Bar-Ilan researchers reveal reason for a good night’s sleep

Some of us spend nine hours every night doing it, and some enjoy far less. All creatures and animals, whether a worm or a jellyfish, do it too. We all need to sleep.Despite evolutionary changes, sleep remains essential to all organisms with a nervous system, despite the dangers faced by prey in the wild by entering a state of reduced responsiveness.While many studies have shown that sleep is important, particularly for memory consolidation and learning ability, little is known regarding why sleep has remained a constant necessity in the animal kingdom.Researchers at Bar-Ilan University have discovered, however, a previously unknown function of sleep that could explain how resting affects brain performance, aging and various brain disorders.By using three-dimensional time-lapse imaging techniques in zebrafish, researchers were able to define sleep in a single chromosome resolution and, for the first time, demonstrate that single neurons (or nerve cells) require sleep to perform nuclear maintenance. Their findings were published on Tuesday in the journal Nature Communications.While DNA in cells can be damaged by a range of factors such as radiation, oxidative stress and simply neuronal activity, DNA repair systems within each cell correct the damage. During wakefulness, when chromosome dynamics are low, this damage consistently accumulates and can even reach dangerous levels.When asleep, chromosome dynamics are increased and normalize the levels of DNA damage in each neuron. While DNA repair is a constant process, including during hours of wakefulness, neurons require an offline sleep period with reduced input to the brain for normalization to occur.“We found that when zebrafish go to sleep at night – they are diurnal creatures like humans – the chromosomes increase their mobility,” Prof. Lior Appelbaum, who led the study, told The Jerusalem Post.“We have shown that those increased chromosome dynamics are essential to the efficiency of DNA repair. When you shut down inputs at night and the cell can be busy with nuclear maintenance, this is the time when balance the DNA damage accumulated during wakefulness.”Zebrafish are a perfect organism, Appelbaum added, to study a single cell within a live animal under physiological conditions, due to their absolute transparency and a very similar brain to humans.Using a high-resolution microscope, DNA movement and nuclear proteins within zebrafish cells can be observed while awake and asleep.“We all know that we have to sleep, but now I think we know one more reason why, said Appelbaum.“If you don’t sleep, you accumulate DNA damage and this can be risky. In the case of chronic loss of sleep, some of the neurons may even die. We think this can even lead to various brain disorders in the end.”