A Novel Developmental Regulatory Motif Required for Stage-Specific Activation of the ɛ-Globin Gene and Nuclear Factor Binding in Embryonic Erythroid Cells

Abstract

Members of the human β-globin gene family are expressed at discrete stages of development and therefore provide an important model system for examining mechanisms of temporal gene regulation. We have previously shown that expression of the embryonic β-like globin gene (e) is mediated by a complex array of positive and negative upstream control elements. Correct developmental stage- and tissue-specific gene expression is conferred by synergistic interactions between a positive regulatory element (termed ɛ-PRE II) which is active only in embryonic erythroid cells and at least two other regulatory domains upstream of the ɛ-globin gene promoter. A nuclear factor highly enriched in cultured embryonic erythroid cells and in mouse embryonic yolk sac binds to a novel, evolutionarily conserved sequence within ɛ-PRE II. We show here that binding of this factor to the conserved element within ɛ-PRE II is critical for transcriptional activity. Point mutations that interfere with protein binding to ɛ-PRE II abolish transcriptional activation of the constitutive ɛ-globin promoter. Adult erythroid nuclei (from cultured cells or adult mouse liver) also contain a factor that binds to this region, but the complex formed migrates more rapidly during nondenaturing electrophoresis, suggesting either that distinct proteins bind to ɛ-PRE II or that a single protein is differentially modified in these cells in a way that modulates its activity. Several lines of evidence suggest that the binding factors in embryonic and adult erythroid cells are distinguished by posttranscriptional differences.