VPA treatment mimics the phenotype of Hdac1 knock-down in vivo. mCG^PR/PR mice were treated with VPA or PBS (CTRL) for 14 days. Then, (A) 12 hours after the last injection, mice were euthanized and bone marrows were collected and analyzed for the expression of Gr-1 and c-Kit (left panel), or colony-forming ability (right panel), or (B) followed for leukemia development. In the graph, leukemia-free survival curves from VPA- and PBS-treated mice (P < .05).