scholarly journals A chromatin insulator protects retrovirus vectors from chromosomal position effects

2000 ◽  
Vol 97 (16) ◽  
pp. 9150-9155 ◽  
Author(s):  
D. W. Emery ◽  
E. Yannaki ◽  
J. Tubb ◽  
G. Stamatoyannopoulos
Genetics ◽  
2000 ◽  
Vol 155 (3) ◽  
pp. 1297-1311
Author(s):  
Julio Vazquez ◽  
Paul Schedl

Abstract Eukaryotic chromosomes are thought to be subdivided into a series of structurally and functionally independent units. Critical to this hypothesis is the identification of insulator or boundary elements that delimit chromosomal domains. The properties of a Notch mutation, facet-strawberry (faswb), suggest that this small deletion disrupts such a boundary element. faswb is located in the interband separating polytene band 3C7, which contains Notch, from the distal band 3C6. The faswb mutation alters the structural organization of the chromosome by deleting the interband and fusing 3C7 with 3C6. Genetic studies also suggest that faswb compromises the functional autonomy of Notch by allowing the locus to become sensitive to chromosomal position effects emanating from distal sequences. In the studies reported here, we show that a DNA fragment spanning the faswb region can insulate reporter transgenes against chromosomal position effects and can block enhancer-promoter interactions. Moreover, we find that insulating activity is dependent on sequences deleted in faswb. These results provide evidence that the element defined by the faswb mutation corresponds to an insulator.


Blood ◽  
2002 ◽  
Vol 100 (6) ◽  
pp. 2012-2019 ◽  
Author(s):  
David W. Emery ◽  
Evangelia Yannaki ◽  
Julie Tubb ◽  
Tamon Nishino ◽  
Qiliang Li ◽  
...  

AbstractWe have previously described the development of oncoretrovirus vectors for human γ-globin using a truncated β-globin promoter, modified γ-globin cassette, and α-globin enhancer. However, one of these vectors is genetically unstable, and both vectors exhibit variable expression patterns in cultured cells, common characteristics of oncoretrovirus vectors for globin genes. To address these problems, we identified and removed the vector sequences responsible for genetic instability and flanked the resultant vector with the chicken β-globin HS4 chromatin insulator to protect expression from chromosomal position effects. After determining that flanking with the cHS4 element allowed higher, more uniform levels of γ-globin expression in MEL cell lines, we tested these vectors using a mouse bone marrow transduction and transplantation model. When present, the γ-globin cassettes from the uninsulated vectors were expressed in only 2% to 5% of red blood cells (RBCs) long term, indicating they are highly sensitive to epigenetic silencing. In contrast, when present the γ-globin cassette from the insulated vector was expressed in 49% ± 20% of RBCs long term. RNase protection analysis indicated that the insulated γ-globin cassette was expressed at 23% ± 16% per copy of mouse α-globin in transduced RBCs. These results demonstrate that flanking a globin vector with the cHS4 insulator increases the likelihood of expression nearly 10-fold, which in turn allows for γ-globin expression approaching the therapeutic range for sickle cell anemia and β thalassemia.


Blood ◽  
2003 ◽  
Vol 101 (6) ◽  
pp. 2175-2183 ◽  
Author(s):  
Derek A. Persons ◽  
Phillip W. Hargrove ◽  
Esther R. Allay ◽  
Hideki Hanawa ◽  
Arthur W. Nienhuis

Increased fetal hemoglobin (HbF) levels diminish the clinical severity of β-thalassemia and sickle cell anemia. A treatment strategy using autologous stem cell–targeted gene transfer of a γ-globin gene may therefore have therapeutic potential. We evaluated oncoretroviral- and lentiviral-based γ-globin vectors for expression in transduced erythroid cell lines. Compared with γ-globin, oncoretroviral vectors containing either a β-spectrin or β-globin promoter and the α-globin HS40 element, a γ-globin lentiviral vector utilizing the β-globin promoter and elements from the β-globin locus control region demonstrated a higher probability of expression. This lentiviral vector design was evaluated in lethally irradiated mice that received transplants of transduced bone marrow cells. Long-term, stable erythroid expression of human γ-globin was observed with levels of vector-encoded γ-globin mRNA ranging from 9% to 19% of total murine α-globin mRNA. The therapeutic efficacy of the vector was subsequently evaluated in a murine model of β-thalassemia intermedia. The majority of mice that underwent transplantation expressed significant levels of chimeric mα2hγ2molecules (termed HbF), the amount of which correlated with the degree of phenotypic improvement. A group of animals with a mean HbF level of 21% displayed a 2.5 g/dL (25 g/L) improvement in Hb concentration and normalization of erythrocyte morphology relative to control animals. γ-Globin expression and phenotypic improvement was variably lower in other animals due to differences in vector copy number and chromosomal position effects. These data establish the potential of using a γ-globin lentiviral vector for gene therapy of β-thalassemia.


