‘Jumping DNA’ helped man’s ancestors lose their tail – 02/29/2024 – Science

The loss of the tail, an anatomical transformation fundamental to the emergence of the human lineage, may have been triggered by a piece of DNA that is capable of “jumping” from one point to another in the genome, says a new study by researchers in the United States. U.S. Analysis of genetic material and experiments with mice corroborate the hypothesis, although it is still unclear why some primates became tailless from about 25 million years ago.

The new research on the topic has just been published in the specialized journal Nature. The team of scientists was led by the trio Bo Xia, Itai Yanai and Jef Boeke, all linked to NYU Langone Health, a research and medical care center at New York University. Interestingly, according to Xia’s interview with Nature, it all started when he himself injured his “tail” – or, at least, what was left of it in the researcher and other human beings.

This is, of course, the coccyx, a set of rudimentary vertebrae at the end of the spine that corresponds precisely to a very shortened and modified shape of the tail of other primates. The coccyx is not exclusive to the Homo sapiensbeing also present in great apes –gibbons, orangutans, gorillas and chimpanzees—, which are also tailless primates.

Xia injured his coccyx riding in a taxi and soon remembered how curious he was about the subject as a child, when he once asked: “Where’s my butt?” With the green light from Yanai and Boeke, his doctoral advisors, he began searching public genomic data bases. His plan was to analyze stretches of DNA that could be linked to the formation of the tail, or the absence of it.

On the one hand, he focused on genes that have relatively well-known mutations (random changes in DNA) in laboratory mice, showing that they actually affect tail development. On the other hand, he checked whether these same genes had changes exclusive to great apes and humans, which would point to a more likely relationship with the lack of tail in this lineage.

The curious thing is that he did not find promising stretches of DNA in the so-called coding regions of the genome — that is, those that contain the code for the production of protein components. For a long time, it was believed that the coding regions were the most important for the development of the organism and the evolution of living beings, but there is increasing evidence that they are just a part of these processes. And, in fact, the study authors identified that the key to the enigma could lie in a non-coding region.

It is a piece of DNA with around 300 chemical “letters”, classified as an “Alu element” – a type of mobile or transposable genetic element, that is, one that can copy itself or change position along the way. genome “library”. Alu elements appear to have been so adept at this task in our lineage’s past that they now make up about 10% of human DNA.

It turns out that the Alu element identified by Bo Xia and his colleagues appears precisely in the DNA sequence of a gene important for tail development. Furthermore, it is exclusive to great apes and humans. In theory, it should not affect the functioning of this gene, because the Alu element is in a region of it that is “cut” during the process of reading the gene by the cell. It’s more or less as if this paragraph contained a passage in square brackets, saying something like: [ignorar esta frase na hora da leitura].

Experiments carried out by the team, however, showed that this is not what happens. In the process of reading the gene by the cell, this Alu element interacts with a similar one, located at a certain distance from it. And the result is that part of the message contained in the gene is eliminated. It’s as if, instead of saying something like “Leave no monkey without a tail”, the words “No” and “none” were cut out. The phrase would be: “Leave a monkey without a tail.”

To confirm that this was indeed what was happening, the researchers carried out a wide range of laboratory tests with genetically modified mouse embryos. They tried to simulate the changes in Alu elements that occur in primates of our lineage in rodents. And the result was that, in fact, the changes actually seem to favor the absence or reduction of the tail.

It is quite likely that this change, although important, was not the only one that led our lineage towards life without a tail. Furthermore, although it is speculated that the absence of a tail was an important element for bipedal locomotion, it is also true that many arboreal or climbing species, such as orangutans, do not have tails either. Therefore, the reasons behind the evolutionary change are still unclear.