Regulated expression of human alpha- and beta-globin genes in transient heterokaryons.

We have examined the expression of human alpha- and beta-like globin genes in transient heterokaryons formed by fusion of human nonerythroid cells with terminally differentiating mouse erythroleukemia (MEL) cells or with a MEL cell variant (GM979) in which the endogenous mouse embryonic beta-globin genes are activated. In both the parental MEL cells and the heterokaryons, the alpha-globin genes were activated at least 12 h earlier than the embryonic, fetal, and adult beta-globin genes. These results suggest that kinetic differences in the activation of alpha- and beta-like globin genes are not simply the result of different rates of accumulation of erythroid-specific regulatory factors but may reflect differences in the mechanisms governing the transcriptional activation of these genes during erythroid cell differentiation. In mouse GM979 x human nonerythroid heterokaryons, the human embryonic beta-globin gene was activated, consistent with our previous demonstration that erythroid cells contain stage-specific trans-acting regulators of globin gene expression. Moreover, a dramatic increase in the ratio of human fetal to adult beta-globin transcription was observed compared with that seen in MEL-human nonerythroid hybrids. This ratio change may reflect competition between the fetal and adult beta-globin genes for productive interactions with erythroid cell-specific regulatory elements. Finally, we demonstrate that the behavior of naturally occurring mutations that lead to aberrant hemoglobin switching in humans also leads to aberrant expression in transient heterokaryons. Therefore, erythroid cells must contain trans-acting factors that interact with mutated regulatory elements to induce high-level expression of the human fetal globin genes.

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Upstream G gamma-globin and downstream beta-globin sequences required for stage-specific expression in transgenic mice

Molecular and Cellular Biology ◽

10.1128/mcb.7.11.4024-4029.1987 ◽

1987 ◽

Vol 7 (11) ◽

pp. 4024-4029

Author(s):

M Trudel ◽

J Magram ◽

L Bruckner ◽

F Costantini

Keyword(s):

Transgenic Mice ◽

Fusion Gene ◽

Globin Gene ◽

Regulatory Elements ◽

Globin Genes ◽

Beta Globin ◽

Erythroid Cells ◽

Base Pairs ◽

Beta Globin Gene ◽

Gamma Globin

The human G gamma-globin and beta-globin genes are expressed in erythroid cells at different stages of human development, and previous studies have shown that the two cloned genes are also expressed in a differential stage-specific manner in transgenic mice. The G gamma-globin gene is expressed only in murine embryonic erythroid cells, while the beta-globin gene is active only at the fetal and adult stages. In this study, we analyzed transgenic mice carrying a series of hybrid genes in which different upstream, intragenic, or downstream sequences were contributed by the beta-globin or G gamma-globin gene. We found that hybrid 5'G gamma/3'beta globin genes containing G gamma-globin sequences upstream from the initiation codon were expressed in embryonic erythroid cells at levels similar to those of an intact G gamma-globin transgene. In contrast, beta-globin upstream sequences were insufficient for expression of 5'beta/3'G gamma hybrid globin genes or a beta-globin-metallothionein fusion gene in adult erythroid cells. However, beta-globin downstream sequences, including 212 base pairs of exon III and 1,900 base pairs of 3'-flanking DNA, were able to activate a 5'G gamma/3'beta hybrid globin gene in fetal and adult erythroid cells. These experiments suggest that positive regulatory elements upstream from the G gamma-globin and downstream from the beta-globin gene are involved in the differential expression of the two genes during development.

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Butyrate induces selective transcriptional activation of a hypomethylated embryonic globin gene in adult erythroid cells

Blood ◽

10.1182/blood.v72.5.1536.bloodjournal7251536 ◽

1988 ◽

Vol 72 (5) ◽

pp. 1536-1542

Author(s):

LJ Burns ◽

JG Glauber ◽

GD Ginder

Keyword(s):

Sodium Butyrate ◽

Transcriptional Activation ◽

Globin Gene ◽

Gene Activation ◽

Globin Genes ◽

Erythroid Cells ◽

Hemoglobin Switching ◽

High Level

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. 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. The action of 5-azacytidine appears to be as an inhibitor of DNA methylation because other S-phase active cytotoxic drugs, when substituted for 5-azacytidine, do not cause demethylation of the embryonic globin genes, nor do they allow transcriptional activation to occur. 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. 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. The possible basis for the selective transcriptional activation by sodium butyrate in this system is discussed.

