Oldest known RNA found in 40,000-year-old woolly mammoth leg

A 40,000-year-old juvenile woolly mammoth named Yuka isn’t just notable because it was discovered almost intact or for the grisly cause of its death. Its muscles provided paleogeneticists with the oldest known RNA sequences ever recovered. Detailed in a study published November 14 in the journal CellThe samples contradict previous hypotheses about the resilience of genetic material while deepening our understanding of the famously extinct megafauna.

Although the last woolly mammoths succumbed to global warming around 4,000 years ago, the vast majority of them lived and died during the last ice age. Since then, paleontologists have unearthed numerous specimens in regions like Siberia, where frozen tundra and permafrost often keep the remains remarkably well preserved.

Among them, a woolly mammoth stands out from all the others. In 2010, local tusk hunters discovered the almost intact remains of a juvenile near the coast of the Dmitry Laptev Strait in Siberia. Later nicknamed Yuka, the specimen still has much of its fur, as well as remains of tusks, trunk and small ears. Even standing nearly 10 feet tall and weighing nearly five tons, Yuka likely died during an attack by cave lions. It has remained the gold standard for woolly mammoths for nearly 25 years and constantly provides researchers with new information about the species and its genetic makeup.

The latest revelations about RNA come from a collaboration between researchers at Stockholm University and the Swedish Museum of Natural History. RNA, short for ribonucleic acid, is a polymer molecule responsible for gene expression and is vital for most biological functions.

“Using RNA, we can obtain direct evidence of which genes are ‘turned on,’ providing insight into the final moments of the life of a mammoth that walked the Earth during the last ice age,” paleogeneticist and study co-author Emilio Mármol said in an accompanying statement. “This is information that cannot be obtained from DNA alone.”

For years, researchers assumed it was nearly impossible to collect this type of genetic evidence from a woolly mammoth. Although the ability to salvage DNA and some other proteins now spans more than a million years, RNA has long been considered too fragile to survive even a few hours after death. But Mármol and his colleagues suspected otherwise.

“We wanted to explore whether we could extend RNA sequencing further back in time than in previous studies,” explained Love Dalén, an evolutionary genomicist from Stockholm University and co-author of the study.

Mármol, Dalén and their collaborators knew that if an ancient specimen still had RNA, it would be a well-preserved mammoth like Yuka. After examining samples of his frozen muscles, Mármol’s team looked through more than 20,000 protein-coding genes, many of which were inactive. They ultimately identified RNA molecules responsible for encoding key protein functions in muscle building and stress-related metabolic regulation. These findings added further evidence to the theory of Yuka’s final moments.

“We found signs of cellular stress, which is perhaps not surprising since previous research suggested that Yuka had been attacked by cave lions shortly before [her] death,” said Mármol.

Besides RNA itself, scientists have also located microRNAs that do not code for proteins.

“[MicroRNAs] “The muscle-specific microRNAs we found in mammoth tissue are direct evidence of gene regulation that was happening in real time in ancient times.” This is the first time anything like this has been done. »

“Our results demonstrate that RNA molecules can survive much longer than previously thought,” Dalén added.

Dalén added that the team now believes it will soon be able to look at “activated” genes in other extinct animals, but that progress isn’t just about creatures from the distant past. Other advances could help sequence RNA viruses like influenza and Ice Age coronaviruses.

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