XB-ART-4578Dev Biol October 15, 2003; 262 (2): 206-24.
Cardiac T-box factor Tbx20 directly interacts with Nkx2-5, GATA4, and GATA5 in regulation of gene expression in the developing heart.
Tbx20 is a member of the T-box transcription factor family expressed in the forming hearts of vertebrate and invertebrate embryos. We report here analysis of Tbx20 expression during murine cardiac development and assessment of DNA-binding and transcriptional properties of Tbx20 isoforms. Tbx20 was expressed in myocardium and endocardium, including high levels in endocardial cushions. cDNAs generated by alternative splicing encode at least four Tbx20 isoforms, and Tbx20a uniquely carried strong transactivation and transrepression domains in its C terminus. Isoforms with an intact T-box bound specifically to DNA sites resembling the consensus brachyury half site, although with less avidity compared with the related factor, Tbx5. Tbx20 physically interacted with cardiac transcription factors Nkx2-5, GATA4, and GATA5, collaborating to synergistically activate cardiac gene expression. Among cardiac GATA factors, there was preferential synergy with GATA5, implicated in endocardial differentiation. In Xenopus embryos, enforced expression of Tbx20a, but not Tbx20b, led to induction of mesodermal and endodermal lineage markers as well as cell migration, indicating that the long Tbx20a isoform uniquely bears functional domains that can alter gene expression and developmental behaviour in an in vivo context. We propose that Tbx20 plays an integrated role in the ancient myogenic program of the heart, and has been additionally coopted during evolution of vertebrates for endocardial cushion development.
PubMed ID: 14550786
Article link: Dev Biol
Grant support: HD042572-01 NICHD NIH HHS , R01 HD042572 NICHD NIH HHS
Genes referenced: gata4 gata5 nkx2-5 tbx20 tbx5 tbxt
Article Images: [+] show captions
|Fig. 10. Overexpression of Tbx20 in early Xenopus embryos. Tailbud embryos following radial (A) or ventral (B) injection with the following synthetic mRNAs; (A, B) HA-Tbx20a mRNA (500 pg) with LacZ mRNA (200 pg); (C) 200 pg LacZ mRNA; (D) HA-Tbx20b mRNA (500 pg) with LacZ mRNA (200 pg). (E) Western blot analysis of embryos injected with HA-Tbx20a or b using an anti-haemagglutinin (HA) epitope antibody. (F) Histological sections of HA-Tbx20a plus LacZ mRNA (left) or LacZ mRNA (right)-injected embryos at tailbud stage after staining for B-galactosidase. (G) Quantitative RT-PCR analysis of expression of indicated genes in total RNA isolated from whole Xenopus embryos at stage 13 or from animal caps removed at stage 9 from whole embryos that were uninjected or had been injected into the animal pole at the two-cell stage with HA-Tbx20a or b mRNA (250 pg) and cultured until sibling embryos reached stage 13. Expression levels are represented relative to those of the ubiquitously expressed ornithine decarboxylase (ODC) gene.|