Sister telomere cohesion is required for double-strand break repair and telomere maintenance. (A and B) SA1- and TIN2-depleted cells are defective in sister chromatid repair after ionizing radiation. siRNA-treated HeLaI.2.11 cells were irradiated with 2 Gy of ionizing radiation (IR), and allowed to recover for 0 or 2 h. Prometaphase spreads were analyzed by hybridization to Cy3-conjugated telomere repeat (CCCTAAA)3 peptide nucleic acid (PNA) probe (red). DNA was stained with DAPI (blue). (A) Chromosome spread of GFP siRNA cells treated with 2 Gy IR. Three enlarged examples of sister chromatid breaks (indicated by arrowheads) are shown. (B) Graphical representation of the percentage of sister chromatid breaks. Approximately 500 chromosomes were scored for each sample from two independent experiments (exp.1, x axis on the left; exp. 2, x axis on the right; see Table II). (C and D) Sister telomeres are lost in SA1- and TIN2-depleted cells. siRNA-treated HeLaI.2.11 cells were processed for PNA-FISH as described above. (C) Chromosome spread of SA1 siRNA cells. Three enlarged examples of sister telomere loss (indicated by arrowheads) are shown. Bars, 5 μm. (D) Graphical representation of the percentage of sister telomere loss. Approximately 500 chromosomes were scored for each sample from two independent experiments (see Table II).
