A schematic of hematopoietic development depicting the specific points in differentiation at which the miRNAs discussed in this review are thought to act. Many additional miRNAs have been found by profiling studies to be expressed at these particular stages of differentiation, but these are not shown. MPP indicates multipotent progenitor; LMPP, lymphoid-primed multipotent progenitor; ETP, early T-cell progenitor; CLP, common lymphoid progenitor; CMP, common myeloid progenitor; GMP, granulocyte-macrophage progenitor; MEP, myeloid-erythroid progenitor, Gran, granulocyte; Mon, monocyte; Plat, platelets; and RBCs, red blood cells.