The early development of the inner ear occurs in three phases: formation of the otic placode; morphogenesis of the otic placode to form the otocyst; and regional patterning of the otocyst. Each phase is characterized by inductive interactions among different tissues. Although several signaling systems have been implicated in the control of the phases, the FGF signaling system clearly plays a critical role and is a focus of this proposal. This project combines the broad technical and scientific expertise of two investigators and use two animal models to examine the cellular, molecular and genetic control of early inner ear development. In aim 1, three sets of experiments will be conducted on the early rudiments of the inner ear to elucidate the cellular plays involved in their development, and the interactions that are required as well as sufficient for their induction, morphogenesis and early patterning. In aim 2, three sets of experiments will be conducted to characterize the roles of FGF signaling in these central events of inner ear development. Collectively, these studies will provide important new information on the normal development of the inner ear and the cellular and molecular factors that regulate this process. Additionally, the results will furnish insight into mechanisms by which development goes awry, causing serious birth defects of the auditory system in humans.