Phosphorylation of histone H2AX onSer139 is a sensitive reporter of DNA damage, particularly if the damage involves induction of DNA double-strand breaks (DSBs). Phosphorylated H2AX has been named γH2AX and its presence in the nucleus can be detected immunocytochemically. Multiparameter analysis of γH2AX immunofluorescence by flow or laser-scanning cytometry allows one to measure extent of DNA damage in individual cells and to correlate it with their position in the cell cycle and induction of apoptosis. This chapter presents the protocols and outlines applications of multiparameter cytometry in analysis of H2AX phosphorylation as a reporter of the presence of DSBs.
