Under the right conditions, DNA has been known to last for thousands of years, allowing scientists to study the genomes of ancient Egyptians, the very first Brits, and even early human ancestors. RNA, on the other hand, degrades much more quickly and was thought impossible to recover in older samples. But now researchers have done exactly that, isolating and sequencing the RNA of a 14,000-year-old wolf found frozen in the Siberian permafrost.
DNA is where genetic information is stored long-term in an organism, and it's so effective at its job that scientists are currently investigating it as a data storage system that could far outlive conventional discs and magnetic drives. But RNA is the "working copy" of genes, giving it a much higher turnover – possibly as short as two minutes. As a result, it was long believed that recovering RNA "transcriptomes" from ancient cells was nigh on impossible.
But there have been a few exceptions. The oldest RNA to be sequenced and verified is 700-year-old maize, while the oldest recovered but not able to be sequenced came from the 5,000-year-old Tyrolean Iceman. So for the new study, researchers from the University of Copenhagen, University of Tübingen, Northeastern Federal University, and the Royal Belgian Institute of Natural Science, examined a much older sample.
This sample came from a specimen nicknamed the Tumat Puppy, which is the mummified remains of a Pleistocene era wolf or dog, dated to around 14,300 years old. The team isolated and analyzed RNA taken from the animal's liver tissue, and compared it to tissue from two much more recent wolf samples, from the 19th and 20th centuries.
The team successfully sequenced the older animal's RNA, and confirmed that it was representative of the creature's RNA as a whole by matching it to liver-specific transcripts from the more modern wolves. That makes this the oldest transcriptome ever sequenced, by at least 13,000 years.
"Ancient DNA researchers have previously been reluctant to attempt to sequence ancient RNA because it is generally more unstable than DNA, and more prone to enzymatic degradation," says Oliver Smith, lead author of the study. "However, following our recent successes in sequencing ancient RNA from plant material, we speculated that a well-preserved animal specimen, frozen in the permafrost, just might retain enough material to sequence. To our delight, we found that not only did we find RNA from various tissues, but in some case the signal was so strong that we could distinguish between tissues in a way that makes biological sense."
The research was published in the journal PLOS Biology.
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