Fig. 4

Frequencies of γ-H2AX positive foci and TIFs in FRDA fibroblast cells. a Average number of γ-H2AX positive foci in FRDA fibroblasts (GM03665, GM03816, GM04078), unaffected fibroblasts (GM07492, GM04503), U2OS ALT-positive control cells (+Ctrl) and HeLa ALT-negative control cells (−Ctrl), n = 50–100. b Average TIFs in each corresponding cell line, n = 50–100. Data are shown as mean ± SEM (^** P < 0.01 and ^*** P < 0.001, evaluated by Student’s t test). c Representative images showing detection of γ-H2AX by immuno-FISH in FRDA and control (normal) fibroblast cells, U2OS ALT-positive control cells (+Ctrl) and HeLa ALT-negative control cells (−Ctrl). Interphase cells were stained with antiphospho-histone γ-H2AX (green) and telomeric Cy3-labeled PNA probes (red). Nuclei were counterstained with DAPI (blue). White arrowheads in merged images indicate TIFs (yellow). Scale bar = 10 μm. All experiments were repeated independently, at least twice