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    Science. 2007 Dec 7;318(5856):1632-6.

    Sensing X chromosome pairs before X inactivation via a novel X-pairing region of the Xic.

    Source

    CNRS UMR218, Curie Institute, 26 rue d'Ulm, Paris 75005, France.

    Abstract

    Mammalian dosage compensation involves silencing of one of the two X chromosomes in females and is controlled by the X-inactivation center (Xic). The Xic, which includes Xist and its antisense transcription unit Tsix/Xite, somehow senses the number of X chromosomes and triggers Xist up-regulation from one of the two X chromosomes in females. We found that a segment of the mouse Xic lying several hundred kilobases upstream of Xist brings the two Xics together before the onset of X inactivation. This region can autonomously drive Xic trans-interactions even as an ectopic single-copy transgene. Its introduction into male embryonic stem cells is strongly selected against, consistent with a possible role in trans-activating Xist. We propose that homologous associations driven by this novel X-pairing region (Xpr) of the Xic enable a cell to sense that more than one X chromosome is present and coordinate reciprocal Xist/Tsix expression.

    PMID:
    18063799
    [PubMed - indexed for MEDLINE]

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