September 30, 2020

Has dinosaur DNA been found? Possibly yes



In the middle of the coronavirus epidemic, it is difficult to break through to scientific news that does not talk about the problem, but it exists and is not trivial. On March 4, an article was published in the National Science Review that suggested finding the first non-fossilized remains of dinosaur DNA. DNA is the molecule that stores the information necessary to form a living being, so not a few have quickly started to flirt with the creation of a Jurassic Park. But let’s stay calm, what’s true in all this? Because retrieving information on extinct species is not as easy as it sounds and if you ask the mammoth.

First of all, what about my mammoth?

There has been talk for a long time of bringing species back to life as the woolly mammoth (Mammuthus primigenius) the most famous of all. In the ice of Siberia specimens have been found whose meat, skin and hair have remained until our time. We are talking about remains that are around 20,000 or 60,000 years old. Attempts to bring them back to life have been many, but so far there have been no great successes.

It is true that scientists have managed to extract the nucleus where their DNA is from some cells in their skin and insert it into an elephant’s egg. The good news is that some genes (something like DNA information packages) were reactivated trying to kick-start their functions and trigger mammoth protein synthesis. However, the genetic material was so damaged that the cells did not survive too long and were unable to divide.

All of this is to be expected, actually. DNA is a delicate molecule whose information can be easily damaged or completely lost. It is estimated that in just over 500 years, half of its information can be considered lost and that in a few thousand years its deterioration is almost complete. In cases of extreme cold and in an environment that is neither too acidic nor excessively dry, these times are supposed to last longer, but how much more?

To all this, another complication must be added, which is that of cloning itself. Something that resists us even with species whose DNA we know perfectly, such as the bucardo (Capra pyrenaica pyrenaica), a subspecies of mountain goat that, after its extinction, we try to recover. We did it, but for just a few minutes before it went extinct a second time.

All this is more important than it seems, because in the case of dinosaurs all these complications multiply. First, its DNA would be at least 66 million years old. Secondly, we would need a living cell in which to introduce its genetic material, and even its closest relatives are quite different from them, so cloning would be infinitely more complicated than in the case of the bucardo. So now I do: Knowing this, what have scientists actually found?

Immunotrucos

There will be those who say that it is not new to find dinosaur DNA, and it will be partly right, because we remember that biologically birds are dinosaurs, dinosaurs tell us, but dinosaurs, after all. Others will say that non-fossilized tissue from the tyrannosaurus itself had already been found and they will also be right. Although in this case not only collagen and other proteins have been found, but what clearly seem like DNA fragments. But how can researchers be so sure?

The sequence of events was as follows. Broadly speaking, they were studying a cut of the cartilage of a young hadrosaur. It was specifically a Hypacrosaurus stebingeri, a duck-billed dinosaur whose cartilage began to calcify transforming into bone. Looking at it under the microscope, the principal investigator, Aida M. Bailleul, noticed something striking. Two of his cells seemed to be dividing cells. What’s more, in one of them, the DNA seemed to have fossilized when it was still squeezed and ordered, forming those cross shapes called chromosomes. With something so exceptional the question was too tempting not to ask: what if it wasn’t really fossilized?

The way to check this is with immunofluorescence and immunohistochemical techniques, which basically involves using molecules called antibodies as tracers. Antibodies will ring a bell for being structures released by our immune cells, capable of recognizing specific bacteria or viruses, like magic bullets that only attack their target. The techniques we have named take advantage of these properties and modify the antibodies so that they not only search for the structures that interest us, but also drag a marker with them, a signal that somehow stains the place where they end up.

In the case of fossils, all this wonder does not work, because the tissues have mineralized, losing the places to which the antibodies should bind. The counterpart to all this is that, if applied to a fossil, they adhere to it by dyeing it, it means that they have found non-fossilized tissue. So that was what the team did, and the result was incredible.

This fossil may contain traces

They tested various markers and found unfossilized fragments of collagen and other molecules that, on their own, would have been a first-rate discovery. However, that was not all. The structure that appeared to be chromosome-condensed DNA had been stained with precisely the antibodies made to detect genetic material.

This is what we know for now, and although it may seem little is great news. Most likely, these are completely washed-out remains and it is impossible to obtain relevant information on the genetic sequence of the dinosaur. However, these traces are a song of hope. They tell us that there must be conditions in which the DNA manages to survive a time enormously superior to what we had thought until now. The reason for this exceptional conservation is not entirely clear, although it is pointed out that, since the DNA was condensed into chromosomes and was in cartilage instead of bone (which is less porous), it could have been more protected from the inclemencies of the environment .

However, you may have read some criticism of his work. Some researchers suggest that this DNA could be a contamination, not really from the dinosaur, but from some microorganism that had colonized the sample or even from the researchers themselves. The answer of the authors of the article is clear: the study has been done in conditions of extreme care and the location of the dye coincides with the place where the chromosomes appeared to be.

In any case, it is sensible criticism. Working with DNA is very sensitive and contamination is so easy that sterile conditions become almost an obsession for scientists. It is early to say beyond a doubt that the DNA remains are really hadrosaurs, and although it is convenient to remain skeptical, if they are finally right, it could be one of the greatest discoveries of the last decades. Perhaps not as a promise of de-extinction, but as an immeasurable step in the field of molecular paleontology, helping us to understand better than ever who those strange ancestors of our birds were.

DON’T NECK IT:

  • Ancient DNA studies, as they are called, date back to the 1980s. They are nothing new and traces of readable DNA were found at that time in a dissected specimen of quagga (Equus quagga quagga) from the University of Berkeley, an extinct subspecies of common zebra.
  • When making this kind of discovery, other scientists are quick to suggest that it could be due to a mistake by the researchers. However, we are facing a fairly safe case and the possibility of contamination is low, although it exists, of course.

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