Xist
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| Aliases | XIST, DXS1089, DXS399E, LINC00001, NCRNA00001, SXI1, swd66, X inactive specific transcript (non-protein coding) | ||||||
| External IDs | GeneCards: XIST | ||||||
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| Species | Human | Mouse | |||||
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| Location (UCSC) | Chr X: 73.82 – 73.85 Mb | n/a | |||||
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Xist (X-inactive specific transcript) is an RNA gene on the X chromosome of the placental mammals that acts as a major effector of the X inactivation process. It is a component of the Xic - X-chromosome inactivation centre - along with two other RNA genes (Jpx and Ftx) and two protein genes (Tsx and Cnbp2). The Xist RNA, a large (17 kb in humans) transcript, is expressed on the inactive chromosome and not on the active one. It is processed in a similar way to mRNAs, through splicing and polyadenylation. However, it remains untranslated. It has been suggested that this RNA gene evolved at least partly from a protein coding gene that became a pseudogene. The inactive X chromosome is coated with this transcript, which is essential for the inactivation. X chromosomes lacking Xist will not be inactivated, while duplication of the Xist gene on another chromosome causes inactivation of that chromosome.
X inactivation is an early developmental process in mammalian females that transcriptionally silences one of the pair of X chromosomes, thus providing dosage equivalence between males and females (see dosage compensation). The process is regulated by several factors, including a region of chromosome X called the X inactivation center (XIC). The XIST gene is expressed exclusively from the XIC of the inactive X chromosome. The transcript is spliced but apparently does not encode a protein. The transcript remains in the nucleus where it coats the inactive X chromosome. Alternatively spliced transcript variants have been identified, but their full length sequences have not been determined.
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