ABSTRACT
The α- and ß-globin loci harbor developmentally expressed genes, which are silenced throughout post-natal life. Reactivation of these genes may offer therapeutic approaches for the hemoglobinopathies, the most common single gene disorders. Here, we address mechanisms regulating the embryonically expressed α-like globin, termed ζ-globin. We show that in embryonic erythroid cells, the ζ-gene lies within a ~65 kb sub-TAD (topologically associating domain) of open, acetylated chromatin and interacts with the α-globin super-enhancer. By contrast, in adult erythroid cells, the ζ-gene is packaged within a small (~10 kb) sub-domain of hypoacetylated, facultative heterochromatin within the acetylated sub-TAD and that it no longer interacts with its enhancers. The ζ-gene can be partially re-activated by acetylation and inhibition of histone de-acetylases. In addition to suggesting therapies for severe α-thalassemia, these findings illustrate the general principles by which reactivation of developmental genes may rescue abnormalities arising from mutations in their adult paralogues.
Subject(s)
Gene Expression Regulation, Developmental , Gene Silencing , Transcriptional Activation , zeta-Globins/genetics , Acetylation , Animals , Chromatin/metabolism , DNA-Binding Proteins/metabolism , Enhancer Elements, Genetic , Erythroid Cells/metabolism , Gene Expression Regulation, Developmental/drug effects , Gene Silencing/drug effects , Histone Deacetylase Inhibitors/pharmacology , Humans , Mice , Repressor Proteins/metabolism , Transcription Factors/metabolism , Transcriptional Activation/drug effects , alpha-Globins/geneticsABSTRACT
We report a novel hemoglobin (Hb) variant with a ß chain amino acid substitution at codon 78 (CTG>CCG) (HBB: c.236T>C), detected through prenatal screening via capillary electrophoresis (CE) in an otherwise healthy and asymptomatic 38-year-old female of Southeast Asian ancestry. The variant, named Hb Penang after the proband's Malaysian city of origin, underwent further characterization through high performance liquid chromatography (HPLC), reversed phase HPLC, Sanger sequencing, isopropanol stability testing and isoelectric focusing (IEF).
Subject(s)
Hemoglobins, Abnormal/genetics , Prenatal Diagnosis , beta-Globins/genetics , Adult , Chromatography, High Pressure Liquid , Electrophoresis, Capillary , Female , Humans , Isoelectric Focusing , Malaysia , Pregnancy , Protein Stability , Sequence Analysis, DNAABSTRACT
We review and report here the genotypes and phenotypes of 60 novel thalassemia and abnormal hemoglobin (Hb) mutations discovered following the adoption of routine DNA sequencing of both α- and ß-globin genes for all UK hemoglobinopathy samples referred for molecular investigation. This screening strategy over the last 10 years has revealed a total of 11 new ß chain variants, 15 α chain variants, 19 ß-thalassemia (ß-thal) mutations and 15 α(+)-thalassemia (α(+)-thal) mutations. The large number of new thalassemia alleles confirms the wide racial heterogeneity of mutations in the UK immigrant population. Eleven of the new variants ran with Hb A on high performance liquid chromatography (HPLC), demonstrating the value of routine sequencing of both α- and ß-globin genes for all hemoglobinopathy investigations. The new ß chain variants are: Hb Bury [ß22(B4)Glu â Asp (HBB: c.69A > T)], Hb Fulwood [ß35(C1)Tyr â His (HBB: c.106T > C)], Hb Little Venice [ß42(CD1)Phe â Cys (HBB: c.128T > G)], Hb Cork [ß57(E1)Asn â Ser (HBB: c.173A > G), Hb Basingstoke [ß118(GH1)Phe â Ser (HBB: c.356T > C)], Hb Howden [ß20(B2)Val â Ala (HBB: c.62T > C)], Hb Wilton [ß41(C7)Phe â Leu (HBB: c.126C > A)], Hb Belsize Park [ß120(GH3)Lys â Asn (HBB: c.363A > T)], Hb Hampstead Heath [ß2(NA2)His â Gln;ß26(B8)Glu â Lys (HBB: c.[6C > G;79G > A])], Hb Grantham [ß85(F1)Phe â Cys (HBB: c.257T > G)] and Hb Calgary [ß64(E8)Gly â Val (HBB: c.194G > T). The new α chain variants are: Hb Edinburgh [α70(E19)Val â Gly (HBA2: c.212T > G)], Hb Walsgrave [α116(GH4)Glu â Val (HBA2: c.350A > T)], Hb Wexham [α117(GH5) and 118(H1) insertion Ser (HBA1: c.354-355insTCA)], Hb Coombe Park [α127(H10)Lys â Glu (HBA2: c.382A > G)], Hb Oxford [α17(A15)Val â Asp (HBA2: c.53T > A)], Hb Bridlington [α32(B13)Met â Thr (HBA1: c.98T > C), Hb Wolverhampton [α81(F2)Ser â Tyr (HBA2: c.9245C > A)], Hb Little Waltham [α13(A11)Ala â Asp (HBA2: c.41C > A)], Hb Derby [α61(E10)Lys â Arg (HBA1: c.185A > G)], Hb Uttoxter [α74(EF3)Tyr â Asp (HBA2: c.223G > T)], Hb Harehills [α124(H7)Ser â Cys (HBA1: c.374C > G)], Hb Hekinan II [α27(B8)Glu â Asp (HBA1: c.84G > T)], Hb Manitoba IV [α102(G9)Ser â Arg (HBA1: c.307A > C), Hb Witham [α139(HC1)Lys â Arg (HBA2: c.419A > G) and Hb Farnborough [α9(A7)Asn â Asp (HBA1: c.28A > G). In addition, 10 more paralogous α-globin chain variants have been discovered. The novel ß-thal alleles are: HBB: c.-138C > G, HBB: c.-121C > T, HBB: c.-80T > G, HBB: c.18_19delTG, HBB: c.219_220insT, HBB: c.315 + 2_315 + 13delTGAGTCTATGGG, HBB: c.316-70C > G, HBB: c.345_346insTGTGCTG, HBB: c.354delC, HBB: c.376-381delCCAGTG, HBB: c.393T > A, HBB: c.394_395insA, HBB: c.375_376insA, HBB: c.*+95_*+107delTGGATTCTinsC, HBB: c.* + 111_*+112delAA, HBB: c.*+112A > T, HBB: c.394C > T, HBB: c.271delG and HBB: c.316-3C > T. The novel α (+ )-thal alleles are: HBA1: c.95+1G > C, HBA1: c.315C > G [Hb Donnington, α104(G11)Cys â Trp], HBA1: c.327delC, HBA1: c.333_345del, HBA1: c.*+96G > A, HBA2: c.2T > G, HBA2: c.112delC, HBA2: c.143delA, HBA2: c.143_146delACCT, HBA2: c.156_157insG, HBA2: c.220_223delGTGG, HBA2: c.305T > C [Hb Bishopstown, α101(G8)Leu â His], HBA2: c.169_170delAA, HBA2: c.1A > T and HBA2: c.-3delA.
