Single-cell transcriptomics reveals glial cells integrate homeostatic and circadian processes to drive sleep-wake cycle

The sleep-wake cycle is determined by a circadian and a sleep homeostatic process. However, the molecular impact of these two processes and their interaction on different cell populations in the brain remain unknown. To fill this gap, we have profiled the single-cell transcriptome of adult fruit fly brains across the sleep-wake cycle and different circadian times. We show cell type-specific transcriptomic changes between sleep/wakefulness states, different levels of sleep drive, and varying circadian times, with glial cells displaying the largest variations. Furthermore, the cell types whose transcriptomic dynamics correlate with the sleep homeostat or circadian clock are largely non-overlapping, with the exception of glial cells. Diminishing the circadian clock only in glial cells impairs the homeostatic sleep rebound after sleep deprivation. These findings reveal a comprehensive picture of different effects of sleep homeostatic and circadian processes on different cell types and define glial cells as the interaction sites of these two processes to determine sleep-wake dynamics. Single-cell RNA-seq (10X Genomics) on adult Drosophila brain at different sleep, wake, sleep deprivation and Zeitgeber (ZT) times