What does the Xist gene do and why is only expressed in females?
X inactive-specific transcript (XIST) RNA is involved in X chromosome silencing in female cells and allows X chromosome equilibration with males.
Does Xist function in the initiation phase of X-inactivation?
(A) Xist triggers reversible chromosomal silencing in the initiation phase of X-inactivation. In differentiated cells, the silent state no longer depends on Xist and is irreversible.
What determines which X chromosome will be inactivated in a female?
X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell. Because X-inactivation is random, in normal females the X chromosome inherited from the mother is active in some cells, and the X chromosome inherited from the father is active in other cells.
How does Xist coat the X chromosome?
The Xist gene is encoded in the X-inactivation center (Xic), an X-linked cis-element that is essential for XCI. Xist RNA spreads from the Xic to coat the X and contributes to the initial establishment of silencing and subsequent maintenance of XCI [2].
What is the function of the Xist gene?
Xist (X-inactive specific transcript) is a non-coding RNA 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).
Do males have Xist?
A subset of differentiating XΔTsixY and XΔTsixX cells display ectopic Xist RNA coating of the XΔTsix; thus, male cells harbor a single Xist RNA coat and females possess two Xist coats.
What does Xist gene do?
How is Xist transcribed?
Xist is spliced and polyadenylated and, during XCI onset, becomes transcribed only from the future inactive X chromosome (Xi) (Borsani et al. 1991; Brockdorff et al. 1991, 1992; Brown 1991). The processed Xist transcript coats the Xi in cis (Brown et al.
What is the result of the activation of the Xist gene in mammals?
In female embryos, one X chromosome per cell becomes inactivated through the action of the XIST gene, thus forming the sex chromatin body. The early embryo has distinct patterns of X-chromosomal inactivation. The early mammalian embryo is highly regulative.
Where is the Xist gene?
Gene location The human Xist RNA gene is located on the long (q) arm of the X chromosome. The Xist RNA gene consists of conserved repeats within its structure and is also largely localized in the nucleus.
Does Xist act in CIS?
Xite, which is located just upstream of Tsix, acts in cis as an enhancer of Tsix, but is itself also transcribed (Ogawa and Lee 2003). Interestingly, the putative regulatory elements within Linx and Chic1 were identified due to their long range cis-interactions with the Tsix promoter or its enhancer Xite (Nora et al.
What is the XIC and the Xist gene?
The Xist RNA gene lies within the X-inactivation centre (XIC), which plays a major role in Xist expression and X-inactivation. The XIC is located on the q arm of the X chromosome (Xq13). XIC regulates Xist in cis X-inactivation, where Tsix, an antisense of Xist, downregulates the expression of Xist.
Why is a Barr body only found in females?
Barr Bodies can be found in various biological samples such as hair, buccal cells, and blood. Since women have two X chromosomes, one being inactivated, a single Barr Body is present in female mammal cells while males typically have no Barr Body present since they have only one X chromosome.
Why do females show a Barr body in their cells?
Barr body is formed as a result of inactivation of genes on one of the X chromosomes present in females. It is done to prevent the double expression of genes present on the X chromosome as compared to males who have only one X chromosome.
Why Barr body is not present in male?
Why are Barr bodies only found in females?
Since women have two X chromosomes, one being inactivated, a single Barr Body is present in female mammal cells while males typically have no Barr Body present since they have only one X chromosome.
Does Xist have properties of the X-chromosome inactivation centre?
“Xist has properties of the X-chromosome inactivation centre”. Nature. 386 (6622): 272–5. Bibcode: 1997Natur.386..272H. doi: 10.1038/386272a0. PMID 9069284. S2CID 4371247. ^ Lee JT, Davidow LS, Warshawsky D (April 1999).
What is the Xist gene?
In 1991 the Xist gene was identified as a candidate for the Xic. Xist is expressed in all adult female tissues, but only from the allele on the inactive X. The Xist transcript does not encode a protein but remains sequestered within the nucleus and co-localises with the inactive X chromosome.
Is X chromosome inactivation mediated by Xist RNA stabilization?
“X chromosome inactivation is mediated by Xist RNA stabilization”. Cell. 90 (5): 907–16. doi: 10.1016/S0092-8674 (00)80355-4.
Why do Xist and Tsix mutations cause primary non-random X-chromosome inactivation?
Because Xist and Tsix mutations cause primary non-random X-chromosome inactivation, it is likely that these non-coding RNAs function in the choice of the XA and XI before silencing is initiated.
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