Woolly mammoth DNA exceptionally preserved in freeze-dried ‘jerky’

by Pelican Press
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Woolly mammoth DNA exceptionally preserved in freeze-dried ‘jerky’

Legs of a juvenile female woolly mammoth named Yuka

The legs of a 39,000-year-old woolly mammoth

Love Dalén/Stockholm University

A woolly mammoth that died 52,000 years ago is so well preserved that it is possible both to read its full genome and to reconstruct the three-dimensional structure of its chromosomes – information that can provide unprecedented details about how the animal’s genes behaved during its life. The extraordinary feat was possible because the animal’s remains were naturally freeze-dried, preserving its DNA in a glass-like state.

Scientists found the mammoth remains in a cave in Siberia in 2018 where they had been preserved in the permafrost. The mammoth’s tissues were dry, “but not as dry as commercial beef jerky”, says Olga Dudchenko at Baylor College of Medicine in Texas, “and it was actually woolly”. Eager to see what genetic information they could glean, Dudchenko and her colleagues sampled flesh behind the mammoth’s ear and sequenced the DNA.

Because molecules of DNA begin to break down when an animal dies, scientists have previously only been able to find tiny snippets of the woolly mammoth genome – but to the researchers’ surprise, the animal’s chromosomes were perfectly preserved. “This does not match with anything that we have analysed before that was 52,000 years old, so that was very surprising,” says Juan Antonio Rodríguez at the University of Copenhagen in Denmark, a member of the research team.

They also found that the mammoth had 28 pairs of chromosomes – the same number as their closest living relative, the Asian elephant. The chromosomes’ three-dimensional structure was also preserved, which helps distinguish active genes from inactive ones. The researchers found, for example, that the gene responsible for hair growth was more active in the mammoth than in elephants, explaining their shaggy coats.

Identifying which genes are active in woolly mammoths versus elephants may boost so-called de-extinction efforts, says Hendrik Poinar at McMaster University in Canada, who was not involved in the work. “To get as close to a real mammoth as possible, one needs to know how the [genetic] architecture differs from an Asian elephant,” he says. Understanding which genes to tweak – such as those that produce lots of hair – could help create more realistic-looking and sounding animals that closely resemble the ancient pachyderms, though they would not be true woolly mammoths.

But how did this DNA stay intact for more than 50,000 years without unravelling? The researchers credit the ideal conditions of the cave, which simultaneously chilled and desiccated the animal. “The sample lost much of its water into the cold and dry Siberian winter,” says Dudchenko. She adds that a broadly similar drying process occurs during the production of foods like prosciutto.

To check their theory, the researchers put fresh and freeze-dried beef liver through a series of tough tests. After three days at room temperature, the DNA in the fresh beef was in fragments. But the freeze-dried stuff kept its chromosome structure on the nanometre scale even after a year. “At that point, we were like, okay, time doesn’t kill it – what does?” says Dudchenko.

So they fired a shotgun at the mock mammoth jerky, ran over it with a car and had a former professional baseball player throw a fastball at it, all to try to destroy its DNA. Each time, the dried beef liver shattered into small pieces but maintained its microscopic structure, preserving the DNA inside. “We found out that it works – it survives,” says Rodríguez.

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