Hemoglobin synthesis in individual bursts from normal adult blood: All bursts and subcolonies synthesize Gγ- and Aγ-globin chains

Gamma-globulin chain synthesis has been evaluated in individual bursts and subcolonies that were generated by normal adult blood erythroid burst-forming units (BFU-Es) in methylcellulose cultures containing semipurified erythropoietin (Ep) and then analyzed via either isoelectric focusing (IEF) of globin chains or immunofluorescence techniques. At variance with previously reported results, based on plasma clot culture and immunofluorescence, all bursts and subcolonies analyzed synthesize γ-globin chains. Identification of γ-chains has been confirmed by preparative IEF of hemoglobin F (HbF), followed by either carboxymethylcellulose chromatography or IEF analysis of the resulting globin chains. In all bursts analyzed, the relative synthesis of the two types of γ-globin chains (Gγ and Aγ) shows an adult ratio (i.e., approximately 1:1). The results obtained via IEF have been confirmed by immunofluorescence studies, which apparently showed presence of at least some HbF-positive cells within all scrutinized bursts or subcolonies. The significance of these studies is discussed in the light of current hypotheses on mechanism(s) underlying HbF synthesis in normal adults.