DNA gone viral

Mitochondria, the tiny powerhouses that energize human cells and have their own unique DNA, can also be troublemakers. In brain cells, mitochondria can transfer snippets of their DNA into the cells’ nuclei, where they may enter the genome and cause mutations.

In a new study published Aug. 22 in PLOS Biology, researchers at Columbia University and the University of Michigan found that these mitochondria DNA transfers, previously thought to be extremely rare, are relatively frequent. They also appear to be more common in people who die younger.

The scientists collected blood and brain tissue samples from nearly 1,200 deceased people. They found that the majority of mitochondrial DNA insertions in brain tissue were located in the prefrontal cortex, the part of the brain responsible for cognitive ability. Analysis revealed that individuals with a higher number of these insertions in the prefrontal cortex died earlier than did those with fewer insertions. For individuals with no cognitive impairment, every two additional insertions correlated with dying a decade earlier.

Among people who had dementia, though, the researchers found no such link between mutations and age at death. They noted that while the results suggest these brain mutations are harmful, they do not cause Alzheimer’s.

Fast physiology

Intermittent fasting provides health benefits like lowered blood pressure, but what happens when chomping down resumes? New evidence suggests breaking fast could be a double-edged sword: It promotes both cell regeneration and tumor formation.

An MIT-led team of researchers evaluated intestinal stem cell proliferation in mice during a 24-hour fast and a subsequent refeeding. They found that stem cell regeneration peaked at the end of the 24-hour refeeding period. The team also discovered the stem cells activate a cellular signaling pathway that bolsters their growth, producing proteins and poly­amines needed for cells to grow and multiply.

But the peaked cell regeneration came with baggage—the growth of precancerous cells. Turning on a cancer-causing gene during the refeeding period resulted in far greater precancerous growths than when the gene was turned on during the fasting period. More studies are needed to see if the findings, published Aug. 21 in Nature, are applicable to humans. —H.F.

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Tablets and tempers

Screen time can temporarily right a toddler’s bad mood, but the long-term effects might not be worth it. A study published Aug. 12 in JAMA Pediatrics noted a link between early childhood tablet use and outbursts of anger. Greater tablet use at 3½ years old was associated with significantly increased fits of anger and frustration at 4½, which in turn was linked to increased tablet use at 5½ years old. Lead author Caroline Fitzpatrick said parents should swap the digital pacifier for physical activities and other forms of play that encourage self-regulation. —H.F.