The developmental switch in embryonic rho-globin expression is correlated with erythroid lineage-specific differences in transcription factor levels.
During chicken embryogenesis, the rho-globin gene is expressed only in the early developmental stages. We have examined the mechanisms that are responsible for this behavior. The transcription of the rho-globin gene is strongly correlated with the presence during development of primitive erythroid lineage cells, consistent with the idea that the expression of the rho-globin gene is restricted to that lineage. The "switching off" of rho-globin during development thus reflects the change from primitive to definitive cell lineages which occurs during erythropoiesis in chicken. We use transient expression assays in primary erythroid and other cells to show that the information for lineage- and tissue-specific expression of the rho-globin gene is contained in a 456 bp region upstream of the gene's translational start site. DNA-binding studies, coupled with analysis of the effect on expression of deletions and binding site mutations, were used to identify important control elements within this 456 bp region. We find that binding sites for the ubiquitous transcription factor Sp1, and the specific hematopoietic factor GATA-1, are crucial for expression of the gene in primitive erythroid cells. Quantitative analysis shows that nuclei of the primitive erythroid lineage contain 10-fold more of these factors than do the nuclei of definitive cells. We show that in principle these differences in factor concentration are sufficient to explain the lineage-specific behavior that we observe in our assays. We suggest that this may be an important part of the mechanism for lineage-restricted rho-globin expression during chicken erythroid development. Similar mechanisms may be involved in regulation of other (but not all) members of the globin family.
Minie
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ME
Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Kimura
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Felsenfeld
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D000818:Animals; D002642:Chick Embryo; D004268:DNA-Binding Proteins / Q000235:genetics; D004586:Electrophoresis; D015672:Erythroid Precursor Cells / Q000502:physiology*; D050981:Erythroid-Specific DNA-Binding Factors; D004920:Erythropoiesis / Q000235:genetics; D015870:Gene Expression / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology*; D005812:Genes, Switch / Q000235:genetics*; D005914:Globins / Q000235:genetics*; D016329:Sp1 Transcription Factor / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics
D004268:DNA-Binding Proteins; D050981:Erythroid-Specific DNA-Binding Factors; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; D005914:Globins