How is the X chromosome inactivated?

X-chromosome inactivation occurs randomly for one of the two X chromosomes in female cells during development. Inactivation occurs when RNA transcribed from the Xist gene on the X chromosome from which it is expressed spreads to coat the whole X chromosome.

What causes skewed X inactivation?

It can be caused by primary nonrandom inactivation, either by chance due to a small cell pool or directed by genes, or by secondary nonrandom inactivation, which occurs by selection. X-chromosome inactivation occurs in females to provide dosage compensation between the sexes.

Is heterochromatin involved in X inactivation in mammals?

X-inactivation is the coordinated silencing of nearly all genes on one of the two X chromosomes in female mammals. X-inactivation requires the cis-actingXist gene. This paper presents new findings that suggest that X-inactivation involves transvection and harnesses heterochromatin association.

What are the consequences of X chromosome inactivation?

If an X-linked mutation results in the absence of a certain protein, a cell which has inactivated the wild-type, X-chromosome will experience problems from the protein absence, possibly resulting in growth disadvantage of that cell, or even cell death, which will result in selection against mutant cells.

What does it mean when an X chromosome is deactivated?

X-chromosome inactivation, or simply X-inactivation, entails the stochastic silencing of a single X-chromosome in female mammals.

Can a Dicer mutant have an inactive X chromosome?

These results indicate that one X chromosome can be selected as the inactive X and Xist RNA can coat that X chromosome in Dicer mutant embryos. Thus, X-chromosome inactivation seems unaffected by Dicer deficiency in vivo.

How is X inactivation mediated by chromosomal pairing?

Silencing during X inactivation is mediated by chromosomal pairing and the establishment of heterochromatic structures (reviewed by Marahrens, 1999 ). The noncoding RNA Xist (belonging to the Xic center) is required for the initiation of X inactivation in both imprinted and random X inactivation.

How is X inactivation skewed in heterozygous females?

The differentiation of phenotype in heterozygous females is furthered by the presence of X-inactivation skewing. Typically, each X-chromosome is silenced in half of the cells, but this process is skewed when preferential inactivation of a chromosome occurs.