Characterization of the mechanotransduction complex in hair cells

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 DESCRIPTION (provided by applicant): Mutations in Protocadherin 15 (PCDH15) cause deafness in fish, mice, and humans. As a central and conserved component of the mechanotransduction complex in sensory hair cells, this unusual cadherin forms part of the extracellular filaments at the tips of stereocilia. These so-called `tip links' are thought to gate mechanically sensitive channels. To gain a better understanding of how PCDH15 is coupled to the mechanotransduction machinery, we performed an unbiased molecular screen using zebrafish Pcdh15a as bait in a membrane-based yeast two-hybrid screen. We identified a positive interaction with Tmc2a, an orthologue of mammalian TMC2. Tmc2 was recently implicated in deafness and vestibular dysfunction in mice, and its closely related gene, Tmc1, is associated with both recessive and dominant forms of hearing loss in mice and humans (DFNA36 and DFNB7/11). Our preliminary results recapitulate the protein interactions found in the screen among both the zebrafish and mouse TMC and PCDH15 orthologues. In addition, we have discovered both loss-of-function and gain-of-function effects on hair-cell mechanosensitivity upon overexpression of fragments of Tmc2a in wild-type fish. Together, the link to Pcdh15 and the dominant negative or activating effects in hair cells provide compelling evidence that Tmc1/2 proteins are central players of the mechanotransduction complex in hair cells. We will characterize the interaction of Pcdh15 with Tmc1/2 proteins with genetic and biochemical methods, and study structure/function aspects of the complex in vivo. This work will increase our knowledge of the molecular basis of mechanotransduction and the understanding of how lesion of Tmc1 leads to hearing loss.