Scientists Recover DNA From Time of Dinosaurs : Genetics: Fragment is from an ancient weevil locked in amber. But sorry, ‘Jurassic Park’ fans, extinction is forever.
From an insect trapped in ancient amber, the scientists whose work inspired “Jurassic Park” have extracted the oldest known fragments of DNA--genetic material that was fresh when dinosaurs were alive and the world was their buffet.
Scientists from UC Berkeley and Cal Poly San Luis Obispo recovered the fossil DNA from an extinct weevil that jumped and skittered 120 million to 135 million years ago, making it about 80 million years older than any other known sample.
Their work, reported today in the scientific journal Nature, demonstrates for the first time that the fragile molecular chains of DNA at the heart of every living cell can survive such vast expanses of time. The discovery is the first genetic material that dates from the age of the dinosaurs.
So far, researchers have teased ancient DNA from fossils as varied as a 40-million-year-old bumble bee, which contained the previous oldest-known DNA; a 17-million-year-old magnolia leaf; a 40,000-year-old woolly mammoth calf, and even the 8,000-year-old soft tissues of a prehistoric human brain. In each instance, the genes offer new insights into the pace of evolution and the relationships among species. And in work scheduled to be published shortly, genes recovered from extinct plants have revealed clues to the movements of drifting continents.
But the newest finding takes scientists no closer to the science fiction fantasy embodied by the book and film “Jurassic Park,” in which ancient genes could one day be used to resurrect an extinct animal such as a Tyrannosaurus rex or a remote human ancestor like Neanderthal man.
Extinction, the scientists acknowledged, is still forever.
But scientists do not need a living dinosaur to satisfy their research ambitions. Even a single legible dinosaur gene would be more than enough to make them happy. The current discovery makes some believe that the goal is well within a scientist’s grasp.
“This does show you how long DNA can survive and it also gives you supporting information showing it may be possible to get dinosaur DNA,” said Raul J. Cano, molecular biologist at Cal Poly San Luis Obispo. “We are within the realm of possibility.”
Cano performed the analysis with Berkeley entomologist George O. Poinar Jr., who was among those who first proposed more than a decade ago that dinosaur DNA might be recovered from blood preserved inside biting insects trapped in ancient amber. From that theory, author Michael Crichton drew the plot for his best-selling 1990 novel. Hendrik Poinar, George’s son and a graduate student in Cano’s laboratory, also worked on the project.
Unlike most dinosaur fossils seen in museums, in which bone has long since been replaced by minerals, amber can preserve the actual tissue of an organism, even the contents of its stomach. Because almost every cell contains the complete genetic blueprint of the plant or animal to which it belongs, a well-preserved cell could yield, in theory, an intact set of genes.
The fossil weevil, barely the size of a pinhead, yielded about one millionth of the insect’s entire genetic blueprint, Cano said, not even enough DNA to make up a single gene of the hundreds or thousands the organism may have required.
But it was enough to allow the researchers to conclude that “the majority of animal remains in amber have preserved DNA that can be extracted and studied, thus making amber a treasure chest for molecular paleontologists.”
Hendrik Poinar and Cano say they are attempting to recover genes from what they suspect may be blood swallowed by midges preserved in a piece of 75-million-year-old amber--well within the time that dinosaurs dominated the planet.
Cano admits that even if they are successful he will have a hard time convincing skeptical colleagues that he has indeed discovered the molecular raw material of an earth-shaking 90-ton Brachiosaurus or a horned Triceratops.
The researchers acknowledge that they do not know what the genes of a dinosaur might look like. They will have to identify the genetic material by a process of elimination and a leap of faith.
A computer database helps them compare the ancient DNA to all known genetic sequences of organisms living today. If a suspected dinosaur gene does not match the sequence of any other animal or plant on the computer, they can attempt to narrow the search by looking for a family resemblance among the genes of what scientists believe are the living descendants of dinosaurs--birds and reptiles. From there, the researchers will have to rely on educated guesswork and peer review.
“How to recognize dinosaur DNA is a real tough question,” Cano said. “This is our stumbling block. We can tell bacteria DNA from insect DNA. We can tell the difference between insects and vertebrates. If our work is correct and we get something that might be a dinosaur, we will have to come up with some kind of consensus concerning what we are looking at.
“It is going to be a tedious job,” he said.
Some scientists caution that any claims concerning antique DNA should be treated cautiously. Tomas Lindahl, a researcher at the Imperial Cancer Research Fund’s Clare Hall Laboratories in England, warned last month in the same scientific journal that published today’s report that “much better experimental documentation is required before such claims can be seriously considered.”
He argues that genetic material--a long, twisted strand of molecules that contains all the basic information of heredity--is so chemically unstable that even the best-preserved fossil DNA would decompose after a few million years. And the process that scientists use to amplify the molecules of fossil DNA is itself so sensitive that it can deceive a researcher into believing he is looking at the stuff of an extinct species when he has only succeeded in amplifying a molecule of something from under his fingernails.
Russell Higuchi, a research investigator at Roche Molecular Systems in Emeryville who helped recover genetic material from the 40,000-year-old body of a woolly mammoth, said, “The problem with the amplification process is that you can take any single molecule and get something. There could be contamination from modern DNA.”
