24 November 2015

Other people's genes help us live

Geneticists have revealed the secret of animals capable of living in outer space

Tardigrades, the only multicellular animals on Earth capable of living and even reproducing in outer space, probably acquired this ability by borrowing about 18% of their DNA from archaea, bacteria, plants and even fungi, according to an article published in the journal Proceedings of the National Academy of Sciences (Boothby et al., Evidence for extensive horizontal gene transfer from the draft genome of a tardigrade).

"We had no idea that the genome of some animal could contain so much alien DNA. We knew that many animals often borrow genes from other creatures, but we did not expect at all that this could happen on such an industrial scale," said Bob Goldstein from the University of North Carolina at Chapel Hill (in a press release from the University of North Carolina at Chapel Hill A huge chunk of a tardigrade's genome comes from foreign DNA – VM).

In 2007, scientists made an amazing discovery by analyzing data collected by the Russian Photon-M3 biosatellite: it turned out that tichodods, small invertebrates, distant relatives of crayfish and insects, are able to survive for a very long time in outer space and even reproduce in conditions of complete weightlessness and lack of food and water.These unusual qualities, as Goldstein says, attracted the attention of many biologists, geneticists and planetary scientists, and they decided to decipher and analyze the genome of these unusual invertebrates, choosing as experimental slow–moving species Hypsibius dujardini, who had been in space aboard the probe (electronic photo from Wikipedia - VM).

The genome of these creatures is relatively large for their size and position on the tree of evolution – it contains about 215 million "letters"-nucleotides, which is about twice as much as that of nematode worms, which scientists use for experiments with invertebrates.

When scientists began to count and study genes, they were in for a big surprise – over 6.5 thousand DNA sections from 38 thousand genes were "borrowed" from other organisms. Most of them were obtained from extremophile bacteria, but the genes of plants, fungi and archaea are also present in the genome of slow walkers.

How did this invertebrate manage to "expropriate" all these six thousand genes? According to Goldstein and his colleagues, the reason for this is the incredible ability of this creature to survive.

Slow-walkers, as explained by genetics, are able to tolerate extreme forms of dehydration when the proportion of water in their body drops to 1-2% of the norm. When their body is dried, the DNA of Hypsibius dujardini most likely breaks down into large fragments. At the moment when the period of extreme conditions ends, their body is refilled with water, and special proteins "stitch" and repair damaged DNA.

At this moment, fragments of someone else's DNA can get into the cells, thanks to the expanded pores, which are "sewn" into the genome and remain in it, if their appearance does not lead to fatal consequences for the slow-moving and helps it survive. Thanks to this, the DNA of the slow-walkers has become a mosaic of many of their own and others' sites over 550 million years of evolution of these creatures.

Given that many of these genes are responsible for responding to stress, repairing DNA and countering various extreme factors, it is quite possible that these creatures have acquired the ability to survive in space thanks to borrowed genes.

According to Goldstein and his colleagues, their discovery suggests that the so–called horizontal exchange of genes - borrowing them from other organisms, conducts not only the evolution of microbes, among which it is common, but also multicellular creatures.

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