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Dev Biol. 2000 Sep 15;225(2):294-303.

X inactivation in the mouse embryo deficient for Dnmt1: distinct effect of hypomethylation on imprinted and random X inactivation.

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Cardiovascular Research Center, Cancer Center and Department of Medicine, Harvard Medical School, Massachusetts General Hospital-East, 149, 13th Street, Charlestown, Massachusetts 02129, USA.


It has been suggested that DNA methylation plays a crucial role in genomic imprinting and X inactivation. Using DNA methyltransferase 1 (Dnmt1)-deficient mouse embryos carrying X-linked lacZ transgenes, we studied the effects of genomic demethylation on X inactivation. Based on the expression pattern of lacZ, the imprinted X inactivation in the visceral endoderm, a derivative of the extraembryonic lineage, was unaffected in Dnmt1 mutant embryos at the time other imprinted genes showed aberrant expression. Random X inactivation in the embryonic lineage of Dnmt1 mutant embryos, however, was unstable as a result of hypomethylation, causing reactivation of, at least, one lacZ transgene that had initially been repressed. Our results suggest that maintenance of imprinted X inactivation in the extraembryonic lineage can tolerate extensive demethylation while normal levels of methylation are required for stable maintenance of X inactivation in the embryonic lineage.

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