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Butyrate induces selective transcriptional activation of a hypomethylated embryonic globin gene in adult erythroid cells

Blood ◽

10.1182/blood.v72.5.1536.1536 ◽

1988 ◽

Vol 72 (5) ◽

pp. 1536-1542 ◽

Cited By ~ 32

Author(s):

LJ Burns ◽

JG Glauber ◽

GD Ginder

Keyword(s):

Sodium Butyrate ◽

Transcriptional Activation ◽

Globin Gene ◽

Gene Activation ◽

Globin Genes ◽

Erythroid Cells ◽

Hemoglobin Switching ◽

High Level

Abstract 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. 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. The action of 5-azacytidine appears to be as an inhibitor of DNA methylation because other S-phase active cytotoxic drugs, when substituted for 5-azacytidine, do not cause demethylation of the embryonic globin genes, nor do they allow transcriptional activation to occur. 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. 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. The possible basis for the selective transcriptional activation by sodium butyrate in this system is discussed.

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Upstream G gamma-globin and downstream beta-globin sequences required for stage-specific expression in transgenic mice.

Molecular and Cellular Biology ◽

10.1128/mcb.7.11.4024 ◽

1987 ◽

Vol 7 (11) ◽

pp. 4024-4029 ◽

Cited By ~ 25

Author(s):

M Trudel ◽

J Magram ◽

L Bruckner ◽

F Costantini

Keyword(s):

Transgenic Mice ◽

Fusion Gene ◽

Globin Gene ◽

Regulatory Elements ◽

Globin Genes ◽

Beta Globin ◽

Erythroid Cells ◽

Base Pairs ◽

Beta Globin Gene ◽

Gamma Globin

The human G gamma-globin and beta-globin genes are expressed in erythroid cells at different stages of human development, and previous studies have shown that the two cloned genes are also expressed in a differential stage-specific manner in transgenic mice. The G gamma-globin gene is expressed only in murine embryonic erythroid cells, while the beta-globin gene is active only at the fetal and adult stages. In this study, we analyzed transgenic mice carrying a series of hybrid genes in which different upstream, intragenic, or downstream sequences were contributed by the beta-globin or G gamma-globin gene. We found that hybrid 5'G gamma/3'beta globin genes containing G gamma-globin sequences upstream from the initiation codon were expressed in embryonic erythroid cells at levels similar to those of an intact G gamma-globin transgene. In contrast, beta-globin upstream sequences were insufficient for expression of 5'beta/3'G gamma hybrid globin genes or a beta-globin-metallothionein fusion gene in adult erythroid cells. However, beta-globin downstream sequences, including 212 base pairs of exon III and 1,900 base pairs of 3'-flanking DNA, were able to activate a 5'G gamma/3'beta hybrid globin gene in fetal and adult erythroid cells. These experiments suggest that positive regulatory elements upstream from the G gamma-globin and downstream from the beta-globin gene are involved in the differential expression of the two genes during development.

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Context-Specific Roles for Erythroid Krüppel-Like Factor (EKLF) in Co-Ordinate High Level Expression of the Murine α- and β-Globin Genes.

Blood ◽

10.1182/blood.v108.11.365.365 ◽

2006 ◽

Vol 108 (11) ◽

pp. 365-365 ◽

Cited By ~ 1

Author(s):

Valerie M. Jansen ◽

Shaji Ramachandran ◽

Aurelie Desgardin ◽

Jin He ◽

Vishwas Parekh ◽

...

