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Nat Rev Genet. 2001 Jan;2(1):59-67.

X-chromosome inactivation: counting, choice and initiation.

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Unité de Génétique Moléculaire Murine Institut Pasteur, 25 rue du Docteur Roux, Paris 75015, France.


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.

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