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Tbx2 and Tbx3 regulate the dynamics of cell proliferation during heart remodeling.

Ribeiro I, Kawakami Y, Büscher D, Raya A, Rodríguez-León J, Morita M, Rodríguez Esteban C, Izpisúa Belmonte JC - PLoS ONE (2007)

Bottom Line: Cardiomyocytes in the future chamber myocardium acquire different cellular and physiological characteristics through activation of a chamber-specific genetic program, which is in part mediated by T-box genes.We characterize two new zebrafish T-box transcription factors, tbx3b and tbx2a, and analyze their role during the development of the atrioventricular canal.Loss- and gain-of-function analyses demonstrate that tbx3b and tbx2a are necessary to repress the chamber-genetic program in the non-chamber myocardium.

View Article: PubMed Central - PubMed

Affiliation: Gene Expression Laboratory, The Salk Institute for Biological Studies, La Jolla, California, United States of America.

ABSTRACT

Background: The heart forms from a linear tube that is subject to complex remodeling during embryonic development. Hallmarks of this remodeling are the looping of the heart tube and the regionalization into chamber and non-chamber myocardium. Cardiomyocytes in the future chamber myocardium acquire different cellular and physiological characteristics through activation of a chamber-specific genetic program, which is in part mediated by T-box genes.

Methodology/principal finding: We characterize two new zebrafish T-box transcription factors, tbx3b and tbx2a, and analyze their role during the development of the atrioventricular canal. Loss- and gain-of-function analyses demonstrate that tbx3b and tbx2a are necessary to repress the chamber-genetic program in the non-chamber myocardium. We also show that tbx3b and tbx2a are required to control cell proliferation in the atrioventricular canal and that misregulation of cell proliferation in the heart tube influences looping. Furthermore, we characterize the heart phenotype of a novel Tbx3 mutation in mice and show that both the control of cell proliferation and the repression of chamber-specific genetic program in the non-chamber myocardium are conserved roles of Tbx3 in this species.

Conclusions/significance: Taken together, our results uncover an evolutionarily conserved role of Tbx2/3 transcription factors during remodeling of the heart myocardium and highlight the importance of controlling cell proliferation as a driving force of morphogenesis.

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Heart morphology in embryos overexpressing Tbx3 and Tbx2.Side views (A–C) and ventral views (D–F) of wild type embryos (A, D) and embryos injected with 100 pg capped mRNA for mouse Tbx3 (B, E) or human TBX2 (C, F). (A, B, C) mlc2a::GFP embryos at 60 hpf; (D, E, F) 48 hpf. (B, C) 44.5% of Tbx3-injected embryos and 60% of Tbx2-injected embryos present a pipe-like heart that lacks chamber growth and looping. (D, E, F) Zebrafish bmp10 is strongly expressed in the chamber myocardium in wild type embryos, but is significantly downregulated from the heart in Tbx3- or Tbx2-injected embryos. a, atrium; v, ventricle.
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pone-0000398-g003: Heart morphology in embryos overexpressing Tbx3 and Tbx2.Side views (A–C) and ventral views (D–F) of wild type embryos (A, D) and embryos injected with 100 pg capped mRNA for mouse Tbx3 (B, E) or human TBX2 (C, F). (A, B, C) mlc2a::GFP embryos at 60 hpf; (D, E, F) 48 hpf. (B, C) 44.5% of Tbx3-injected embryos and 60% of Tbx2-injected embryos present a pipe-like heart that lacks chamber growth and looping. (D, E, F) Zebrafish bmp10 is strongly expressed in the chamber myocardium in wild type embryos, but is significantly downregulated from the heart in Tbx3- or Tbx2-injected embryos. a, atrium; v, ventricle.

Mentions: We next asked if the ectopic expression of Tbx3 and Tbx2 in chamber myocardium was able to prevent chamber formation. Tbx3-injected embryos developed at comparable rates as the GFP-injected embryos. At 60 hpf, 44.5% of the embryos overexpressing Tbx3 presented a swollen pericardiac cavity and a delay in heart looping. Most notably, however, was the lack of chamber growth, which, added to the increasing pericardial swelling due to low circulation, gave rise to a thin heart tube that stretched from the base of the head to the yolk (Fig. 3B; compare to 3A), a condition previously described as pipe-like heart [27]. In 60% Tbx2-injected embryos the pericardiac cavity was swollen from 48 hpf onwards (Fig. 3C). A similar pipe-like heart phenotype was visible at 3 dpf. In line with the lack of chamber growth, zebrafish bmp10 was significantly downregulated in the heart in Tbx3- and Tbx2-injected embryos (Fig. 3D,E,F). Transcripts of anf were not downregulated from the AVC of Tbx3- and Tbx2-overexpressing hearts at 48 hpf and presented levels of expression similar to the wild type 24 hpf heart (data not shown). The overexpression of Tbx3 or Tbx2 did not affect the expression of notch1b or bmp4 (data not shown). Thus, the specification and differentiation of non-chamber myocardium is not altered in the presence of ectopic Tbx3 or Tbx2 in the heart tube. However, the presumptive chambers do not grow from the primitive heart tube, and maintain levels of expression of chamber markers characteristic of primary myocardium.


