High Basal [gamma]H2AX Levels Sustain Self-Renewal of Mouse Embryonic and Induced Pluripotent Stem Cells

Phosphorylation of histone H2AX ([gamma]H2AX) is known to be the earliest indicator of DNA double-strand breaks. Recently, it has been shown that mouse embryonic stem cells (mESCs) have very high basal levels of [gamma]H2AX, even when they have not been exposed to genotoxic agents. As the specialized role of high basal [gamma]H2AX levels in pluripotent stem cells is still debated, we investigated whether H2AX phosphorylation is important in maintaining self-renewal of these cells. Here, we report that not only mESCs but also mouse-induced pluripotent stem cells (miPSCs), have high basal levels of [gamma]H2AX. We show that basal [gamma]H2AX levels decrease upon ESC and iPSC differentiation and increase when the cells are treated with self-renewal-enhancing small molecules. We observe that self-renewal activity is highly compromised in H2AX-/- cells and that it can be restored in these cells through reconstitution with a wild-type, but not a phospho-mutated, H2AX construct. Taken together, our findings suggest a novel function of H2AX that expands the knowledge of this histone variant beyond its role in DNA damage and into a new specialized biological function in mouse pluripotent stem cells. STEM CELLS2012;30:1414-1423