The effect of sleep on individual neurons in live zebrafish is reported in a paper in Nature Communications this week. The study finds that sleep increases the movement of chromosomes (chromosome dynamics), which alters their structure to enable reduction of DNA damage. The results suggest that chromosome dynamics could be a potential marker to define individual sleeping neurons.

Prolonged sleep deprivation can be lethal, and sleep disturbances are associated with various deficiencies in brain performance. Although the critical importance of sleep is known, it is unclear what effects it has at a cellular level. This is because sleep has previously been defined by behavioural criteria, as it has not been possible to study sleep-dependent cellular processes under the microscope.

Lior Appelbaum and colleagues report a new method for time-lapse imaging of chromosome dynamics in individual neurons of live zebrafish. Using this approach, the authors demonstrate that sleep increases chromosome dynamics by two-fold, specifically in neurons, while neuronal activity has the opposite effect. They show that sleep-dependent increases in chromosome dynamics are essential for the repair of DNA double-strand breaks.

Although this work provides causal evidence that sleep has a key role in enabling cellular maintenance in neurons, it also illustrates that the cost of wakefulness and cellular activity is the accumulation of DNA damage. Further studies on additional vertebrate and invertebrate animals are required to establish if chromosome dynamics could be an evolutionarily conserved marker of cellular sleep.