The modulation of Hb F synthesis in adult erythroid progenitor (burst-forming unit) cultures reflects changes in gamma-globin gene transcription and chromatin structure.

Abstract

Fetal hemoglobin production can be reactivated in vivo in adult persons with various hemoglobinopathies and other hemopoietic disorders, and in cultures of adult erythroid progenitors. We show that the activation of Hb F in adult cells is transcriptional in nature and is accompanied by the appearance of DNase I-hypersensitive sites and undermethylation of Hpa II sites 5' to the y-globin genes. Production of Hb F in culture is strongly modulated by the environment, and the repression of Hb F synthesis by specific culture conditions has been reported. By nuclear runoff, chromatin, and methylation analyses, we show that this inhibition of Hb F production in vitro is at the level of transcription with the concomitant loss of characteristic y hypersensitive sites and methylation of Y Hpa II sites. These data indicate, first, that the organization of globin chromatin of adult cells that produce fetal hemoglobin resembles that of fetal erythroid cells and, second, that this organization switches from a fetal to an adult pattern in response to changes in the environment of the erythroid cells.

DNA methylation: a secondary event in globin gene switching?

“…Furthermore, inhibition of reactivated HbF production by switching activities re sults in methylation of 7-gene Hpall sites (Groudine et al 1986). We find that preswitch hybrids expressing the 7-globin genes have unmethylated 7-globin genes.…”

“…HbF in adult cells is accompanied by 7-gene undermethylation (Groudine et al 1986). Furthermore, inhibition of reactivated HbF production by switching activities re sults in methylation of 7-gene Hpall sites (Groudine et al 1986).…”