DESCRIPTION (from applicant's abstract): Homeostasis of inner ear endolymph is critical to sensory transduction in the inner ear. Failure to maintain endolymph homeostasis is thought to result in deafness, vestibular dysfunction and tinnitus in pathologies such as Meniere's disease or certain forms of hereditary hearing impairment. The endolymphatic duct and sac (ELDS) are key structures in maintaining this fluid homeostasis. Therefore, data on the molecular development of the ELDS are very relevant. By focusing on a mouse mutant (kreisler) with an ELDS phenotype, this application seeks to define the molecular pathways involved in induction and differentiation of the ELDS. To determine early targets of kr signaling, this application will test the hypothesis that expression of early molecular markers of the ELDS anlage is down-regulated in homozygote kr embryos at embryonic day 10-11 compared to controls. The effects of kr mutation on cellular differentiation within the developing ELDS will be studied by testing the hypothesis that expression of a battery of genes specific for cells in the embryonic day 12 to 18 ELDS is down-regulated in kreisler homozygotes compared to controls. To facilitate direct experimental manipulation of the developing ELDS, this application will develop an in vitro model of the developing kreisler otocyst and ELDS. Experiments will first test the hypothesis that cultured kreisler otocysts developmentally mimic the in vivo system morphologically and functionally. This model will then be used to test the hypothesis that virally mediated expression of kr can rescue the ELDS phenotype in vitro. To test the hypothesis that hindbrain sources of kr induce ELDS differentiation, we will culture kreisler otocysts with wild-type hindbrain explants. Such data will provide insights into the molecular pathways involved in kr signaling and in development of the ELDS. The PI's obvious commitment to medicine and science has been demonstrated by his extensive pursuit of training in the clinical and basic science facets of inner ear biology. The success of these efforts are reflected in his publications which also demonstrate his ability to accomplish quality basic science investigation. In combination with the outstanding academic environment at Children's Hospital Research Foundation, the RCA will allow the PI to continue a rigorous scientific training and successfully address the specific aims outlined in the application. The proposed program of study and the science generated will undoubtedly advance the PI toward his goals of successfully competing for a future R01, and in the long term, becoming a successful independent Clinician scientist. Significantly, this proposal includes challenging but achievable goals that will provide important knowledge to the field of inner ear development.