Figure 3.

DNA damage-induced phase-response curves (PRCs) in PER2::LUC mouse embryonic fibroblast (MEF) cells. (A) A representative PRC in which the phase shift is plotted as a function of when methyl methane sulfonate (MMS) treatment was given; the diamond, square, triangle, and × are the Δφ for each individual experiment, and the circle is the mean ± SD. The mean Δφ and standard deviation are as follows: 14: 5.8 ± 1.6 h, 18: 5.4 ± 1.9 h, 20:4.5 ± 0.7 h, 22: 4.48 ± 1.8 h, 24: 3.5 ± 2.1 h, 26: 4.5 ± 1.25 h, 28: 2.8 h ± N/A, 30: 3.7 ± 1.4 h, 32:1.55 ± 2.05 h, and 34: −0.7 ± N/A. MMS treatment at various points over the first cycle of PER2::LUC expression yields maximum phase advances at phases when PER2::LUC levels are increasing (see text for details). (B) Comparison of published DNA damage-induced PRC data from RAT-1 cells (gray boxes, replotted from Oklejewicz et al., 2008) with PER2::LUC MEF cells (black diamonds). The data points shown represent the mean values from each PRC experiment for each individual time point. (C and D) DNA damage 34 h after serum shock results in a variable phase response, where the magnitude of the phase change is dependent on the phase of PER2 expression. In panel C, PER2 levels are declining during DNA damage, which results in a Δφ of −0.7 h, whereas DNA damage during the beginning of the next cycle of PER2 results in a Δφ of +6.9 h. Raw data with no smoothing or background subtraction are shown.