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=16

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=<p>Afferent synapses of cochlear inner hair cells (IHCs) employ a unique molecular machinery. Otoferlin is a key player in this machinery, and its genetic defects cause human auditory synaptopathy. We employed site-directed mutagenesis in mice to investigate the role of Ca<sup>2+</sup> binding to the C<sub>2</sub>F domain of otoferlin. Substituting two aspartate residues of the C<sub>2</sub>F top loops, which are thought to coordinate Ca<sup>2+</sup>-ions, by alanines (<italic>Otof<sup>D1841/1842A</sup></italic>) abolished Ca<sup>2+</sup>-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<sup>2+</sup> 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 C<sub>2</sub>F domain in otoferlin targeting and of Ca<sup>2+</sup> binding by the C<sub>2</sub>F domain for IHC exocytosis and hearing.</p>