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Mechanism of developmental regulation of alpha pi, the chicken embryonic alpha-globin gene
1Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892.
Insights
Chicken alpha pi-globin gene expression is specific to primitive red blood cells during development. Promoter analysis reveals transcription factor concentrations, not their presence, dictate stage-specific gene expression.
Area of Science:
- Developmental biology
- Gene regulation
- Erythropoiesis
Background:
- The chicken alpha pi-globin gene exhibits lineage-specific expression, restricted to primitive erythrocytes.
- Understanding the regulatory mechanisms governing this stage-specific expression is crucial for comprehending erythroid development.
Purpose of the Study:
- To investigate the role of the alpha pi-globin promoter in conferring stage-specific expression.
- To identify the trans-acting factors and their binding sites within the promoter that regulate this specificity.
Main Methods:
- Transfection of plasmids containing the alpha pi promoter into primary erythroid cells from different developmental lineages.
- Site-directed mutagenesis of putative transcription factor binding sites within the promoter.
- Analysis of protein-DNA interactions and their impact on gene expression.
Main Results:
- The alpha pi promoter alone is sufficient to confer stage-specific expression in both primitive and definitive erythroid cells.
- Key transcription factors are present in both lineages, but their concentrations vary.
- NF1, Y-box, and Sp1-like factors interact to modulate transcription, with GATA-1 also playing a role.
Conclusions:
- Stage-specific expression of the chicken alpha pi-globin gene is determined by the concentration-dependent action of specific transcription factors within the promoter.
- Differential concentrations of these factors, rather than their mere presence or absence, orchestrate lineage-specific gene regulation during erythropoiesis.
Abstract:
The chicken alpha pi-globin gene is expressed during 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.