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LaCroix AJ, Stabley D, Sahraoui R, Adam MP, Mehaffey M, Kernan K, Myers CT, Fagerstrom C, Anadiotis G, Akkari YM, Robbins KM, Gripp KW, Baratela WAR, Bober MB, Duker AL, Doherty D, Dempsey JC, Miller DG, Kircher M, Bamshad MJ, Nickerson DA, Mefford HC, Sol-Church K. GGC Repeat Expansion and Exon 1 Methylation of XYLT1 Is a Common Pathogenic Variant in Baratela-Scott Syndrome. Am J Hum Genet 2019; 104:35-44. [PMID: 30554721 PMCID: PMC6323552 DOI: 10.1016/j.ajhg.2018.11.005] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 11/05/2018] [Indexed: 01/25/2023] Open
Abstract
Baratela-Scott syndrome (BSS) is a rare, autosomal-recessive disorder characterized by short stature, facial dysmorphisms, developmental delay, and skeletal dysplasia caused by pathogenic variants in XYLT1. We report clinical and molecular investigation of 10 families (12 individuals) with BSS. Standard sequencing methods identified biallelic pathogenic variants in XYLT1 in only two families. Of the remaining cohort, two probands had no variants and six probands had only a single variant, including four with a heterozygous 3.1 Mb 16p13 deletion encompassing XYLT1 and two with a heterozygous truncating variant. Bisulfite sequencing revealed aberrant hypermethylation in exon 1 of XYLT1, always in trans with the sequence variant or deletion when present; both alleles were methylated in those with no identified variant. Expression of the methylated XYLT1 allele was severely reduced in fibroblasts from two probands. Southern blot studies combined with repeat expansion analysis of genome sequence data showed that the hypermethylation is associated with expansion of a GGC repeat in the XYLT1 promoter region that is not present in the reference genome, confirming that BSS is a trinucleotide repeat expansion disorder. The hypermethylated allele accounts for 50% of disease alleles in our cohort and is not present in 130 control subjects. Our study highlights the importance of investigating non-sequence-based alterations, including epigenetic changes, to identify the missing heritability in genetic disorders.
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Affiliation(s)
- Amy J LaCroix
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195, USA
| | - Deborah Stabley
- Nemours Biomedical Research Department, Alfred I. duPont Hospital for Children, Wilmington, DE 19803, USA
| | - Rebecca Sahraoui
- Nemours Biomedical Research Department, Alfred I. duPont Hospital for Children, Wilmington, DE 19803, USA; Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - Margaret P Adam
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195, USA; Brotman Baty Institute for Precision Medicine, Seattle, WA 98195, USA
| | - Michele Mehaffey
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195, USA
| | - Kelly Kernan
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195, USA
| | | | | | | | | | - Katherine M Robbins
- Nemours Biomedical Research Department, Alfred I. duPont Hospital for Children, Wilmington, DE 19803, USA
| | - Karen W Gripp
- Nemours Biomedical Research Department, Alfred I. duPont Hospital for Children, Wilmington, DE 19803, USA
| | - Wagner A R Baratela
- Division of Orthogenetics, Alfred I. duPont Hospital for Children, Wilmington, DE 19803, USA; Instituto da Criança, Departamento de Pediatria, Universidade de São Paulo, São Paulo, SP Brazil
| | - Michael B Bober
- Division of Orthogenetics, Alfred I. duPont Hospital for Children, Wilmington, DE 19803, USA
| | - Angela L Duker
- Division of Orthogenetics, Alfred I. duPont Hospital for Children, Wilmington, DE 19803, USA
| | - Dan Doherty
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195, USA; Brotman Baty Institute for Precision Medicine, Seattle, WA 98195, USA
| | - Jennifer C Dempsey
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195, USA
| | - Daniel G Miller
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195, USA
| | - Martin Kircher
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Michael J Bamshad
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195, USA; Brotman Baty Institute for Precision Medicine, Seattle, WA 98195, USA
| | - Deborah A Nickerson
- Brotman Baty Institute for Precision Medicine, Seattle, WA 98195, USA; Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Heather C Mefford
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195, USA; Brotman Baty Institute for Precision Medicine, Seattle, WA 98195, USA.
