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The world’s largest study of ‘jumping genes’– small pieces of DNA that can copy themselves throughout a genome and can transfer between species – suggests one jumping gene, called L1, played a vital role in the evolution of mammals.
Researchers at the University of Adelaide traced jumping genes across 759 species of plants, animals and fungi. They found that cross-species transfers, even between plants and animals, have occurred much more frequently throughout evolution than once thought.
“Think of a jumping gene as a parasite,” said Prof David Adelson, who led the research. “Properly called retrotransposons, they copy and paste themselves around genomes, and in genomes of other species. How they do this is not yet known, although ticks or mosquitoes, or possibly viruses, may be involved – it’s still a big puzzle. This process is called horizontal transfer, differing from the normal parent-offspring transfer, and it’s had an enormous impact on mammalian evolution.”
L1 entered the human genome around 150 million years ago. In humans it has previously been associated with cancer and neurological disorders. Understanding the inheritance of this element is important for understanding the evolution of diseases, the researchers say.
The researchers found that the L1 element is abundant in many other plants and animals, as well as fungi. However, it is not present in the Australian monotremes (platypuses and echidnas) showing that the gene entered the mammalian evolutionary pathway after the divergence from monotremes. “We think the entry of L1s into the mammalian genome was a key driver of the rapid evolution of mammals over the past 100 million years,” said Adelson.
The team also looked at the transfer of BovB, a much younger jumping gene that was first discovered in cows. BovB has been shown to jump between a bizarre array of animals including reptiles, elephants and marsupials, potentially due to the action of ticks. The new research suggests that BovB has transferred at least twice between frogs and bats, possibly via bed bugs, leeches and locusts.
The team now hopes to study other jumping genes in animals such as insects and marine worms. “Even though our recent work involved the analysis of genomes from over 750 species, we have only begun to scratch the surface of horizontal gene transfer,” said Adelson. “There are many more species to investigate and other types of jumping genes.”
“THINK OF A JUMPING GENE AS A PARASITE. THEY COPY AND PASTE THEMSELVES AROUND GENOMES, AND IN GENOMES OF OTHER SPECIES”
Australian monotremes ( platypuses and echidnas) do not seem to have the L1 jumping gene
BELOW: Frogs and bats share the BovB jumping gene, which may have been transferred via parasites that feed on blood
ABOVE: The L1 jumping gene can hop between animals, plants and fungi