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This is news that shakes the entire life sciences. We would finally have found the DNA of the most fantasy creature ever populated the Earth: a dinosaur! No, we are not at the beginning of the Jurassic Park movie. The team of American and Chinese paleontologists behind this incredible discovery is very real. And they did not need an unlikely find, such as the mosquito full of blood and trapped in amber imagined by Hollywood writers.
The reality is simpler: it was in a very small fossil discovered several decades ago, an innocuous piece of petrified cartilage, that this treasure hid. As an additional nod, it was the scientific advisor to the famous science fiction film, Jack Horner, who discovered it in the late 1980s, within the Two Medicine rock formation in Montana (United States). On the site rested several remains of a duck-billed dinosaur, of the species Hypacrosaurus stebingeri, a herbivore that could reach 10 m in length and lived in North America 75 million years ago.
And thirty years later, while reanalyzing one of these fossils, a piece of cartilage from a baby's skull, Alida Bailleul, paleontologist at the Chinese Academy of Sciences, observes an amazing phenomenon: inside some cells, especially those frozen in full division, strange dark spots are visible at the very place where DNA is supposed to condense into chromosomes! Feminile, researchers then inject fluorescent molecules into the tissues, which have the property of binding specifically to the nitrogen bases of DNA. "The nucleus inside the cells has colored, proving that DNA has been detected," enthuses Alida Bailleul.
AN UNEXPECTED OUTCOME
However, no DNA is supposed to survive so long... Its laws of degradation are clear.
"So far, all the data showed that DNA cannot be preserved for more than 1 million years," says Céline Bon, a researcher in genetic anthropology at the National Museum of Natural History. Over time, it fragments into small pieces, becoming less and less exploitable, before disappearing completely. And the warmer it is, the more DNA deteriorates. The oldest samples found so far had all been kept in permafrost or ice caps. And even among these, none were more than 1 million years old! So a dinosaur DNA, 75 times older? The result seems simply absurd.
CLONING DREAMS
Despite everything, this discovery gives researchers hope to increase their knowledge of dinosaurs like never before. "For the moment, we only study them through birds, which are Avian dinosaurs," recalls Céline Bon. And if scientists have already found proteins in fossils 195 million years old (see box), "the information is much less rich than that contained in DNA," points out Thierry Grange.
It is a reconstruction of the entire phylogenetic tree of dinosaurs, but also a better knowledge of their ecology, even their diseases, that a future study of their genome would suggest - not to mention cloning dreams. To achieve this, there might be no need for new and miraculous finds. Because museums and collections are already full of fossils. How many of them still hide within them a tiny DNA fragment, certainly a little degraded, but ready to reveal itself?
But if we exclude this possibility, how to explain the observed structures and, above all, the results of the coloring test? External contamination of the samples, a major enemy of paleontologists, is of course possible. Many organic or mineral structures, of more recent origin than fossils, can be deposited there during fossilization or analysis by scientists. In addition, "the DNA detection methods used are not very specific. Dyes can react with other organic substances," warns Thierry Grange, head of the Epigenome and Paleogenome team at the Jacques-Monod Institute.
Except that for Alida Bailleul, this hypothesis is not possible: "Staining was observed inside the cells, precisely at the location of the nucleus," she sweeps. This would not have been the case if organisms, such as bacteria or viruses, had interfered in the sample: the staining would then have spread throughout its surface. So what? Anything we thought we knew about DNA conservation would be false? Decoding the genome of a tyrannosaurus, or why not Lucy the australopitheca, would become the domain of the possible? For Alida Bailleul, this discovery leads to a review of some a priori: "The entire scientific community does not know enough about genome degradation in very old fossils." To fill this gap, it will have to overcome a powerful cognitive barrier: "We are not yet ready to consider keeping DNA for so long. But ten years ago, no one would have believed anyone saying they had found fragments 1 million years old, "says Thierry Grange.R
We are therefore at a real turning point. But there is still a long way to go. Already, "these experiments should be replicated in other laboratories by other teams," comments Céline Bon. Alida Bailleul is already looking further, and would like to "analyze more fossils and use different tests to better understand the DNA preservation process. But to do this, it will have to be studied with new chemistry, histology and new sequencers methods, and therefore innovate". With the ultimate goal of one day being able to sequence the DNA discovered, that is to say, determine the order of the bases that make up the molecule and thus obtain crucial genetic information about our duck-billed dinosaur. But the team does not think this is possible immediately. "Current DNA sequencing technologies do not work properly on very old fossils, like this," admits Alida Bailleul. First of all, we should start by better understanding how the genome is deteriorating...
