Roles of β-catenin in inner ear development in SD rat embryos

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In vertebrates, inner-ear development begins when surface ectoderm is induced to form the otic placodes by signals from surrounding tissues. In preliminary experiments, we observed that high levels of β-catenin appear in rat inner ears transiently corresponding to their morphogenesis. In this study, we examined the roles of β-catenin in inner ear development in rat embryos using immunostaining and antisense experiments. High levels of β-catenin appeared transiently in the optic cup during inner ear development. While β-catenin accumulation was not yet observed in the thickened surface ectoderm at the otic placode, it became to be detected at the apical surface of the otic cup. Then it disappeared from the otocyst. When embryos were treated with the β-catenin antisense oligodeoxynucleotide, accumulation of β-catenin in the otic cup was suppressed and the β-catenin protein level was significantly less in treated embryos than in controls. The number of cells in the otic cup in treated embryos was smaller than in control embryos. Cells that incorporated bromodeoxyuridine in the otic placode were fewer in number in treated embryos than in controls. In control embryos, acoustic neurons were detected by 2H3 (anti-neurofilament 165 KDa antibody) staining within the acoustic neural crest complex, while only a little staining of 2H3 was observed in the complex of the treated embryos. These results suggested that β-catenin plays a role in cell proliferation in the otic placode and in differentiation of acoustic neurons within the acoustic neural crest complex.