TY - JOUR
T1 - Reptilian heart development and the molecular basis of cardiac chamber evolution
AU - Koshiba-Takeuchi, Kazuko
AU - Mori, Alessandro D.
AU - Kaynak, Bogac L.
AU - Cebra-Thomas, Judith
AU - Sukonnik, Tatyana
AU - Georges, Romain O.
AU - Latham, Stephany
AU - Beck, Laural
AU - Henkelman, R. Mark
AU - Black, Brian L.
AU - Olson, Eric N.
AU - Wade, Juli
AU - Takeuchi, Jun K.
AU - Nemer, Mona
AU - Gilbert, Scott F.
AU - Bruneau, Benoit G.
N1 - Funding Information:
Acknowledgements We thank J. N. Wylie and L. Davidson for technical assistance, M. Harris and J. Fallon for alligator embryos, T. Sanger and J. Gibson-Brown for unpublished data on Anolis staging, T. Ogura for chick Tbx5 and Tbx20 probes, and G. Howard and S. Ordway for editorial assistance. This work was funded in part by the March of Dimes Birth Defects Foundation (B.G.B.), the J. David Gladstone Institutes (B.G.B.), William H. Younger Jr (B.G.B.); a National Institutes of Health program project grant (P01HL089707 to B.G.B., B.L.B.); scholarships from the Natural Sciences and Engineering Research Council of Canada, the Heart and Stroke Richard Lewar Centre for Excellence, University of Toronto, and Ontario Graduate Scholarship (A.D.M.); the Fumi Yamamura Memorial Foundation for Female Natural Scientists and Grants-in-Aid for Scientific Research (C) (K.K.-T.), MEXT’s program for young independent researchers (K.K.-T., J.K.T.), Sumitomo Foundation and Nakajima Foundation (J.K.T.), a Canada Research Chair in Imaging (R.M.H.), the Heart and Stroke foundation of Canada and the Canadian Institutes for Health Research (M.N.), and grants from the National Science Foundation (RUI-0748508 to S.F.G., J.C.-T. and IOS-0742833 to J.W.). Funding for the J. David Gladstone Institutes from a National Institutes of Health/ National Center for Research Resources grant (C06 RR018928) is also acknowledged.
PY - 2009/9/3
Y1 - 2009/9/3
N2 - The emergence of terrestrial life witnessed the need for more sophisticated circulatory systems. This has evolved in birds, mammals and crocodilians into complete septation of the heart into left and right sides, allowing separate pulmonary and systemic circulatory systems, a key requirement for the evolution of endothermy. However, the evolution of the amniote heart is poorly understood. Reptilian hearts have been the subject of debate in the context of the evolution of cardiac septation: do they possess a single ventricular chamber or two incompletely septated ventricles? Here we examine heart development in the red-eared slider turtle, Trachemys scripta elegans (a chelonian), and the green anole, Anolis carolinensis (a squamate), focusing on gene expression in the developing ventricles. Both reptiles initially form a ventricular chamber that homogenously expresses the T-box transcription factor gene Tbx5. In contrast, in birds and mammals, Tbx5 is restricted to left ventricle precursors. In later stages, Tbx5 expression in the turtle (but not anole) heart is gradually restricted to a distinct left ventricle, forming a left-right gradient. This suggests that Tbx5 expression was refined during evolution to pattern the ventricles. In support of this hypothesis, we show that loss of Tbx5 in the mouse ventricle results in a single chamber lacking distinct identity, indicating a requirement for Tbx5 in septation. Importantly, misexpression of Tbx5 throughout the developing myocardium to mimic the reptilian expression pattern also results in a single mispatterned ventricular chamber lacking septation. Thus ventricular septation is established by a steep and correctly positioned Tbx5 gradient. Our findings provide a molecular mechanism for the evolution of the amniote ventricle, and support the concept that altered expression of developmental regulators is a key mechanism of vertebrate evolution.
AB - The emergence of terrestrial life witnessed the need for more sophisticated circulatory systems. This has evolved in birds, mammals and crocodilians into complete septation of the heart into left and right sides, allowing separate pulmonary and systemic circulatory systems, a key requirement for the evolution of endothermy. However, the evolution of the amniote heart is poorly understood. Reptilian hearts have been the subject of debate in the context of the evolution of cardiac septation: do they possess a single ventricular chamber or two incompletely septated ventricles? Here we examine heart development in the red-eared slider turtle, Trachemys scripta elegans (a chelonian), and the green anole, Anolis carolinensis (a squamate), focusing on gene expression in the developing ventricles. Both reptiles initially form a ventricular chamber that homogenously expresses the T-box transcription factor gene Tbx5. In contrast, in birds and mammals, Tbx5 is restricted to left ventricle precursors. In later stages, Tbx5 expression in the turtle (but not anole) heart is gradually restricted to a distinct left ventricle, forming a left-right gradient. This suggests that Tbx5 expression was refined during evolution to pattern the ventricles. In support of this hypothesis, we show that loss of Tbx5 in the mouse ventricle results in a single chamber lacking distinct identity, indicating a requirement for Tbx5 in septation. Importantly, misexpression of Tbx5 throughout the developing myocardium to mimic the reptilian expression pattern also results in a single mispatterned ventricular chamber lacking septation. Thus ventricular septation is established by a steep and correctly positioned Tbx5 gradient. Our findings provide a molecular mechanism for the evolution of the amniote ventricle, and support the concept that altered expression of developmental regulators is a key mechanism of vertebrate evolution.
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U2 - 10.1038/nature08324
DO - 10.1038/nature08324
M3 - Article
C2 - 19727199
AN - SCOPUS:69949094996
SN - 0028-0836
VL - 461
SP - 95
EP - 98
JO - Nature
JF - Nature
IS - 7260
ER -