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Proc Natl Acad Sci U S A. 2004 May 18;101(20):7636-40. Epub 2004 May 10.

The effect of interspecific oocytes on demethylation of sperm DNA.

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  • 1Division of Gene Expression and Development, Roslin Institute, Roslin EH25 9PS, United Kingdom.


In contrast to mice, in sheep no genome-wide demethylation of the paternal genome occurs within the first postfertilization cell cycle. This difference could be due either to an absence of a sheep demethylase activity that is present in mouse ooplasm or to an increased protection of methylated cytosine residues in sheep sperm. Here, we use interspecies intracytoplasmic sperm injection to demonstrate that sheep sperm DNA can be demethylated in mouse oocytes. Surprisingly, mouse sperm can also be demethylated to a limited extent in sheep oocytes. Our results suggest that the murine demethylation process is facilitated either by a sperm-derived factor or by male pronuclear chromatin composition.

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