Fig. 1.

Response of ES cells in culture 24 hrs following exposure to minimally toxic ROS. A. Cells were exposed to H₂O₂ for 15 min, recovered in normal medium for 20 hrs, then the number of viable cells in culture scored (dead cells were excluded by trypan blue). Data are the average and standard deviation of at least 4 independent experiments. B. Dose-dependent accumulation of single-strand breaks (SSBs) following exposure to H₂O₂ for 15 min. Pulse field gel electrophoresis of agarose embedded DNA without (−; DSB) or with (+; SSB and DSB) S1 nuclease digestion. DNA fragmentation was not evident in samples exposed to H₂O₂ at lower doses. Fragmentation was observed at higher doses (1mM and 5mM). As expected, visible fragmentation was detected in all samples, including untreated, following S1 nuclease digestion. Visible fragments were within the 0.3-1 Mb range. C. Time-dependent accumulation of 50 kb fragments following exposure (Exp) to 100 M H₂O₂ with or without recovery (Rec). 50 kb fragments observed only after chronic 24 hour continuous exposure and no recovery. M -- size standard marker.