Figure 7

Comet assays show that rate of DNA repair is linked to initial levels of DNA damage. (A) Comet assay showing efficient repair of peroxide-induced damage in an abattoir sample. The high level of DNA damage (indicated by long comet tails) in the middle panel is evident in cells collected immediately after peroxide treatment. Much of this damage is repaired after a 1 h recovery period with the result that the comet ‘tails’ are lost in the right hand panel. (B) CometScore analyses indicate cells which have been selected from bitmaps; these are converted into histograms by CometScore which quantifies %DNA in comet tails. The cells used in this panel are control cells. These are either undamaged (left hand panel) or have been treated with increasing concentrations of the DNA damaging agent etoposide (left to right). (C) CometScore analyses indicate levels of DNA damage following peroxide treatment of two populations from the same horse (PM group). The upper graph shows comet data for EP cells; the lower graph shows comet data for LP cells. The damage induced by peroxide treatment is markedly greater for the LP group; repair of DNA during the recovery period is also delayed for LP cells. Triplicate independent experiments were conducted with at least 50 comets analysed per condition. Outliers at 1.5 box-lengths or more from the edge of the box are indicated by spheres; extreme outliers at 3 or more box-lengths are indicated by black squares. The upper and lower boundaries of the box indicate the interquartile range; the line across the middle of the box represents the median value. Extreme outliers may indicate apoptotic cells or cells that have sustained irreparable damage; wide data distributions indicate these cell fate outcomes together with cells that are repairing, or have repaired, their DNAs.