Giant Chromosomes Discovered in Conserved 'Ice-Preserved' Dermis
Ancient Mammoth Genomes: A Stunning Find
Crafty scientists have stumbled upon an extraordinary find in the tiniest bits of a colossal creature's remains: impeccably preserved genetic makeup in the 52,000-year-old relics of a woolly mammoth. The amazingly well-preserved hide contains intact mammoth chromosomes, granting researchers an unparalleled peek into the long-lost beast's biology.
As the last millennia ticked by, these hirsute behemoths became extinct around the same time as the early stages of Egyptian civilization flourished. For this groundbreaking study, though, the team scrutinized remains dating back about 52,000 and 39,000 years, a period when anatomically modern humans and Neanderthals cohabited the Earth.
Woolly mammoth remains dot the vast steppe where they once roamed, often found preserved in permafrost – permanently frozen soil. The cycle of thawing and refreezing can wreak havoc on the microscopic structures within the animals' soft tissue, but preservation can sometimes be nothing short of astounding. In 2022, for example, an incredibly preserved mammoth calf was found in a Yukon gold mine. Yet, this recent discovery showcases preservation on an unprecedented scale: molecular preservation. The researchers' findings were unveiled today in Cell.
"We probed, excavated, and eventually zoomed in," said Erez Lieberman Aiden, a computer scientist, geneticist, and study co-author, during a press conference last Tuesday, "and we found ourselves in the presence of something new – a previously unknown kind of fossil."
Chromosomal Survival: Ancient Secrets Revealed
The 52,000-year-old samples still retained fine hairs at the millimeter scale, indicating that the woolly mammoth froze because it was flash-frozen. According to the researchers, this freeze-drying preservation method suggests that the animal froze around 10,000 years before Neanderthals disappeared, as the hair implies no thawing since then. Consequently, the skin and fur remained intact, cells within their regions, including the intricate folds of chromosomes. The study team could even observe the genetic loops that controlled gene expression.
"This sample effectively turned into beef jerky," Leiberman Aiden explained, referring to meat that has undergone a glass transition, making it enduring. When it freeze-dried, the mammoth's hide became a molecular traffic jam on a microscopic scale, preventing chromosomes from diffusing. The skin samples became time capsules for the ancient molecules, which the team dubbed "chromoglass."
The researchers' findings enabled the first genome assembly in an extinct species. Indeed, mammoths shared 28 chromosomes with elephants, unlike humans with our 23. The team has reconstructed the mammoth's chromosomes in three dimensions; to them, it resembles a labyrinthine Gordian knot. However, for scientists, it is a breathtakingly precise snapshot of the microscopic structures that constructed the Ice Age titans.
"The genetic variation that this mammoth genome reveals is opening a new door for comparisons between species," said Cynthia Pérez Estrada, a researcher at Baylor College of Medicine and co-author of the paper, during the press conference. "Just having that DNA blueprint in three-dimensional space is extraordinary."
Mammoth 'Jerky' Protected the Chromosomes' Molecular Structure
The team subjected the chromoglass to a torrent of tests aimed at destroying its molecular structure. In place of the desiccated mammoth hide, they used Boar's Head beef bologna, which shares the same molecular structure. The researchers soaked the chromoglass beef in water, acid, and liquid nitrogen; they microwaved it, hit it with baseballs and a mallet, ran it over with a car, and shot it with shotgun shells (as illustrated below). Despite the material becoming fragmented, the chromosomal structure stayed intact on a microscopic scale.
"We might have produced the first [preserved chromosomes]", said Olga Dudchenko, a genomics researcher at Rice University and Baylor College of Medicine, and co-author of the research. "We suspect many more will be found in the coming years."
The new research reveals previously unseen molecular preservation in ancient remains. While older DNA has been found – in fact, a handful of the study's authors were part of the team that published research on the oldest preserved DNA, in million-year-old mammoth tusks – the newly described remains now enable scientists to explore gene expression and genome assembly within these mammoths. The current record-holder for the oldest sequenced DNA belongs to a swath of environmental DNA recovered from northern Greenland, from which researchers were able to reconstruct the ancient environment of the early Pleistocene.
Teasing Apart the Tree of Life
The Asian elephant serves as the woolly mammoth's closest living relative. By studying elephant genes, scientists can improve their understanding of mammoth genetics, and vice versa. Artificial intelligence (AI) tools can help scientists decipher protein binding sites and folding patterns within mammoth DNA, even with limited data. Beyond the Asian elephant, AI tools can place the mammoth genome within the broader context of the tree of life.
"Even a smidgen of genetic data about mammoths can yield a wealth of information," Lieberman Aiden explained to Gizmodo.
The marvelous fusion of new technologies, innovative techniques, and good fortune is unveiling the ancient world in ways never before imagined. Understanding the mighty mammoth on molecular scales sheds light on the remote past, but it also sheds light on the conservation and study of contemporary animals for the future.
- The extraordinary chromosomal preservation found in 52,000-year-old mammoth remains provides a breathtakingly precise snapshot of the Ice Age titans for scientists.
- Researchers believe that many more preserved chromosomes similar to the one found will be discovered in the coming years, thanks to advancements in technology and preservation techniques.
- The study of mammoth chromosomes, combined with AI tools, could help placed the mammoth genome within the broader context of the tree of life, providing important insights about contemporary animals and future conservation efforts.
- In 2022, an incredibly preserved mammoth calf was found in a Yukon gold mine, demonstrating astounding preservation on a scale not previously seen in ancient remains.
