Figure 1: Cells exhibit cell-to-cell variability in p21 expression.
(a) Image of p21-GFP (magenta) and mRuby-PCNA (turquoise) expressing hTert-RPE1 cells. Scale bar is 10 μm. (b) Cell features captured by automated image analysis (Methods) from a single cell expressing mRuby-PCNA and p21-GFP. (c) Single-cell traces of p21-GFP levels aligned to S/G2; n=51 cells. Tracks are coloured according to p21-GFP intensity. Black circles represent mitosis. (d) Correlation between maximum G1 p21-GFP intensity and G1 length (Pearson’s Correlation R=0.62** (P<0.01)). Three different 488 nm exposures are shown: Exp1, n=206 cells; Exp2, n=90; Exp3, n=52 (Methods). (e) Correlation in G1 p21-GFP levels between sister cells—G1 Daughter1 (G1D1) and G1 Daughter2 (G1D2; n=62, Pearson’s Correlation R=0.81** (P<0.01)). Data points are coloured to represent correlation between G1 length in each daughter cell, calculated as the difference between the maximum and minimum G1 length divided by the sum of the sister G1 lengths, n=62. (f) Single-cell traces of p21-GFP levels aligned to mitotic exit; n=51 cells. Grey line marks 600 min time point used to define G1pm arrest. Red curves are cells that enter a G1pm arrest, blue curves are cells that enter S-phase (cycle). (g) Mean p21-GFP intensity in G2M separated by daughter cell fate: cycling, n=49 cells; single arrest, n=9; twin arrest, n=10. Significant differences are observed between arrested and cycling states using a two-sample t-test on log-transformed data. Error bar is s.d. *P<0.05, **P<0.01.
