Human granulocyte-macrophage colony-stimulating factor (hGM-CSF) stimulates primitive and definitive erythropoiesis in mouse embryos expressing hGM-CSF receptors but not erythropoietin receptors

Although erythropoietin (EPO) and its receptor (EPOR) are crucial for the p roliferation, survival, and terminal differentiation of erythroid progenito rs, it remains to be elucidated whether EPOR-unique signaling is required f or erythropoiesis. To address this issue, human granulocyte-macrophage colo ny-stimulating factor (hGM-CSF) receptor (hGMR)-transgenic mice and heteroz ygous EPOR mutant mice were crossed by in vitro fertilization. In methylcel lulose clonal culture of fetal liver (FL) cells of generated hGMR-expressin g EPOR-/- embryos at embryonic day (E) 12.5 of gestation, hGM-CSF stimulate d erythroid colony formation under serum-containing and serum-free conditio ns. Analysis of globin expression in individual erythrocyte-containing colo nies formed from E12.5 FIL cells showed that hGM-CSF supports primitive and definitive erythropoiesis even in EPOR-/- embryos. In comparison of activi ties between hGM-CSF and EPO in hGMR-expressing EPOR+/+ embryos, the 2 subs tances supported the formation of similar numbers of erythroid colonies in clonal culture of E12.5 FL cells; enhanced adult, but not embryonic, globin synthesis; and induced increase of GATA-1 expression and decrease of eryth roid Kruppel-like factor and cMyb expression in the FIL cells. On the other hand, in E8.0 yolk sac erythropoiesis, both substances had a similar effec t on erythroid colony formation, but hGM-CSF induced an increase of p-major globin expression, while EPO did not. All together, the results of the pre sent study demonstrated that hGM-CSF can stimulate the proliferation and di fferentiation of primitive and definitive erythroid cells independently of EPOR signal If they express hGMR, and the activity Is comparable to that of EPO In definitive, but not primitive, erythropoiesis. (C) 2001 by The Amer ican Society of Hematology.