Figure 1. Impact of short term quiescence induction (3×9 days) in MRC-5 and WI-38 fibroblasts.

(A & B) Growth curve of 2 independent MRC-5 (A) and WI-38 (B) fibroblast cell lines (control with no quiescence induction and a cell line where quiescence was induced 3 times separately for a span of 9 days by contact inhibition) maintained in culture at 20% O₂ as triplicates from an early PD until senescence at late PDs. Each growth curve is measured in triplicate. Data points of all measurements are displayed (not the mean). (B, C, D, E & F) Percentage of SA-β gal positive cells at different time points of their growth in culture in the control MRC-5 (C & E) and WI-38 (D & F) fibroblast cell line and in the cell line where quiescence was induced 3 times separately. Fig. 1 C and D are plotted with PDs, whereas Fig. 1 E and F are plotted with days in culture in the y-axis. Each curve is measured in triplicate, the mean value is displayed with error bar (± S.E). (G & H) Quiescence was induced by contact inhibition in short periods of 9 days at 3 stages of the lifespan of MRC-5 (at PDs = 36, 44, 56) and WI-38 (at PDs = 33, 43, 51) fibroblasts maintained in culture at 20% O₂. The plot shows the number of days spent by MRC-5 (G) and WI-38 (H) fibroblasts in culture between PDs 38 and 44, 46 and 56, and 58 and 69 for MRC-5 (G) and between PDs 35 and 43, 45 and 51, and 53 and 59 for WI-38 (H) for cells having been repeatedly quiescent compared to the control fibroblasts. (I & J) Percentage of SA-β gal positive cells at PD immediately after quiescence induction compared to their respective non-quiescence induced MRC-5 (I) and WI-38 (J) controls. The bars indicate the mean ± S.D. Values statistically different from their controls (t-test) are indicated with an asterix: * p<0.05, ** p<0.01, *** p<0.001. n = 3