Alpha II‐Spectrin Interacting Partners in the Inner Ear Serve as Pointers to the Protein Composition of the Striated Organelle

Inner ear hair cells sense sound and head movements via apically‐placed stereocilia. These stereocilia are comprised of paracrystalline arrays of parallel actin filaments that pack more densely at the base to form stereociliar rootlets. The later, generally described in the literature as anchored in the cuticular plate, have been observed by our lab to extend well into the cell body where they associate with an underlying cytoskeletal structure called the striated organelle (SO). Made up of alternating thin (~10nm) and thick (~35nm) filaments, the function of this organelle remains unknown. To ascertain its function, we are attempting to determine its protein composition. So far, we have been using α‐II‐spectrin, an actin crosslinking and molecular scaffold protein, as a biological marker for the SO since we localized it there with confocal fluorescent and EM immunogold studies (Vranceanu et al., submitted). Further employing α‐II‐spectrin as bait, we pulled down interacting partners in vestibular endorgan tissue using co‐immunoprecipitation and liquid chromatography mass spectroscopy. Here we identify some of these interacting proteins and present evidence that they also localize to the SO. Based on this putative protein composition, we can now speculate as to probable function for the organelle in inner ear electro‐mechanotransduction. Grant Funding Source : American Hearing Research Foundation