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Press Release 09-164
Secrets of the Four Chambers Revealed by Reptile Hearts

The molecular blueprint for evolution from cold-blooded to warm-blooded has been found

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A panorama of animals and embryonic heart diagrams showing evolution from frog to human.

Embryo hearts show evolution of the heart from a three-chambered in frogs to a four-chambered in mammals.

Credit: Zina Deretsky, National Science Foundation after Benoit Brueau, the Gladstone Institute of Cardiovascular Disease


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Benoit Bruneau of the Gladstone Institute of Cardiovascular Disease explains the discovery of the first genetic link in the evolution of the heart from three- to four-chambered. He walks through the anatomy of the cold-blooded frog heart that has three chambers; talks about its differences with the warm-blooded four-chambered heart, and explains some evolutionary advantages of being warm-blooded. He explains the molecular pattern of the protein Tbx5 and how it is different in embryo frog hearts compared with embryo mammal hearts. When the protein is present throughout the entire heart, three chambers form. However, when Tbx5 is restricted only to the left side of the heart, then the wall separating the two ventricles forms and four chambers result. When irregularities in the amounts of the protein occur in human babies, congenital heart defects of the septum result.

Credit: National Science Foundation/Gladstone Institute

 

Diagram shows separation of oxygenated and deoxygenated blood in the heart of three animal types.

The three-chambered frog heart mixes oxygenated and deoxygenated blood in the ventricle. Therefore, the body never receives fully oxygen-rich blood. In turtles, where a septum begins to form and separate the ventricles, the body receives slightly richer blood in oxygen. It is only in the warm-blooded model, in birds and mammals, that the two circulatory systems become fully separate sending low-pressure pumping to the lungs, and a high-pressure flow of blood to the rest of the body. In this model, the animal's muscles receive fully oxygenated blood.

Credit: Credit: Zina Deretsky, National Science Foundation


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Images of embryo turtle heart on the left and embryo lizard heart on the right.

Embryo turtle heart on the left. Embryo lizard heart on the right.

Credit: Bogac Kaynak and Benoit Bruneau, Gladstone Institute of Cardiovascular Disease


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Photo of a turtle embryo.

Turtle embryo.

Credit: Sample obtained and photographed by Judy Cebra-Thomas and Scott Gilbert, Swarthmore College.


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