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by Rahul Jayaram '21 edited by Rishi Patel '21 We have all been put in situations where we wish that sleep was not necessary. From college students racing against the clock to finish term papers, to parents struggling to quiet bawling infants at midnight, many of us have probably questioned the importance of sleep and the purpose it serves. Years of research have proven that that sleep has crucial roles in roles in learning, memory formation, toxin removal, blood pressure maintenance, and more [1] [2]. However, the core cellular function of sleep still remains unknown. In humans, sleep can be defined by specific electroencephalography (EEG) rhythms, while in non-mammals, sleep is solely defined on the basis of behavior, such as posture during sleep and changes in arousal levels with regard to external stimuli. Yet, across all animals there has been no defined marker that can be used to define sleep in a single cell [3]. That is, until now. Recently, scientists at Bar-Ilan University found that individual neurons perform nuclear maintenance, or DNA restoration, during sleep, suggesting another critical role sleep plays for our bodies at the cellular level. The researchers used advanced imaging techniques in live zebrafish to show how neurons perform nuclear maintenance to repair micro-level chromosomal damage that takes place during the day. Chromatin contains DNA and is present in each cell of the body. Many regulatory processes must be maintained in order to ensure proper cellular processing, DNA replication, transcription, and epigenetics. These processes, known as chromatin dynamics, repair damage done to our DNA as a byproduct of high cellular activity, and are imperative to the vitality of our cells. Using high resolution microscopy paired with 3D-time lapse imaging, the researchers were able to observe the movement of DNA and nuclear proteins in both the organism’s “sleeping” and “awake” states. They discovered that these chromosomal processes were more vigorous at night than they were during the day. By demonstrating that sleep is the optimal state for the body’s cells to repair DNA, the study has shed light on a key molecular mechanism that further justifies the importance of sleep [3]. To better understand this idea conceptually, Prof. Lior Appelbaum, of Bar-Ilan University uses the analogy of repairing road damage. "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."[4]  Live time-lapse imaging of a single neuron nucleus shows the movement of chromosomes measured over 9.5 min. Dashed box shows high magnification of a single trajectory [3] The fact that our bodies use sleep to repair DNA damage that has accumulated over the course of the day is key to our understanding of why sleep is important at the level of a single cell. The cells in our body are continuously performing incredibly complex tasks to enable use to carry out the smallest and largest aspects of human functionality, and it is not surprising that within this crossfire some harm may happen. Sleep is a powerful mechanism that restores debilitated cells and provides a suitable environment for chromatin dynamics to take place, ensuring that we are equipped to tackle the next day with full force. Works Cited: [1] Rasch B, Born J. About sleep's role in memory.PubMed[Internet]. 2013. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3768102/ [2] Eugene AR, Masiak J. The Neuroprotective Aspects of Sleep. PubMed [Internet]. 2015. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4651462/ [3] Zada D, Bronshtein I, Lerer-Goldshtein T, Garini Y, L Appelbaum. Sleep increases chromosome dynamics to enable reduction of accumulating DNA damage in single neurons. Nature. 2019; 10 [4] Sleep tight! Researchers identify the beneficial role of sleep: Sleep increases chromosome dynamics that clear out DNA damage accumulated during waking hours. ScienceDaily [Internet]. 2019. Available from: www.sciencedaily.com/releases/2019/03/190305170106.htm
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