The Xenopus Bowline/Ripply family proteins negatively regulate the transcriptional activity of T-box transcription factors
Original Article | Published: 1 May 2009
Keisuke Hitachi1, Hiroki Danno1, Shunsuke Tazumi2, Yuko Aihara2, Hideho Uchiyama2, Koji Okabayashi3, Akiko Kondow1 and Makoto Asashima*,1,3,4
1Department of Life Sciences (Biology), Graduate School of Arts and Sciences, The University of Tokyo, Meguro-ku, Tokyo, 2International Graduate School of Arts and Sciences, Yokohama City University, Kanazawa-ku, Yokohama, 3ICORP Organ Regeneration Project, Japan Science and Technology Agency (JST), Meguro-ku, Tokyo and 4Organ Development Research Laboratory, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 4, Tsukuba, Ibaraki, Japan
Bowline, which is a member of the Xenopus Bowline/Ripply family of proteins, represses the transcription of somitogenesis-related genes before somite segmentation, which makes Bowline indispensable for somitogenesis. Although there are three bowline/Ripply family genes in each vertebrate species, it is not known whether the Bowline/Ripply family proteins share a common role in development. To elucidate their developmental roles, we examined the expression patterns and functions of the Xenopus Bowline/Ripply family proteins Bowline, Ledgerline, and a novel member of this protein family, xRipply3. We found that the expression patterns of bowline and ledgerline overlapped in the presomitic mesoderm (PSM), whereas ledgerline was additionally expressed in the newly formed somites. In addition, we isolated xRipply3, which is expressed in the pharyngeal region. Co-immunoprecipitation assays revealed that Ledgerline and xRipply3 interacted with T-box proteins and the transcriptional co-repressor Groucho/TLE. In luciferase assays, xRipply3 weakly suppressed the transcriptional activity of Tbx1, while Ledgerline strongly suppressed that of Tbx6. In line with the repressive role of Ledgerline, knockdown of Ledgerline resulted in enlargement of expression regions of the somitogenesis-related-genes mespb and Tbx6. Inhibition of histone deacetylase activity increased the expression of mespb, as seen in the Bowline and Ledgerline knockdown experiments. These results suggest that the Groucho-HDAC complex is required for the repressive activity of Bowline/Ripply family proteins during Xenopus somitogenesis. We conclude that although the Xenopus Bowline/Ripply family proteins Bowline, Ledgerline and xRipply3 are expressed differentially, they all act as negative regulators of T-box proteins.