Inducible Expression of Exogenous Potassium Channels in Hair Cells
The goal of this R21 research project is to develop and characterize a new mouse model that will be used to silence auditory and vestibular hair cell activity. We will generate a transgenic mouse line that allows for inducible, hair-cell expression of TREK1 potassium channels; also known as KCNK2 or K2P2.1 channels. Because TREK1 channels are open at rest and are not voltage-gated their expression will introduce an electrical shunt into the hair cell membrane which will effectively "clamp" the hair cell near the potassium equilibrium potential, about -80 mV. This simple model will render hair cells electrically silent, unable to perform voltage-dependent functions.
The mouse model will be used to investigate, in a manner not available by other techniques, a number of functions in the auditory and vestibular systems that depend on the hair cell membrane potential. We plan to use the model to examine the role of the outer hair cell membrane potential in cochlear amplification, the role of spontaneous activity in synaptogenesis at the hair cell / 8th nerve afferent junction, the role of stimulus-evoked activity in the development and maturation of the auditory and vestibular systems. We will also use this system to investigate experience-dependent plasticity in a mouse model of age- related hearing and balance dysfunction, as well as during recovery of function.
To generate our novel mouse model we will use a form of the bacterial Lac operator / repressor system that has been modified for use in mice (Cronin et al., 2001). We will introduce Lac operators into the Myosin7a promoter. The Myo7a promoter is active in hair cells throughout the animal's lifespan beginning as early as embryonic day 12 (Boeda et al., 2001). The modified Myo7a promoter will be inactive in the presence of Lac I protein. Simply by addition of the inducer, a nontoxic lactose analog, (IPTG), repression will be relieved and expression of TREK1 will commence. Therefore, using a simple chemical switch we will be able to turn on or off hair cell activity at any time point during the lifespan of the mouse. We feel this work will be important for understanding the contribution of the receptor potential to a number of critical hair-cell functions. Development of this novel inducible system will also provide a powerful tool that can be modified to control hair-cell expression for any exogenous gene of interest. As such, this new tool will allow us to address several long standing questions regarding the basic biology of auditory and vestibular function and may also be developed into novel strategies for investigating hearing and balance disorders, which collectively affect >250 million people worldwide.