Schematic representation of DNA methylation changes during differentiation and aging. Promoter DNA methylation of a set of myeloid-specific differentiation genes in hematopoietic progenitor cells is lost during myeloid differentiation. A similar, albeit reduced, effect is also observed during HPC aging, in addition to de novo methylation. Both changes might contribute to the reduced phenotypic plasticity of aged hematopoietic progenitor cells.