| | - Katia Sol-Church
- Nemours Biomedical Research Department, Alfred I. duPont Hospital for Children, Wilmington, DE 19803, USA; Department of Pathology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
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2
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Tabolacci E, Chiurazzi P. Epigenetics, fragile X syndrome and transcriptional therapy. Am J Med Genet A 2013; 161A:2797-808. [PMID: 24123753 DOI: 10.1002/ajmg.a.36264] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Accepted: 09/06/2013] [Indexed: 12/13/2022]
Abstract
Epigenetics refers to the study of heritable changes in gene expression that occur without a change in DNA sequence. Epigenetic mechanisms therefore include all transcriptional controls that determine how genes are expressed during development and differentiation, but also in individual cells responding to environmental stimuli. The purpose of this review is to examine the basic principles of epigenetic mechanisms and their contribution to human disorders with a particular focus on fragile X syndrome (FXS), the most common monogenic form of developmental cognitive impairment. FXS represents a prototype of the so-called repeat expansion disorders due to "dynamic" mutations, namely the expansion (known as "full mutation") of a CGG repeat in the 5'UTR of the FMR1 gene. This genetic anomaly is accompanied by epigenetic modifications (mainly DNA methylation and histone deacetylation), resulting in the inactivation of the FMR1 gene. The presence of an intact FMR1 coding sequence allowed pharmacological reactivation of gene transcription, particularly through the use of the DNA demethylating agent 5'-aza-2'-deoxycytydine and/or inhibitors of histone deacetylases. These treatments suggested that DNA methylation is dominant over histone acetylation in silencing the FMR1 gene. The importance of DNA methylation in repressing FMR1 transcription is confirmed by the existence of rare unaffected males carrying unmethylated full mutations. Finally, we address the potential use of epigenetic approaches to targeted treatment of other genetic conditions.
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Ruchlemer R, Polliack A. Geography, ethnicity and “roots” in chronic lymphocytic leukemia. Leuk Lymphoma 2012; 54:1142-50. [DOI: 10.3109/10428194.2012.740670] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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4
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Richard GF, Kerrest A, Dujon B. Comparative genomics and molecular dynamics of DNA repeats in eukaryotes. Microbiol Mol Biol Rev 2008; 72:686-727. [PMID: 19052325 PMCID: PMC2593564 DOI: 10.1128/mmbr.00011-08] [Citation(s) in RCA: 335] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Repeated elements can be widely abundant in eukaryotic genomes, composing more than 50% of the human genome, for example. It is possible to classify repeated sequences into two large families, "tandem repeats" and "dispersed repeats." Each of these two families can be itself divided into subfamilies. Dispersed repeats contain transposons, tRNA genes, and gene paralogues, whereas tandem repeats contain gene tandems, ribosomal DNA repeat arrays, and satellite DNA, itself subdivided into satellites, minisatellites, and microsatellites. Remarkably, the molecular mechanisms that create and propagate dispersed and tandem repeats are specific to each class and usually do not overlap. In the present review, we have chosen in the first section to describe the nature and distribution of dispersed and tandem repeats in eukaryotic genomes in the light of complete (or nearly complete) available genome sequences. In the second part, we focus on the molecular mechanisms responsible for the fast evolution of two specific classes of tandem repeats: minisatellites and microsatellites. Given that a growing number of human neurological disorders involve the expansion of a particular class of microsatellites, called trinucleotide repeats, a large part of the recent experimental work on microsatellites has focused on these particular repeats, and thus we also review the current knowledge in this area. Finally, we propose a unified definition for mini- and microsatellites that takes into account their biological properties and try to point out new directions that should be explored in a near future on our road to understanding the genetics of repeated sequences.
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Affiliation(s)
- Guy-Franck Richard
- Institut Pasteur, Unité de Génétique Moléculaire des Levures, CNRS, URA2171, Université Pierre et Marie Curie, UFR927, 25 rue du Dr. Roux, F-75015, Paris, France.
