40,000-year-old woolly mammoth RNA offers a peek into its last moments

In the final moments of Yuka the woolly mammoth’s life, he may have been trying to outsprint a cave lion.

Yuka’s hind legs bear scratches — and in his muscle tissue, scientists have detected molecular signs of stress. Molecules called RNA hint that the mammoth’s muscles may have been exhausted. Sequences of those RNA molecules, which offer peeks into Yuka’s life 40,000 years ago, are the oldest ever recovered, scientists report November 14 in Cell. 

Scientists have sequenced ancient RNA before, determining the individual building blocks of the preserved molecules. But until now, the oldest RNA sequenced was about 14,000 years old, from a Pleistocene wolf. The new work suggests that ancient RNA may be able to persist far longer than scientists suspected, says Love Dalén, a biologist at Stockholm University.

When delving into the molecular biology of Ice Age animals, researchers typically focus on analyzing DNA — not RNA. “I think people just assumed that it wouldn’t work,” Dalén says, “so they haven’t tried.”

RNA has long been considered DNA’s more delicate cousin. Textbooks suggest that RNA degrades almost immediately after death. But in certain conditions, like the freezing environment that mummified Yuka’s remains, ancient RNA may stick around long term.

If DNA is the complete genetic instructions for how to build an animal, RNA is the building contractor that tells cells exactly what to build and when. Looking at RNA can give scientists a snapshot of a cell’s activity at a particular time, showing which genes were switched on or off, says Emilio Mármol-Sánchez, a geneticist at the University of Copenhagen. That can offer information about tissue type, and even an animal’s health and disease status.

Mármol-Sánchez, Dalén and their colleagues analyzed RNA from 10 woolly mammoths whose tissue had long laid frozen in the Siberian permafrost. RNA from Yuka was preserved enough for the team to uncover some new biological details. The researchers discovered signs of cellular stress, as well as molecules called microRNAs that could potentially play a role in making a mammoth a mammoth, Dalén says. For instance, the difference between mammoths and elephants — which have highly similar genetic blueprints — might lie in microRNAs that regulate activity of certain genes in one species and not the other.

The team’s paper offers a road map for working with ancient RNA, Mármol-Sánchez says. And that could help uncover new details about the lives and deaths of the iconic animals that once roamed Earth’s icy plains.