Xist and X chromosome inactivation.
X inactivation acts in female mammals to equalise X-linked gene dosage between XX females and XY males. X inactivation is controlled by a single X-linked cis-acting locus called the X inactivation centre (Xic). 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. Transgenic and knockout studies have shown that a genomic region covering only a few kilobases either side of Xist carries all of the functions attributed to the Xic. The major questions currently occupying researchers studying X inactivation are: how do cells count their number of X chromosomes to determine whether X inactivation is necessary, and how does the Xist transcript inactivate all genes on the X chromosome?
Queensland Institute of Medical Research, PO Royal Brisbane Hospital, Australia. grahamK@qimr.edu.au
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D004303:Dosage Compensation, Genetic; D005260:Female; D018392:Genomic Imprinting; D006801:Humans; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D014157:Transcription Factors / Q000235:genetics* / Q000502:physiology; D014960:X Chromosome / Q000235:genetics*
D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D014157:Transcription Factors; C077885:XIST non-coding RNA