Keyword(s):

Gene Expression ◽

Gene Transcription ◽

Globin Gene ◽

Erythroid Cell ◽

Gene Promoters ◽

Globin Genes ◽

Context Specific ◽

High Level ◽

Kinetics Of ◽

Globin Gene Expression

Abstract Binding of EKLF to the proximal promoter CACC motif is essential for high-level tissue-specific β-globin gene expression. More recent studies have demonstrated that EKLF regulates expression of other erythroid-specific genes, suggesting a broad role for EKLF in co-ordinating gene transcription in differentiating erythroblasts. Given these observations, we hypothesized that EKLF may play a role in synchronizing α- and β-globin gene expression. Supporting this model, studies of fetal erythroblasts derived from EKLF-null embryos revealed a 3-fold reduction in murine α-globin gene expression in fetal erythroblasts when compared to wild type littermate controls. A similar reduction in primary α-globin RNA transcripts was observed in these studies. To further examine the molecular consequences of EKLF function at the α- and β-globin genes in vivo, we utilized an erythroid cell line derived from EKLF null fetal liver cells. We have demonstrated previously that introduction into these cells of the wildtype EKLF cDNA, fused in frame with a mutant estrogen response element results in tamoxifen-dependent rescue of β-globin gene expression. Consistent with our observations in primary erythroblasts, α-globin gene expression is present in the absence of functional EKLF. However, with tamoxifen induction, we observed a 3–5 fold increase in α-globin gene transcription. Interestingly, the kinetics of the changes in transcription of the α- and β-gene transcripts were similar. Enhancement in α-gene transcription was associated with EKLF binding at the α- and β-globin promoters as determined by a quantitative chromatin immunoprecipitation (ChIP) assay. Interestingly, maximal EKLF binding and α-gene transcription was observed within 2 hours of tamoxifen induction. We hypothesized that the role of EKLF may differ function at the promoters, given that a basal level of α-globin gene expression occurs in absence of EKLF binding. Supporting this hypothesis, we observed sequential recruitment of p45NF-E2, RNA polymerase II (Pol II) and the co-activator CBP to the β-promoter with tamoxifen induction. No change in GATA-1 binding was observed. In contrast, p45NF-E2 does not bind to the α-promoter and the kinetics of GATA-1 and PolII association is unchanged after tamoxifen induction. Taken together, our results demonstrate that EKLF regulates the co-ordinate high-level transcription of the α- and β-globin genes, binding in a kinetically identical manner to the gene promoters. However, the effects of EKLF on transacting factor recruitment (and chromatin modification) differ between the promoters, consistent with the idea that EKLF acts in a context-specific manner to modulate gene transcription.

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Analysis of mice containing a targeted deletion of beta-globin locus control region 5' hypersensitive site 3.

Molecular and Cellular Biology ◽

10.1128/mcb.16.6.2906 ◽

1996 ◽

Vol 16 (6) ◽

pp. 2906-2912 ◽

Cited By ~ 133

Author(s):

B A Hug ◽

R L Wesselschmidt ◽

S Fiering ◽

M A Bender ◽

E Epner ◽

...

Keyword(s):

Developmental Stages ◽

Germ Line ◽

Globin Gene ◽

Globin Genes ◽

Beta Globin ◽

Erythroid Cells ◽

Hypersensitive Site ◽

Targeted Deletion ◽

Gamma Globin ◽

Gene Switching

To examine the function of murine beta-globin locus region (LCR) 5' hypersensitive site 3 (HS3) in its native chromosomal context, we deleted this site from the mouse germ line by using homologous recombination techniques. Previous experiments with human 5' HS3 in transgenic models suggested that this site independently contains at least 50% of total LCR activity and that it interacts preferentially with the human gamma-globin genes in embryonic erythroid cells. However, in this study, we demonstrate that deletion of murine 5' HS3 reduces expression of the linked embryonic epsilon y- and beta H 1-globin genes only minimally in yolk sac-derived erythroid cells and reduces output of the linked adult beta (beta major plus beta minor) globin genes by approximately 30% in adult erythrocytes. When the selectable marker PGK-neo cassette was left within the HS3 region of the LCR, a much more severe phenotype was observed at all developmental stages, suggesting that PGK-neo interferes with LCR activity when it is retained within the LCR. Collectively, these results suggest that murine 5' HS3 is not required for globin gene switching; importantly, however, it is required for approximately 30% of the total LCR activity associated with adult beta-globin gene expression in adult erythrocytes.

