SHARPENED COCHLEAR TUNING IN A MOUSE WITH A GENETICALLY MODIFIED TECTORIAL MEMBRANE

Frequency tuning in the cochlea is determined by the passive mechanical properties of the basilar membrane and active feedback from the outer hair cells, sensory-effector cells that detect and amplify sound-induced basilar membrane motions. The sensory hair bundles of the outer hair cells are imbedded in the tectorial membrane, a sheet of extracellular matrix that overlies the cochlea’s sensory epithelium. The tectorial membrane contains radially-organised collagen fibrils imbedded in an unusual, striated-sheet matrix formed by two glycoproteins, Tecta and Tectb. In Tectb(−/−) mice the structure of the striated-sheet matrix is disrupted. Although these mice have a low-frequency hearing loss, basilar membrane and neural tuning are both significantly enhanced in the high-frequency regions of the cochlea, with little loss in sensitivity. These findings can be attributed to a reduction in the acting mass of the tectorial membrane, and reveal a novel role for this structure in controlling interaction along the cochlea.