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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). "Itâ€™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 donâ€™t have a good fossil record of, so we donâ€™t know exactly
what it looked like, we just know what its current ancestors are. Thatâ€™s
one of the reasons why we wanted to learn more about the behavior of this creature,"
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 archosaurâ€™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 Parkâ€™ is definitely a leap of
the imagination," says Sakmar's collaborator Belinda
Chang. "I donâ€™t think we are anywhere near recreating ‘Jurassic
Parkâ€™ 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.
“Itâ€™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. Thatâ€™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