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IGERT Mentor is Presidential Early Career Award Winner


Work accomplished by IGERT trainee Sean Carroll, along with IGERT faculty Joe Thornton and post-doctoral fellow Jamie Bridgham, was recognized by the Presidential Early Career Award for Scientists and Engineers to advisor Thornton. The award was bestowed by President of the United States G.W. Bush with an accompanying handshake and some personal words of congratulations.

The workers wanted to know how two closely related receptors, one for the stress hormone cortisol and the other for the kidney regulator aldosterone, came to recognize their respective specific hormones. The team began by analyzing the gene sequences of a huge database of hormone receptors. They found that the two receptors originated when a single ancient receptor gene was duplicated in the genome some 450 million years ago, just as animals with backbones were evolving. They used statistical methods to reconstruct the gene sequence of that ancient receptor, “resurrected” the gene by synthesizing its structure in the test tube, and then used laboratory tests to determine its functions. They found that the ancestral gene worked beautifully and was sensitive to both aldosterone and cortisol.

This result was surprising, Thornton said, because aldosterone itself didn’t evolve for at least another 50 million years, around the time vertebrates came out of the water and began to colonize the land. Importantly, however, it explained how a new hormone-receptor pair evolved: When aldosterone came on the scene, the ancient receptor with its tendency to bind both hormones had been duplicated, and as random mutations caused the two duplicate genes to change over time, one became specialized by natural selection to prefer aldosterone while the other copy retained a preference for cortisol.

Christoph Adami of the Keck Graduate Institute of Applied Sciences in Claremont, Calif., described the importance of the finding. Even Charles Darwin saw specialized lock-and-key relationships, such as a flower that can only be fertilized by a moth with particularly long mouthparts and the moth itself or hormones and their receptors, as a point where his theory was potentially vulnerable, Adami wrote that intelligent design advocates hold that such relationships demonstrate irreducible complexity and could not have evolved, and that such studies solidly refute all parts of the intelligent design argument. Those ‘alternate’ ideas, unlike the hypotheses investigated in these papers, remain thoroughly untested. Consequently, whatever debate remains must be characterized as purely political".

Bridgham JT, Carroll SM, Thornton JW. (2006) Evolution of hormone-receptor complexity by molecular exploitation. Science. 2006 Apr 7;312(5770):97-101.

Address Goals

The research integrates across genomics, computational biology, physiology and biochemistry, and the physics of macromolecular structure to address a fundamental misconception perpetrated by creationists regarding the mechanisms of evolution. Given the ways in which creationists try to drive science out of our school curricula, this is an important general contribution to an enlightened society. In addition, of course, and of primary importance it answers an important, long-standing problem in biology.