POT1 partial knockdown prevents replication fork uncoupling at telomeres of WRN-depleted HCA2-T+ cells. (A) Efficient knockdown of WRN (>90%) (lanes 2,4,6) combined to partial knockdown of POT1 (50%–60% compared with control) (lanes 1,2) with two different POT1 siRNAs (P#1, lanes 3,4; P#2, lanes 5,6) in HCA2-T+, revealed by Western blot. (B) POT1 partial knockdowns have no effect on telomere replication. The histogram represents mean CO-FISH signal intensities after POT1 knockdown, represented as percentages (%) of control siRNA. (C) POT1 knockdown leads to shortening of both C-rich (green) and G-rich (red) strands in HCA2-T+ cells depleted for WRN. Quantification results are represented in percentages of control siRNA for WRN.