About one sixth of the tardigrades genome was borrowed from other organisms

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    Researchers at the University of North Carolina have deciphered the gene for tardigrades , a microscopic invertebrate creature. A surprise for biologists was the fact that more than 17% of their genome tardigrades were borrowed from other animals and plants.

    “We had no idea that the animal’s genome could contain such a large percentage of foreign DNA,” Bob Goldstein, co-author of his work, shared his surprise. “Science has known cases of DNA borrowing, but we have never seen this on such a scale.”

    Over 6,500 alien tardigene genes borrowed from bacteria, plants, fungi and archaea. Borrowing occurs through horizontal gene transfer - a process in which an organism transfers genetic material to another organism that is not its descendant. The opposite of this process is vertical gene transfer, when the body receives genetic material from its ancestors. In particular, genetic engineering is engaged in artificial horizontal gene transfer.

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    Most animals have no more than 1% of genes borrowed from other species. Until now, rotifers kept a record for the content of foreign DNA . These are microscopic multicellular animals, which received a name from their so-called rotator apparatus - ciliary formation on the front end of the body, which is used for nutrition and movement. But the rotifers, the percentage of foreign genes did not exceed 8%.

    Tardigrades belong to extremophiles - they are amazingly hardy, and are able to tolerate extreme forms of dehydration, when the proportion of water in their body drops to 1-2% of the norm. In full accordance with the proverb “Slower you go, you will continue”, they withstand staying for 20 months in liquid oxygen at −193 ° C, heating to 60-65 ° C for 10 hours, pressure up to 6000 atmospheres, staying for several days in outer space. A dose of 570,000 x-rays (1,000 times the lethal dose for humans) kills only half of the irradiated tardigrades.

    When their body is dried, the DNA most likely breaks up into large fragments. At that moment, when the period of extreme conditions ends, their body is re-filled with water, and special proteins “cross-link” and restore damaged DNA. At this moment, thanks to the expanded pores, fragments of foreign DNA can enter the cells, which also integrate into the genome.

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    “We habitually think about the tree of life and vertical gene transfer, in which DNA is passed on to us from mom and dad,” says Thomas Boothby, one of the authors of the work. - But as we study and acknowledge the work of the mechanism of horizontal gene transfer, we change our understanding of the course of evolution, changes in genetic material and the stability of genomes. Instead of the tree of life, we should present a web of life along which genetic information travels. We are starting to change our minds about the evolutionary scheme of work, and that’s great. ”

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