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The primitive-looking coelacanth has long been considered a “ living fossil, ” with extant specimens very much like fossils dating from the Cretaceous period. But although the body of the coelacanth has changed little, its genome tells a different story.
Latimeria chalumnae off Pumula on the south coast of KwaZulu-Natal, South Africa, November 22, 2019. Image credit: Bruce Henderson, doi: 10.17159 / sajs.2020 / 7806.
Coelacanths are lobed fin fish that were believed to be extinct for 65 million years, until a first living specimen was accidentally discovered in South Africa in 1938 by a South African museum curator on a local fishing trawler.
There are two species of coelacanths: Latimeria chalumnae form the Comoros Islands off the east coast of Africa, and Latimeria menadoensis waters off Sulawesi, Indonesia.
Coelacanths exhibit several unique and intriguing characteristics such as unpaired lobed fins much resembling paired fins and highly modified lung / swim bladder.
Along with the lungs, they are the closest relatives of tetrapods and share with them several morpho-anatomical features not found in more distant vertebrates such as ray-finned fish.
When the first extant coelacanth was discovered, it recalled so many fossil forms from the Cretaceous that it was referred to as a “living fossil”, that is, a species whose morphology has not changed much over the years. A long period.
To account for this morphological stasis, it has often been suggested that coelacanths have a slowly evolving genome or not.
“The coelacanths may have evolved a little slower, but they are definitely not a fossil,” said Isaac Yellan, a graduate student in the Department of Molecular Genetics at the University of Toronto.
In their new study, Yellan and colleagues found that Latimeria chalumnae acquired 62 new genes through encounters with other species 10 million years ago.
What’s even more fascinating is how these genes were born. Their sequences suggest that they are derived from transposons, also known as “selfish genes”.
They are parasitic pieces of DNA whose sole purpose is to make more copies of themselves, which they sometimes do by moving between species.
“Our results provide a rather striking example of this phenomenon of transposons contributing to the host genome,” said Professor Tim Hughes, a researcher at the Donnelly Center for Cellular and Biomolecular Research at the University of Toronto.
“We don’t know what these 62 genes do, but many of them code for DNA binding proteins and probably play a role in gene regulation, where even subtle changes are important in evolution. . “
The results were published in the journal Molecular biology and evolution.
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Isaac yellan et al. Various eukaryotic CGG binding proteins produced by independent domestication of hAT transposons. Molecular biology and evolution, published online February 9, 2021; doi: 10.1093 / molbev / msab007
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