Or living fossils: How the Coelacanth has recently developed dozens of new genes

Catch the first live Coelacanth, a powerful ocean predator, off the coast of South Africa on the rise in 1938, 65 million years after its extinction. It became known as a “living fossil” because of its anatomy looking almost identical to the fossil record. But although the Coelacanthhis body may not have changed much, his genome tells another story.

Toronto scientists have now revealed that the African Coelacanth, Latimeria chalumnae, discovered 62 new genes through encounters with other species 10 million years ago. Their findings are reported in the journal Molecular Biology and Evolution.

What is even more interesting is how these genes evolved. Their lines suggest that they evolved from transposons, also known as “selfish genes”. These are parasitic DNA elements and their sole purpose is to make more copies of themselves, which they sometimes achieve by switching between species.

The findings illustrate the potentially dramatic effect of DNA transposon travel on gene formation and give us an insight into some of the forces that shaped the genome of one of the oldest organisms. and most secretive.

“Our findings provide a very impressive example of this phenomenon of transposons contributing to the host genome,” said Tim Hughes, senior study author and professor of molecular genetics at the Donnelly Center for Cellular and Cellular Research. Biomolecular at the University of Toronto.

“We don’t know what these 62 genes do, but many of them encode DNA-binding proteins and appear to have a place in gene regulation, where even small changes are important in micro- said Hughes, who is Research Chair of Canada in Decoding. Gene Control and John W. Billes Chair of Medical Research at the Temerty Faculty of Medicine at U of T.

Transposons are sometimes called “jump genes” because they change their location in the genome, thanks to a self-encoding enzyme that recognizes and passes its own DNA code through a “cut and pack” machine. New copies can arise through serendipitous genes during cell division when the entire genome is reproduced.

Over time, the enzyme’s code shifts to a bad state and the jump stops. But if the modified sequence gives the guest even a selective advantage, it can start a new life as a bona fide host gene.

There are many examples of genes derived from transposons across species, but the Coelacanth stands out for how big it is.

“It was surprising to see coelacanths emerge among vertebrates as a large number of these transposon-derived genes because they have an undeserved reputation as a living fossil,” says a graduate student Isaac Yellan led the investigation.

“The Coelacanth it may have slowed down a little bit but it is definitely not a fossil, “he says.

Yellan made the discovery while looking for peers in other species of human gene he was studying. He knew that the gene, CGGBP1, had evolved from a specific type of transposon in the common ancestor of mammals, birds and reptiles. It was named after the protein it encodes, which binds DNA sequences containing CGG, but was difficult to study in part because it is unlike other commonly studied species, such as electricity -dè.

After scanning all available genomes, Yellan was able to detect related genes, but the distribution across species was inconsistent and not as you would expect from common ancestry . In addition to the same CGGBP-like gene in all mammals, birds and reptiles, Yellan found copies in some, but not all, fish he looked at, as well as in eels. trout, a primordial vertebra, and a type of fungus. Worms, molluscs, and most insects had none. And then there were 62 in the Coelacanth, whose genome became available in 2013.

With controlled common ancestry, it seems instead that the transposons came to different sequences at different times by being transported between species through what is known as horizontal gene transfer.

“Horizontal gene transfer raises the picture of where the transposons came from but we know from other species that it can happen through parasites,” says Yellan. “The most likely explanation is that they have been introduced several times through the history of evolution.”

It is not clear what the genes do but several lines of evidence indicate a well-tuned place in gene regulation. Computational modeling and test tube experiments have established that the results of the genes are proteins that bind specific signatures on the DNA, showing a place in gene expression, similar to the human replica. In addition, the genes are differentially converted over a dozen or so Coelacanth organs for which data are present, noting fine functions specific to compression.

Where did the genes originally come from and what do they do in the Coelacanth perhaps it remains a mystery. Research samples are occasionally taken up from fishing vessels and it took until 1998 to establish which other living species were known. Latimeria menadoensis, in the Indonesian fish market.

The species diverged before the new genes emerged, controlling them from driving profiteering. However, they may have shaped the African Coelacanth we know today with a majestic armor of royal blue blades casting a shadow over its brown-colored ally, Yellan said noting that profiteering this is true.

In fact, we may never know.

“The Coelacanththey are very rare, “said Yellan.” And they are very good at hiding. ”

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