PROJECT SUMMARY Within the stereocilia of hair cells of the inner ear, a variety of molecules including proteins and lipids assemble into a mechanotransduction (MET) complex. This complex converts mechanical stimuli from sound waves into electrical signals that can then be propagated through the auditory pathway. Although many protein elements of the MET complex have been discovered, the lipid elements of this complex are poorly defined. Here, I propose to elucidate the molecular function of PIP2 in hair cell mechanotransduction. PIP2 has been shown to bind to TMIE, an essential subunit of the MET complex of cochlear hair cells that binds to TMC1, the likely pore-forming subunit of the MET channel. In addition, pharmacological depletion of PIP2 in hair cells decreases MET suggesting that the binding of PIP2 to TMIE affects MET channel function. To test this model and to define the mechanisms by which PIP2 affects MET in cochlear hair cells, I propose to combine biochemistry and electrophysiology in order to elucidate how TMIE mutations that perturb PIP2 binding affect MET. I anticipate that my studies will provide insights into the molecular mechanisms by which a phospholipid that is implicated in the regulation of the function of many ion channels contributes to the regulation of the mechanotransduction process in hair cells.