As part of a landmark study, a team of researchers from Stockholm University and the Swedish Museum of Natural History have successfully isolated and sequenced RNA molecules from a juvenile woolly mammoth that lived in the frozen wilderness of Siberia roughly 40,000 years ago.
The study, published today in the journal Cell, offers proof that RNA, like DNA and proteins, can be preserved for long periods of time.
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It was long thought RNA was too fragile to survive such long periods and that it would never be found in animal remains beyond a certain time. Prior to this latest study, the oldest RNA on record came from a 14,300-year-old prehistoric dog that was also found preserved in Siberian permafrost.
“With RNA, we can obtain direct evidence of which genes are ‘turned on’, offering a glimpse into the final moments of life of a mammoth that walked the Earth during the last Ice Age. This is information that cannot be obtained from DNA alone,” says the study’s lead author Emilio Mármol.
RNA is a single-stranded molecule found in all living cells. It acts as a messenger, carrying instructions from DNA to the structures inside cells that synthesise proteins. While DNA can tell us about an animal’s genome and its evolutionary history, it’s RNA that tells us exactly how its genes are expressed - in other words, which genes are turned 'on’ and which genes are turned 'off’.
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Amongst the frozen muscle remains dissected from Yuka, the juvenile woolly mammoth that formed the basis of this recent study, researchers discovered RNA molecules that code for proteins with key functions in muscle contraction and metabolic regulation under stress.
“We found signs of cell stress, which is perhaps not surprising since previous research suggested that Yuka was attacked by cave lions shortly before his death,” explains Mármol.
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The team also found a large number of RNA molecules that regulate gene activity in the mammoth’s muscles.
“RNAs that do not encode for proteins, such as microRNAs, were among the most exciting findings we got,” says co-author Marc Friedländer. “The muscle-specific microRNAs we found in mammoth tissues are direct evidence of gene regulation happening in real time in ancient times. It is the first time something like this has been achieved.”
The implications of this latest study are huge, explains senior author Love Dalén: “Our results demonstrate…it will also be possible to sequence RNA viruses, such as influenza and coronaviruses, preserved in Ice Age remains.”
The team hopes to conduct further studies that combine prehistoric RNA with DNA, proteins, and other preserved biomolecules to get a better idea of how long-extinct animals, such as mammoths, lived.
“Such studies could fundamentally reshape our understanding of extinct megafauna as well as other species, revealing the many hidden layers of biology that have remained frozen in time until now,” Mármol concludes.
Top image: Yuka slowly emerging from the Siberian permafrost in 2010, at the site of Oyogos Yar in northeastern Siberia. Credit: Grigory Gorokhov
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