The hypervariable DXS255 locus contains a LINE-1 repetitive element with a CpG island that is extensively methylated only on the active X chromosome.
The DXS255 locus at Xp11.22 is highly polymorphic due to a 26-bp variable number of tandem repeats (VNTR) motif. In previous studies, one of the MspI sites flanking the VNTR manifested a correlation between methylation and X chromosome inactivation. Here we show, by DNA sequence analysis, that this MspI site is located within the CpG island at the 5' end of a LINE-1 element, which is 2.5 kb from the VNTR. The methylation status of the CpG island was assessed in Southern blotting experiments using the methylation-sensitive enzymes HpaII, HhaI, and BssHII. All these sites were completely methylated on active X chromosomes, consistent with previously reported findings of full methylation of LINE-1 elements throughout the genome. However, on inactive X chromosomes these sites were predominantly unmethylated, although patterns were found to be heterogeneous. The results suggest that LINE-1 elements on the inactive X chromosome are not suppressed by full methylation of their CpG islands. The differential methylation of the DXS255 CpG island provides the basis for a highly informative X inactivation analysis system.
Hendriks
R W
RW
Department of Biochemistry, University of Oxford, United Kingdom.
Hinds
H
H
Chen
Z Y
ZY
Craig
I W
IW
D001483:Base Sequence; D015139:Blotting, Southern; D004247:DNA; D019003:Deoxyribonuclease HpaII; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D015226:Dinucleoside Phosphates / Q000378:metabolism*; D004303:Dosage Compensation, Genetic; D005260:Female; D014644:Genetic Variation; D006801:Humans; D008297:Male; D008745:Methylation; D008969:Molecular Sequence Data; D012091:Repetitive Sequences, Nucleic Acid; D015183:Restriction Mapping; D014407:Tumor Cells, Cultured; D014960:X Chromosome
D004247:DNA; D019003:Deoxyribonuclease HpaII; D015252:Deoxyribonucleases, Type II Site-Specific; D015226:Dinucleoside Phosphates; C015772:CpG dinucleotide