Sleep increases chromosome dynamics to enable reduction of accumulating DNA damage in single neurons
Why should we “waste” one-third of our lives on sleep? As the studies go deeper, more interest is aroused. It has become one of the hottest research topics for scientists today.
Sleep is known to be a common and essential behavior for all organisms with a nervous system, including invertebrates, such as flies, worms, and even jellyfish. In a new study published in Nature Communications, researchers from Bar-Ilan University in Israel revealed a novel and unexpected function of sleep. They believe the findings could explain how sleep and sleep disorders affect brain power, aging, and various brain diseases. The researchers studied the living zebra fish’s single chromosome’s resolution through 3D time-lapse imaging techniques, and proved for the first time that individual neurons need sleep to maintain their cell nucleus.
DNA damage can be caused by many factors, such as radiation, oxidative stress, and even neuronal activity. Normally, the DNA repair system within the cell will repair the damage. Current studies have shown that when awake, chromosome activity (chromosome dynamics) is lower, and DNA damage will continue to accumulate, even reaching unsafe levels.
The function of sleep is to increase chromosome activity so that the DNA damage in each neuron can be repaired to normal levels. Obviously, this DNA maintenance process is not as efficient when we are awake as when we are asleep.
Professor Lior Appelbaum from the School of Life Sciences of Bar-Ilan University and Gonda Center for Multidisciplinary Brain Research said: “DNA damage is a bit like the uneven pits on the road. The road is continually worn and torn, especially during daytime traffic peaks, and the most appropriate and effective repair time is at night, when there isn’t much traffic.”
Appelbaum called the accumulation of DNA damage “the cost of being awake.” He and his PhD student, David Zada, the study’s first author, supposed that sleep could consolidate and synchronize cell nucleus maintenance in individual neurons and they decided to begin validating the theory.
They should thank the zebra fish, whose characters made this discovery possible. The body of the zebra fish is transparent and its brain structure is very similar to that of humans, so it is an ideal organism for studying single cells in living animals. With high-resolution microscopes, researchers observed the movement of DNA and nuclear proteins in the cells both when the zebrafish was awake and asleep. They were surprised to find that the zebrafish’s chromosomes were more active at night when they were asleep, meaning higher efficiency to repair DNA damage.
The results indicate that chromosome dynamics is a potential marker of single cells, and the repair function of sleep enhances cell nucleus maintenance. Professor Appelbaum said: “We have found that sleep, chromosome dynamics, neuronal activity, and DNA damage and repair are directly related to the physiology of the organism.” Sleep just provides a chance to reduce brain DNA damage accumulated during the waking hours.
“Despite the risk of reduced environmental awareness, animals must sleep to enable their neurons to perform effective DNA maintenance, which may be the reason why sleep has been kept in the animal kingdom along the evolutionary track,” the Professor concluded.
