H2AX in mouse embryonic stem cells: Distribution during differentiation and following -irradiation

Phosphorylated histone H2AX (gamma H2AX) represents a sensitive molecular marker of DNA double-strand breaks (DSBs) and is implicated in stem cell biology. We established a model of mouse embryonic stem cell (mESC) differentiation and examined the dynamics of gamma H2AX foci during the process. Our results revealed high numbers of gamma H2AX foci in undifferentiated mESCs, decreasing as the cells differentiated towards the endothelial cell lineage. Notably, we observed two distinct patterns of gamma H2AX foci: the typical discrete gamma H2AX foci, which colocalize with the transcriptionally permissive chromatin mark H3K4me3, and the less well-characterized clustered gamma H2AX regions, which were only observed in intermediate progenitor cells. Next, we explored responses of mESCs to gamma-radiation (137Cs). Following exposure to gamma-radiation, mESCs showed a reduction in cell viability and increased gamma H2AX foci, indicative of radiosensitivity. Despite irradiation, surviving mESCs retained their differentiation potential. To further exemplify our findings, we investigated neural stem progenitor cells (NSPCs). Similar to mESCs, NSPCs displayed clustered gamma H2AX foci associated with progenitor cells and discrete gamma H2AX foci indicative of embryonic stem cells or differentiated cells. In conclusion, our findings demonstrate that gamma H2AX serves as a versatile marker of DSBs and may have a role as a biomarker in stem cell differentiation. The distinct patterns of gamma H2AX foci in differentiating mESCs and NSPCs provide valuable insights into DNA repair dynamics during differentiation, shedding light on the intricate balance between genomic integrity and cellular plasticity in stem cells. Finally, the clustered gamma H2AX foci observed in intermediate progenitor cells is an intriguing feature, requiring further exploration.