Limits...
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.

Show MeSH

Related in: MedlinePlus

The pattern of proliferation along the heart tube is dynamic and is regulated by Tbx3 and Tbx2.All images represent reconstructions of confocal Z-stack sections imaged on whole embryos at 31hpf (A) and 33 hpf (B–G). (A, B) During the first steps of looping, the pattern of proliferation shifts from homogenous throughout the heart tube (31 hpf, A) to a heterogenous one in which dividing cells are more concentrated in the future chambers (33 hpf, B). (C, D) In Tbx3- (C) and Tbx2- (D) injected embryos at 33 hpf this shift has not occurred and the number of dividing cells was significantly decreased and dividing cells were homogenously distributed (H). (E–G) MO-injected embryos against tbx3b (E), tbx2a (F) or both (G) display the same (E, F) or higher (G) number of proliferating cells than wild type at 33 hpf. However, proliferating cells remain homogenously distributed throughout the heart tube. (H) Histogram showing the average of the total number of BrdU positive cells in the heart of 33 hpf embryos: wt, 31.4±1.661 (n = 5); Tbx3 mRNA, 17.5±1.708 (p<0.001; n = 6); Tbx2 mRNA, 17.0±1.000 (p<0.001; n = 7); tbx3b MO, 28.0±0.408 (n = 4); tbx2a MO, 31.3±2.658 (n = 4); double MO, 36.8±1.797 (n = 4). a, atrium; h, heart; nt, neural tube; v, ventricle.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC1851989&req=5

pone-0000398-g004: The pattern of proliferation along the heart tube is dynamic and is regulated by Tbx3 and Tbx2.All images represent reconstructions of confocal Z-stack sections imaged on whole embryos at 31hpf (A) and 33 hpf (B–G). (A, B) During the first steps of looping, the pattern of proliferation shifts from homogenous throughout the heart tube (31 hpf, A) to a heterogenous one in which dividing cells are more concentrated in the future chambers (33 hpf, B). (C, D) In Tbx3- (C) and Tbx2- (D) injected embryos at 33 hpf this shift has not occurred and the number of dividing cells was significantly decreased and dividing cells were homogenously distributed (H). (E–G) MO-injected embryos against tbx3b (E), tbx2a (F) or both (G) display the same (E, F) or higher (G) number of proliferating cells than wild type at 33 hpf. However, proliferating cells remain homogenously distributed throughout the heart tube. (H) Histogram showing the average of the total number of BrdU positive cells in the heart of 33 hpf embryos: wt, 31.4±1.661 (n = 5); Tbx3 mRNA, 17.5±1.708 (p<0.001; n = 6); Tbx2 mRNA, 17.0±1.000 (p<0.001; n = 7); tbx3b MO, 28.0±0.408 (n = 4); tbx2a MO, 31.3±2.658 (n = 4); double MO, 36.8±1.797 (n = 4). a, atrium; h, heart; nt, neural tube; v, ventricle.

Mentions: The absence of chamber growth in Tbx3- and Tbx2-injected embryos prompted us to investigate the cell division and apoptosis levels during heart looping. In wild type embryos between 31 and 48 hpf, no significant numbers of apoptotic cells, as evaluated by acridine orange staining, were observed in the heart (data not shown). Additionally, no differences were observed between Tbx3- or Tbx2-injected and wild type embryos in the number of apoptotic cells in the heart tube (data not shown). To study the pattern of proliferation in the looping heart we gave a one-hour pulse of BrdU by injecting a BrdU solution in the pericardiac cavity. In 31 hpf wild type embryos the heart presented no signs of looping and chamber formation. The BrdU-positive cells were equally distributed throughout the extent of the heart tube (Fig. 4A). At 33 hpf, the anterior region of the heart tube, the future ventricle, has jogged to the right, allowing a rough distinction between the two future chambers and the future AVC. At this stage, the BrdU positive cells were more concentrated in the future chamber regions, leaving the AVC region devoid of BrdU-positive cells (Fig. 4B). At 36 hpf the initial phase of heart looping is already completed and it is possible to clearly identify the ventricle and the atrium, as well as the OFT and the AVC. Thus, a dynamic pattern of cell proliferation along the heart tube accompanies chamber outgrowth, and a crucial differentiation step occurs at 33 hpf, concomitant with the rightward jogging of the future ventricle.


