High impact information on HBE1

• Comparison with the sequences of the chicken rho-globin and beta-globin genes reveals the presence of two regions that are identical or nearly identical in epsilon and rho [1].
• To elucidate further the mechanism of methylation-induced silencing, an expression construct consisting of 235 bp of 5' promoter sequence of the rho-globin gene along with a strong 5' erythroid enhancer driving a chloramphenicol acetyltransferase reporter gene, rho-CAT, was transfected into primary avian erythroid cells derived from 5-day embryos [2].
• The ability of the 235-bp rho-globin gene promoter to bind to a DNA Methyl Cytosine binding Protein Complex (MeCPC) was tested in electrophoretic mobility shift assays utilizing primary avian erythroid cell nuclear extract [2].
• Sodium butyrate treatment also caused a DNase I-hypersensitive site to be exposed at the 5' end of the rho-globin gene only after 5-azacytidine induced demethylation of several CpG sites in and around the gene [3].
• The amino acid sequence of the globin encoded by this insert is identical to the sequence of embryonic rho-globin, except for four amino acid residues near the carboxy terminus [4].

Biological context of HBE1

• These studies show that demethylation by 5-azacytidine is a prerequisite but not sufficient cis-regulatory event for a high level of transcriptional activation of the embryonic rho-globin gene in adult erythroid cells in vivo [5].
• Embryonic rho-globin gene activation in this model is not due to selection of primitive erythroid cells since a subpopulation of primitive erythroid cells is not evident either morphologically or when cells are probed for embryonic and adult globin RNA by in situ hybridization [5].
• Methylation of just the 235-bp rho-globin gene promoter fragment at every CpG resulted in a 20- to 30-fold inhibition of transcription, and this effect was not overridden by the presence of potent erythroid-specific enhancers [2].
• The methylation pattern of the rho-globin gene promoter, proximal transcribed region, and distal transcribed region on both DNA strands was examined during development in chicken erythroid cells [6].
• In the course of studying regulatory elements that affect avian embryonic rho-globin gene expression, the multipotential hematopoietic cell line K562 was transiently transfected with various rho-globin gene constructs containing or lacking an avian erythroid enhancer element [7].

Anatomical context of HBE1

• The rho globin is the major beta-like chain found in 5-day-old chick embryos [8].
• Mononucleosomes were prepared from primitive and definitive stage embryonic red blood cells of chick embryos, adult reticulocytes, adult reticulocytes in which embryonic rho-globin transcription was induced, and adult thymus cells [9].
• Induction of cardiogenesis was accompanied by a marked decrease in the expression of rho-globin, implying that PPS cells were being induced by anterior endoderm to become cardiac myocytes instead of blood-forming tissue [10].
• Definitive red blood cells, which would be synthesizing little rho globin protein at this stage, appear to be responsible for the rho gene transcription [11].

Associations of HBE1 with chemical compounds

• Previously, we have shown that a methyl cytosine-binding complex binds to the methylated rho-globin gene in vitro [12].

Other interactions of HBE1

• The rho globin ought to be functionally equivalent to the adult chicken beta globin [8].
• In vitro nuclear runoff transcription assays using erythroid nuclei from treated birds show that the mechanism of activation of the rho-globin gene is transcriptional whereas no transcriptional activation of the embryonic epsilon-globin gene occurs [5].

Analytical, diagnostic and therapeutic context of HBE1

• An animal model of hemoglobin switching has been developed in which anemic adult chickens are treated with 5-azacytidine and sodium butyrate or alpha-aminobutyric acid, thereby resulting in activation of the embryonic rho-globin gene in adult erythroid cells [5].

References