2023-07-12 06:00:27
They are called “jumping genes” or “transposons”. These small, ultramobile DNA fragments travel very freely within genomes, or from one genome to another. Many can also reproduce and disperse in this genomic universe.
Cheerfully crossing the boundaries between species, these globetrotters are powerful drivers of evolution. By moving and then inserting themselves into new genome sites, they can profoundly modify gene activity, create new cellular functions, ensure gene transfer between species. Brief, “they bring great plasticity to the genomes of living beings”, explains Gael Cristofari, from the Côte d’Azur University (CNRS-Inserm), in Nice. They notably contributed, lists the researcher, “to the appearance of acquired immunity, and to the invention of the placenta and a synapse protein”, those areas of junction between neurons that make brains so malleable and adaptable. Excuse a bit.
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By dint of multiplying, these jumping genes become invasive. “Half of the human genome is thus made up of mobile elements”, notes Cedric Feschotte, professor of genetics at Cornell University, in the State of New York. Or, more exactly, to “moving element relics”he adds, because 99% of them, formerly itinerant, ended up settling.
But how do certain genes jump from one species to another? Part of the puzzle is revealed in the magazine Science of June 29. The hero of the case? A hybrid vector, named Maverick, which is “a missing link between viruses and transposons”notes the New York researcher and one of its discoverers in 2005. This stray DNA, in fact, allowed a transfer of genes between two species of nematode worms as far apart as the human species is from fish.
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This discovery was made “completely by chance”, admits Sonya Widen, first author of this work carried out by a team from the University of Vienna. The authors were interested in another evolutionary curiosity, present in a small nematode worm, Caenorhabditis briggsae. In this case, a pair of genes that allows the production of both a protein toxic to the worm and its antidote (an antitoxin). “It is a parasitic and selfish system, because it works for its own diffusion, without bringing benefits to its hosts”note Cedric Feschotte.
pirate genes
While investigating the origin of these pirate genes, the researchers were surprised to find them, almost identically, in another species of nematode worm, C. folded even though it separated from C. briggsae tens of millions of years ago. “These genes appear far too similar to result from a phenomenon of convergent evolution, occurring independently in the two species”, says Gael Cristofari. Second surprise, at C. folded these genes are inserted into a Maverick element. This is the key clue that allowed the researchers to trace this trail.
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