Hemoglobin Switching in Humans

Background: Understanding the mechanism of developmental regulation of hemoglobin switching has scientific as well as clinical relevance because of the influence of fetal hemoglobin (HbF) production in adulthood on the clinical manifestation of thalassemia and sickle cell anemia. We have previously found that the normal developmental patterns of globin gene expression are recapitulated in an experimental system of primary cultures that support differentiation of erythroid progenitors. We further found that high activities of the transcriptional activators, GATA-1 and SPI, are associated with normal adult erythroid differentiation. Materials and Methods: In the present work, we have studied the activities of GATA-1 and SPI during differentiation of cultured erythroid progenitors derived from cord blood and from fetal livers, as well as from ,3Othalassemia patients. Results: The results showed high GATA-1 binding activity and very low SPI activity in the fetal liver cultures. This pattern was in contrast to cultures derived from normal adult peripheral blood, in which both GATA-1 and SPI activities were high. Cord blood cultures showed an additive combination of "adult" and "fetal" patterns. The progenitors derived from a 13-thalassemia patient with high HbF production showed "fetal" pattern. On the other hand, in cultures of 2 13-thalassemia patients without high HbF, "adult" pattern was observed. Conclusions: In the present work, we show that human fetal and adult erythroid progenitors are distinct in their transcription factors, and that the commitment to fetal or adult program occurs at a very early differentiation stage. Our studies also demonstrate that under anemic stress, recruitment of fetal progenitors may occur in adulthood.