miR-15a inhibits colony formation by normal human bone marrow progenitor cells. Normal human bone marrow mononuclear or CD34⁺ cells were transfected with control miR or a miR-15a mimic. Effects on CD34⁺ cell–derived colony-forming unit–erythroid (CFU-E; 3 × 10³/35-mm dish; A), marrow mononuclear cell–derived colony-forming unit–erythroid (CFU-E) and burst-forming unit–erythroid (BFU-E; 1.2 × 10⁵/35-mm dish; B); and CD34⁺ cell–derived colony-forming unit–granulocyte, macrophage (CFU-GM; 3 × 10³/35-mm dish; C) are shown.