Fossils of ancient chromosomes with intact three-dimensional structure belonging to extinct woolly mammoth have been discovered from 52,000 old sample preserved in Siberian permafrost. This is the first case of fully preserved ancient chromosome. Study of fossil chromosomes can shed light on the history of life on Earth.
Fossils of ancient chromosomes have been discovered from the skin of a 52,000 years old woolly mammoth remains found in Siberian permafrost in 2018. Woolly mammoth (Mammuthus primigenius) is an extinct species. Their closest living relatives are modern elephant.
The fossil chromosome showed remarkable similarity with the modern chromosomes. The fossil had same 28 pairs of chromosomes as in the closest living relative. The shape of the fossil chromosomes displayed chromosome compartmentalization, i.e., separation of the active and inactive regions of the genome. Therefore, the researchers could identify active genes in the woolly mammoth. The fossil chromosomes had the entire 3D arrangement of DNA intact down to the nm (10-9) scale. Tiny chromatin loops which measure about 50 nm and play an important role in activation of sequences were observed in the fossil chromosomes.
The source animal of the fossil had died 52,000 years ago. The DNA segments in the fossil chromosomes remained unchanged and intact with their three-dimensional structures for such a long time because the animal remains had undergone glass transition through natural freeze-drying process and had remained in glass-like rigid state that forbade movement of fragments or particles in the sample.
This is first case of discovery of fully preserved fossil chromosomes and is significant because study of fossil chromosomes can shed light on the history of life on Earth. Ancient DNA research has limitation because aDNA fragments isolated from the archaeological samples are seldom longer than 100 base pairs. On the other hand, fossil chromosomes offer opportunity to study entire DNA sequence of an organism. Knowledge of complete genome and three-dimensional structure of chromosomes can also enable re-creation of entire DNA segment of an extinct organism.
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References
- Sandoval-Velasco, M. et al. 2024. Three-dimensional genome architecture persists in a 52,000-year-old woolly mammoth skin sample. Cell. Volume 187, Issue 14, p3541-3562.E51. 11 July 2024. DOI: https://doi.org/10.1016/j.cell.2024.06.002
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