Erythropoietin (EPO) stimulates proliferation and differentiation or late erythroid precursor cells (CFU-E) and thereby determines the rate of erythropoiesis, Liver is the major erythropoietic site in a fetus. We dealt with developmental changes in CFU-E and EPO receptor (EPO-R) of fetal mouse liver. The affinity of the EPO-R to EPO was unchanged during fetal development. The popupation size of CFU-E, the number of EPO-R per liver cell, and EPO-R mRNA decreased as gestation proceeded, in a pattern indicating that the expression of EPO-R on erythroid precursor cells in fetal mouse liver is governed mostly by the process of mRNA production.
