AbstractThe biological activity of the recombinant murine erythropoietin receptor (muEpoR) has so far been ascertained only in nonerythroid, established cell lines ectopically expressing the exogenous receptor. Here we show that the regulation of proliferation and differentiation by the muEpoR can be studied in chicken erythroid cells capable of terminal differentiation. The cloned muEpoR was introduced into primary and immortalized chicken erythroblast clones transformed by conditional oncogenes, using retroviral gene transfer. After turning off oncoprotein function, these cells terminally differentiated in response to human erythropoietin (rhu-Epo), similar to cells treated with chicken anemic serum containing avian Epo. Control vector-containing erythroblasts were totally unresponsive to rhu-Epo, but differentiated normally in presence of avian Epo. The avian erythroblasts expressed biologically active muEpoR at physiological levels and bound rhu-Epo with similar high affinity as mammalian erythroblasts expressing endogenous EpoR. Finally, rhu-Epo synergized with insulin in these cells similar to avian Epo. Our results demonstrate that the exogenous muEpoR is able to mediate normal, terminal differentiation in avian erythroid progenitors.