We once thought that only the hard parts of an animal fossilized, and that it was therefore impossible to recover genetic material from a fossil. Then we discovered that, under certain conditions, even DNA and proteins can be preserved for thousands of years; until recently, however, we thought that RNA, i.e. the “active part” of DNA, was too fragile, and only lasted a few hours after the death of an organism.
Now, a group of researchers from Stockholm University has also dispelled this last myth in a study published in Cell: The team succeeded for the first time in extracting RNA from a woolly mammoth that died 40,000 years ago.
Yuka and the lions. The credit for this discovery, in addition to obviously the scientists who made it, must be attributed to the Siberian permafrost: it is there that, 40,000 years ago, the woolly mammoth named Yuka died, ending up trapped in the ice – an ideal condition for the perfect preservation of its tissues and the genetic material it contains.
Yuka was a young specimen, who died a violent death: previous studies on the animal showed that he had just suffered an attack by a pride of cave lions. This detail is not secondary: the RNA found in Yuka’s tissues is linked to the production of some proteins that control muscle contraction, and others that are instead linked to the regulation of metabolism in the event of stress.
Molecular time machine. Yuka’s RNA, therefore, demonstrates that it is possible to study “genetic regulation in real time even in an extinct animal” according to one of the study’s authors, Marc Friedländer. Among the most interesting molecules found in mammoth tissues are, among other things, small pieces of non-coding RNA, the so-called microRNA; some of these have made it possible, among other things, to identify new genes, an absolute novelty in the field.
The importance of the study is summarized thus by another of the study’s authors, Love Dalén: «These results demonstrate that RNA molecules survive much longer than we believed. This will allow us not only to study which genes were active at the time of the death of an extinct animal, but also to sequence RNA viruses preserved in these fossils.”
The next step will be to understand exactly how long RNA can survive in a fossil, and establish how far back in time it allows us to go.