Murine erythroid differentiation kinetics in vivo under normal and anemic stress conditions.

Our current understanding of the kinetics and dynamics of erythroid differentiation is based almost entirely on the ex vivo expansion of cultured hematopoietic progenitor cells. In this study, we used an erythroid-specific, inducible transgenic mouse line to investigate for the first time, the in vivo erythroid differentiation kinetics under steady-state conditions. We demonstrated that bipotent premegakaroycyte/erythroid (PreMegE) progenitor cells differentiate into erythroid-committed proerythroblast/basophilic erythroblasts (ProBasoE) after 6.6 days under steady-state conditions. During this process, each differentiation phase (from PreMegE to precolony forming unit-erythroid [PreCFU-E], PreCFU-E to CFU-E, and CFU-E to ProBasoE) took ∼2 days in vivo. Upon challenge with 5-flurouracil (5-FU), which leads to the induction of stress erythropoiesis, erythroid maturation time was reduced from 6.6 to 4.7 days. Furthermore, anemia induced in 5-FU-treated mice was shown to be due not only to depleted bone marrow erythroid progenitor stores but also to a block in reticulocyte exit from the bone marrow into the circulation, which differed from the mechanism induced by acute blood loss.