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

JUAN D. GOUTMAN; MARGOT TERTRAIS; SYLVIE NOUAILLE; DANICA CIRIC; R. BRYAN SUTTON; NICOLAS MICHALSKI; JAMES E. ROTHMAN; JACQUES BOUTET DE MONVEL; CHRISTINE PETIT; ALEXANDRE PARRIN; MARTIN SACHSE; JEAN-PIERRE HARDELIN; SHYAM S. KRISHNAKUMAR; SAAID SAFIEDDINE; SARAH M. AUCLAIR; ALICE EMPTOZ; MARC GUILLON; AMEL BAHLOUL; PAUL AVAN; DIDIER DULON

eLife

eLife

Año: 2017

Hearing relies on rapid, temporally precise, and sustained neurotransmitter release at the ribbon synapses of inner hair cells. Otoferlin, a six C2-domain Ca2+-binding protein, is required for inner hair cell synaptic exocytosis, but its role in the synaptic vesicle cycle is unclear. We produced knock-in mice carrying mutations affecting Ca2+-binding affinity of the otoferlin C2C domain. These mice had preserved ribbon synapse structure, synaptic Ca2+ currents, and otoferlin distribution, but the amplitude of the auditory brainstem response wave-I was reduced. Modulation of intracellular Ca2+ concentrations, either by varying Ca2+ influx through voltage-gated Ca2+-channels or by Ca2+ uncaging, showed reduced Ca2+-sensitivity and delayed response of the fast and sustained components of synaptic exocytosis, monitored by capacitance measurement. Otoferlin thus functions as a Ca2+-sensor setting the rates of both the fusion of primed vesicles with the presynaptic plasma membrane and the synaptic vesicle pool replenishment at the inner hair cell active zone.