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5
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Human chromosome fragility. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2008; 1779:3-16. [DOI: 10.1016/j.bbagrm.2007.10.005] [Citation(s) in RCA: 150] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2007] [Revised: 10/02/2007] [Accepted: 10/03/2007] [Indexed: 11/21/2022]
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6
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Sutherland GR, Richards RI. Unusual inheritance patterns due to dynamic mutation in fragile X syndrome. CIBA FOUNDATION SYMPOSIUM 2007; 197:119-26; discussion 126-36. [PMID: 8827371 DOI: 10.1002/9780470514887.ch7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Fragile X syndrome is the most common form of familial mental retardation and is one of the world's most common genetic diseases. The inheritance patterns of the disease have many unusual features. It is an X-linked disorder yet there are asymptomatic carrier males. The disease is expressed only when the gene is inherited from the mother. The risk of a carrier woman having a child with the syndrome depends upon her position in the pedigree (the Sherman paradox) and her own intellectual status. The discovery that the disease is due to dynamic mutation (which is a multistage process) that inactivates FMR1 has provided an explanation for the unusual inheritance patterns. The finding of linkage disequilibrium between the fragile X mutations and closely linked DNA markers (haplotype) has required a reinterpretation of this phenomenon for dynamic mutations. Only a small number of normal alleles at the fragile X locus have long stretches of perfect repeat (2% with more than 24 copies) and these form a reservoir of alleles that can increase in length into the premutation range. Dynamic mutation is, so far, an exclusively human phenomenon, but this is probably because it has yet to be discovered in other species. Unusual inheritance patterns are a hallmark of dynamic mutation diseases.
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Affiliation(s)
- G R Sutherland
- Department of Cytogenetics and Molecular Genetics, Women's and Children's Hospital, North Adelaide, Australia
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7
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Schwartz M, Zlotorynski E, Kerem B. The molecular basis of common and rare fragile sites. Cancer Lett 2006; 232:13-26. [PMID: 16236432 DOI: 10.1016/j.canlet.2005.07.039] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2005] [Accepted: 07/30/2005] [Indexed: 11/30/2022]
Abstract
Fragile sites are specific loci that form gaps and constrictions on chromosomes exposed to partial replication stress. Fragile sites are classified as rare or common, depending on their induction and frequency within the population. These loci are known to be involved in chromosomal rearrangements in tumors and are associated with human diseases. Therefore, the understanding of the molecular basis of fragile sites is of high significance. Here we discuss the works performed in recent years that investigated the characteristics of fragile sites which underlie their inherent instability.
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Affiliation(s)
- Michal Schwartz
- Department of Genetics, The Life Sciences Institute, The Hebrew University, Jerusalem 91904, Israel
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8
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Sarafidou T, Kahl C, Martinez-Garay I, Mangelsdorf M, Gesk S, Baker E, Kokkinaki M, Talley P, Maltby EL, French L, Harder L, Hinzmann B, Nobile C, Richkind K, Finnis M, Deloukas P, Sutherland GR, Kutsche K, Moschonas NK, Siebert R, Gécz J. Folate-sensitive fragile site FRA10A is due to an expansion of a CGG repeat in a novel gene, FRA10AC1, encoding a nuclear protein. Genomics 2004; 84:69-81. [PMID: 15203205 DOI: 10.1016/j.ygeno.2003.12.017] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2003] [Accepted: 12/31/2003] [Indexed: 11/21/2022]
Abstract
Fragile sites appear visually as nonstaining gaps on chromosomes that are inducible by specific cell culture conditions. Expansion of CGG/CCG repeats has been shown to be the molecular basis of all five folate-sensitive fragile sites characterized molecularly so far, i.e., FRAXA, FRAXE, FRAXF, FRA11B, and FRA16A. In the present study we have refined the localization of the FRA10A folate-sensitive fragile site by fluorescence in situ hybridization. Sequence analysis of a BAC clone spanning FRA10A identified a single, imperfect, but polymorphic CGG repeat that is part of a CpG island in the 5'UTR of a novel gene named FRA10AC1. The number of CGG repeats varied in the population from 8 to 13. Expansions exceeding 200 repeat units were methylated in all FRA10A fragile site carriers tested. The FRA10AC1 gene consists of 19 exons and is transcribed in the centromeric direction from the FRA10A repeat. The major transcript of approximately 1450 nt is ubiquitously expressed and codes for a highly conserved protein, FRA10AC1, of unknown function. Several splice variants leading to alternative 3' ends were identified (particularly in testis). These give rise to FRA10AC1 proteins with altered COOH-termini. Immunofluorescence analysis of full-length, recombinant EGFP-tagged FRA10AC1 protein showed that it was present exclusively in the nucleoplasm. We show that the expression of FRA10A, in parallel to the other cloned folate-sensitive fragile sites, is caused by an expansion and subsequent methylation of an unstable CGG trinucleotide repeat. Taking advantage of three cSNPs within the FRA10AC1 gene we demonstrate that one allele of the gene is not transcribed in a FRA10A carrier. Our data also suggest that in the heterozygous state FRA10A is likely a benign folate-sensitive fragile site.
