McDonel, Patrick E. Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts.
Last reviewed:August 2018
- Xist expression and localization
- Xist domains and associated proteins
- Mechanisms of Xist spreading and silencing of transcription on the Xi
- Links to Primary Literature
- Additional Readings
A long noncoding ribonucleic acid, specific to the female inactive X chromosome, that orchestrates X-chromosome inactivation in eutherian mammals. The X-inactive specific transcript, Xist (Fig. 1), is essential for inactivation of the X chromosome in female eutherian mammals (note that Eutheria is a higher-level taxon that includes all mammals, except monotremes and marsupials). In eutherian mammals, such as humans, rodents, and livestock, sex determination is controlled by the X and Y chromosomes. Females have two X chromosomes and males have an X and a Y, whereas both males and females have two copies of all other chromosomes (termed autosomes). In all somatic (non-germline) cells, however, the expression levels of most X-linked genes are the same among males and females, despite females having an extra X chromosome. This equalization, called dosage compensation, is essential for embryonic survival because it maintains the correct gene expression balance between sex chromosomes and autosomes in every somatic cell. See also: Cell (biology); Cell biology; Chromosome; Dosage compensation of the active X chromosome; Embryology; Eutheria; Gene; Genetics; Human genetics; Long noncoding RNAs (long ncRNAs); Mammalia; Ribonucleic acid (RNA); Sex chromosomes; Sex determination
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