Ledgerline, a novel Xenopus laevis gene, regulates differentiation of presomitic mesoderm during somitogenesis

Segmentation of the vertebrate body via the sequential formation of somites is an important process in embryogenesis. This sequential process is governed by the activation and regulation of Notch-related molecular oscillators by fibroblast growth factor and retinoic acid (RA) signaling. In this study, we identified ledgerfine, a novel gene of Xenopus laevis expressed specifically in the presomitic mesoderm. Knockdown of ledgerfine using antisense morpholino oligonucleotides shifted the developing somite front and altered the expression of genes that regulate molecular oscillation, including Delta2, ESR5, Hairy2a, and Thylacinel. Knockdown of ledgerline also downregulated RALDH-2 expression. Injection of RAR alpha-CA, a constitutively active mutant of the RA receptor RARa, subsequently reduced the altered Thylacinel expression. These results strongly suggest that ledgerfine is essential for mesodermal RA activity and differentiation of the presomitic mesoderm during Xenopus somitogenesis.