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Affiliation(s)
- Theologia Sarafidou
- Department of Biology, University of Crete, and Institute of Molecular Biology and Biotechnology(IMBB), Foundation of Research and Technology (FORTH-GR), P.O. Box 2208, 714 09 Heraklion, Crete, Greece
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9
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Astolfi P, Bellizzi D, Losso MA, Sgaramella V. Triplet repeats, over-expanded in neuromuscular diseases, are under-represented in mammalian DNA: a survey of models. Brain Res Bull 2001; 56:265-71. [PMID: 11719260 DOI: 10.1016/s0361-9230(01)00581-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Simple tandem repeats represent more than 1% of the human genome: occasionally they exhibit intergenerational expansibility and are associated with neuromuscular diseases. In transgenic mice the same sequences elicit similar symptoms, but do not expand. We have searched for di-, tri-, and tetra-repeats in the published DNA sequences of chromosomes 21 and 22 of Homo sapiens, as well as in more than five megabases of Mus musculus DNA. Human and murine DNA sequences show a shortage in frequency and base coverage of tri-repeats as compared to di- and tetra-repeats. In murine sequences the cumulative frequency of di-, tri-, and tetra-repeats and their overall base coverage are about threefold higher than in human. Models for both the shortage of tri-repeats found in man and mouse and for their dynamic expansions are discussed. We propose that some of the 10 possible tri-repeats may be more prone than others to assume unusual structures capable of interfering with DNA synthesis: hence the shortage of tri-repeats. If such repeats are located at the 3'end of a chain growing and thus approaching another chain annealed to the same template, as Okazaki fragments do during discontinuous and encumbered replication, a combination of strand displacement, template switch, and branch migration may produce structures resistant to removal, hence the expansion of tri-repeats.
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Affiliation(s)
- P Astolfi
- Department of Genetics and Microbiology, University of Pavia, Pavia, Italy.
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10
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Sakamoto N, Larson JE, Iyer RR, Montermini L, Pandolfo M, Wells RD. GGA*TCC-interrupted triplets in long GAA*TTC repeats inhibit the formation of triplex and sticky DNA structures, alleviate transcription inhibition, and reduce genetic instabilities. J Biol Chem 2001; 276:27178-87. [PMID: 11325966 DOI: 10.1074/jbc.m101852200] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Large expansions of GAA.TTC repeats in the first intron of the frataxin (X25) gene are the principal mutation responsible for Friedreich's ataxia (FRDA). Sticky DNA, based on R.R.Y triplexes, was found at the expanded GAA.TTC repeats from FRDA patients. The (GAAGGA.TCCTTC)(65) repeat occurs in the same frataxin locus but is nonpathogenic and does not form sticky DNA. To elucidate the behavior of sticky DNA, we introduced various extents of GGA.TCC interruptions into the long GAA.TTC repeat. More than 20% of GGA.TCC interruptions abolished the formation of sticky DNA. However, the GAA.TTC repeats with less than 11% of GGA.TCC interruptions formed triplexes and/or sticky DNA similar to the uninterrupted repeat sequence. These triplexes showed different P1 nuclease sensitivities, and the GGA.TCC interruptions were slightly more sensitive than the surrounding GAA.TTC repeats. Furthermore, genetic instability investigations in Escherichia coli revealed that a small number (4%) of interruptions substantially stabilized the long GAA.TTC tracts. Furthermore, the greater the extent of interruptions of the GAA.TTC repeats, the less inhibition of in vitro transcription was observed, as expected, based on the capacity of interruptions to inhibit the formation of sticky DNA. We propose that the interruptions introduce base mismatches into the R.R.Y triplex, which explains the observed chemical and biological properties.
