Embryonic hemoglobins are expressed in definitive cells

Human embryonic zeta and epsilon globin chains are synthesized in yolk sac- derived primitive erythroid cells, and decrease rapidly during definitive e rythropoiesis. Examination of zeta and epsilon globin expression at the cel lular level using dual-color immunofluorescence staining with specific mono clonal antibodies showed that embryonic globin proteins are present in defi nitive erythroid cells. More than half of fetal erythrocytes were positive for zeta and similar to 5% for epsilon globin. Approximately one third of n ewborn red blood cells were zeta-positive and less than 1% epsilon-positive . Adult erythrocytes did not have embryonic globins. Erythroblasts that dev eloped in liquid cultures also contained embryonic globin in amounts which declined with ontogenic age, and the proportion of positive cells in vitro was less than in the comparable erythrocytes that developed in vivo. Thus, embryonic globin chains are synthesized in definitive erythroid cells and d ecrease with ontogeny. Modulation of embryonic globin gene expression is no t solely due to a switch from primitive to definitive erythropoiesis, (C) 1 999 by The American Society of Hematology.