As direct descendants of ancient bacteria, mitochondria have always been a little alien. Now a study shows that mitochondria are possibly even stranger than we thought. Mitochondria in our brain cells frequently fling their DNA into the nucleus, the study found, where the DNA becomes integrated into the cells' chromosomes.
And these insertions may be causing harm: Among the study's nearly 1,200 participants, those with more mitochondrial DNA insertions in their brain cells were more likely to die earlier than those with fewer insertions. "We used to think that the transfer of DNA from mitochondria to the human genome was a rare occurrence," says Martin Picard, mitochondrial psychobiologist and associate professor of behavioral medicine at Columbia University Vagelos College of Physicians and Surgeons and in the Robert N. Butler Columbia Aging Center.
Picard led the study with Ryan Mills of the University of Michigan. "It's stunning that it appears to be happening several times during a person's lifetime, Picard adds. "We found lots of these insertions across different brain regions, but not in blood cells, explaining why dozens of earlier studies analyzing blood DNA missed this phenomenon.
" Mitochondrial DNA behaves like a virus Mitochondria live inside all our cells, but unlike other organelles, mitochondria have their own DNA, a small circular strand with about three dozen genes. Mitochondrial DNA is a remnant from the organelle's forebears: ancient bacteria that settled in.