Why do humans “waste” a third time of their lives sleeping? Throughout the animal kingdom, sleep is universal and essential to all organisms with a nervous system, including invertebrates such as flies, worms, and even jellyfish. But the evolutionary reason for sleep, which puts an animal at significant risk of predators for part of its day, is considered among the biggest unanswered questions in life sciences.
In a new study, researchers at Bar-Ilan University in Israel reveal a novel and unexpected function of sleep that they believe could explain how sleep and sleep disturbances affect brain performance, aging and various brain disorders.
Using 3D time-lapse imaging techniques in live zebrafish, the researchers were able to define sleep in a single chromosome resolution and show, for the first time, that single neurons require sleep in order to perform nuclear maintenance.
DNA damage can be caused by many processes, and DNA repair systems within each cell correct this damage. The current work shows that during wakefulness, when chromosome dynamics are low, DNA damage consistently accumulates and can reach unsafe levels. Therefore, sleep is necessary to give the body time for repairs.
“It’s like potholes in the road,” says Prof. Lior Appelbaum, who led the study. “Roads accumulate wear and tear, especially during daytime rush hours, and it is most convenient and efficient to fix them at night, when there is light traffic.”
Appelbaum calls the accumulation of DNA damage the “price of wakefulness”.
“Despite the risk of reduced awareness to the environment, animals — ranging from jellyfish to zebrafish to humans — have to sleep to allow their neurons to perform efficient DNA maintenance, and this is possibly the reason why sleep has evolved and is so conserved in the animal kingdom,” concludes Prof. Appelbaum.
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