Could We Clone Dinosaurs?

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Somewhere in South America, a miner finds a piece of amber. Inside the fossil tree resin, he notes what seems to be a mosquito. Using advanced equipment, scientists extract the last meal of the blood-sucking insect. Thanks to the genetic code perfectly preserved in the still intact blood cells, the scientists then clone a dinosaur. The 1990 science-fiction novel and later successful movie franchise “Jurassic Park” popularized the idea that amber could preserve soft tissue and even DNA-molecules over millions of years. But real attempts to extract DNA from amber or similar substances were unsuccessful to this day, and resin-embedded samples were deemed unsuitable for genetic examinations.

Unlike in the movies, fossil tree resin is not a good choice to preserve DNA, a fragile molecule carrying genetic instructions for the development, functioning, growth and reproduction of all known organisms. When a viscous substance traps a small animal, the soft tissue starts to decay immediately and most DNA is lost before the entire animal is even encapsulated. Even if some DNA is preserved, the resin’s chemical compounds will react with it, destroying it over time.

In 2020, a study published in the journal PLOS ONE attempted to determine if and how long the DNA of insects enclosed in resinous materials can be preserved. The researchers collected small ambrosia beetles that were trapped in the resin of amber trees (Hymenaea), a species endemic to the island of Madagascar. The chemical composition of this modern tree resin is very similar to fossilized amber. The samples were stored for 2 to 6 years and then processed.

The study concluded that although it is very fragile, DNA was still preserved in the samples. First attempts using ethanol to dissolve the resin surrounding the beetles proved to be counterproductive. The alcohol reacts with the resin, destroying any DNA. This observation may explain why past attempts to extract DNA were always unsuccessful. Even after perfecting the extraction process switching chemicals, new problems emerged. The polymerase chain reaction (or PCR) is widely used to replicate small fragments of DNA, but the researchers discovered that this method is not very effective with DNA extracted from resinous materials. It is possible, so the authors, that substances found in the resin inhibit the chemicals used to copy single DNA strings. Only after carefully cleaning the samples and repeating the PCR-process various times, enough DNA was replicated to study the genomics of the embedded organism.

It is still not clear just how long any genetic material can survive inside the resin. The researchers hope to apply the new method to other examples of resin-embedded soft tissue and so determine the decay rate of DNA. Water also seems to play an essential role in the preservation potential. The resin creates a waterproof barrier, keeping moisture in the soft tissue. This could also affect the stability of the genetic material.

Surprisingly enough, recent discoveries suggest that DNA traces can be preserved even in rock.

In 2021, a team of scientists from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences and Shandong Tianyu Museum of Nature (STM) successfully identified DNA-like molecules preserved in cells from a 125-million-year-old dinosaur fossil.

The dinosaur, called Caudipteryx, was a small peacock-sized omnivore with long tail feathers. It roamed the shores of the shallow lakes of the Jehol Biota in Liaoning province during the Early Cretaceous.

“Geological data has accumulated over the years and shown that fossil preservation in the Jehol Biota was exceptional due to fine silicon-rich volcanic ashes that entombed the carcasses and preserved them down to the cellular level,” said LI Zhiheng, Associate Professor at IVPP and a co-author of this study published in the journal Communications Biology.

The scientists extracted a piece of distal articular cartilage from the right femur of this specimen, decalcified it, and used different microscopy and chemical methods to analyze it. They realized that all the cells had been mineralized by silicification after the death of the animal. This silicification is most likely what allowed the excellent preservation of these cells.

Furthermore, the team isolated some cells and stained them with a chemical used in biological laboratories worldwide. This purple chemical, called hematoxylin, is known to bind to the nuclei of cells. After staining the dinosaur material, one dinosaur cell showed a purple nucleus with some darker purple threads. This means the 125-million-year-old dinosaur cell has a nucleus so well-preserved that it retains some original biomolecules and threads of chromatin.

Chromatin within the cells of all living organisms on Earth is made of tightly packed DNA molecules. The results of this study thus provide preliminary data suggesting that remnants of original dinosaur DNA may still be preserved. But to precisely test this, the team needs to do a lot more work and use chemical methods that are much more refined than the staining they used here.

“Let’s be honest, we are obviously interested in fossilized cell nuclei because this is where most of the DNA should be if DNA was preserved,” said study author Alida Bailleul. In 2020, she published another study reporting exceptional nuclear and biomolecule preservation in the cartilage cells of a dinosaur from Montana.” So, we have good preliminary data, very exciting data, but we are just starting to understand cellular biochemistry in very old fossils. At this point, we need to work more.”

Despite their optimism to add this type of analysis of very old DNA to more common methods – like DNA recovered from skeletal material, mummified and frozen tissues of much younger fossils – the researchers have no intention of cloning dinosaurs in the near future.

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