FIGURE 5.

FEN1 depletion results in fragile site expression at telomeres. A, representative FISH of metaphases obtained from BJ fibroblasts (BJ) or BJ fibroblasts expressing SV40 Large T antigen and telomerase (BJLT). Cells expressing a control hairpin (shSCR) or depleted of FEN1 (shFEN3) are indicated. Chromosomes were hybridized with the PNA telomere probe Cy3-(CCCTAA)₃ (red) and stained with DAPI (blue). Magnified images show representative fragile telomeres (arrowheads). B, quantification of telomere fragility, depicted as the number of fragile telomeres observed per chromosome. No fewer than 60 metaphases from two independent experiments were analyzed for each condition, and an average of the two experiments is shown (*, p < 0.0001; Δ, p < 0.001). Error bars represent S.E.