Histone acetylation at the human β-globin locus changes with developmental age

Abstract

To delineate the relationship between epigenetic modifications and hemoglobin switching, we compared the pattern of histone acetylation and pol II binding across the ␤-globin locus at fetal and adult stages of human development. To make this comparison possible, we introduced an external control into experimental samples in chromatin immunoprecipitation (ChIP) assays. Using this common standard, we found that the locus control region (LCR) was acetylated to the same level at all stages, whereas acetylation levels at the individual gene regions correlated with the state of transcription. In the active genes, the promoters were less acetylated compared with the coding regions. Furthermore, all globin promoters were acetylated to a similar level irrespective of the state of transcription. However, after correction for the loss of nucleosomes, the level of acetylation per histone at the active ␥ and ␤ promoters was 5-to 7-fold greater than that at the inactive promoter. Although the histone acetylation level within the LCR was developmentally stable, pol II binding in fetal erythroblasts was 2-to 3-fold greater than that in adult erythroblasts. These results demonstrate that dynamic changes in histone acetylation and pol II take place as the human ␤-globin gene region undergoes its developmental switches. IntroductionThe human ␤-globin locus consists of around 100 kb found on chromosome 11 and is composed of 5 functional genes: ε, G ␥, A ␥, ␦, and ␤, which are arranged in the order of their expression during development. The locus also contains a locus control region (LCR) that consists of 5 DNase I hypersensitive sites (HS). The LCR is essential for physiologic level expression in mice, although it is not required for chromatin opening activities. 1,2 The tissue-specific expression of the embryonic, fetal, and adult globin genes is developmentally regulated and the globin genes undergo 2 switches in expression during development. The ε-globin gene is expressed in embryonic development at the blood island of the yolk sac. At approximately 6 to 8 weeks of gestation, ε-globin is silenced, whereas the G ␥-and A ␥-globin genes are activated in the fetal liver. The second switch occurs late in gestation when the fetal ␥-globin genes are progressively silenced, although ␤-globin is eventually expressed at high levels after birth. 3 The exact mechanism by which these complex switches occur is not yet fully understood.Chromatin epigenetic changes have long been thought to play a role in the expression of genes. 4,5 With regard to the core histones, the effects of covalent modifications are 2-fold. First, modifications such as acetylation, methylation, and phosphorylation help change the access of trans-acting factors to the genetic elements found within the chromatin and affect the binding specificity of certain trans-factors. 6 Second, these modifications can affect the physical property of chromatin, such as compactness, stability, and flexibility. [7][8][9] Generally, histone acetylation makes the chromatin more flexibl...

Fetal hemoglobin chemical inducers for treatment of hemoglobinopathies

“…In the active genes, the promoters were less acetylated compared with the coding regions. Finally, the level of acetylation per histone at the active γ and β promoters was clearly higher than that at the inactive ɛ promoter [44].…”

“…Only recently, the histone acetylation of the genes present at the level of the β-globin locus was explored in primary erythroblasts corresponding at various ontogenic stages (fetal vs. adult stage). This analysis showed that the LCR was acetylated to the same level at all stages, whereas acetylation levels at the individual gene regions correlated with the state of transcription [44]. In the active genes, the promoters were less acetylated compared with the coding regions.…”

“…The comparative analysis of the histone acetylation profiles of the human β-globin cluster between the fetal and adult stages of development showed that: the LCR was acetylated at the same level in both fetal and adult erythroblasts, while the acetylation in the globin gene regions correlated to the state of transcription (the promoter in an active globin gene was acetylated to a lower level compared with the coding region); all promoters, irrespective of the state of transcription, were acetylated to the same steady-state levels in both fetal and adult erythroblasts, but, concerning the acetylation levels per histone, the active γ and β promoters are more acetylated than the inactive ɛ promoter [105].…”

Histone deacetylase inhibitors and hemoglobin F induction in β-thalassemia

“…C) Diagram of the β-globin locus on chromosome 11 and acetylation status of H3 (top panel) and H4 (middle panel) and polymerase II (pol II, bottom panel) recruitment at the promoter region of the ε, γ and β globin genes in cells expressing high (fetal erythroblasts or adult erythroblasts treated with butyrric acid, white columns) or low (adult cells, grey column) levels of HbF. Acetylation of both H3 and H4 and binding of the pol II complex is relatively higher at the γ or β locus in cells expressing high or low levels of HbF, respectively (modified from Aerbajinai, Zhu, Gao, Chin, & Rodgers, 2007;Yin et al, 2007;Fathallah, Weinberg, Galperin, Sutton, & Atweh, 2007). Table 1 A) Induction of apoptosis in the myeloid leukaemia U937 cell line (white bars) and normal erythroid cells (grey bars) of compound 9, 11 and 24.…”

Thalassemia and its Management during Pregnancy

“…They are thought to act through epigenetic mechanisms since a durable association exists between epigenetic change and the developmental shape of globin gene expression. [61][62][63] The combined administration of recombinant EPO together with cytotoxic drugs has also been found to be beneficial for patients with low baseline EPO levels.…”