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Three-dimensional genome architecture persists in a 52,000-year-old woolly mammoth skin sample – publication
A team led by scientists from Baylor College of Medicine, University of Copenhagen, and Centre Nacional d’Anàlisi Genòmica and Centre for Genomic Regulation report discovering fossils of ancient chromosomes in the remains of a woolly mammoth that died 52,000 years ago.
The fossils preserve the structure of the ancient chromosomes down to the nanometer scale – billionths of a meter. Fossil chromosomes are a powerful new tool for studying the history of life on Earth. That’s because typical ancient DNA fragments are rarely longer than 100 base pairs, or 100 letters of the genetic code – far smaller than the full DNA sequence of an organism, which is often billions of letters long. By contrast, fossil chromosomes can span hundreds of millions of genetic letters. Since the fossil chromosomes came from a mammoth, one of the first things the team did was to determine the number of chromosomes that the woolly mammoth possessed. By examining the fossil chromosomes, which derived from the mammoth’s skin, it was possible to see which genes were active. This is because of a phenomenon called chromosome compartmentalization – the fact that active and inactive DNA tends to segregate into two spatial neighborhoods inside the cell nucleus. For most genes, the activity state matches what researchers saw in modern elephant skin. But not always. The researchers saw more than just compartmentalization in the shape of these ancient chromosomes. In fact, the chromosomes shared many structural features with modern chromosomes. The most spectacular of these features was also the tiniest: chromatin loops, structures as small as 50nm that the Baylor team had mapped in humans, for the first time, only 10 years ago.