Researchers have reconstructed the woolly mammoth’s genetic code in unprecedented detail after discovering fossilized chromosomes in the skin of a 52,000-year-old carcass preserved in Siberian permafrost.
The mammoth’s generous crepe led researchers to name it after Chris Waddle, the former England footballer. It was freeze-dried after death, a process that preserved the 3D structure of the chromosomes in the animal’s skin.
Armed with the ancient genetic material, scientists were able to assemble the mammoth’s genome, determine that it had 28 pairs of chromosomes and see which genes were turned on or off, details that are essential to understanding what it means to be mammoth.
Prof Erez Lieberman Aiden, director of the Center for Genome Architecture at Baylor College of Medicine in Houston, said the samples were “a new type of fossil” that “preserved biomolecules over long periods of time” and contained much more information than those of studied. money.
Dr Olga Dudchenko, also at Baylor, said the discovery of fossil chromosomes was a “game changer” because knowing the shape of an organism’s chromosomes made it possible to assemble the entire DNA sequence of an extinct creature, providing knowledge in their biology that they were before. of achievement.
The international team of researchers tested dozens of samples over five years before striking gold with a piece of skin taken from behind the ear of a mammoth excavated in northern Siberia in 2018. They believe the animal’s skin spontaneously freeze-dried shortly after death. , preserving tissue through a similar process used to make corned beef.
The mammoth was named Chris Waddle when scientists who found the carcass noticed the impressive mane. “It is not clear that it is exactly the hairstyle the mammoth had when it was alive,” Dudchenko said. “And later it turned out that the mammoth was female.”
Analysis of the skin revealed that the 3D structure of the mammoth chromosomes was preserved in the dehydrated cells after it was transformed into a hard glass-like material. Once formed, the fossil samples, named chromoglass, could last for millions of years, the researchers write in the journal Cell. In a series of unusual tests, researchers showed that DNA can survive in tissue hit by a car, hit by a baseball or blasted by a gun.
Until now, ancient DNA recovered from extinct species has been very fragmented. The pieces allow scientists to distinguish small-scale genetic differences between extinct animals and their living relatives, but little else. In contrast, the new samples contain hundreds of millions of letters of code, revealing the large-scale structure of the genome.
Beyond being able to assemble the mammoth’s genome and count its chromosomes, the scientists discovered that the arrangement of chromosomes within cells indicated which genes were activated, including genes related to fur and cold tolerance.
The work spurs plans to bring back the woolly mammoth, a feat researchers hope to achieve by rewriting the genome of an Asian elephant to match that of a mammoth. “Is it enough for extinction? Probably not,” said Prof Marc Marti-Renom at the National Center for Genomic Analysis in Barcelona. “There is still a lot of work to be done if one wants to transform a modern elephant into a mammoth. It’s a step forward in that direction.”
Researchers hope to find more fossil chromosomes in other extinct animals and in Egyptian mummies, many of which may already exist in museum collections.
Prof Adrian Lister, a senior expert at the Natural History Museum, who was not involved in the study, called the research “amazing”.
“Ancient DNA research has so far relied on a ‘soup’ of small DNA fragments extracted from ancient tissues,” he said. “The researchers were able, in the case of this mammoth carcass preserved in Arctic permafrost, to obtain intact chromosomes with their DNA and the chromatin protein essential to their function intact.”
He added: “This new work opens up huge new opportunities to explore the biology of extinct species. This remarkable preservation can be found in fossils much older than the 51,000-year-old mammoth, 2 million years ago, opening the possibility to investigate the biology of much older extinct species and their relationships and differences from their relatives. alive