July 24, 2024

Researchers have reconstructed the genetic code of the woolly mammoth in unprecedented detail after discovering fossilized chromosomes in the skin of a 52,000-year-old carcass preserved in the Siberian permafrost.

The mammoth’s luxuriant mane led researchers to name it after it Chris Waddle, the mulleted former English footballer. It became freeze-dried upon 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 piece together the mammoth genome, determine that it had 28 pairs of chromosomes, and see which genes were turned on or off, details crucial to understanding what it means to be a mammoth.

Prof Erez Lieberman Aiden, the director of the Center for Genome Architecture at Baylor College of Medicine in Houston, said the samples were “a new kind of fossil” that “preserved biomolecules for large periods of time” and contained far more information than those studied is. before.

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 piece together the entire DNA sequence of an extinct creature , which provides insight into their biology that was previously unknown. of reach.

The scientists believe that the animal’s skin spontaneously freeze-dried shortly after death. Photo: Love Dalén/Stockholm University

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 unearthed in northern Siberia in 2018. They believe the animal’s skin had spontaneously freeze-dried shortly after death, preserving the tissue through a similar process used to make beef.

The mammoth was named Chris Waddle when scientists who found the carcass noticed its impressive mane. “It is not clear that this is exactly the hairstyle the mammoth had while it was alive,” said Dudchenko. “And it later turned out that the mammoth was female.”

Analysis of the skin revealed that the 3D structure of the mammoth’s chromosomes was preserved in the dehydrated cells after being transformed into a robust glassy material. Once formed, the fossil specimens, labeled chromoglas, can last for millions of years, the researchers said written in the journal Cell. In a series of unusual tests, the researchers showed that the DNA can survive in tissues that have been run over by a car, hit with a baseball or blasted from a shotgun.

Until now, ancient DNA recovered from extinct species was highly fragmented. The scraps allow scientists to see small-scale genetic differences between extinct animals and their living relatives, but little else. In contrast, the new samples contain hundreds of millions of code letters, revealing the large-scale structure of the genome.

As well as being able to assemble the mammoth’s genome and count its chromosomes, the scientists found that the arrangement of chromosomes within the cells showed which genes were activated, including genes linked to woolliness and cold tolerance.

The work promotes plans to bring back the woolly mammoth, a feat researchers hope to accomplish by rewriting the genome of an Asian elephant to match that of a mammoth. “Is that sufficient 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 someone wants to transform a modern elephant into a mammoth. This is one step forward in that direction.”

The 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 giant expert at the Natural History Museum who was not involved in the study, called the research “amazing”.

“Until now, ancient DNA research has relied on a ‘soup’ of small bits of DNA extracted from ancient tissues,” he said. “In the case of this mammoth carcass preserved in arctic permafrost, the researchers were able to recover chromosomes with their DNA intact, and the chromatin protein essential for their function intact.”

He added: “This new work opens up huge new possibilities for investigating the biology of extinct species. This exceptional preservation can be found in fossils much older than the 51,000-year-old mammoth, back to 2 million years ago, opening up the possibility of investigating the biology of much older extinct species and their relationship to and differences from living relatives .

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