Cellular regulation of fetal hemoglobin synthesis in man: Investigation of γ and β mRNA accumulation in clonal erythroid cultures initiated from erythroid progenitors derived from fetuses, neonates, and adult individuals

Abstract

The accumulation of globin mRNA in erythroid cells during human development was investigated in clonal cultures of fetal, newborn, and adult origin erythroid progenitors and in control uncultured erythroblasts and reticulocytes. The relative concentrations of α, β, and γ mRNA sequences were measured by hybridization with purified α, β, and γ[ 3H]cDNA probes. We found that the amount of γ mRNA is characteristic of the developmental stage from which the erythroid progenitor cells are obtained. In colonies from fetal liver cells, 89% of the non-α mRNA is γ mRNA. Colonies derived from neonatal (cord blood) cells produce an average of 55% γ mRNA, while colonies generated from either adult bone marrow or progenitors circulating in the peripheral blood of the adult individual produce γ mRNA ranging from 15 to 38% of the non-α sequences. When compared with erythroid cells (erythroblasts or reticulocytes) from the same tissues, the fetal liver colonies produce identical proportions of γ mRNA as liver cells in vivo. Colonies from circulating erythroid progenitors from the perinatal (switchover) period accumulate somewhat less γ mRNA (55%) than do circulating reticulocytes in vivo (64%). The concentration of γ mRNA (15 to 38%) in colonies of adult marrow or peripheral blood origin is substantially higher than the trace amounts (<1%) found in mature erythroid cells in vivo. The amounts of β and γ globin chain synthesis from fetal liver, cord blood, and adult peripheral blood are proportional to β and γ mRNA ( r = 0.97) and thus indicate that selective translation of β and γ mRNA is not a significant factor in the switch from Hb F to Hb A production. (However, both neonatal reticulocytes in vivo and erythroid colonies in vitro contain excess non-α mRNA but exhibit balanced globin chain synthesis; translational control mechanisms apparently prevent excess synthesis of total non-α chains.) The expression of stage-specific patterns of γ and β mRNA in erythroid colonies suggests that the erythroid progenitor cells in vivo possess the potential for unique programs of γ and β mRNA accumulation before they actually enter the pathway to terminal maturation.