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Table 1 Factors involved in X chromosome inactivation

From: Xist localization and function: new insights from multiple levels

Factors involved in XCI Function in the context of XCI References
PRC2 The polycomb repressive complex 2 (PRC2) is known to be recruited early on the inactive X (Xi) during differentiation of embryonic stem cells (ESCs) and embryonic development and catalyzes methylation of histone H3 at K27 on chromatin [40, 80, 81]
PRC1 The activity of polycomb repressive complex 1 (PRC1) on chromatin reinforces gene silencing by ubiquitylation of histone H2A at K119 and chromatin compaction. The order of recruitment of PRC2 and PRC1 to the Xi is still a matter of debate [82, 83]
Saf-A (HnrnpU) The Saf-A (HnrnpU) factor directly binds to Xist and mediates its interaction with chromatin through direct interaction with SARS/MARS elements [21, 23, 44, 56, 58]
SHARP (Spen) SHARP (Spen) directly binds to Xist and mediates the functional interaction between Xist and the NCoR complex [21, 23, 44]
CTCF The CCCTC-binding factor (CTCF) might work as a genomic insulator. In the context of X chromosome inactivation (XCI), it might serve as a barrier to Xist-induced chromatin reorganization [21, 67]
SATB1 The special AT-rich sequence-binding protein-1 (SATB1) cellular regulator of higher chromatin organization has a role in the initiation of XCI. However, its precise role in XCI is not clear [59, 84]
YY1 Yin-Yang 1 (YY1) is a bivalent protein with DNA-binding and RNA-binding motifs. It might have a role in tethering Xist to chromatin (spreading in cis) as well as a role in the regulation of Xist [44, 60, 85]
SmchD1 The protein structural maintenance of chromosome hinge domain 1 (SmchD1) has a role in maintaining a correct pattern of DNA methylation on the Xi during the maintenance phase of XCI [21, 86]
WTAP Wilms’ tumor-associated protein (WTAP) is a splicing factor and interactor with Xist. It is involved in regulating RNA methylation. It might have a role in the post-transcriptional modification of Xist [21, 23, 44]
LBR The lamin B receptor (LBR) was recently identified as an Xist-binding protein. It is known to localize with the nuclear lamina and to interact with repressive complexes as well as with lamin B [21, 23]
Rbm15 Rbm15 belongs to the SPEN family of transcriptional repressors and directly binds to Xist RNA [23]
hnRNPK Heterogeneous nuclear ribonucleoprotein K (hnRNPK) is an RNA-binding protein that interacts with Xist and plays a role in the Xist-mediated recruitment of repressive chromatin marks [21, 44]
Oct4, Sox2, Rex1, Nanog, PRDM14, Klf4 Pluripotency factors and epigenetic regulators that have been shown to control XCI through the regulation of Xist and Tsix [2, 74, 87, 88]
Rnf12 The Rnf12 protein seems to regulate the expression of Xist through degradation of Rex1 [75]
Atrx The protein alpha thalassemia/mental retardation syndrome X-linked (Atrx) is involved in the recruitment of PRC2 on the inactive X chromosome [21, 89]
Xist/Tsix Xist is the master regulator of XCI, and Tsix is its major antagonist. Regulation of the levels of Xist and Tsix regulates the initiation of XCI [2]
Jpx The Jpx ncRNA seems to act as an activator of Xist [2]
Ftx The Ftx ncRNA seems to be an Xist activator [2]
Genomic elements   
LINEs The LINEs class of genomic repeats colocalize with inactive genes in the Xi territory and might have a role in the establishment and maintenance of XCI [43, 90, 91]
SARS/MARS Facultative scaffold/matrix attachment regions enriched in open chromatin and gene bodies where Xist accumulates [7, 66]