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The reprogramming of X-chromosome inactivation during the acquisition of pluripotency in vivo and in vitro (1) is accompanied by the repression of Xist (2), the trigger of X-inactivation (3), and the upregulation of its antisense counterpart Tsix (4). We have shown that key factors supporting pluripotency--Nanog, Oct4 and Sox2--bind within Xist intron 1 in undifferentiated embryonic stem cells (ESC) to repress Xist transcription (5). However, the relationship between transcription factors of the pluripotency network and Tsix regulation has remained unclear (5,6). Here we show that Tsix upregulation in embryonic stem cells depends on the recruitment of the pluripotent marker Rex1, and of the reprogramming-associated factors Klf4 and c-Myc, by the DXPas34 minisatellite associated with the Tsix promoter. Upon deletion of DXPas34, binding of the three factors is abrogated and the transcriptional machinery is no longer efficiently recruited to the Tsixpromoter. Additional analyses including knockdown experiments further demonstrate that Rex1 is critically important for efficient transcription elongation of Tsix. Hence, distinct embryonic-stem-cell-specific complexes couple X-inactivation reprogramming and pluripotency, with Nanog, Oct4 and Sox2 repressing Xist to facilitate the reactivation of the inactive X, and Klf4, c-Myc and Rexl activating Tsix to remodel Xist chromatin (7-10) and ensure random X-inactivation upon differentiation (1). The holistic pattern of Xist/Tsix regulation by pluripotent factors that we have identified suggests a general direct governance of complex epigenetic processes by the machinery dedicated to pluripotency., X-inactivation reprogramming in female mice is a model for the epigenetic processes underlying the acquisition of pluripotency (1). The inactivation of the paternal X chromosome that characterizes the earliest cleavage-stages [...]

A precisely defined Xist promoter region flanked by CTCF is maintained by Tsix in a heterochromatic-like state in undifferentiated embryonic stem (ES) cells and shifts to a pseudoeuchromatic structure upon Tsix truncation is shown. It is observed that the Tsix mediated epigenetic regulation of Xist, which resulted in Xist promoter activation, and initiation of X inactivation, in differentiating ES cells.

Research has been conducted on the histone H3 Lys-9 methylation. The ability of this methylation to initiate and propagate X inactivation has been investigated and the results are reported.

INTRODUCTION The presence of heteromorphic sex chromosomes, i.e. sex chromosomes clearly distinguishable in form and genetic content, has been accompanied by the development of mechanisms of dosage compensation. Dosage compensation [...]

Abstract Background Delimiting distinct chromatin domains is essential for temporal and spatial regulation of gene expression. Within the X-inactivation centre region (Xic), the Xist locus, which triggers X-inactivation, is juxtaposed to a large domain of H3K27 trimethylation (H3K27me3). Results We describe here that developmentally regulated transcription of Tsix, a crucial non-coding antisense to Xist, is required to block the spreading of the H3K27me3 domain to the adjacent H3K4me2-rich Xist region. Analyses of a series of distinct Tsix mutations suggest that the underlying mechanism involves the RNA Polymerase II accumulating at the Tsix 3'-end. Furthermore, we report additional unexpected long-range effects of Tsix on the distal sub-region of the Xic, involved in Xic-Xic trans-interactions. Conclusion These data point toward a role for transcription of non-coding RNAs as a developmental strategy for the establishment of functionally distinct domains within the mammalian genome.

A demonstration that RNA polymerase II preintiation complex recruitment and H3 Lys 4 (H3-K4) methylation at the Xist promoter form the basis of the Xist expression profiles that drives both imprinted and random X-chromosome inactivation (XCI) is presented. X-chromosome inactivation (XCI) is highly dynamic during early mouse embryogenesis and strictly depends on the Xist noncoding RNA.