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X-Chromosome Inactivation in Cloned Mouse Embryos

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Science  24 Nov 2000:
Vol. 290, Issue 5496, pp. 1578-1581
DOI: 10.1126/science.290.5496.1578

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Abstract

To study whether cloning resets the epigenetic differences between the two X chromosomes of a somatic female nucleus, we monitored X inactivation in cloned mouse embryos. Both X chromosomes were active during cleavage of cloned embryos, followed by random X inactivation in the embryo proper. In the trophectoderm (TE), X inactivation was nonrandom with the inactivated X of the somatic donor being chosen for inactivation. When female embryonic stem cells with two active X chromosomes were used as donors, random X inactivation was seen in the TE and embryo. These results demonstrate that epigenetic marks can be removed and reestablished on either X chromosome during cloning. Our results also suggest that the epigenetic marks imposed on the X chromosomes during gametogenesis, responsible for normal imprinted X inactivation in the TE, are functionally equivalent to the marks imposed on the chromosomes during somatic X inactivation.

  • * These authors contributed equally to this work.

  • To whom correspondence should be addressed. E-mail: jaenisch{at}wi.mit.edu

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