Epigenetic variation illustrated by DNA methylation patterns of the fragile-X gene FMR1.
Genomic methylation patterns of mammals can vary among individuals and are subject to dynamic changes during development. In order to gain a better understanding of this variation, we have analyzed patterns of cytosine methylation within a 200 bp region at the CpG island of the human FMR1 gene from leukocyte DNA. FMR1 is normally methylated during inactivation of the X chromosome in females and it is also methylated and inactivated upon expansion of CGG repeats in fragile-X syndrome. Patterns of methylation (epigenotypes) were determined by the sequencing of bisulfite-treated alleles from normal males and females and alleles from a family of five brothers who are methylation mosaics and are affected to various degrees by the fragile-X syndrome. Our data indicate that: (i) methylation of individual CpG cytosines is strikingly variable in hypermethylated epigenotypes obtained from a single individual, suggesting that maintenance of cytosine methylation is a dynamic process; (ii) methylation of non-CpG cytosines in the region studied may occur but is rare; (iii) mosaicism of methylation in the analyzed fragile-X males is remarkably similar to that found for the active X and inactive X alleles in normal females, suggesting that the methylation mosaicism of some fragile-X males reflects similar on and off states of FMR1 expression that exist in normal females; (iv) hypermethylation is slightly more pronounced on fragile-X alleles than on normal inactive X alleles of females; (v) the general dichotomy of hypo- and hypermethylated alleles persisted over the 5 year period that separated samplings of the fragile-X males; (vi) methylation variability was most pronounced at a consensus binding sequence for the alpha-PAL transcription factor, a sequence that may play a role in regulating expression of FMR1.
Stöger
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Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA. rstoeger@fred.fhcrc.org or claird@fred.fhcrc.org
Kajimura
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TM
Brown
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Laird
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D000483:Alleles; D001483:Base Sequence; D002869:Chromosome Aberrations; D003001:Cloning, Molecular; D018899:CpG Islands; D003596:Cytosine / Q000378:metabolism; D004247:DNA; D019175:DNA Methylation; D005260:Female; D051860:Fragile X Messenger Ribonucleoprotein 1; D005600:Fragile X Syndrome / Q000235:genetics*; D014644:Genetic Variation; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D016601:RNA-Binding Proteins; D013447:Sulfites; D013997:Time Factors; D014960:X Chromosome
D003596:Cytosine; D004247:DNA; D051860:Fragile X Messenger Ribonucleoprotein 1; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; D013447:Sulfites; C497683:FMR1 protein, human; C009279:sodium bisulfite