Cultures of peripheral blood or bone marrow erythroidprogenitors display stimulated production of fetal hemoglobin. We investigated whether this stimulation is due to factors contained in the sera of the culture medium.Comparisons of y/y + @ biosynthetic ratios in erythroid colonies grown in fetal calf serum (FCS) or in charcoal treated FCS IC-FCS) showed that FCS-grown cells had significantly higher y/y + @ ratios. This increase in globin chain biosynthesis was reflected by an increase in relative amounts of steady-state y-globin mRNA. In contrast to its HE INDUCTION OF fetal hemoglobin (HbF) in adult T erythroid cell cultures was first documented when erythroid colonies were analyzed for globin chain expression, either with fluorescent antibodies or by globin chain biosynthesis.' Several studies subsequently described the activation of HbF in culture,'-I4 but there have also been discrepancies in experimental results.2.3 One of the initial interpretations of such discrepancies was that the culture media may differ in their capacity to stimulate HbF." We have attributed the activation of H b F in culture to a "deficient" culture environment, which leads to a high incidence of premature commitment of erythroid progenitors.I6 Terasawa et al" and Ogawa'* suggested that H b F was induced by the burst promoting activity present in the culture medium. In contrast to cultures done with fetal calf serum (FCS), there is low y-globin expression in cultures done with fetal sheep serum (FSS).'9*20 Rosenblum et a1 reported that y-globin expression in culture can also be substantially reduced when the serum is treated with activated charcoal.*'In the studies reported here we examine the effect of sera on fetal globin expression. We observed a stimulation of H b F production in FCS-containing cultures of adult erythroid progenitors. This stimulation is reflected by higher y-globin mRNA accumulation in FCS cultures. Treatment of FCS with activated charcoal results in a consistent decrease of y/y + / 3 ratios in peripheral blood or bone marrow erythroid colonies, but not in fetal burst forming unit-erythroid (BFU-E) colonies. Furthermore, dose-response experiments show that the induction of y-globin expression by FCS is concentration-dependent. These results indicate that FCS contains
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