Phosphorylation State Of The Histone Variant H2a.X Controls Human Stem And Progenitor Cell Fate Decisions

Histone variants (HVs) are a subfamily of epigenetic regulators implicated in embryonic development, but their role in human stem cell fate remains unclear. Here, we reveal that the phosphorylation state of the HV H2A.X (gamma H2A.X) regulates self-renewal and differentiation of human pluripotent stem cells (hPSCs) and leukemic progenitors. As demonstrated by CRISPR-Cas deletion, H2A.X is essential in maintaining normal hPSC behavior. However, reduced levels of gamma H2A.X enhances hPSC differentiation toward the hematopoietic lineage with concomitant inhibition of neural development. In contrast, activation and sustained levels of phosphorylated H2A.X enhance hPSC neural fate while suppressing hematopoiesis. This controlled lineage bias correlates to occupancy of gamma H2A.X at genomic loci associated with ectoderm versus mesoderm specification. Finally, drug modulation of H2A.X phosphorylation overcomes differentiation block of patientderived leukemic progenitors. Our study demonstrates HVs may serve to regulate pluripotent cell fate and that this biology could be extended to somatic cancer stem cell control.