Nature Reviews Genetics 2, 59-67 (2001)


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Figure 5 | A model for X inactivation.  The model indicates speculative roles of some of the proposed players in the initiation of X inactivation. a | Before inactivation, Xist RNA is expressed in an unstable form (dotted red lines) and the postulated blocking factor(s) (red) prevents Xist upregulation and/or its association with the chromosome in cis. b | Xist RNA becomes upregulated through stabilization, transcriptional upregulation or release of the blocking factor. LINEs might participate in the spreading process in some way — either through association with nucleoprotein complexes including Xist or by a mechanism such as REPEAT-INDUCED GENE SILENCING (RIGS). c | Stabilized Xist RNA coats the X chromosome before its inactivation. d | Transcriptional silencing of genes on the X chromosome occurs as a result of Xist RNA coating using an unknown mechanism and is rapidly followed by a shift to asynchronous replication timing of the X chromosome. e | Chromatin modifications, such as the histone deacetylation and methylation of promoters of X-linked genes, as well as the recruitment of the histone variant macroH2A, presumably transform the Xist RNA-coated chromosome into a stably inactive and condensed chromatin state.
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