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All of the human beta-type globin genes compete for LCR enhancer activity in embryonic erythroid cells of yeast artificial chromosome transgenic mice.

ABSTRACT: In primitive erythroid cells of human beta-globin locus transgenic mice (TgM), the locus control region (LCR)-proximal epsilon- and gamma-globin genes are transcribed, whereas the distal delta- and beta-globin genes are silent. It is generally accepted that the beta-globin gene is competitively suppressed by gamma-globin gene expression at this developmental stage. Previously, however, we observed that epsilon-globin gene expression was severely attenuated when its distance from the LCR was extended, implying that beta-globin gene might also be silenced because of its great distance from the LCR. Here, to clarify the beta-globin gene silencing mechanism, we established TgM lines carrying either gamma- or epsilon- plus gamma-globin promoter deletions, without significantly altering the distance between the beta-globin gene and the LCR. Precocious expression of delta- and beta-globin genes was observed in primitive erythroid cells of mutant, but not wild-type TgM, which was most evident when both the epsilon and gamma promoters were deleted. Thus, we clearly demonstrated that the repression of the delta- and beta-globin genes in primitive erythroid cells is dominated by competitive silencing by the epsilon- and gamma-globin gene promoters, and that epsilon- and the other beta-like globin genes might be activated by two distinct mechanisms by the LCR.

SUBMITTER: Okamura E

PROVIDER: S-EPMC2812047 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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All of the human beta-type globin genes compete for LCR enhancer activity in embryonic erythroid cells of yeast artificial chromosome transgenic mice.

Okamura Eiichi E Matsuzaki Hitomi H Campbell Andrew D AD Engel James Douglas JD Fukamizu Akiyoshi A Tanimoto Keiji K

FASEB journal : official publication of the Federation of American Societies for Experimental Biology 20090818 12

In primitive erythroid cells of human beta-globin locus transgenic mice (TgM), the locus control region (LCR)-proximal epsilon- and gamma-globin genes are transcribed, whereas the distal delta- and beta-globin genes are silent. It is generally accepted that the beta-globin gene is competitively suppressed by gamma-globin gene expression at this developmental stage. Previously, however, we observed that epsilon-globin gene expression was severely attenuated when its distance from the LCR was exte ...[more]

PMID: 19690216

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Project description:Fetal hemoglobin is a major genetic modifier of the phenotypic heterogeneity in patients with sickle cell disease and certain β-thalassemias. Normal levels of fetal hemoglobin postnatally are approximately 1% of total hemoglobin. Patients who have hereditary persistence of fetal hemoglobin, characterized by elevated synthesis of γ-globin in adulthood, show reduced disease pathophysiology. Hereditary persistence of fetal hemoglobin is caused by β-globin locus deletions (deletional hereditary persistence of fetal hemoglobin) or γ-globin gene promoter point mutations (non-deletional hereditary persistence of fetal hemoglobin). Current research has focused on elucidating the pathways involved in the maintenance/reactivation of γ-globin in adult life. To better understand these pathways, we generated new β-globin locus yeast artificial chromosome transgenic mice bearing the (A)γ-globin -175 T > C or -195 C > G hereditary persistence of fetal hemoglobin mutations to model naturally occurring hereditary persistence of fetal hemoglobin. Adult -175 and -195 mutant β-YAC mice displayed a hereditary persistence of fetal hemoglobin phenotype, as measured at the mRNA and protein levels. The molecular basis for these phenotypes was examined by chromatin immunoprecipitation of transcription factor/co-factor binding, including YY1, PAX1, TAL1, LMO2, and LDB1. In -175 HPFH versus wild-type samples, the occupancy of LMO2, TAL1 and LDB1 proteins was enriched in HPFH mice (5.8-fold, 5.2-fold and 2.7-fold, respectively), a result that concurs with a recent study in cell lines showing that these proteins form a complex with GATA-1 to mediate long-range interactions between the locus control region and the (A)γ-globin gene. Both hereditary persistence of fetal hemoglobin mutations result in a gain of (A)γ-globin activation, in contrast to other hereditary persistence of fetal hemoglobin mutations that result in a loss of repression. The mice provide additional tools to study γ-globin gene expression and may reveal new targets for selectively activating fetal hemoglobin.

Project description:UNLABELLED: BACKGROUND: The ?-globin gene domains of vertebrate animals constitute popular models for studying the regulation of eukaryotic gene transcription. It has previously been shown that in the mouse the developmental switching of globin gene expression correlates with the reconfiguration of an active chromatin hub (ACH), a complex of promoters of transcribed genes with distant regulatory elements. Although it is likely that observations made in the mouse ?-globin gene domain are also relevant for this locus in other species, the validity of this supposition still lacks direct experimental evidence. Here, we have studied the spatial organization of the chicken ?-globin gene domain. This domain is of particular interest because it represents the perfect example of the so-called 'strong' tissue-specific gene domain flanked by insulators, which delimit the area of preferential sensitivity to DNase I in erythroid cells. RESULTS: Using chromosome conformation capture (3C), we have compared the spatial configuration of the ?-globin gene domain in chicken red blood cells (RBCs) expressing embryonic (3-day-old RBCs) and adult (9-day-old RBCs) ?-globin genes. In contrast to observations made in the mouse model, we found that in the chicken, the early embryonic ?-globin gene, ?, did not interact with the locus control region in RBCs of embryonic lineage (3-day RBCs), where this gene is actively transcribed. In contrast to the mouse model, a strong interaction of the promoter of another embryonic ?-globin gene, ?, with the promoter of the adult ?-globin gene, ?A, was observed in RBCs from both 3-day and 9-day chicken embryos. Finally, we have demonstrated that insulators flanking the chicken ?-globin gene domain from the upstream and from the downstream interact with each other, which places the area characterized by lineage-specific sensitivity to DNase I in a separate chromatin loop. CONCLUSIONS: Taken together, our results strongly support the ACH model but show that within a domain of tissue-specific genes, the active status of a promoter does not necessarily correlate with the recruitment of this promoter to the ACH.

Dataset Information

All of the human beta-type globin genes compete for LCR enhancer activity in embryonic erythroid cells of yeast artificial chromosome transgenic mice.

Publications

All of the human beta-type globin genes compete for LCR enhancer activity in embryonic erythroid cells of yeast artificial chromosome transgenic mice.

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