The circadian clock mediates daily bursts of cell differentiation by periodically restricting cell differentiation commitment

Abstract

Most mammalian cells have an intrinsic circadian clock that coordinates their metabolic activity with the daily rest and wake cycle. In addition, the circadian clock is known to regulate cell differentiation, but how continuous daily oscillations of the internal clock control a much longer, multi-day differentiation process is not known. Here we simultaneously monitor the circadian clock and progression of adipocyte differentiation live in single cells. Strikingly, we find a bursting behavior in the cell population whereby individual preadipocytes commit to differentiate primarily during a 12-hour window each day corresponding to the time of rest. Daily gating of differentiation occurs because cells can irreversibly commit to differentiate within a few hours, which is faster than the rest phase and much faster than the overall multi-day differentiation process. We show that the daily bursts in differentiation are driven by a variable and slow increase in expression of PPARG, the master regulator of adipogenesis, combined with rapid, clock-driven expression of CEBPA, which is in a fast positive feedback relationship with PPARG. During each rest cycle, the increase in CEBPA causes a brief step increase in PPARG so that some cells can reach the threshold to irreversibly commit to differentiate, causing the consecutive daily bursts in cell differentiation at the population level. Our findings are broadly relevant given that most differentiating somatic cells are regulated by the circadian clock. Having a restricted time each day when differentiation occurs may open therapeutic strategies to use timed treatment relative to the clock to promote tissue regeneration. Significance StatementCells rely on a circadian clock that coordinates cellular activities with the day-night cycle. Defects in circadian clock genes dysregulate cell differentiation processes in immune, muscle, skin and fat cells. However, how a perpetual daily clock can regulate a multi-day long cell differentiation process was not understood. Here we show that the circadian clock controls a fast upregulation of the transcription factor CEBPA during each daily rest phase which in turn controls a fast irreversible step during the overall slow multi-day differentiation of fat cells, causing daily bursts of cell differentiation. Our finding opens potential therapeutic strategies to enhance tissue regeneration by timing when during the day drugs are administered.