Otoferlin acts as a Ca2+ sensor for vesicle fusion and vesicle pool replenishment at auditory hair cell ribbon synapses
Abstract
Hearing relies on rapid, temporally precise, and sustained neurotransmitter release at the ribbon synapses of sensory cells, the inner hair cells (IHCs). This process requires otoferlin, a six C2-domain, Ca2+-binding transmembrane protein of synaptic vesicles. To decipher the role of otoferlin in the synaptic vesicle cycle, we produced knock-in mice (OtofAla515,Ala517/Ala515,Ala517) with lower Ca2+-binding affinity of the C2C domain. The IHC ribbon synapse structure, synaptic Ca2+ currents, and otoferlin distribution were unaffected in these mutant mice, but auditory brainstem response wave-I amplitude was reduced. Lower Ca2+ sensitivity and delay of the fast and sustained components of synaptic exocytosis were revealed by membrane capacitance measurement upon modulations of intracellular Ca2+ concentration, by varying Ca2+ influx through voltage-gated Ca2+-channels or Ca2+ uncaging. Otoferlin thus functions as a Ca2+ sensor, setting the rates of primed vesicle fusion with the presynaptic plasma membrane and synaptic vesicle pool replenishment in the IHC active zone.
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Author details
Funding
Foundation Raymonde et Guy Strittmatter (Research project grant)
- Christine Petit
Foundation BNP Parisbas (Research project grant)
- Christine Petit
LHW-Stiftung (Research project grant)
- Christine Petit
LabExLifesenses (ANR‐10‐LABX‐65)
- Christine Petit
Investissements d'Avenir (ANR‐11‐IDEX‐0004‐02)
- Christine Petit
Agir pour l'Audition (Prix Emergence scientifique)
- Nicolas Antoine Michalski
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: Animal experiments were carried out in accordance with European Community Council Directive 2010/63/UE under authorizations 2012-028, 2012-038, and 2014-005 from the Institut Pasteur ethics committee for animal experimentation.
Copyright
© 2017, Michalski et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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