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Affiliation(s)
- N Sakamoto
- Institute of Biosciences and Technology, Center for Genome Research, Texas A & M University System Health Science Center, Texas Medical Center, Houston, Texas 77030, USA
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11
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Richard GF, Hennequin C, Thierry A, Dujon B. Trinucleotide repeats and other microsatellites in yeasts. Res Microbiol 1999; 150:589-602. [PMID: 10672999 DOI: 10.1016/s0923-2508(99)00131-x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Microsatellites are direct tandem DNA repeats found in all genomes. A particular class of microsatellites, called trinucleotide repeats, is responsible for a number of neurological disorders in humans. We review here our current state of knowledge on trinucleotide repeat instability, and discuss the molecular mechanisms that may be involved in trinucleotide repeat expansions leading to fatal diseases in humans. We also present original data on microsatellite distribution in several microbial genomes, and on the use of microsatellites as physical markers to accurately and easily genotype yeast strains.
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Affiliation(s)
- G F Richard
- Unité de génétique moléculaire des levures, URA1300 CNRS, UFR927, université Pierre et Marie Curie, Institut Pasteur, Paris, France
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12
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Sutherland GR, Richards RI. Fragile sites-cytogenetic similarity with molecular diversity. Am J Hum Genet 1999; 64:354-9. [PMID: 9973272 PMCID: PMC1377744 DOI: 10.1086/302267] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Affiliation(s)
- G R Sutherland
- Department of Cytogenetics and Molecular Genetics, Women's and Children's Hospital, Adelaide 5006, Australia. gsutherland@medicine. adelaide.edu.au
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13
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Mangel L, Ternes T, Schmitz B, Doerfler W. New 5'-(CGG)n-3' repeats in the human genome. J Biol Chem 1998; 273:30466-71. [PMID: 9804814 DOI: 10.1074/jbc.273.46.30466] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We identified new, potentially unstable loci in the human genome containing 5'-(CGG)n-3' trinucleotide repeats by screening a human subgenomic library as well as a chromosome 16 library with a 5'-(CGG)17-3' oligodeoxyribonucleotide probe. Five different clones were isolated, two from the chromosome 16 library and three from the subgenomic library. Determinations of the nucleotide sequences have revealed that the E7 clone displayed, in addition to the 5'-(CGG)n-3' trinucleotide repeat, a 5'-(CAG)n-3' and a 5'-(CCT)n-3' trinucleotide repeat. Two clones, CL16-1 and P5-5, had homologies to known genes, the human casein kinase II alpha' subunit (chromosome 16) and the human calcium-activated potassium channel (chromosome 10), respectively. Clones E7 and P4 were assigned to chromosome 6, whereas CL16-8 mapped to chromosome 16. Their potential coding capacities were assessed by RNA transfer (Northern blotting) experiments. Four different transcripts were identified by using the E7 clones as hybridization probes, three of them being brain-specific. The P4 clone was expressed in placenta and skeletal muscle. Minor polymorphisms within the repeats were observed in normal and in fragile X individuals. Lung and colon carcinoma cell lines in which some microsatellites were shown to be unstable were also investigated. Expansions of the 5'-(CGG)n-3' repeats were not found.
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MESH Headings
- Alleles
- Blotting, Northern
- Chromosome Mapping
- Chromosomes, Human, Pair 10
- Chromosomes, Human, Pair 16
- Chromosomes, Human, Pair 6
- Fragile X Mental Retardation Protein
- Fragile X Syndrome/genetics
- Genome, Human
- HeLa Cells
- Humans
- Intellectual Disability/genetics
- Molecular Sequence Data
- Nerve Tissue Proteins/genetics
- RNA-Binding Proteins/genetics
- Repetitive Sequences, Nucleic Acid
- Transcription, Genetic
- Tumor Cells, Cultured
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Affiliation(s)
- L Mangel
- Institute of Genetics, University of Cologne, D-50931 Koeln, Germany
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14
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Hirst MC, White PJ. Cloned human FMR1 trinucleotide repeats exhibit a length- and orientation-dependent instability suggestive of in vivo lagging strand secondary structure. Nucleic Acids Res 1998; 26:2353-8. [PMID: 9580685 PMCID: PMC147547 DOI: 10.1093/nar/26.10.2353] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The normal human FMR1 gene contains a genetically stable (CGG) n trinucleotide repeat which usually carries interspersed AGG triplets. An increase in repeat number and the loss of interspersions results in array instability, predominantly expansion, leading to FMR1 gene silencing. Instability is directly related to the length of the uninterrupted (CGG) n repeat and is widely assumed to be related to an increased propensity to form G-rich secondary structures which lead to expansion through replication slippage. In order to investigate this we have cloned human FMR1 arrays with internal structures representing the normal, intermediate and unstable states. In one replicative orientation, arrays show a length-dependent instability, deletions occurring in a polar manner. With longer arrays these extend into the FMR1 5'-flanking DNA, terminating at either of two short CGG triplet arrays. The orientation-dependent instability suggests that secondary structure forms in the G-rich lagging strand template, resolution of which results in intra-array deletion. These data provide direct in vivo evidence for a G-rich lagging strand secondary structure which is believed to be involved in the process of triplet expansion in humans.
