 So far, there is no sufficient evidence that "in vivo", EpoR signaling can induce erythroid progenitors to undergo cell division, or whether Epo levels can modulate the cell cycle.EpoR signaling may still have a proliferation effect upon BFU-e progenitors, but these progenitors cannot be directly identified, isolated and studied.CFU-e progenitors enter the cell cycle at the time of GATA-1 induction and PU.1 suppression in a developmental manner rather than due to EpoR signaling.