Escape from gene silencing in ICF syndrome: evidence for advanced replication time as a major determinant.
Chromosomal abnormalities associated with hypomethylation of classical satellite regions are characteristic for the ICF immunodeficiency syndrome. We, as well as others, have found that these effects derive from mutations in the DNMT3B DNA methyltransferase gene. Here we examine further the molecular phenotype of ICF cells and report several examples of extensive hypomethylation that are associated with advanced replication time, nuclease hypersensitivity and a variable escape from silencing for genes on the inactive X and Y chromosomes. Our analysis suggests that all genes on the inactive X chromosome may be extremely hypomethylated at their 5' CpG islands. Our studies of G6PD in one ICF female and SYBL1 in another ICF female provide the first examples of abnormal escape from X chromosome inactivation in untransformed human fibroblasts. XIST RNA localization is normal in these cells, arguing against an independent silencing role for this RNA in somatic cells. SYBL1 silencing is also disrupted on the Y chromosome in ICF male cells. Increased chromatin sensitivity to nuclease was found at all hypomethylated promoters examined, including those of silenced genes. The persistence of inactivation in these latter cases appears to depend critically on delayed replication of DNA because escape from silencing was only seen when replication was advanced to an active X-like pattern.
Hansen
R S
RS
Department of Medicine, Box 357360, University of Washington, Seattle, WA 98195, USA. supreme@u.washington.edu
Stöger
R
R
Wijmenga
C
C
Stanek
A M
AM
Canfield
T K
TK
Luo
P
P
Matarazzo
M R
MR
D'Esposito
M
M
Feil
R
R
Gimelli
G
G
Weemaes
C M
CM
Laird
C D
CD
Gartler
S M
SM
D000483:Alleles; D002478:Cells, Cultured; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D004261:DNA Replication / Q000235:genetics*; D004276:DNA, Satellite / Q000235:genetics; D004303:Dosage Compensation, Genetic; D005260:Female; D005347:Fibroblasts; D020868:Gene Silencing; D008040:Genetic Linkage / Q000235:genetics; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics; D006801:Humans; D007153:Immunologic Deficiency Syndromes / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D023282:Nuclease Protection Assays; D010641:Phenotype; D010735:Phosphoglycerate Kinase / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D050683:R-SNARE Proteins; D062085:RNA, Long Noncoding; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D022661:RNA, Untranslated / Q000032:analysis / Q000235:genetics; D013997:Time Factors; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics; D014960:X Chromosome / Q000235:genetics; D014998:Y Chromosome / Q000235:genetics
D002843:Chromatin; D004276:DNA, Satellite; D008565:Membrane Proteins; D050683:R-SNARE Proteins; D062085:RNA, Long Noncoding; D012333:RNA, Messenger; D022661:RNA, Untranslated; D014157:Transcription Factors; C121241:VAMP7 protein, human; C077885:XIST non-coding RNA; D005954:Glucosephosphate Dehydrogenase; D010735:Phosphoglycerate Kinase