title: CGG Repeat-Induced FMR1 Silencing Depends on the Expansion Size in Human iPSCs and Neurons Carrying Unmethylated Full Mutations.
abstract: In fragile X syndrome (FXS), CGG repeat expansion greater than 200 triplets is believed to trigger FMR1 gene silencing and disease etiology. However, FXS siblings have been identified with more than 200 CGGs, termed unmethylated full mutation (UFM) carriers, without gene silencing and disease symptoms. Here, we show that hypomethylation of the FMR1 promoter is maintained in induced pluripotent stem cells (iPSCs) derived from two UFM individuals. However, a subset of iPSC clones with large CGG expansions carries silenced FMR1. Furthermore, we demonstrate de novo silencing upon expansion of the CGG repeat size. FMR1 does not undergo silencing during neuronal differentiation of UFM iPSCs, and expression of large unmethylated CGG repeats has phenotypic consequences resulting in neurodegenerative features. Our data suggest that UFM individuals do not lack the cell-intrinsic ability to silence FMR1 and that inter-individual variability in the CGG repeat size required for silencing exists in the FXS population.
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Urszula
authors.initials: U
authors.lastname: Brykczynska
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Eline
authors.initials: E
authors.lastname: Pecho-Vrieseling
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Anke
authors.initials: A
authors.lastname: Thiemeyer
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Jessica
authors.initials: J
authors.lastname: Klein
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Fruh
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Thierry
authors.initials: T
authors.lastname: Doll
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Carole
authors.initials: C
authors.lastname: Manneville
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Sascha
authors.initials: S
authors.lastname: Fuchs
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Mariavittoria
authors.initials: M
authors.lastname: Iazeolla
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Beibel
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Guglielmo
authors.initials: G
authors.lastname: Roma
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Naumann
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Kelley
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Oakeley
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Mueller
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Baltazar
authors.initials: B
authors.lastname: Gomez-Mancilla
authors.affiliation: Friedrich Miescher Institute for Biomedical Research, 4058 Basel, Switzerland; University of Basel, 4003 Basel, Switzerland.
authors.forename: Marc
authors.initials: M
authors.lastname: Bühler
authors.affiliation: Institute of Genomic Medicine, Catholic University, 00168 Rome, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Tabolacci
authors.affiliation: Institute of Genomic Medicine, Catholic University, 00168 Rome, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Chiurazzi
authors.affiliation: Institute of Genomic Medicine, Catholic University, 00168 Rome, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Neri
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland.
authors.forename: Tewis
authors.initials: T
authors.lastname: Bouwmeester
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland. Electronic address: francesco.di_giorgio@novartis.com.
authors.forename: Francesco Paolo
authors.initials: FP
authors.lastname: Di Giorgio
authors.affiliation: Novartis Institutes for Biomedical Research, 4056 Basel, Switzerland. Electronic address: barna.fodor@novartis.com.
authors.forename: Barna D
authors.initials: BD
authors.lastname: Fodor
mesh_terms: D002454:Cell Differentiation / Q000235:genetics; D002999:Clone Cells; D019175:DNA Methylation / Q000235:genetics*; D044127:Epigenesis, Genetic; D005260:Female; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics*; D005600:Fragile X Syndrome / Q000235:genetics; D020868:Gene Silencing; D056426:Genetic Loci; D006801:Humans; D057026:Induced Pluripotent Stem Cells / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009154:Mutation / Q000235:genetics*; D009474:Neurons / Q000378:metabolism*; D010375:Pedigree; D019680:Trinucleotide Repeat Expansion / Q000235:genetics*
chemical_list: D051860:Fragile X Messenger Ribonucleoprotein 1
keywords: CGG repeat; DNA methylation; FMR1; de novo silencing; fragile X syndrome; fragile X tremor ataxia syndrome; neuron; triplet expansion; ubiquitin inclusion; unmethylated full mutation