X-chromosome kiss and tell: how the Xs go their separate ways.
Loci associated with noncoding RNAs have important roles in X-chromosome inactivation (XCI), the dosage compensation mechanism by which one of two X chromosomes in female cells becomes transcriptionally silenced. The Xs start out as epigenetically equivalent chromosomes, but XCI requires a cell to treat two identical X chromosomes in completely different ways: One X chromosome must remain transcriptionally active while the other becomes repressed. In the embryo of eutherian mammals, the choice to inactivate the maternal or paternal X chromosome is random. The fact that the Xs always adopt opposite fates hints at the existence of a trans-sensing mechanism to ensure the mutually exclusive silencing of one of the two Xs. This paper highlights recent evidence supporting a model for mutually exclusive choice that involves homologous chromosome pairing and the placement of asymmetric chromatin marks on the two Xs.
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Howard Hughes Medical Institute, Department of Molecular Biology, Massachusetts General Hospital, Department of Genetics, Harvard Medical School, Boston, Massachusetts 02114, USA.
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Lee
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D000818:Animals; D023902:Chromosome Pairing / Q000235:genetics; D005260:Female; D008297:Male; D008957:Models, Genetic; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics; D014960:X Chromosome / Q000235:genetics*; D049951:X Chromosome Inactivation
D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; C077885:XIST non-coding RNA