X-chromosome inactivation: counting, choice and initiation.
In many sexually dimorphic species, a mechanism is required to ensure equivalent levels of gene expression from the sex chromosomes. In mammals, such dosage compensation is achieved by X-chromosome inactivation, a process that presents a unique medley of biological puzzles: how to silence one but not the other X chromosome in the same nucleus; how to count the number of X's and keep only one active; how to choose which X chromosome is inactivated; and how to establish this silent state rapidly and efficiently during early development. The key to most of these puzzles lies in a unique locus, the X-inactivation centre and a remarkable RNA--Xist--that it encodes.
Unité de Génétique Moléculaire Murine Institut Pasteur, 25 rue du Docteur Roux, Paris 75015, France. pavner@pasteur.fr
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D000818:Animals; D002874:Chromosome Mapping; D004303:Dosage Compensation, Genetic; D004331:Drosophila melanogaster / Q000235:genetics; D005260:Female; D008297:Male; D012313:RNA / Q000235:genetics; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics* / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D014960:X Chromosome
D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D014157:Transcription Factors; C077885:XIST non-coding RNA; D012313:RNA