Jurassic Park notwithstanding, the oldest fossil DNA everextracted from amber and analyzed dates from the Cretaceousgeologic period (120-135 million years ago), not the Jurassic(180 million). Nor did the ancient insect extracted from itsresinous integument dine on dinosaur blood, but on the pollenof conifer trees.
Today's Nature reports this record-breaking feat of molecularpaleontology under the title "Amplification and sequencing ofDNA from a 120-135-million-year-old weevil." Its lead authoris molecular biologist Raul Cano of California Polytechnic StateUniversity in San Luis Obispo. But the story begins with itsprincipal co-author, entomologist George Poinar of theUniversity of California, Berkeley.
Eleven years ago, Aftim Acra of the American University ofBeirut sent Poinar a lump of Lebanese amber an inch or so longto add to his collection of worldwide amber specimens, nownumbering some 10,000 pieces. At one end, this lumpentrapped the fossil weevil, which measured 2.5 millimeters(one-tenth of an inch) from snout to rear.
Poinar and Cano had previously collaborated on isolating andanalyzing DNA from a fossilized stingless bee (Hymenoptera,Apidae) caught in amber of the Tertiary Period (25-40 millionyears old) in the Dominican Republic.
Their weevil, states the Nature paper, "represents the oldestknown amber containing insect inclusions" and "the oldestfossil DNA ever extracted and sequenced, extending by 80million years the age of any previously reported DNA."
Amber specimens are dated mainly by the geologic formationsin which they are embedded, and by nuclear magneticresonance. NMR, Cano explained to BioWorld, measures theconcentration of exometal groups in a sample of amber. Theolder it is, the fewer the groups that remain.
To exhume the weevil non-destructively, they froze its surface-sterilized amber tomb rock-hard in liquid nitrogen, thendripped several drops of hot saline solution on it near the edgewhere the insect lay. This heat shock put a crack in the amber,through which a slender hypodermic needle was able to suctiontwo tissue pellets, one from the insect's gut, the other from itsthorax.
Cano's lab treated these samples with a chelating agent toremove heavy metals and facilitate DNA extraction. The 315-and 226-base-pair fragments were amplified approximately 1billion times by polymerase chain reaction, then sequenced.
As Cano related, "We were using 500 units of Taq polymerase aweek, and that's a bunch. Five hundred amplifications for overthree months, and probably having a success rate of 16 or 17percent." He explained, "We were looking primarily forribosomal genes, of which there were many copies in each cell,so we were bound to find enough targets to work with."
By comparing its nucleic-acid sequences with genomes ofseveral living weevils and other insects, the team confirmedthat their extinct insect is a new genus and species of weevil,Libanorhinus succinus, from the extinct Eobelinae subfamily ofthe Nemonychidae family, in the Curculionidea super family ofbeetles (Coleoptera).
DNA data from fossils, said Poinar, "may provide an insight intothe pattern of molecular evolutionary change, and gauge therate of genetic mutation through time." He added, "This workshows how tenacious DNA really is."
Cano's "personal research goals" follow two tracks:
A) "To trace the evolution of viral and protozoal parasites thatare transmitted by insects to humans -- especially the agentsof malaria.
B) "To see if we can study the evolution of dinosaurs,something along the lines of the Jurassic Park strategy."
As for that best-selling, major-movie strategy, though, Canostated, "I don't think it's doableHto reconstruct a livingdinosaur from an insect that's made a meal on extinct dinosaurblood, a la Jurassic Park." He goes on: "You'd have to put littlepieces of DNA together, in the right chromosomes, guess howmany chromosomes, where the genes go. It's impossible."
He explains why: "We can't even clone a modern lizard. We cantake its cells, take DNA, but we're still unable to clone thewhole animal. We don't know the technique, the environment,what's going on in the cell during development."
He and his team are now examining fossil insects that appear tohave fed on the blood of very large animals in the CretaceousPeriod, Cano said, such as dinosaurs. "We are looking at twonuclear and two mitochondrial genes, to try to justify thestatement: 'Yes, this is dinosaur DNA; no it isn't.' "
What DNA analysis of amber-trapped plant and animal life caneventually do, Poinar suggested, is "clear up a long-standingquestion: Whether dinosaurs are more closely related to birdsor to reptiles."
Poinar and Cano have also been investigating fossil bacteriaand plants. "Within the next week or so," Cano said, "we expectto have another paper in Nature on extinct legumes fromDominican Republic amber. We are trying to see the spectrumof organisms and the span of time from which DNA can beretrieved."
-- David N. Leff Science Editor
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