In 1 in 4000 births, mitochondrial DNA infiltrates our genomes

Researchers believed this didn’t happen long before humans diverged from their primate cousins, yet a study has just shown otherwise. The DNA of our mitochondria, these small cell batteries, is able to integrate into our “main” DNA, the one contained in the nucleus. But by acting as a bandage when the latter is damaged, mitochondrial DNA can also cause cancer.

One in 4,000 births is a lot “.comments to Science and the future Patrick Chinnery, who led this work published in the magazine Nature. It is, however, the frequency with which mitochondrial DNA (mtDNA) is introduced into the nucleus of one of our gametes, thus into the DNA it contains. A modified DNA, which will then be passed on to the descendants.

To understand we must remember that each of our cells contains a nucleus, whose membrane is porous and which contains our long and essential DNA molecule. Around it are several hundred mitochondria, the cell’s energy sources, each protected by its own membrane. Each of these mitochondria contains mtDNA, a DNA molecule uniquely inherited from its mother. However, in 2018, works published in PNAS discover the mtDNA inherited from the paternal lineage. How is it possible ?

NUMT, these insertions of mitochondrial DNA into nuclear DNA

It is to clear up this mystery that the team examined the genomes of over 66,000 Brits, including more than 12,000 cancer patients, in order to find mtDNA fragments. These inserts, called NUMT (“nuclear mitochondrial segments”), were until then “considered ancient remains “ of past entries, “often shared between related species “, the researchers explain. These NUMTs must therefore date back to before our human ancestors diverged from monkeys, and potentially even earlier, as mitochondria have appeared in what will become our cells (as well as those of animals and plants), there are 1.45 billion of years. But if so, all humans should have the same NUMTs. That’s not what the scientists found.

More than 90% of the entries are recent

Out of 1,637 NUMTs found in these DNAs, “more than 90% (…) was inserted into the nuclear genome after the divergence between man and other primates “the researchers report in the publication.

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