![\"\"](\"https:\/\/images.newscientist.com\/wp-content\/uploads\/2024\/08\/22162218\/SEI_218234646.jpg\")
<\/div>Pieces of mitochondrial DNA can get added to the main genome of cells<\/p>\n
wir0man\/Getty Images<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
Mutations that involve DNA from energy-producing mitochondria being mistakenly added to the main genome of cells were thought to be exceedingly rare. Now, a study of brain tissue shows these mutations are happening inside all of us, and the number of them could be a factor in ageing<\/a>.<\/p>\n \u201cNot only are they present, but they\u2019re present a lot more in the dorsal lateral prefrontal cortex, which is a region of the brain associated with cognitive ability,\u201d says Ryan Mills<\/a> at the University of Michigan.<\/p>\n In every human cell, almost all the DNA<\/a> \u2013 around 6 billion letters of it \u2013 is found within the nucleus. But the energy-generating organelles called mitochondria have their own tiny genome, at around 16,600 letters long.<\/p>\n That is because mitochondria were once free-living bacteria<\/a> with a larger genome of their own. Over the 2 billion or so years since those bacteria formed a symbiotic relationship with our distant ancestor, most of the original bacterial genome has either been lost or transferred to the main genome in the nucleus.<\/p>\n <\/p>\n Because of the evidence for this transfer, biologists have long known it must be possible for pieces of mitochondrial DNA to somehow get into the nucleus and then get added to the main genome<\/a>. Yet it was assumed this kind of mutation was very rare, says Mills. In the past few years, studies by his team and others have shown that it is much less unusual than we thought, at least in cancerous cells<\/a>.<\/p>\n Now, Mills and his colleagues have shown that this kind of mutation also happens in non-cancerous cells. The team analysed DNA sequences from samples of brain<\/a> tissue taken from 1200 people during post-mortem examinations.<\/p>\n The sampling and sequencing was done by another team, but Mills and his colleagues looked for any mutations involving mitochondrial DNA being added to the nuclear genome. \u201cWe were just curious,\u201d says Mills.<\/p>\n Not only did they find such mutations, they also saw that they were more common, on average, in people who died younger.<\/p>\n Whether these mutations are just a sign of ageing or one of its causes isn\u2019t clear, says Mills. \u201cThe jury is still very much out,\u201d he says. \u201cBut it\u2019s hard for me to believe that if you take an entire mitochondrial sequence and you plop it somewhere in the genome, that it may not have an effect.\u201d<\/p>\n Topics:<\/p>\n<\/section><\/div>\n