Fig 1: Anaphase bridges are formed by NHEJ and HR and are inhibited by CtIP-dependent end resection.(A) Representative western blots showing the siRNA-mediated depletion of XRCC4, CtIP, or XRCC3 in HeLaS3 cells as well as control siRNA-treated cells. (B) Frequency of anaphase bridge formation in HeLaS3 cells transfected with an siRNA targeting XRCC4, CtIP, or XRCC3 (or control siRNA) with (+Etp) or without (-Etp) induction of mitotic DSBs by etoposide. Anaphase cells (=50) were scored for each experiment and condition. Error bars show the standard deviation from three independent experiments. Statistical significance was analyzed with the Student's t-test. ** P-value<0.01, ns, not significant. (C) Anaphase bridge formation was observed with time-lapse live-cell imaging of a typical HeLa cell at the indicated time after release from etoposide treatment with (AB) or without (-) anaphase bridge formation. In addition, shown is an average of duration when required to transit to anaphase in non-treated (-Etp) or etoposide-treated (+Etp) cells with numbers of cells analyzed. Statistical significance was analyzed with the Student's t-test. Scale bar, 5 µm; ns, not significant. (D) Anaphase-bridge formation observed by time-lapse imaging after DSB induction in the indicated knockdown cells. Prometaphase cells (=25) were chosen and analyzed for anaphase bridge formation for each experiment. Error bars show standard deviation from 3 to 11 independent experiments. Statistical significance was analyzed with the Student's t-test. ** P-value<0.01, * P-value<0.05.