Polish researcher show how the cell fights parasitic "jumping genes"
Some of the smallest parasites we carry are... jumping genes. Fortunately, our cells have ways to stop these genetic parasites from multiplying. In the prestigious journal "Cell", Polish researcher explain the new defence mechanism against the so-called retrotransposons.
Some of the smallest parasites that inhabit the human body are retrotransposons. They are simply fragments of DNA woven into our genome. They do nothing for the "common good" of the whole organism, they only produce machinery for copying themselves. Their goal is to paste their own copies into the DNA. This way, their genes can "jump" all over our DNA.
Retrotransposons are not the same as viruses, explains Prof. Andrzej Dziembowski from the Institute of Biochemistry and Biophysics PAS in Warsaw. Viruses have a shell that allows them to leave the cell and attack other cells. Retrotrasposons are unable to leave the cell: they multiply in the DNA of the same cell from which they originate. They are transferred from generation to generation because they are also present in the reproductive cells.
In any case, these genetic parasites make a great mess in our genome. "As much as 17 percent of DNA in the human genome are LINE-1 elements encoding retrotransposons" - the researcher says. His team composed of young scientists: Dr. Zbigniew Warkocki - the first author of the publication, Dr. Paweł Krawczyk and Dorota Adamska published an article describing a previously unknown way in which a cell can block these small genes from further expansion (https://doi.org/10.1016/j.cell.2018.07.022).
The scientist explains that each of us has 80 to 100 active retrotransposons in the cells. "We do not need them, they are actually harmful" - says the scientist. By pasting themselves into DNA they leads to the formation of mutations, they often accompany cancer or even cause it.
According to Prof. Dziembowski, if a person`s cells can not properly control retrotransposons, it may be associated with complete infertility. And that`s not the end of problems. That is why in the cells have defence mechanisms against multiplication of these genetic parasites.
The scientist explains how the parasitic genes are copied. The LINE-1 elements are stored in our DNA, in the cell nucleus. There, the DNA is transcribed into RNA, which is able to reproduce the DNA and paste it into the DNA of the same cell using a "copy-paste" mechanism.
It has been described, for example, how a cell can use methylation to block its DNA fragment with the LINE-1 element and render it inactive. So it is not transcribed at all. There are known mechanisms that do not allow retrotransposon to start copying. Now Polish scientists have explained how a cell can defend against genetic parasites at a later stage - when retrotransposon is already activated.
The Polish team discovered that in order to stop the "invasion" of the genetic parasite, a retrotransposon RNA uridylation may occur in the cell. It involves attaching additional uridyl nucleotides that act like a ball and chain to the end of the RNA. "We were the first to describe how this mechanism works" - says the researcher from the Institute of Biochemistry and Biophysics PAS. Such blocked RNA is no longer dangerous. With its ball and chain, it can no longer jump all over the genome and paste new DNA fragments into it. And with time it is removed by the cell.
PAP - Science in Poland, Ludwika Tomala
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