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Affiliation(s)
- M C Hirst
- Institute of Molecular Medicine, The John Radcliffe Hospital, Headley Way, Headington, Oxford OX3 9DS, UK.
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15
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Hewett DR, Handt O, Hobson L, Mangelsdorf M, Eyre HJ, Baker E, Sutherland GR, Schuffenhauer S, Mao JI, Richards RI. FRA10B structure reveals common elements in repeat expansion and chromosomal fragile site genesis. Mol Cell 1998; 1:773-81. [PMID: 9660961 DOI: 10.1016/s1097-2765(00)80077-5] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A common mechanism for chromosomal fragile site genesis is not yet apparent. Folate-sensitive fragile sites are expanded p(CCG)n repeats that arise from longer normal alleles. Distamycin A or bromodeoxyuridine-inducible fragile site FRA16B is an expanded AT-rich approximately 33 bp repeat; however, the relationship between normal and fragile site alleles is not known. Here, we report that bromodeoxyuridine-inducible, distamycin A-insensitive fragile site FRA10B is composed of expanded approximately 42 bp repeats. Differences in repeat motif length or composition between different FRA10B families indicate multiple independent expansion events. Some FRA10B alleles comprise a mixture of different expanded repeat motifs. FRA10B fragile site and long normal alleles share flanking polymorphisms. Somatic and intergenerational FRA10B repeat instability analogous to that found in expanded trinucleotide repeats supports dynamic mutation as a common mechanism for repeat expansion.
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Affiliation(s)
- D R Hewett
- Department of Cytogenetics and Molecular Genetics, Women's and Children's Hospital, North Adelaide, SA, Australia
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16
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Ritchie RJ, Chakrabarti L, Knight SJ, Harding RM, Davies KE. Population genetics of the FRAXE and FRAXF GCC repeats, and a novel CGG repeat, in Xq28. AMERICAN JOURNAL OF MEDICAL GENETICS 1997; 73:463-9. [PMID: 9415475 DOI: 10.1002/(sici)1096-8628(19971231)73:4<463::aid-ajmg16>3.0.co;2-p] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Most of the rare folate sensitive fragile sites cloned to date arise from expansion of a CGG:CCG trinucleotide repeat array. Analysis of the CAG repeat at the Huntington Disease (HD) locus showed a positively skewed repeat distribution leading to the proposal that microsatellites are subject to a mutational bias toward expansion. Such a mutational bias predicts an increase in mean repeat size at all microsatellite loci. We present an analysis of repeats at two fragile site loci, FRAXE and FRAXF, and a novel CGG repeat in Xq28, in five different human populations, which suggests that these loci may also be subject to the same mutation process. The novel repeat array may represent the first evidence for the existence of a fourth fragile site in Xq27.3-28.
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Affiliation(s)
- R J Ritchie
- Department of Biochemistry, University of Oxford, United Kingdom
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17
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Boldog F, Gemmill RM, West J, Robinson M, Robinson L, Li E, Roche J, Todd S, Waggoner B, Lundstrom R, Jacobson J, Mullokandov MR, Klinger H, Drabkin HA. Chromosome 3p14 homozygous deletions and sequence analysis of FRA3B. Hum Mol Genet 1997; 6:193-203. [PMID: 9063739 DOI: 10.1093/hmg/6.2.193] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Loss of heterozygosity (LOH) involving 3p occurs in many carcinomas but is complicated by the identification of four distinct homozygous deletion regions. One putative target, 3p14.2, contains the common fragile site, FRA3B, a hereditary renal carcinoma-associated 3;8 translocation and the candidate tumor suppressor gene, FHIT. Using a approximately 300 kb comsid/lambda contig, we identified homozygous deletions in cervix, breast, lung and colorectal carcinoma cell lines. The smallest deletion (CC19) was shown not to involve FHIT coding exons and no DNA sequence alterations were present in the transcript. We also detected discontinuous deletions as well as deletions in non-tumor DNAs, suggesting that FHIT is not a selective target. Further, we demonstrate that some reported FHIT aberrations represent normal splicing variation. DNA sequence analysis of 110 kb demonstrated that the region is high in A-T content, LINEs and MER repeats, whereas Alu elements are reduced. We note an intriguing similarity in repeat sequence composition between FRA3B and a 152 kb segment from the Fragile-X region. We also identified similarity between a FRA3B segment and a small polydispersed circular DNA. In contrast to the selective loss of a tumor suppressor gene, we propose an alternative hypothesis, that some putative targets including FRA3B may undergo loss as a consequence of genomic instability. This instability is not due to DNA mismatch repair deficiency, but may correlate in part with p53 inactivation.
