Roles of beta-catenin in somitogenesis in rat embryos.

We studied the roles of beta-catenin in somitogenesis using immunostaining and antisense experiments in rat embryos. High levels of beta-catenin appeared transiently in the developing rat somites. Initially, beta-catenin accumulation was observed in the core cells of presomitic cell aggregates and then in the lumen of epithelial vesicles. Subsequently, it was confined to the dermomyotomes and their lumen and then the myotomes. High levels of cyclin D1 were observed in the core cells, in the lumen of epithelial vesicles, in myotomes, and in mesenchymal sclerotomes. When embryos were cultured in medium supplemented with beta-catenin antisense oligodeoxynucleotide (ODN), the accumulation of beta-catenin, but not of cyclin D1, in the nascent somites and dermomyotomes was suppressed, while the number of somites was the same as that observed in control embryos. The number of myosin-positive somites and the amount of myosin per somite in embryos treated with the antisense ODN were lower than those in controls. These results suggested that beta-catenin promotes development of myotomal cells during somitogenesis. The function of beta-catenin in the development of myotomes may not be correlated to cyclin D1.