AUTHOR=Chen Han , Fang Qinghua , Benseler Fritz , Brose Nils , Moser Tobias 

TITLE=Probing the role of the C2F domain of otoferlin

JOURNAL=Frontiers in Molecular Neuroscience

VOLUME=Volume 16 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/molecular-neuroscience/articles/10.3389/fnmol.2023.1299509

DOI=10.3389/fnmol.2023.1299509

ISSN=1662-5099

ABSTRACT=Afferent synapses of cochlear inner hair cells (IHCs) employ a unique molecular machinery. Otoferlin is a key player of this machinery and its genetic defects cause human auditory synaptopathy. We employed site-directed mutagenesis in mice to investigate the role of Ca 2+ binding to the C2F-domain of otoferlin. Substituting two aspartate residues of the C2F top loops, which are thought to coordinate Ca 2+ -ions, by alanines (Otof D1841/1842A ) abolished Ca 2+ -influx-triggered IHC exocytosis and synchronous signaling in the auditory pathway despite substantial expression (~60%) of the mutant otoferlin in the basolateral IHC pole. Ca 2+ influx of IHCs and their resting membrane capacitance, reflecting IHC size, as well as the number of IHC synapses were maintained. The mutant otoferlin showed a strong apex to base abundance gradient in IHCs, suggesting impaired protein targeting. Our results indicate a role of the C2F-domain in otoferlin targeting and of Ca 2+ binding by the C2F domain for IHC exocytosis and hearing.