A Mammoth Job

With its shaggy coat and giant, up-turned tusks, the woolly mammoth was well-adapted to Ice-Age cold. That same cold held the secrets of the animal's DNA for some 28,000 years until scientists from Penn State and McMaster Universityuncovered it last year.

From a mammoth jawbone recovered near a frozen riverbank in northern Siberia, a team led by Stephan Schuster, associate professor of biomolecular biology at Penn State, and Hendrik Poinar, associate professor of anthropology at McMaster, was able to obtain the first genomic sequence for the long-extinct mammal. They did it using a computational sequencing technique that allowed them to compare the mammoth's DNA to that of modern elephants.

"We are trying to explore the limits of DNA sequencing in my lab, and one of the challenges is mapping old, fragmented DNA," Schuster explains. "For a long time people believed it wouldn't be possible to sequence substantial amounts from extinct organisms." At a remove of thousands of years, environmental contamination inevitably dilutes the genetic "signal," meaning scientists working with ancient fragments were forced to rely on mitochondrial DNA, which is much more robust than the DNA located in the cell nucleus, but contains only a tiny fraction of an organism's genetic information.

With the new technique, however, and an exceptionally well-preserved specimen, the Schuster-Poinar team was able to focus on the nuclear DNA. They sequenced 28 million base pairs, Schuster says, and found that fully half of that DNA came from the mammoth. "Fifty per cent is absolutely amazing. All the previous studies working with DNA from extinct mammals found not even one percent."

The remaining DNA identified in the sample was traceable to plants, nematodes, and other organisms that had fused to the bone during all those years in the permafrost, Schuster explains, and even some to bacteria encountered during the purification process.

When they compared the mammoth DNA to that of the modern African elephant, he adds, they found it to be 98.5 percent identical, confirming the estimates of paleontologists that the two species diverged between 5 and 6 million years ago.

The team is seeking funding to complete sequencing of the mammoth genome. But already their success has signaled that other extinct species, conserved in ice, may yield up their genetic—and evolutionary—secrets.

Stephan C. Schuster, Ph.D., is associate professor of biochemistry and molecular biology in the Eberly College of Science; scs19@psu.edu.

Last Updated September 11, 2006