In the vast, icy expanses of Siberia, nature has preserved the remains of woolly mammoths with a level of detail that has captivated scientists for decades. Now, a team of researchers has harnessed the power of these cryogenic chronicles to unravel the genetic tapestry of these iconic Ice Age creatures.
The study, published in the prestigious journal Cell, focuses on two remarkably well-preserved woolly mammoth specimens: a 52,000-year-old individual and a 39,000-year-old specimen named Yuka, regarded as one of the most intact mammoths ever discovered. By analyzing small skin samples from these frozen giants, the researchers have achieved a remarkable feat – the reconstruction of the mammoths' three-dimensional genomes.
Look at that woolly mammoth. It's beautiful, marveled Erez Lieberman Aiden, an author of the study and professor of molecular and human genetics at Baylor College of Medicine, where he directs the Center for Genome Architecture. The hair is still on it, and you see long stretches of its skin.
The key to this breakthrough lies in the unique preservation conditions of the Siberian landscape. The dry, frigid winters of the region have allowed these mammoths to enter a dehydrated state shortly after death, protecting them from the ravages of fungi and bacteria that typically degrade ancient DNA samples.
This work is about the fact that under certain circumstances, ancient samples can be preserved in this special way about which we didn't know, explained Olga Dudchenko, another study author and assistant professor at Baylor College of Medicine.
Most ancient DNA samples are severely fragmented, making it challenging to reconstruct the full genome. However, the researchers found that the mammoth DNA fragments in their samples had remained relatively intact, with the chromosomes still organized into clear territories within the skin cells.
Knowing the structure of the genome, you can figure out which genes were active in that particular animal at the moment that it died and which genes were repressed, said Marc A. Marti-Renom, an author of the study and professor at the National Center for Genomic Analysis in Barcelona.
The team developed a new technique, called Paleo Hi-C, which allowed them to interpret the 3D structure of the mammoth's genome. Their findings revealed that the mammoths had 28 pairs of chromosomes, just like their closest living relative, the elephant.
By analyzing the chromosome arrangements, the researchers were able to identify genes that may have been responsible for the mammoths' distinctive features, such as their thick fur and ability to thrive in cold environments.
This allows you to computationally reconstruct the genome to a much better extent, said Anders Sejr Hansen, an associate professor of biological engineering at MIT who was not involved in the study.
The implications of this breakthrough extend beyond the realm of ancient genomics. Patrícia Chrzanová Pečnerová, an assistant professor of evolutionary genetics at the University of Copenhagen, emphasized the importance of understanding the natural state of species for conservation efforts.
If we want to be able to understand what is natural, we have to go back in the past, Pečnerová said. We have to study how the species and how the population looked like before, for example, people started hunting it a lot or before climate change happened.
Eriona Hysolli, head of biological sciences at Colossal Biosciences, a company working to reintroduce a version of the woolly mammoth to the Arctic, noted that the 3D chromosome structures found in the study could reveal features of the genome that might be relevant to mammoth de-extinction.
As the scientific community continues to unravel the mysteries of the past, the cryogenic chronicles of woolly mammoths have once again proven to be a treasure trove of information, shedding new light on the genetic tapestry of these iconic Ice Age giants.
