title: Expanded GAA repeats impair FXN gene expression and reposition the FXN locus to the nuclear lamina in single cells.
abstract: Abnormally expanded DNA repeats are associated with several neurodegenerative diseases. In Friedreich's ataxia (FRDA), expanded GAA repeats in intron 1 of the frataxin gene (FXN) reduce FXN mRNA levels in averaged cell samples through a poorly understood mechanism. By visualizing FXN expression and nuclear localization in single cells, we show that GAA-expanded repeats decrease the number of FXN mRNA molecules, slow transcription, and increase FXN localization at the nuclear lamina (NL). Restoring histone acetylation reverses NL positioning. Expanded GAA-FXN loci in FRDA patient cells show increased NL localization with increased silencing of alleles and reduced transcription from alleles positioned peripherally. We also demonstrate inefficiencies in transcription initiation and elongation from the expanded GAA-FXN locus at single-cell resolution. We suggest that repressive epigenetic modifications at the expanded GAA-FXN locus may lead to NL relocation, where further repression may occur.
authors: Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, UK, Faculdade de Medicina, Universidade de Lisboa, Lisboa 1649-028, Portugal and.
authors: Ana M
authors: AM
authors: Silva
authors: Medical Research Council, Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK.
authors: Jill M
authors: JM
authors: Brown
authors: Medical Research Council, Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK.
authors: Veronica J
authors: VJ
authors: Buckle
authors: Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, UK, richard.wade-martins@dpag.ox.ac.uk michele.lufino@dpag.ox.ac.uk.
authors: Richard
authors: R
authors: Wade-Martins
authors: Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, UK, richard.wade-martins@dpag.ox.ac.uk michele.lufino@dpag.ox.ac.uk.
authors: Michele M P
authors: MM
authors: Lufino
mesh_terms: D000483:Alleles; D002460:Cell Line; D015870:Gene Expression; D023061:Gene Order; D020868:Gene Silencing; D056426:Genetic Loci; D006801:Humans; D033862:Iron-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D034881:Nuclear Lamina / Q000378:metabolism*; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics; D059010:Single-Cell Analysis; D024363:Transcription Initiation Site; D061785:Transcription Initiation, Genetic; D014158:Transcription, Genetic; D019680:Trinucleotide Repeat Expansion; D000096923:Frataxin
chemical_list: D033862:Iron-Binding Proteins; D012333:RNA, Messenger; D000096923:Frataxin