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Affiliation(s)
- F Boldog
- Division of Medical Oncology, University of Colorado Health Sciences Center, Denver 80262, USA
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Richards RI, Crawford J, Narahara K, Mangelsdorf M, Friend K, Staples A, Denton M, Easteal S, Hori TA, Kondo I, Jenkins T, Goldman A, Panich V, Ferakova E, Sutherland GR. Dynamic mutation loci: allele distributions in different populations. Ann Hum Genet 1996; 60:391-400. [PMID: 8912792 DOI: 10.1111/j.1469-1809.1996.tb00437.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
To assess the relative contributions of trans-acting factors (replication and repair functions) and cis-acting elements (repeat and flanking DNA composition) to the mechanism of trinucleotide repeat sequence mutation we have analysed the distribution of copy number polymorphisms at 12 loci associated with dynamic mutations in 15 populations of different ethnic origins. Genome wide instability of repeats in a particular population would be evidence of trans-acting factor instigation of the mutation process, whereas instability at a particular locus (perhaps even in several populations) would be evidence that the composition of the particular locus was the most significant factor contributing to mutation. The FRA16A locus is highly polymorphic in only the European population. Some other loci exhibit distinct distributions of alleles between different populations. Therefore sequences in the vicinity of the repeat -- the cis component of a particular locus -- appear(s) to be more important in the mutation mechanism than sporadic genome-wide instability induced by trans-acting factors such as the DNA mismatch repair enzymes.
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Affiliation(s)
- R I Richards
- Department of Cytogenetics and Molecular Genetics, Women's and Children's Hospital, North Adelaide, Australia
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19
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Holden JJ, Walker M, Chalifoux M, White BN. Trinucleotide repeats at the FRAXF locus: frequency and distribution in the general population. AMERICAN JOURNAL OF MEDICAL GENETICS 1996; 64:424-7. [PMID: 8844097 DOI: 10.1002/(sici)1096-8628(19960809)64:2<424::aid-ajmg38>3.0.co;2-f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
FRAXF, the third X-chromosomal fragile site to be cloned, has been shown to harbour a polymorphic compound triplet array: (GCCGTC)n (GCC)n. Expansion and methylation of the GCC-repeat and the neighbouring CpG-rich region result in chromosomal fragility. DNAs from 500 anonymous consecutive newborn males were examined to determine the incidence of various repeat numbers. The range of repeats was from 10-38, with the most common alleles having 14 (52.7%), 12 (16.6%), 21 (9.0%), and 22 (5.2%) triplets. Based on the distribution of repeat numbers, we suggest that the 21-repeat allele resulted from hairpin formation involving 7 GCC-repeats in a 14-repeat allele, accompanied by polymerase slippage. Examination of dinucleotide repeats near the FRAXF repeat will be important in testing this hypothesis. Since the clinical phenotype, if any, of FRAXF is unknown, this database will also be valuable for comparisons with repeat numbers in individuals from special populations.
