MECHANISM OF DEVELOPMENTAL REGULATION OF ALPHA-PI, THE CHICKEN EMBRYONIC ALPHA-GLOBIN GENE

The chicken alpha(pi)-globin gene is expressed development only in the primitive erythrocyte lineage and not in the definitive lineage. We show that stage-specific expression is maintained when plasmids containing the alpha(pi) promoter are transfected into primitive and definitive lineage primary erythroid cells and that the information contained in the promoter is sufficient to confer this specificity. Detailed analysis of binding sites in the promoter for trans-acting factors, together with studies of the effects of mutagenesis on expression, reveals that the factors critical to stage-specific expression are all present in both primitive and definitive lineages, but at various concentrations. We identify three proteins, an NF1 family member, a Y-box factor, and an Sp1-like factor, which interact to stimulate or inhibit transcription. We propose that the concentration-dependent action of these factors, together with the general erythroid factor GATA-1, is responsible for the stage-specific expression of the alpha(pi)-globin gene.