Tbx2 and Tbx3 regulate the dynamics of cell proliferation during heart remodeling.

Ribeiro I, Kawakami Y, Büscher D, Raya A, Rodríguez-León J, Morita M, Rodríguez Esteban C, Izpisúa Belmonte JC - PLoS ONE (2007)

Heart morphology in embryos overexpressing Tbx3 and Tbx2.Side views (A–C) and ventral views (D–F) of wild type embryos (A, D) and embryos injected with 100 pg capped mRNA for mouse Tbx3 (B, E) or human TBX2 (C, F). (A, B, C) mlc2a::GFP embryos at 60 hpf; (D, E, F) 48 hpf. (B, C) 44.5% of Tbx3-injected embryos and 60% of Tbx2-injected embryos present a pipe-like heart that lacks chamber growth and looping. (D, E, F) Zebrafish bmp10 is strongly expressed in the chamber myocardium in wild type embryos, but is significantly downregulated from the heart in Tbx3- or Tbx2-injected embryos. a, atrium; v, ventricle.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1851989&req=5

pone-0000398-g003: Heart morphology in embryos overexpressing Tbx3 and Tbx2.Side views (A–C) and ventral views (D–F) of wild type embryos (A, D) and embryos injected with 100 pg capped mRNA for mouse Tbx3 (B, E) or human TBX2 (C, F). (A, B, C) mlc2a::GFP embryos at 60 hpf; (D, E, F) 48 hpf. (B, C) 44.5% of Tbx3-injected embryos and 60% of Tbx2-injected embryos present a pipe-like heart that lacks chamber growth and looping. (D, E, F) Zebrafish bmp10 is strongly expressed in the chamber myocardium in wild type embryos, but is significantly downregulated from the heart in Tbx3- or Tbx2-injected embryos. a, atrium; v, ventricle.
Mentions: We next asked if the ectopic expression of Tbx3 and Tbx2 in chamber myocardium was able to prevent chamber formation. Tbx3-injected embryos developed at comparable rates as the GFP-injected embryos. At 60 hpf, 44.5% of the embryos overexpressing Tbx3 presented a swollen pericardiac cavity and a delay in heart looping. Most notably, however, was the lack of chamber growth, which, added to the increasing pericardial swelling due to low circulation, gave rise to a thin heart tube that stretched from the base of the head to the yolk (Fig. 3B; compare to 3A), a condition previously described as pipe-like heart [27]. In 60% Tbx2-injected embryos the pericardiac cavity was swollen from 48 hpf onwards (Fig. 3C). A similar pipe-like heart phenotype was visible at 3 dpf. In line with the lack of chamber growth, zebrafish bmp10 was significantly downregulated in the heart in Tbx3- and Tbx2-injected embryos (Fig. 3D,E,F). Transcripts of anf were not downregulated from the AVC of Tbx3- and Tbx2-overexpressing hearts at 48 hpf and presented levels of expression similar to the wild type 24 hpf heart (data not shown). The overexpression of Tbx3 or Tbx2 did not affect the expression of notch1b or bmp4 (data not shown). Thus, the specification and differentiation of non-chamber myocardium is not altered in the presence of ectopic Tbx3 or Tbx2 in the heart tube. However, the presumptive chambers do not grow from the primitive heart tube, and maintain levels of expression of chamber markers characteristic of primary myocardium.

Bottom Line: Cardiomyocytes in the future chamber myocardium acquire different cellular and physiological characteristics through activation of a chamber-specific genetic program, which is in part mediated by T-box genes.We characterize two new zebrafish T-box transcription factors, tbx3b and tbx2a, and analyze their role during the development of the atrioventricular canal.Loss- and gain-of-function analyses demonstrate that tbx3b and tbx2a are necessary to repress the chamber-genetic program in the non-chamber myocardium.

View Article: PubMed Central - PubMed

Affiliation: Gene Expression Laboratory, The Salk Institute for Biological Studies, La Jolla, California, United States of America.

ABSTRACT

Background: The heart forms from a linear tube that is subject to complex remodeling during embryonic development. Hallmarks of this remodeling are the looping of the heart tube and the regionalization into chamber and non-chamber myocardium. Cardiomyocytes in the future chamber myocardium acquire different cellular and physiological characteristics through activation of a chamber-specific genetic program, which is in part mediated by T-box genes.

Methodology/principal finding: We characterize two new zebrafish T-box transcription factors, tbx3b and tbx2a, and analyze their role during the development of the atrioventricular canal. Loss- and gain-of-function analyses demonstrate that tbx3b and tbx2a are necessary to repress the chamber-genetic program in the non-chamber myocardium. We also show that tbx3b and tbx2a are required to control cell proliferation in the atrioventricular canal and that misregulation of cell proliferation in the heart tube influences looping. Furthermore, we characterize the heart phenotype of a novel Tbx3 mutation in mice and show that both the control of cell proliferation and the repression of chamber-specific genetic program in the non-chamber myocardium are conserved roles of Tbx3 in this species.

Conclusions/significance: Taken together, our results uncover an evolutionarily conserved role of Tbx2/3 transcription factors during remodeling of the heart myocardium and highlight the importance of controlling cell proliferation as a driving force of morphogenesis.

Show MeSH
Related in: MedlinePlus