Genetics ◽  
2000 ◽  
Vol 155 (3) ◽  
pp. 1195-1211 ◽  
Author(s):  
Albert Briscoe ◽  
John E Tomkiel

Abstract In Drosophila melanogaster, the rDNA loci function in ribosome biogenesis and nucleolar formation and also as sex chromosome pairing sites in male meiosis. These activities are not dependent on the heterochromatic location of the rDNA, because euchromatic transgenes are competent to form nucleoli and restore pairing to rDNA-deficient X chromosomes. These transgene studies, however, do not address requirements for the function of the endogenous rDNA loci within the heterochromatin. Here we describe two chromosome rearrangements that disrupt rDNA functions. Both rearrangements are translocations that cause an extreme bobbed visible phenotype and XY nondisjunction and meiotic drive in males. However, neither rearrangement interacts with a specific Y chromosome, Ymal+, that induces male sterility in combination with rDNA deletions. Molecular studies show that the translocations are not associated with gross rearrangements of the rDNA repeat arrays. Rather, suppression of the bobbed phenotypes by Y heterochromatin suggests that decreased rDNA function is caused by a chromosomal position effect. While both translocations affect rDNA transcription, only one disrupts meiotic XY pairing, indicating that there are different cis-acting requirements for rDNA transcription and rDNA-mediated meiotic pairing.


Genetics ◽  
1998 ◽  
Vol 148 (1) ◽  
pp. 331-339
Author(s):  
Daniel R Mallin ◽  
Jane S Myung ◽  
J Scott Patton ◽  
Pamela K Geyer

Abstract The suppressor of Hairy-wing [SU(HW)] binding region disrupts communication between a large number of enhancers and promoters and protects transgenes from chromosomal position effects. These properties classify the SU(HW) binding region as an insulator. While enhancers are blocked in a general manner, protection from repressors appears to be more variable. In these studies, we address whether repression resulting from the Polycomb group genes can be blocked by the SU(HW) binding region. The effects of this binding region on repression established by an Ultrabithorax Polycomb group Response Element were examined. A transposon carrying two reporter genes, the yellow and white genes, was used so that repression and insulation could be assayed simultaneously. We demonstrate that the SU(HW) binding region is effective at preventing Polycomb group repression. These studies suggest that one role of the su(Hw) protein may be to restrict the range of action of repressors, such as the Polycomb group proteins, throughout the euchromatic regions of the genome.


1999 ◽  
Vol 19 (5) ◽  
pp. 3714-3726 ◽  
Author(s):  
Mark C. Walters ◽  
Steven Fiering ◽  
Eric E. Bouhassira ◽  
David Scalzo ◽  
Scott Goeke ◽  
...  

ABSTRACT A constitutive DNase I-hypersensitive site 5′ of the chicken β-globin locus, termed 5′HS4 or cHS4, has been shown to insulate a promoter from the effect of an upstream enhancer and to reduce position effects on mini-white expression in Drosophilacells; on the basis of these findings, it has been designated a chromatin insulator. We have examined the effect of the cHS4 insulator in a system that assays both the level of gene expression and the rate of transcriptional silencing. Because transgenes flanked by insulator elements are shielded from position effects in Drosophilacells, we tested the ability of cHS4 to protect transgenes from position effects in mammalian cells. Flanking of an expression vector with the cHS4 insulator in a colony assay did not increase the number of G418-resistant colonies. Using lox/cre-based recombinase-mediated cassette exchange to control integration position, we studied the effect of cHS4 on the silencing of an integrated β-geo reporter at three genomic sites in K562 erythroleukemia cells. In this assay, enhancers act to suppress silencing but do not increase expression levels. While cHS4 blocked enhancement at each integration site, the strength of the effect varied from site to site. Furthermore, at some sites, cHS4 inhibited the enhancer effect either when placed between the enhancer and the promoter or when placed upstream of the enhancer. These results suggest that the activity of cHS4 is not dominant in all contexts and is unlikely to prevent silencing at all genomic integration sites.


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