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The Corfu delta beta zero thalassemia: a small deletion acts at a distance to selectively abolish beta globin gene expression [published erratum appears in Blood 1988 May;71(5):1509]

Blood ◽

10.1182/blood.v71.2.457.457 ◽

1988 ◽

Vol 71 (2) ◽

pp. 457-462 ◽

Cited By ~ 25

Author(s):

AE Kulozik ◽

N Yarwood ◽

RW Jones

Keyword(s):

Globin Gene ◽

Gene Promoters ◽

Globin Genes ◽

Beta Globin ◽

Promoter Regions ◽

Beta Globin Gene ◽

Gamma Globin ◽

Exon 1 ◽

Normal Gene ◽

High Level

Abstract The Corfu delta beta zero thalassemia is characterized by the clinical picture of thalassemia intermedia. In the homozygous state there is a complete absence of hemoglobin (Hb) A and Hb A2 and a high level of Hb F. A DNA fragment containing the gamma and beta globin genes has been cosmid cloned, and the deletion breakpoint region, the beta globin gene and the promoter regions of the gamma globin genes sequenced. The deletion removes 7,201 base pairs (bp) containing part of the delta globin gene and sequences upstream. The beta globin gene contains a G--- -A mutation at IVS 1 position 5. The gamma globin gene promoters are normal. Analysis of the transcription of the mutated beta globin gene in transfected HeLa cells shows that normal message is produced at a level of approximately 20% compared with a normal gene, the remaining 80% being spliced at cryptic sites in exon 1 and intron 1. This indicates that the mutation in the beta globin gene is not the sole cause of the absence of Hb A in Corfu delta beta zero thalassemia. It is concluded that the 7.2 kilobase (kb) of deleted DNA contains sequences necessary for the normal activation of the beta globin gene. Possible mechanisms for the effect of the deletion on the expression of beta and gamma globin genes are discussed.

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Erythroid Specificity and Safety of Globin-Encoding Lentiviral Vectors

Blood ◽

10.1182/blood-2020-142989 ◽

2020 ◽

Vol 136 (Supplement 1) ◽

pp. 29-29

Author(s):

Annalisa Cabriolu ◽

Ashlesha Odak ◽

Friederike Kogel ◽

Michel Sadelain

Keyword(s):

Bone Marrow ◽

Sickle Cell ◽

Research Funding ◽

Bone Marrow Cells ◽

Globin Gene ◽

Regulatory Elements ◽

Beta Globin ◽

Erythroid Cells ◽

Hematopoietic Progenitor ◽

Enhancer Blocking

The beta-thalassemias and sickle cell disease are the most common monogenic inherited blood disorders, both arising from mutations affecting the beta-globin locus. Recent clinical trials utilizing lentiviral-mediated beta-globin gene transfer in autologous CD34+ cells have shown encouraging results in patients with non-beta-zero thalassemias and sickle cell anemia. A case report of insertional mutagenesis in a beta-thalassemia patient resulted in a prolonged clonal expansion that eventually regressed without progressing to leukemic transformation. Nonetheless, this occurrence and the need to insert multiple vector copies per cell when using globin vectors that provide insufficient globin expression to achieve curative responses from a single integrated copy per cell, raise some questions about the erythroid specificity and safety of globin vectors. We thus found it imperative to investigate globin vector expression in hematopoietic progenitors and in non-erythroid cells. To this end, we investigated what regulatory elements, including locus control region (LCR) hypersensitive sites (HS) and others, achieve the highest beta-globin expression per vector copy while at the same time minimizing non-erythroid transcriptional activity. We developed an invivo assay to track the enhancer/promoter activity of different HS elements in hematopoietic progenitor and differentiated cell subsets. We designed lentiviral vectors expressing hrGFP under the control of a short β-globin promoter (137bp) controlled by a set of LCR HS elements and/or a novel biliverdin (BLV) enhancer. Analysis of hrGFP expression in bone marrow cells derived from C57BL6 mice transplanted with transduced syngeneic bone marrow cells revealed that many of the vectors encompassing elements thought to encode erythroid-specific elements were in fact expressed in long term-HSC (LT-HSC), short term-HSC (ST-HSC), multipotent progenitors (MPP), pre-GM, Granulocyte/macrophage progenitors (GMP) and megakaryocyte progenitors (MKP). These findings confirmed that ectopically integrated erythroid regulatory elements can serve as transcriptional enhancers in non-erythroid cells. This transcriptional leakiness was confirmed in therapeutic globin vectors harboring a combination of LCR elements. To avoid these effects, we flanked the globin transcription unit with a small human enhancer-blocking element called A1, kindly provided by the late George Stamatoyannopoulos (Liu, M. et al. 2015). The insulated vector showed markedly reduced non-erythroid expression in non-erythroid cells including ST-HSC, MPP, Pre-GM and GMP. Expression in mature erythroid cells was unchanged. Our findings underscore the benefits of selecting lineage-specific regulatory elements with the least lineage promiscuity for therapeutic vectors, with the eventual addition of enhancer-blocking elements. Based on these results, we are now investigating new globin expression vectors with optimal combination of HS elements. Such novel globin vectors should minimize the risk of oncogene trans-activation in hematopoietic progenitor cells and therefore improve the safety of globin gene therapy while providing lineage-specific high-level expression. Disclosures Sadelain: Mnemo: Patents & Royalties; Fate Therapeutics: Patents & Royalties, Research Funding; Atara: Patents & Royalties, Research Funding; Takeda: Patents & Royalties, Research Funding; Minerva: Other: Biotechnologies , Patents & Royalties.

