May 21, 2003 

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Dino Gene (video)
March 06, 2003

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Interviewees: Thomas P. Sakmar and Belinda Chang, Rockefeller University

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Produced by Liza Acevedo and Joyce Gramza.

Copyright © ScienCentral, Inc. with additional footage from ABC News

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Genetics researchers can now learn things about extinct animals like dinosaurs that they could never find out from fossils.

It may sound like "Jurassic Park", but as this ScienCentral News video reports, scientists at Rockefeller University recreated a gene that had not existed for 240 million years.

Ancestral Gene Reconstruction

The scientists traced the gene sequence of a vision protein called rhodopsin back to the extinct archosaur.

“An archosaur is a prehistoric dinosaur that probably existed 240 million years ago," says Tom Sakmar, who heads the research (Sakmar is also Acting President of Rockefeller University). "It’s a branch that would have given rise to the reptiles in modern lineage, but then again, the archosaur is a type of creature that we don’t have a good fossil record of, so we don’t know exactly what it looked like, we just know what its current ancestors are. That’s one of the reasons why we wanted to learn more about the behavior of this creature," Sakmar says.

Even if the fossil record was good, DNA and proteins aren't preserved the way bones are in fossils. So the scientists developed a computer program to perform what they call "ancestral gene reconstruction," says Sakmar. It compared the DNA sequence of the dinosaur's living relatives, from birds to crocodiles, and tracked the DNA's evolution backward in time, guessing at the sequence of the archosaur's gene.

Once the team had arrived at the DNA sequence for the archosaur’s rhodopsin, they needed to turn that DNA sequence into protein. So they "took that sequence and recreated it in the laboratory by synthesizing the gene, putting it in tissue culture cells, having the cells make lots of this putative protein, purifying it and then measuring it in the lab."

“Comparing it to ‘Jurassic Park’ is definitely a leap of the imagination," says Sakmar's collaborator Belinda Chang. "I don’t think we are anywhere near recreating ‘Jurassic Park’ with our studies here. However, what I can say is that this one molecule does represent our best guess as to what an archosaur, which lived 240 million years ago, would have had in its eye. We have been able to take that sequence, recreate it in the laboratory and measure its function to show that it functions as you would expect a vision protein to function.”

When they tested the rhodopsin protein in the lab, they found that it was sensitive to dim light, suggesting that archosaurs might have been nocturnal. "We learn [the gene's sequence] from evolution, but we also learn what may have been specific behaviors of the archosaur even though they have not been around for 240 million years,” says Sakmar.

Chang and Sakmar have been testing this technique for two years. “We always have to test educated guesses. We make a hypothesis, we design an experiment, we carry out the experiment, and the results tell us whether we were right or not," says Sakmar. " We learn, however, from both failures and successes, because if the experiment fails that means that we sort of have to go back to the drawing board and re-think our early assumptions, so we keep working. The successes are great, but the failures are great to help us go back and revise things and that helps us make it better,” he says.

The success may have paved the way for future researchers to explore the future by looking toward the past.

“It’s important to study the molecular evolution of proteins in order to better understand how they function, because how they function now is a result of the path they took to get to this point," Chang says. "If we have proteins that, for example, cause disease or if we have certain mutations or certain dysfunctional proteins, they can have very severe consequences in humans. That’s certainly the case for rhodopsin and all kinds of related proteins that are involved in vision. [It is important] to understand its function so that we can better understand the cases in which it goes wrong. One of the ways you can do that is through historical perspective—to study it from the perspective of its molecular evolutionary history.”

The research was published in the Molecular Biology & Evolution in September 2002. It was funded by the Howard Hughes Medical Institute, the Allene Reuss Memorial Trust, the National Science Foundation, and the Ellison Medical Foundation.

by Liza Acevedo

Joyce Gramza

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