Fig. 4: PARP1 inhibition causes transient DNA damage at telomeres.

a HeLa cells were transfected with siRNAs against siPARP1, siTRF1 or a scrambled sequence, alone or in the indicated combinations and against a scrambled sequence. Then samples were fixed at the specified endpoints after transfection and processed for IF-FISH against γH2AX and telomere repeats by a Cy3-Telo PNA probe and counterstained with DAPI. Signals were acquired by Leica Deconvolution fluorescence microscope (representative images at 63X magnification are shown), the percentage of TIFs positive cells (displaying >4 γH2AX/telomere co-localizations) and the mean number of TIFs/nucleus among γH2AX displaying nuclei were scored and reported in histograms in b and c respectively. The average of three independent experiments is shown, bars are SD. P value was determined by unpaired two tailed t-student test *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001, ****P ≤ 0.0001.