Researchers from the University of Konstanz and other institutions Africa(Protopterus annectens) and South American lungfish (Lepidosiren paradoxa)The genome of the South American lungfish (approximately 91 gigabases, about 30 times the size of the human genome) is the largest animal genome sequenced to date. Australia(Neoceratodus forsteri) African lungfish.
South American lungfish (Lepidosiren paradoxaImage courtesy of Katherine Seghers, Louisiana State University.
Lungfish are freshwater vertebrates belonging to the order Dipnoi (Pulmonaceae) and have existed for 400 million years, from the Devonian to the present day.
Some people consider lungfish to be “living fossils” because their morphology has changed very little over the years.
They, like all terrestrial vertebrates, have the ability to breathe air through lungs similar to our own.
Only six species of lungfish remain today: four live in Africa, one in South America, and one in Australia.
“These ancient 'living fossils' still resemble their ancestors so closely that they seem to have been forgotten during evolution,” said biologist Axel Meyer of the University of Konstanz and his colleagues.
“Since our genetic material, DNA, is made up of nucleobases and the sequence of these nucleobases contains the actual genetic information, a comparative analysis of the lungfish genome will only be possible if we know its complete sequence.”
“We already knew that the lungfish genome was large, but until now it was unclear how large it really was and what we could learn from it,” the researchers added.
“Sequencing the lungfish genome has therefore been very labor-intensive and complex, both from a technical and bioinformatics point of view.”
In a new study, scientists have sequenced the genome of African and South American lungfish.
“The South American species' DNA is 91 gigabases (or 91 billion bases), the largest of any animal genome and more than twice the size of the genome of the previous record holder, the Australian lungfish,” Dr Meyer said.
“Eighteen of the South American lungfish's 19 chromosomes are each larger than the entire human genome, about 3 billion base pairs in length.”
The largest genome sequence to date, that of the Australian lungfish, was also sequenced by the same team.
“Autonomous transposons are responsible for the large size of the lungfish genome over time,” the authors write.
“These are DNA sequences that are 'replicated' and change position in the genome, which causes the genome to grow.”
“Although similar phenomena have occurred in other organisms, our analysis shows that the South American lungfish has by far the fastest rate of genome expansion ever recorded; every 10 million years, its genome has expanded to a size equivalent to the entire human genome.”
“And it continues to grow. We now have evidence that the transposon responsible is still active.”
“We have identified a mechanism for this enormous genome growth. This extreme expansion is due, at least in part, to the very low presence of piRNAs.”
“This type of RNA is normally part of the molecular mechanism that silences transposons.”
Team paper Published in the journal Nature.
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M. Chartres othersAll lungfish genomes provide information on genome expansion and tetrapod evolution. NaturePublished online August 14, 2024, doi: 10.1038/s41586-024-07830-1
Source: www.sci.news
