Fossils of ancient chromosomes discovered

To explain this apparent contradiction, the researchers realized that the chromosome fossils were in a very special state, closely resembling the state of molecules in glass. “Chromoglass is a lot like the glass in your window: it’s rigid, but it’s not an ordered crystal,” said Dr. Erez Lieberman Aiden, co-corresponding author of the study, director of the Center for Genome Architecture and professor at the Baylor College of Medicine. “If you zoom in on the individual particles, a piece of glass – or a piece of chromoglass – is basically a bumper-to-bumper nano-scale traffic jam, in a world with no lane markers. Individual particles, or individual fragments of ancient DNA, just can’t move very far in that situation. Even if you wait for thousands and thousands of years.”

The idea that the mammoth remains, unearthed in 2018 in Siberian permafrost, were preserved in a glass-like state is not so farfetched. Without realizing it, many civilizations developed ways to induce a “glass transition” in their food as a way to preserve it, usually by a combination of cooling and dehydration. This resulted in foods, like tortilla chips and beef jerky – that are more brittle than the original food, but that last much longer. And it is why the glass transition has become a key concept for modern food scientists. Essentially, the researchers discovered that the chromosome fossils had been trapped inside a piece of freeze-dried woolly mammoth jerky.

“We confirmed this theory by doing experiments on old, freeze-dried beef jerky, which is much easier to find than woolly mammoth jerky,” explained Dr. Cynthia Pérez Estrada, co-first author of the study and a researcher at the Center for Genome Architecture and at Rice University’s Center for Theoretical Biological Physics. “We fired a shotgun at it. We ran over it with a car. We had a former starting pitcher for the Houston Astros throw a fastball at it. Each time, the jerky broke into tiny bits – shattering like a glass. But at the nano-scale, the chromosomes were intact, unchanged. That’s the reason these fossils can survive. That’s the reason that they were there, 52,000 years later, just waiting for us to find them.”

Other authors include Marianne Dehasque, Claudia Fontsere, Sarah S. T. Mak, Ruqayya Khan, Vinícius G. Contessoto, Antonio B. Oliveira Junior, Achyuth Kalluchi, Bernardo J. Zubillaga Herrera, Jiyun Jeong, Renata P. Roy, Ishawnia Christopher, David Weisz, Arina D. Omer, Sanjit S. Batra, Muhammad S. Shamim, Neva C. Durand, Brendan O’Connell, Alfred L. Roca, Maksim V. Plikus, Mariya A. Kusliy, Svetlana A. Romanenko, Natalya A. Lemskaya, Natalya A. Serdyukova, Svetlana A. Modina, Polina L. Perelman, Elena А. Kizilova, Sergei I. Baiborodin, Nikolai B. Rubtsov, Gur Machol, Krisha Rath, Ragini Mahajan, Parwinder Kaur, Andreas Gnirke, Isabel Garcia-Treviño, Rob Coke, Joseph P. Flanagan, Kelcie Pletch, Aurora Ruiz-Herrera, Valerii Plotnikov, Innokentiy S. Pavlov, Naryya I. Pavlova, Albert V. Protopopov, Michele Di Pierro, Alexander S. Graphodatsky, Eric S. Lander, M. Jordan Rowley, Peter G. Wolynes, José N. Onuchic and Love Dalén.

See the publication for a full list of funding sources. Tom Gilbert and Erez Lieberman Aiden are advisors to Colossal Biosciences.

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