Developmental Regulation of the Human Embryonic β-Like Globin Gene is Mediated by Synergistic Interactions Among Multiple Tissue- and Stage-Specific Elements

Abstract

The stage-specific regulation of mammalian embryonic globin genes has been an experimentally elusive problem, in part because of the developmentally early timing of their expression. We have carried out a systematic analysis of truncation and internal deletion mutations within the 5′-flanking region of the human embryonic β-like globin gene (∊) in erythroid and nonerythroid cell lines. Within a 670-bp region upstream from the constitutive promoter are multiple positive and negative control elements. Of these, a positive regulatory element (∊-PRE II) which is active only in embryonic erythroid cells is of particular interest. Remarkably, although it is inactive on its own, in the presence of other sequences located further upstream, it confers tissue- and developmental stage-specific expression on a constitutive ∊-globin or heterologous promoter. The activity of ∊-PRE II is also modulated by another positive regulatory domain located further downstream to direct erythroid cell-specific, but little or no embryonic stage-specific, transcription. A nuclear factor highly enriched in embryonic erythroid cells binds specifically within a 19-bp region of ∊-PRE II. Nuclei from adult erythroid cells also contain a factor that binds to this region but forms a complex of faster electrophoretic mobility. We speculate that interactions between ∊-PRE II and other upstream control elements play an important role in the developmental regulation of the human embryonic β-like globin gene.