03-P077 Cytoskeletal reorganisation at the edge of the eye field is required for early stages of eye morphogenesis

We are using zebrafish as a model system for human deafness and vestibular disorders. big ears (bge) is an adult viable zebrafish mutation isolated in a large-scale mutagenesis screen. The lauscher (lau) mutant is allelic to bge by complementation assay. The inner ears of these mutants become swollen at the end of the third day of embryogenesis. Epithelial projections forming the semicircular canal system show morphological and gene expression abnormalities and fail to fuse correctly. Preliminary data suggest that the swelling is a secondary result of the failure of the projections to fuse in the mutant. We have identified the bge gene by genetic mapping and a candidate gene approach. Orthologous genes have been cloned in the human and mouse, but their function is still unknown. Expression of bge appears to be ear-specific, and is restricted to the epithelial projections of the developing semicircular canal system. Point mutations were found in cDNA and genomic DNA for bge and lau, and have been confirmed by PCR-based genotyping assays. Both are missense mutations that predict the substitution of conserved amino acid residues in the protein. A splice site morpholino designed to knock down function of the bge gene phenocopies the semicircular canal projection defects seen in the mutant.