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)

The pattern of proliferation along the heart tube is dynamic and is regulated by Tbx3 and Tbx2.All images represent reconstructions of confocal Z-stack sections imaged on whole embryos at 31hpf (A) and 33 hpf (B–G). (A, B) During the first steps of looping, the pattern of proliferation shifts from homogenous throughout the heart tube (31 hpf, A) to a heterogenous one in which dividing cells are more concentrated in the future chambers (33 hpf, B). (C, D) In Tbx3- (C) and Tbx2- (D) injected embryos at 33 hpf this shift has not occurred and the number of dividing cells was significantly decreased and dividing cells were homogenously distributed (H). (E–G) MO-injected embryos against tbx3b (E), tbx2a (F) or both (G) display the same (E, F) or higher (G) number of proliferating cells than wild type at 33 hpf. However, proliferating cells remain homogenously distributed throughout the heart tube. (H) Histogram showing the average of the total number of BrdU positive cells in the heart of 33 hpf embryos: wt, 31.4±1.661 (n = 5); Tbx3 mRNA, 17.5±1.708 (p<0.001; n = 6); Tbx2 mRNA, 17.0±1.000 (p<0.001; n = 7); tbx3b MO, 28.0±0.408 (n = 4); tbx2a MO, 31.3±2.658 (n = 4); double MO, 36.8±1.797 (n = 4). a, atrium; h, heart; nt, neural tube; v, ventricle.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0000398-g004: The pattern of proliferation along the heart tube is dynamic and is regulated by Tbx3 and Tbx2.All images represent reconstructions of confocal Z-stack sections imaged on whole embryos at 31hpf (A) and 33 hpf (B–G). (A, B) During the first steps of looping, the pattern of proliferation shifts from homogenous throughout the heart tube (31 hpf, A) to a heterogenous one in which dividing cells are more concentrated in the future chambers (33 hpf, B). (C, D) In Tbx3- (C) and Tbx2- (D) injected embryos at 33 hpf this shift has not occurred and the number of dividing cells was significantly decreased and dividing cells were homogenously distributed (H). (E–G) MO-injected embryos against tbx3b (E), tbx2a (F) or both (G) display the same (E, F) or higher (G) number of proliferating cells than wild type at 33 hpf. However, proliferating cells remain homogenously distributed throughout the heart tube. (H) Histogram showing the average of the total number of BrdU positive cells in the heart of 33 hpf embryos: wt, 31.4±1.661 (n = 5); Tbx3 mRNA, 17.5±1.708 (p<0.001; n = 6); Tbx2 mRNA, 17.0±1.000 (p<0.001; n = 7); tbx3b MO, 28.0±0.408 (n = 4); tbx2a MO, 31.3±2.658 (n = 4); double MO, 36.8±1.797 (n = 4). a, atrium; h, heart; nt, neural tube; v, ventricle.
Mentions: The absence of chamber growth in Tbx3- and Tbx2-injected embryos prompted us to investigate the cell division and apoptosis levels during heart looping. In wild type embryos between 31 and 48 hpf, no significant numbers of apoptotic cells, as evaluated by acridine orange staining, were observed in the heart (data not shown). Additionally, no differences were observed between Tbx3- or Tbx2-injected and wild type embryos in the number of apoptotic cells in the heart tube (data not shown). To study the pattern of proliferation in the looping heart we gave a one-hour pulse of BrdU by injecting a BrdU solution in the pericardiac cavity. In 31 hpf wild type embryos the heart presented no signs of looping and chamber formation. The BrdU-positive cells were equally distributed throughout the extent of the heart tube (Fig. 4A). At 33 hpf, the anterior region of the heart tube, the future ventricle, has jogged to the right, allowing a rough distinction between the two future chambers and the future AVC. At this stage, the BrdU positive cells were more concentrated in the future chamber regions, leaving the AVC region devoid of BrdU-positive cells (Fig. 4B). At 36 hpf the initial phase of heart looping is already completed and it is possible to clearly identify the ventricle and the atrium, as well as the OFT and the AVC. Thus, a dynamic pattern of cell proliferation along the heart tube accompanies chamber outgrowth, and a crucial differentiation step occurs at 33 hpf, concomitant with the rightward jogging of the future ventricle.

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