The Striated Organelle: A Molecular Motor In Vestibular Type I Hair Cells

Abstract

The striated organelle (STO) is a structure located in the subcuticular region of hair cells, consisting of alternating thick and thin bands (Friedman, 1965; Ross and Bourne, 1983). Although present in all cochlear and vestibular hair cells, the STO is particularly well-developed in type I hair cells, where it is shaped like an inverted open cone that contacts the cell membrane along its entire circumference. It is separated from the cuticular plate by a layer of mitochondria. In other hair cells, it is a much smaller structure and appears to be free-floating. We studied its structure using electron microscopic (EM) tomography in type I hair cells. In three-dimensional reconstructions, we found that it is connected to at least some actin rootlets. It may also be associated with microtubules, mitochondria and smooth endoplasmic reticulum. Confocal immunohistochemistry places yotiao (an AKAP protein) in the same area as the STO, and the actin-binding protein, alpha-fodrin (non-erythroid spectrin), where the STO contacts the cell membrane. The contact with the rootlets suggests that the STO might regulate hair-bundle stiffness. Its association with the cell membrane suggests that the STO may help in the formation of the constricted neck characteristic of type I hair cells.Supported by NIH DC-02521 and the 2008 Tallu Rosen Grant in Auditory Science from the National Organization for Hearing Research Foundation.