Hair cells of the inner ear have the exclusive role of converting head movements and sound into electrical signals that are transmitted to the brain. How hair cells accomplish this unique function has been the focus of intense and fruitful investigation over the last quarter century. A few of the molecular players have been identified, however the identity of the transduction channel itself and much of the associated transduction complex remains elusive. The lag in molecular identification of the hair cell transduction complex is a consquence of the low number of hair cells per sensory organ (2-16 thousand) and the few tranduction molecules per cell (50-100). To circumvent these difficulties we propose a novel and compelling approach that will take advantage of the precise temporal and regional developmental pattern in the acquisition of mechanotransduction in the mouse cochlea. In the first part of this project we will determine when hair cells become mechanosensitive as a function of developmental stage and position along the cochlea and we will characterize tonotopic differences in the properties of mechanotransduction. We hypothesize that genes required for hair cell mechanosensation will be enriched around the time of transduction onset. Thus, we will analyze the spatio-temporal pattern of gene expression for various candidate molecules during the development of the Organ of Corti. Molecules with expression patterns that parallel the pattern of acquisition of mechanosensitivity will be identifed as transduction candidates. To determine the precise role of the candidate molecules we will inhibit their functional expression and use in vitro and in vivo assays for disruption of hair cell and auditory function. In particular, we will use RNA interference and dominant- negative inhibition and assay for suppression of mechanotransduction in developing hair cells. To examine gene function in vivo we will generate inducible, hair cell expression of mutant candidate genes and assay for loss of auditory function. Lay summary: This study is designed to identify the genetic basis of deafness and balance disorders. We will examine the sensory cells of the normal inner ear during development to identify when the cells begin to function and which genes are turned on. We will use several genetic tricks to block the activity of those genes and examine their effect on hearing. Loss of hearing function will confirm which genes are necessary for normal hearing and which genes may cause genetic deafness when mutated.
