Fig. 1. S phase-specific localization of TCOF1 at telomeres.

a Localization of TCOF1 in nuclei of U2OS cells during S and non-S phase of cell cycle. EdU labeling was used to indicate S phase cells. Nucleoli were shown by staining the fibrillarin marker protein. b Quantification of (a). The percentage of cells with TCOF1 localized outside of nucleoli was determined (n ≥ 100 cells). All values are the average ±SEM of three independent experiments. The unpaired Student’s two-tailed t-test was used to determine the statistical significance (**P < 0.01). c U2OS cells were synchronized at G1/S and released into S phase for 4.5 h, corresponding to middle S phase. Asynchronous cells were used as a control. Left: flow cytometry analysis of the cell cycle. Right: co-staining of TCOF1 and fibrillarin in cells. d Quantification of (c). The percentage of cells with TCOF1 localized outside of nucleoli was determined. All values are the average ±SEM of three independent experiments (n ≥ 100 cells). e Quantification of (c). The percentage of TCOF1 outside of nucleoli in individual cells during S phase was quantified by determining the fluorescence intensity of TCOF1 after IF staining (n ≥ 100 cells). The unpaired Student’s two-tailed t-test was used to determine the statistical significance (***P < 0.001). f U2OS cells were synchronized at G1/S and released for 0, 3, 6, and 9 h, respectively. Left: flow cytometry analysis of the cell cycle. Right: co-staining TCOF1 and telomeres at indicated timing. g Quantification of (f). The percentage of cells with ≥5 telomeric TCOF1 foci was determined (n ≥ 100 cells). All values are the average ±SEM of three independent experiments.