γH2AX in adherent MCF7 cells and mammospheres. Adherent MCF7 cells (A) and mammosphere-derived cells (B, C) were seeded onto Lab-Tek chamber slides and allowed to adhere overnight. Cells were fixed using methanol:acetone and stained for γH2AX (red). Nuclear staining was achieved by DAPI (blue). Images were obtained by confocal microscopy. Level of γH2AX staining area was measured compared to total nuclear area and plotted (D). Images represent 3 different mammosphere cultures.