Fig. 3: Cell size control in vivo depends on the RB pathway.

A Schematic of the RB pathway. The S phase-inhibiting activities of Rb1 and Rbl1 are repressed by dilution as cells grow larger in G1. B Intravital imaging of cells within the mouse hindpaw or ear epidermis. En face and side views are shown of hindpaw epidermis expressing the K14-H2B-Cerulean nuclear marker and the FUCCI-G1-mCherry cell cycle phase reporter. Dotted yellow line indicates the location of the basal layer. C A single stem cell in the hinpaw tracked from birth to division. D Epidermal stem cell birth nuclear size is inversely proportional to the amount of nuclear growth during G1 phase. Binned medians ± SEM are shown in red. Slope = −0.63 (p < 0.0001). N = 2 mice, 254 cells. E 4OHT or vehicle was applied topically to the left and right ears of a mouse homozygous for Rbl1–/– and tamoxifen-inducible Rbl1-floxP. F The relationship between nuclear size at birth and the duration of G1 phase is shown for SKO (cyan) and DKO (red) cells. Linear regression is solid line. 95% confidence intervals are shaded. Errorbars are medians ±  SEM. SKO: Pearson’s R = −0.46 (p < 0.001), 57 cells; DKO: R = −0.01 (p > 0.9), 49 cells. G The coefficient of variation (CV) of nuclear size is shown for cells prior to the indicated treatment and 5 days after ethanol or 4OHT treatment. H The number of visible dying nuclear bodies are shown for SKO and DKO tissues relative to the timing of drug treatment. Solid line denotes the mean. Shaded region denotes the 95% confidence interval. N = 3 regions. I The number of 53BP1 foci per nuclei is quantified for SKO and DKO tissues. SKO: N = 112 cells, DKO: N = 115 cells (J). Rbl1 protein concentration was quantified in NIH3T3 cells under control or Rb1-knockdown conditions by subtracting the median Rbl1 intensity in Rbl1-knockdown cells with similar nuclear size. P values are two-sided T test test. Source data are provided as a Source Data file.