Slow elimination of phosphorylated histone γ-H2AX from DNA of terminally differentiated mouse heart cells in situ

Phosphorylation of replacement histone H2AX occurs in megabase chromatin domains around double-strand DNA breaks (DSBs) and this modification (called γ-H2AX) may serve as a useful marker of genome damage and repair in terminally differentiated cells. Here using immunohistochemistry we studied kinetics of γ-H2AX formation and elimination in the X-irradiated mouse heart and renal epithelial tissues in situ. Unirradiated tissues have 3–5% γ-H2AX-positive cells and in tissues fixed 1 h after X-irradiation γ-H2AX-positive nuclei are induced in a dose-dependent manner approaching 20–30% after 3 Gy of IR. Analysis of mouse tissues at different times after 3 Gy of IR showed that maximal induction of γ-H2AX in heart is observed 20 min after IR and then is decreased slowly with about half remaining 23 h later. In renal epithelium maximum of the γ-H2AX-positive cells is observed 40 min after IR and then decreases to control values in 23 h. This indicates that there are significant variations between non-proliferating mammalian tissues in the initial H2AX phosphorylation rate as well as in the rate of γ-H2AX elimination after X-irradiation, which should be taken into account in the analysis of radiation responses.