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Researchers believed this didn’t happen long before humans split from their primate relatives, but a study has proven otherwise. The DNA of our mitochondria, these tiny cellular batteries, can integrate into our “core” DNA in the nucleus. The latter acts as a bandage when damaged, mitochondrial DNA can also cause cancer.
“About one in 4,000 births.”comments Science and the future Patrick Chinnery led the work published in the journal Nature. However, the frequency with which mitochondrial DNA (mtDNA) is introduced into the nucleus of one of our gametes, then the DNA it contains. The modified DNA is then passed on to offspring.
To understand, we must remember that each of our cells contains a nucleus, whose membrane contains pores and our long and essential DNA molecule. Surrounding 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, the works were published PNAS Detect paternally inherited mtDNA. How is that possible?
NUMTs, these insertions of mitochondrial DNA into nuclear DNA
To unravel this mystery, the team analyzed the genomes of more than 66,000 Britons, including more than 12,000 cancer patients, to find fragments of mtDNA. These insertions, known as NUMTs (“nuclear mitochondrial compartments”) were until then “considered an ancient relic” past insertions, “are often shared between related species”, researchers explain. Therefore, these NUMTs must have existed before our human ancestors split from the apes, and even before that, as mitochondria appeared in our cells (as well as animals and plants) dating back 1.45 billion years. But then, all humans must have the same NUMTs. This is not what scientists have discovered.
More than 90% of insertions are recent
Of the 1,637 NUMTs found in these DNAs, ““More than 90% (…) were inserted into the nuclear genome after the divergence between humans and other animals.”The researchers report in the publication.
Researchers believed this didn’t happen long before humans split from their primate relatives, but a study has proven otherwise. The DNA of our mitochondria, these tiny cellular batteries, can integrate into our “core” DNA in the nucleus. The latter acts as a bandage when damaged, mitochondrial DNA can also cause cancer.
“About one in 4,000 births.”comments Science and the future Patrick Chinnery led the work published in the journal Nature. However, the frequency with which mitochondrial DNA (mtDNA) is introduced into the nucleus of one of our gametes, then the DNA it contains. The modified DNA is then passed on to offspring.
To understand, we must remember that each of our cells contains a nucleus, whose membrane contains pores and our long and essential DNA molecule. Surrounding 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, the works were published PNAS Detect paternally inherited mtDNA. How is that possible?
NUMTs, these insertions of mitochondrial DNA into nuclear DNA
To unravel this mystery, the team analyzed the genomes of more than 66,000 Britons, including more than 12,000 cancer patients, to find fragments of mtDNA. These insertions, known as NUMTs (“nuclear mitochondrial compartments”) were until then “considered an ancient relic” past insertions, “are often shared between related species”, researchers explain. Therefore, these NUMTs must have existed before our human ancestors split from the apes, and even before that, as mitochondria appeared in our cells (as well as animals and plants) dating back 1.45 billion years. But then, all humans must have the same NUMTs. This is not what scientists have discovered.
More than 90% of insertions are recent
Of the 1,637 NUMTs found in these DNAs, ““More than 90% (…) were inserted into the nuclear genome after the divergence between humans and other animals.”, the researchers report in the publication. Ultimately, Patrick Chinnery explains, only 750 NUMTs are old and therefore shared by all humans and some apes. Considering the human population, researchers estimate that more than 99% of individuals have at least one of the identified NUMTs. 1 in 8 people have NUMT “Extremely Rare” Less than 0.1% of the population. “What we’re showing is that these insertions happen all the time. So there are many others that haven’t been known before, which makes us different.”, analyzes Patrick Chinnery. “all the time”, is one of 4,000 births in which mitochondrial DNA is inserted into the gamete’s nuclear DNA. These findings easily explain the results of a 2018 study: Researchers thought mitochondrial DNA was passed down paternally, and in fact these insertions.
Genetic Band-Aids
For scientists, these insertions are not a coincidence, they have a function. “By examining the DNA sequence surrounding NUMTs, we can see that they are not randomly inserted into the genome.”, explains Patrick Chinnery. They are actually close to the DNA sequences, which are often recombined and therefore modified during the formation of gametes. The proximity of these transient zones suggests that NUMTs have a transient repair role, and in most cases meiosis ends by eliminating NUMTs that have become useless. “NUMTs may act as temporary band-aid solutions, fixing DNA strands until they are removed during meiosis.”, the researchers explain.
Rare cases of cancer
But it is not without its flaws. “New mtDNA entering the nucleus has important implications because they can disrupt protein-coding genes and cause disease.”, scientists in the publication explain. In the cancer DNA analyzed, one new NUMT was found in every 1,000 cancers. Of the more than 12,000 known cancers, fortunately the remaining cancers are “rare”Comments by Patrick Chinnery.
