<Tr> <Td_colspan="2"> View / Edit Human </Td> <Td_colspan="2"> View / Edit Mouse </Td> </Tr> <P> 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 . </P> <P> 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 . </P> <P> The functional role of the Xist transcript was definitively demonstrated in mouse female ES cells using a novel antisense technology, called peptide nucleic acid (PNA) interference mapping . In the reported experiments, a single 19 - bp antisense cell - permeating PNA targeted against a particular region of Xist RNA prevented the formation of Xi and inhibited cis - silencing of X-linked genes . The association of the Xi with macro-histone H2A is also disturbed by PNA interference mapping . </P>

What is the role of xist in x inactivation