We propose to employ the cre/loxP recombination system to induce a tissue-specific mutation in the Bone Morphogenetic Protein Receptor-1A (Bmpr) during mouse otic vesicle development. Previous work by others has demonstrated that the Hmx3 gene is expressed early in the development of the otic vesicle. We propose to harness the transcriptional regulatory regions of the Hmx3 gene to induce conditional mutations in the Bmpr gene in vivo during inner ear ontogeny. The methodology developed in this proposal will be generally applicable to the analysis of any gene hypothesized to regulate otic vesicle development or function. Undoubtedly, many genes that play important roles in other organ systems and in early embryogenesis will be utilized to regulate inner ear development or function. The traditional knockout of genes for widely-expressed signaling molecules, such as the Bmpr, often leads to early embryonic death. The otic vesicle-specific Hmx3/cre "mutator" pedigree developed in this proposal will make it feasible to induce conditional mutations in any gene of interest specifically in the octic vesicle. Therefore, this pedigree can be utilized by the whole community of scientists studying inner ear development and function to mutagenize in any gene of interest. The specific aim of this proposal is: To induce an otic vesicle-specific mutation in the Bmpr gene to examine its role during sensory epithelial formation. Based on hybridization histochemical analyses, it has been hyposthesized that BMPs play a critical role in the induction of sensory epithelial of the inner ear. We propose to genetically test the hypothesis that the inductive signal for sensory epithelial formation is mediated by Bmpr, the most widely expressed type I receptor for BMPs. Conditional mutation of the floxed Bmpr allele will be accomplished by generating a pedigree of mice that direct expression of cre recombinase to the otic vesicle. This pedigree will be generated by introducing the cre recombinase gene into the locus of an inner-ear specific homeobox gene, Hmx3.