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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.”


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

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