated that these effects are Munc13-1 dependent. Quantitative immunohistochemistry using Munc13-fluorescent protein knock-in mice revealed that Munc13-1 is the most highly expressed Munc13 isoform at the calyx and the only one highly colocalized with Bassoon at the active zone. Based on these data, we conclude that Munc13-2 and Munc13-3 isoforms limit the ability of Munc13-1 to regulate calcium-dependent replenishment of readily releasable pool and slow pool to fast pool conversion in central synapses.
authors: School of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China.
authors: Zuxin
authors: Z
authors: Chen
authors: Benjamin
authors: B
authors: Cooper
authors: Stefan
authors: S
authors: Kalla
authors: Frederique
authors: F
authors: Varoqueaux
authors: Samuel M
authors: SM
authors: Young
mesh_terms: D000367:Age Factors; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001933:Brain Stem / Q000166:cytology; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000235:genetics; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins / Q000172:deficiency / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D018408:Patch-Clamp Techniques; D013569:Synapses / Q000235:genetics / Q000502:physiology*; D009435:Synaptic Transmission / Q000235:genetics / Q000502:physiology; D050598:Vesicular Glutamate Transport Protein 1 / Q000378:metabolism
chemical_list: C498441:Bsn protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D009419:Nerve Tissue Proteins; C493465:Slc17a7 protein, mouse; C503321:Unc13a protein, mouse; C485549:Unc13b protein, mouse; C485550:Unc13c protein, mouse; D050598:Vesicular Glutamate Transport Protein 1; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D002118:Calcium
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