An overview of erythropoiesis: regulation at multiple levels by multiple proteins and miRNAs. Formation of RBCs from HSCs is regulated by signaling through both external factors (blue), such as cytokines and fibronectin, as well as intracellular factors, such as transcription factors (black) and miRNAs (red). Below the differentiation network, a timeline and images are shown for in vitro methylcellulose colony formation of murine BFU-E and CFU-E.