General implications for CpG hot spot mutations: methylation patterns of the human iduronate-2-sulfatase gene locus.
The methylation pattern at CpG sites of a housekeeping gene correlates with the likelihood of mutation. Mucopolysaccharidosis (MPS) type II, an X-linked disorder, results from the deficiency of iduronate-2-sulfatase (IDS). In these patients, over 35% of independent point mutations at the IDS gene locus were found at CpG sites as transitional events. To gain insight into the relationship between methylation status and CpG hot spot mutations, we investigated patterns of cytosine methylation in the entire IDS gene, except for introns 4-8. Bisulfite genomic sequencing was performed on the normal leukocyte DNA. Our data show that: 1) cytosine methylation at the CpG sites was extensive, except for those present from the promoter region to a portion of intron 3; 2) a sharp boundary of methylated-nonmethylated regions was observed at the 5'-flanking region, whereas a gradual change in methylation was observed in the 2.0-kb segment in the 3'-flanking region; 3) the boundary of the 5'-flanking region contained multiple Sp1 sites and the TATA box; 4) the CpG sites in exons 1 and 2 were hypomethylated and were associated only with rare transitional mutations, while the CpG sites in exon 3 were also hypomethylated, yet were associated with a high rate of transitional mutations; 5) there was no striking sex difference in the methylation patterns in active alleles; and, 6) the methylation in both strands was symmetrical, except at the boundary of methylated-unmethylated regions.
Tomatsu
Shunji
S
Department of Pediatrics, Saint Louis University, Pediatric Research Institute, St. Louis, Missouri 63110-2586, USA. tomatsus@slu.edu
Orii
Koji O
KO
Bi
Y
Y
Gutierrez
Monica A
MA
Nishioka
Tatsuo
T
Yamaguchi
Seiji
S
Kondo
Naomi
N
Orii
Tadao
T
Noguchi
Akihiko
A
Sly
William S
WS
D000595:Amino Acid Sequence; D001483:Base Sequence; D041321:Chromosomes, Human, X; D018899:CpG Islands / Q000235:genetics*; D003596:Cytosine; D004247:DNA; D019175:DNA Methylation; D005091:Exons; D005260:Female; D006801:Humans; D007066:Iduronate Sulfatase / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D016133:Polymerase Chain Reaction
D003596:Cytosine; D004247:DNA; D007066:Iduronate Sulfatase