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Affiliation(s)
- J J Holden
- Department of Psychiatry, Queen's University, Kingston, Ontario, Canada
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20
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Longshore JW, Tarleton J. Dynamic mutations in human genes: A review of trinucleotide repeat diseases. J Genet 1996. [DOI: 10.1007/bf02931762] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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21
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Gu Y, Shen Y, Gibbs RA, Nelson DL. Identification of FMR2, a novel gene associated with the FRAXE CCG repeat and CpG island. Nat Genet 1996; 13:109-13. [PMID: 8673086 DOI: 10.1038/ng0596-109] [Citation(s) in RCA: 191] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Five folate-sensitive fragile sites have been identified at the molecular level to date. Each is characterized by an expanded and methylated trinucleotide repeat CGG (CCG). Of the three X chromosome sites, FRAXA, FRAXE and FRAXF, the former two are associated with mental retardation in their expanded forms. FRAXA expansion results in fragile X syndrome due to down regulation of expression of the FMR1 gene, which carries the hypermutable CGG repeat in the 5' untranslated portion of its first exon. Mild mental retardation without consistent physical findings has been found associated with expanded CCG repeats at FRAXE. We have identified a large gene (FMR2) transcribed distally from the CpG island at FRAXE, and down-regulated by repeat expansion and methylation. The gene is novel, expressed in adult brain and placenta, and shows similarity with another human protein, MLLT2, expressed from a gene at chromosome 4q21 involved in translocations found in acute lymphoblastic leukaemia (ALL) cells. Identification of this gene will facilitate further studies to determine the role of its product in FRAXE associated mental deficiency.
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Affiliation(s)
- Y Gu
- Department of Molecular and Human Genetics, Human Genome Center, Baylor College of Medicine, Houston, Texas 77030, USA
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22
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Deissler H, Behn-Krappa A, Doerfler W. Purification of nuclear proteins from human HeLa cells that bind specifically to the unstable tandem repeat (CGG)n in the human FMR1 gene. J Biol Chem 1996; 271:4327-34. [PMID: 8626781 DOI: 10.1074/jbc.271.8.4327] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Autonomous expansions of trinucleotide repeats with the general structure 5'-d(CNG)n-3' are associated with several human genetic diseases. We have characterized nuclear proteins binding to the unstable 5'-d(CGG)n-3' repeat. Its expansion in the human FMR1 gene leads to the fragile X syndrome, one of the most frequent causes of mental retardation in human males. Electrophoretic mobility shift assays using nuclear extracts from several human and other mammalian cell lines and from primary human cells demonstrated specific binding to double-stranded DNA fragments containing only a 5'-d(CGG)17-3' repeat or the repeat and flanking genomic sequences of the human FMR1 gene. Protein binding was inhibited by complete methylation of the trinucleotide repeat. The complex formed with crude nuclear extract apparently did not contain the human transcription factor Sp1 that binds to a characteristic GC-rich sequence. A 20-kDa protein involved in specific binding to the double-stranded 5'-d(CGG)17-3' repeat was purified from HeLa nuclear extracts by DNA affinity chromatography.
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Affiliation(s)
- H Deissler
- Institute of Genetics, University of Cologne, D-50931 Köln, Germany
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Affiliation(s)
- R I Richards
- Department of Cytogenetics and Molecular Genetics, Women's and Children's Hospital, North Adelaide, S.A., Australia
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24
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Heale SM, Petes TD. The stabilization of repetitive tracts of DNA by variant repeats requires a functional DNA mismatch repair system. Cell 1995; 83:539-45. [PMID: 7585956 DOI: 10.1016/0092-8674(95)90093-4] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Simple repetitive tracts of DNA are unstable in all organisms thus far examined. In the yeast S. cerevisiae, we show that a 51 bp poly(GT) tract alters length at a rate of about 10(-5) per cell division. Insertion of a single variant repeat (either AT or CT) into the middle of the poly(GT) tract results in 100-fold stabilization. This stabilization requires the DNA mismatch repair system. Alterations within tracts with variant repeats occur more frequently on one side of the interruption than on the other. The stabilizing effects of variant repeats and polarity of repeat alterations have also been observed in trinucleotide repeats associated with certain human diseases.
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Affiliation(s)
- S M Heale
- Department of Biology, University of North Carolina at Chapel Hill 27599-3280, USA
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25
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Abstract
Fragile sites on chromosomes have been classified into a number of groups according to their frequency and the conditions required to induce them. A number of the rare folate-sensitive fragile sites have been characterized and shown to be amplified methylated CCG trinucleotide repeats. One common fragile site has been partly characterized and appears to be a region of fragility, rather than a single site.
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Affiliation(s)
- G R Sutherland
- Department of Cytogenetics and Molecular Genetics, Women's and Children's Hospital, Adelaide, Australia
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