Evrim Yazgin
Cosmos science journalist
Researchers have assembled the genome and 3D structures of a 52,000-year-old woolly mammoth. It is the first time cell-specific gene activity has been measured in ancient DNA.
The researchers say they discovered an entirely new type of fossil which has superbly preserved ancient remains which led to the first ever 3D assembly of a chromosome.
This was possible because the mammoth’s remains freeze-dried shortly after it died. Its DNA was preserved in a glass-like state.
The woolly mammoth was discovered in Siberia in 2018. The research is published in the journal Cell.
“This is a new type of fossil, and its scale dwarfs that of individual ancient DNA fragments—a million times more sequence,” says corresponding author Erez Lieberman Aiden, Director of the Center for Genome Architecture at Baylor College of Medicine.
Being able to reconstruct the fossilised chromosomes provides insight into how the mammoth’s genome was organised in its living cells and which genes were active in the skin tissue.
Using modern elephants as a baseline, the scientists were able to put the giant DNA puzzle together. It led them to create the first ever ancient karyotype – an individual’s complete set of chromosomes. It revealed woolly mammoths have the same number of chromosomes as today’s African and Asian elephants – 28.
The mammoth’s genomic structure was reconstructed using DNA extracted from the skin on the animal’s ear.
A method called Hi-C was used to detect sections of DNA likely to be in close proximity to and interact with each other.
“Imagine you have a puzzle that has 3 billion pieces, but you don’t have the picture of the final puzzle to work from,” says corresponding author Marc A. Marti-Renom, a Catalan Institution for Research and Advanced Studies research professor. “Hi-C allows you to have an approximation of that picture before you start putting the puzzle pieces together.”
Bringing the DNA together allowed the researchers to see which genes were active and which were turned off in the skin cells.
The mammoth’s skin showed unique gene activation patterns compared to its closest living relative, the Asian elephant. It is possible these genes control its woolly-ness and cold tolerance.
“These results have obvious consequences for contemporary efforts aimed at woolly mammoth de-extinction,” says corresponding author M. Thomas Gilbert from the University of Copenhagen and the Norwegian University of Science and Technology.
The method used could also be applied to other ancient DNA specimens including other mammoths and mummified people from Egypt and other parts of the world.
