Chromosomal silencing and localization are mediated by different domains of Xist RNA.
The gene Xist initiates the chromosomal silencing process of X inactivation in mammals. Its product, a noncoding RNA, is expressed from and specifically associates with the inactive X chromosome in female cells. Here we use an inducible Xist expression system in mouse embryonic stem cells that recapitulates long-range chromosomal silencing to elucidate which Xist RNA sequences are necessary for chromosomal association and silencing. We show that chromosomal association and spreading of Xist RNA can be functionally separated from silencing by specific mutations. Silencing requires a conserved repeat sequence located at the 5' end of Xist. Deletion of this element results in Xist RNA that still associates with chromatin and spreads over the chromosome but does not effect transcriptional repression. Association of Xist RNA with chromatin is mediated by functionally redundant sequences that act cooperatively and are dispersed throughout the remainder of Xist but show little or no homology.
Wutz
Anton
A
Whitehead Institute for Biomedical Research, Nine Cambridge Center, Cambridge, Massachusetts 02142, USA.
Rasmussen
Theodore P
TP
Jaenisch
Rudolf
R
D000818:Animals; D001483:Base Sequence; D002874:Chromosome Mapping; D017124:Conserved Sequence; D004303:Dosage Compensation, Genetic; D005260:Female; D020868:Gene Silencing; D018014:Gene Transfer Techniques; D006657:Histones / Q000378:metabolism; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D007952:Leukemia, Plasma Cell; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D012313:RNA / Q000737:chemistry / Q000235:genetics*; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics*; D013234:Stem Cells / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics*; D014960:X Chromosome / Q000235:genetics / Q000378:metabolism
D006657:Histones; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D014157:Transcription Factors; C077885:XIST non-coding RNA; C120756:macroH2A histone; D012313:RNA; D007041:Hypoxanthine Phosphoribosyltransferase