Figure 7. Circadian phase resetting does not influence the cell cycle and transiently perturbs synchronization of circadian and cell cycles.

• A Raster plots (each line is a cell trace) for cells treated with dexamethasone (Dex), forskolin, and untreated controls. Circadian peaks are in blue and division in red. Traces without division are in the upper parts of the panels above the thin lines. For cells with divisions, traces are sorted from bottom to top according to the time of the first division. This shows that cell divisions occur uniformly and are not affected by the phase resetting and that the second circadian peaks follow division after both dexamethasone and forskolin.
• B–D Synchronization indices over time in dexamethasone-treated cells (red) and controls (black). A value of zero for an index coincides with fully random phases while a value of 1 describes perfect synchronization. The circadian synchronization index R_θ (B) is initially much higher in dex-treated cells, as expected. Synchrony rapidly decays due to divisions (as visible in A, non-dividing cells clearly stay more synchronized). The cell cycle synchronization index (C) Rϕ is low throughout the recordings, indicating that dexamethasone treatment, and thus circadian phase synchronization, does not synchronize the cell cycle (also visible in A since the first divisions do not line up vertically). The synchronization index R_θ,ϕ (D) measuring synchronization of the circadian and cell cycles indicates that dexamethasone treatment transiently reduces synchrony of the two cycles. The initial increase (t < 15 h) in both conditions mostly reflects larger uncertainties in the estimated phases for early times (Supplementary Information). Error bars indicate standard deviations.