Humans lost their tails due to a fragment of DNA

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Humans lost their tails due to a fragment of DNA

If today we are able to walk elegantly in an upright position without having to use a long tail as a balance wheel , we probably owe it to a small fragment of wandering DNA , which 25 million years ago was randomly inserted into a gene responsible for the development of the tail , making it disappear. The change , which occurred in a common ancestor of humans and anthropomorphic apes , would have been very useful in the transition from life in trees to life on the ground , and would have been maintained by evolution despite increasing the risk of congenital defects such as spina bifida, a malformation which affects approximately one in a thousand newborns. Researchers at the Grossman School of Medicine at New York University discovered this with a study that made the cover of Nature.

“The study begins to explain how evolution eliminated our tails, a question that has always intrigued me since I was little,” says the study's first author Bo Xia, who began the research while still a student. while today he works at the Broad Institute of MIT and Harvard.

Together with his colleagues in New York, Bo genes linked to the development of this appendage in vertebrates.

The results showed that the absence of the tail is associated with a change in a gene called TBXT: specifically, it involves the insertion of a small fragment of DNA (an Alu sequence, among the most abundant mobile elements in the human genome ) in a non-coding region of the gene called the 'intron'. Its insertion means that different forms of the corresponding protein can be produced from the same TBXT gene, which in turn determine a different length of the tail or even its disappearance. The researchers verified this directly by reproducing the genetic mechanism in laboratory mice.

“This is a very elegant experimental demonstration, which solidly proves how the disappearance of the tail can be traced back to the insertion of an Alu sequence in the TBXT gene”, comments geneticist Giuseppe Novelli of the University of Rome Tor Vergata.

This result “first of all confirms the suspicions that have been held for years about TBXT, a gene whose protein acts as a transcription factor regulating the expression of genes important for the development of the notochord, i.e. the embryonic structure from which the spinal column is formed: not Randomly – Novelli underlines – alterations similar to the one discovered by Bo Xia have already been found in some families with important congenital defects of the spine”.

Secondly, the study “shows us once again that DNA is not static, but dynamic: the Alu sequences are mobile elements that make up 10% of our genome and when they move – continues the expert – they can cause consequences important, sometimes even tumors. In the case of the disappearance of the tail, the mutation was preserved throughout evolution probably because it led to an advantage that was significantly greater than the risk of incurring malformations of the column”.

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