Identifizierung einer neuen Komponente der Stereozilien äußerer Haarzellen

OHC stereocilia are linked by horizontal top connectors (HTCs) and to the tectorial membrane (TM) by tectorial membrane attachment crowns (TM-ACs). Both protein complexes comprise the secreted proteins stereocilin, otogelin, otogelin-like and colocalize with the intracellular protein tubby. The absence of both component results in hearing loss in humans (DFNB16; DFNB18B; DFNB84B) and mice. The interaction between extracellular components and intracallular tubby remains unclear. We describe a novel transmembrane component (TM_OHC) that is indispensable for the formation of HTCs and TM-ACs. Expression, subcellular localization and distribution was determined using immunohistochemistry in whole mounts of mouse organ of Corti and confocal / STED microscopy. Scanning electron microscopy (SEM) was used to evaluate structural integrity of hair bundles. We identified an uncharacterized membrane protein (TM_OHC), which is expressed in OHCs. TM_OHC immunoreactivity was restricted to the tips of OHC stereocilia, where it closely co-localized with both tubby and stereocilin. STED microscopy revealed a ring-like distribution of both TM_OHC and tubby around the tips of the longest stereocilia. Additionally, TM_OHC labeling co-localized with tubby at the HTCs. In TM_OHC knockout mice, both stereocilin and tubby were lost from in OHC stereocilia and the tectorial membrane imprints were abolished. The structural integrity of OHC stereocilia bundles was compromised in the KO mice. We propose that TM_OHC is a novel integral component of the OHC stereocilia TM-AC and HTC complexes. Future studies will reveal the precise role of TM_OHC in structure, assembly, and maintenance of the stereociliary connectors and help to understand the mechanical framework and its role for OHC transduction.

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