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Elife. 2017 Nov 7;6. pii: e31013. doi: 10.7554/eLife.31013.

Otoferlin acts as a Ca2+ sensor for vesicle fusion and vesicle pool replenishment at auditory hair cell ribbon synapses.

Michalski N1,2,3, Goutman JD4, Auclair SM5, Boutet de Monvel J1,2,3, Tertrais M2,6, Emptoz A1,2,3, Parrin A1,2,3, Nouaille S1,2,3, Guillon M7, Sachse M8, Ciric D1,2,3, Bahloul A1,2,3,9, Hardelin JP1,2,3, Sutton RB10,11, Avan P12,13,14, Krishnakumar SS5,15, Rothman JE5,15, Dulon D#2,6, Safieddine S#1,2,3,9, Petit C#1,2,3,16,17.

Author information

1
Unité de Génétique et Physiologie de l'Audition, Institut Pasteur, Paris, France.
2
UMRS 1120, Institut National de la Santé et de la Recherche Médicale, Paris, France.
3
Sorbonne Universités, UPMC Université Paris 06, Complexité du Vivant, Paris, France.
4
Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina.
5
Department of Cell Biology, Yale University School of Medicine, New Haven, United States.
6
Laboratoire de Neurophysiologie de la Synapse Auditive, Bordeaux Neurocampus, Université de Bordeaux, Bordeaux, France.
7
Wave Front Engineering Microscopy Group, Neurophotonics Laboratory, Centre National de la Recherche Scientifique, UMR 8250, University Paris Descartes, Sorbonne Paris Cité, Paris, France.
8
Center for Innovation & Technological Research, Ultrapole, Institut Pasteur, Paris, France.
9
Centre National de la Recherche Scientifique, France.
10
Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, United States.
11
Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, United States.
12
Laboratoire de Biophysique Sensorielle, Université Clermont Auvergne, Clermont-Ferrand, France.
13
UMR 1107, Institut National de la Santé et de la Recherche Médicale, Clermont-Ferrand, France.
14
Centre Jean Perrin, Clermont-Ferrand, France.
15
Department of Clinical and Experimental Epilepsy, Institute of Neurology, University College London, London, United Kingdom.
16
Syndrome de Usher et Autres Atteintes Rétino-Cochléaires, Institut de la Vision, Paris, France.
17
Collège de France, Paris, France.
#
Contributed equally

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.

KEYWORDS:

deafness; inner hair cell; mouse; neuroscience; neurotransmitter release; synaptic exocytotic machinery; synaptopathy; temporal precision

PMID:
29111973
PMCID:
PMC5700815
DOI:
10.7554/eLife.31013
[Indexed for MEDLINE]
Free PMC Article

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