Mbd2 contributes to DNA methylation-directed repression of the Xist gene.
Transcription of the Xist gene triggers X chromosome inactivation in cis and is therefore silenced on the X chromosome that remains active. DNA methylation contributes to this silencing, but the mechanism is unknown. As methylated DNA binding proteins (MBPs) are potential mediators of gene silencing by DNA methylation, we asked whether MBP-deficient cell lines could maintain Xist repression. The absence of Mbd2 caused significant low-level reactivation of Xist, but silencing was restored by exogenous Mbd2. In contrast, deficiencies of Mbd1, MeCP2, and Kaiso had no detectable effect, indicating that MBPs are not functionally redundant at this locus. Xist repression in Mbd2-null cells was hypersensitive to the histone deacetylase inhibitor trichostatin A and to depletion of the DNA methyltransferase Dnmt1. These synergies implicate Mbd2 as a mediator of the DNA methylation signal at this locus. The presence of redundant mechanisms to enforce repression at Xist and other loci is compatible with the hypothesis that "stacking" of imperfect repressive tendencies may be an evolutionary strategy to ensure leakproof gene silencing.
Barr
Helen
H
Wellcome Trust Centre for Cell Biology, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh, United Kingdom.
Hermann
Andrea
A
Berger
Jennifer
J
Tsai
Hsin-Hao
HH
Adie
Karen
K
Prokhortchouk
Anna
A
Hendrich
Brian
B
Bird
Adrian
A
D000818:Animals; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000378:metabolism; D005786:Gene Expression Regulation; D020868:Gene Silencing; D056572:Histone Deacetylase Inhibitors; D006657:Histones / Q000378:metabolism; D006877:Hydroxamic Acids / Q000378:metabolism; D008297:Male; D051379:Mice; D062085:RNA, Long Noncoding; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D022661:RNA, Untranslated / Q000235:genetics / Q000378:metabolism*; D014960:X Chromosome
D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; C489326:Mbd2 protein, mouse; D062085:RNA, Long Noncoding; D034741:RNA, Small Interfering; D022661:RNA, Untranslated; C077885:XIST non-coding RNA; C012589:trichostatin A; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619381:Dnmt1 protein, mouse