title: Methylation of L1Hs promoters is lower on the inactive X, has a tendency of being higher on autosomes in smaller genomes and shows inter-individual variability at some loci.
abstract: LINE-1 repeats account for ~17% of the human genome. Little is known about their individual methylation patterns, because their repetitive, almost identical sequences make them difficult to be individually targeted. Here, we used bisulfite conversion to study methylation at individual LINE-1 repeats. The loci studied included 39 X-linked loci and 5 autosomal loci. On the X chromosome in women, we found statistically significant less methylation at almost all L1Hs compared with men. Methylation at L1P and L1M did not correlate with the inactivation status of the host DNA, while the majority of L1Hs that were possible to be studied lie in inactivated regions. To investigate whether the male-female differences at L1Hs on the X are linked to the inactivation process itself rather than to a mere influence of gender, we analyzed six of the L1Hs loci on the X chromosome in Turners and Klinefelters which have female and male phenotype, respectively, but with reversed number of X chromosomes. We could confirm that all samples with two X chromosomes are hypomethylated at the L1Hs loci. Therefore, the inactive X is hypomethylated at L1Hs; the latter could play an exclusive role in the X chromosome inactivation process. At autosomal L1Hs, methylation levels showed a correlation tendency between methylation level and genome size, with higher methylation observed at most loci in individuals with one X chromosome and the lowest in XXY individuals. In summary, loci-specific LINE-1 methylation levels show considerable plasticity and depend on genomic position and constitution.
authors.affiliation: Institute of Experimental Hematology and Transfusion Medicine, University of Bonn, Bonn, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Singer
authors.forename: Maja
authors.initials: M
authors.lastname: Walier
authors.forename: Nicole
authors.initials: N
authors.lastname: Nüsgen
authors.forename: Christian
authors.initials: C
authors.lastname: Meesters
authors.forename: Felix
authors.initials: F
authors.lastname: Schreiner
authors.forename: Joachim
authors.initials: J
authors.lastname: Woelfle
authors.forename: Rolf
authors.initials: R
authors.lastname: Fimmers
authors.forename: Thomas
authors.initials: T
authors.lastname: Wienker
authors.forename: Vera M
authors.initials: VM
authors.lastname: Kalscheuer
authors.forename: Tim
authors.initials: T
authors.lastname: Becker
authors.forename: Rainer
authors.initials: R
authors.lastname: Schwaab
authors.forename: Johannes
authors.initials: J
authors.lastname: Oldenburg
authors.forename: Osman
authors.initials: O
authors.lastname: El-Maarri
mesh_terms: D000328:Adult; D041321:Chromosomes, Human, X / Q000235:genetics*; D019175:DNA Methylation; D005260:Female; D059646:Genome Size; D006801:Humans; D007713:Klinefelter Syndrome / Q000235:genetics*; D020084:Long Interspersed Nucleotide Elements; D008297:Male; D016254:Mutagenesis, Insertional; D011401:Promoter Regions, Genetic; D014424:Turner Syndrome / Q000235:genetics*; D049951:X Chromosome Inactivation; D055815:Young Adult