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Controlling Long-Range Genomic Interactions to Reprogram the β-Globin Locus

Blood ◽

10.1182/blood.v120.21.280.280 ◽

2012 ◽

Vol 120 (21) ◽

pp. 280-280

Author(s):

Wulan Deng ◽

Jeremy W Rupon ◽

Hongxin Wang ◽

Andreas Reik ◽

Philip D. Gregory ◽

...

Keyword(s):

Long Range ◽

Globin Gene ◽

Chromatin Interaction ◽

Globin Genes ◽

Erythroid Cells ◽

Distal Enhancer ◽

Adult Type ◽

High Level ◽

Target Promoters

Abstract Abstract 280 Distal enhancers physically contact target promoters to confer high level transcription. At the mammalian β-globin loci long-range chromosomal interactions between a distal enhancer, called the locus control region (LCR), and the globin genes are developmentally dynamic such that the LCR contacts the embryonic, fetal and adult globin genes in a stage-appropriate fashion. LCR-globin gene interactions require the nuclear factor Ldb1. Recently, we employed artificial zinc finger (ZF) proteins to target Ldb1 to the endogenous β-globin locus to force an LCR-promoter interaction. This led to substantial activation of β-globin transcription and suggested that forced chromatin looping could be employed as a powerful tool to manipulate gene expression in vivo (Deng et al., Cell 2012). Reactivation of the fetal globin genes in adult erythroid cells has been a long-standing goal in the treatment of patients with sickle cell anemia. Therefore, building on our findings, we investigated whether the developmentally silenced embryonic globin gene βh1 can be re-activated in adult murine erythroblasts by re-directing the LCR away from the adult type globin gene and towards its embryonic counterpart. To this end, Ldb1 was fused to artificial ZF proteins (ZF-Ldb1) designed to bind to the βh1 promoter. ZF-Ldb1 was introduced into definitive erythroid cells in which only the adult but not the embryonic β-like globin gene is expressed. In vivo binding of the ZF-Ldb1 to its intended target was verified by chromatin immunoprecipitation assay. Strikingly, expression of ZF-Ldb1 re-activated βh1 transcription up to approximately ∼15% of total cellular β-globin production. This suggests that forced tethering of a looping factor to a select promoter can be employed to override a pre-existing developmental long-range chromatin interaction to reprogram a developmentally controlled gene locus. We are now in the process of testing whether our approach might be suitable to reactivate the silent fetal globin genes in adult human erythroid cells. These studies are underway and the results will be discussed at the meeting. Disclosures: Reik: Sangamo BioSciences, Inc.: Employment. Gregory:Sangamo BioSciences, Inc.: Employment.

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