X-Chromosome inactivation in cloned mouse embryos

Science. 2000 Nov 24;290(5496):1578-81. doi: 10.1126/science.290.5496.1578.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alleles
  • Animals
  • Cell Differentiation
  • Cloning, Organism*
  • Dosage Compensation, Genetic*
  • Embryo, Mammalian / cytology
  • Embryo, Mammalian / metabolism*
  • Embryonic and Fetal Development
  • Female
  • Gene Silencing
  • Genes, Reporter
  • Genomic Imprinting
  • Green Fluorescent Proteins
  • Luminescent Proteins / genetics
  • Male
  • Mice
  • Muridae
  • Nuclear Transfer Techniques
  • Oocytes
  • Placenta / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Stem Cell Transplantation
  • Stem Cells / metabolism
  • Transgenes
  • X Chromosome / genetics*
  • X Chromosome / metabolism


  • Luminescent Proteins
  • Green Fluorescent Proteins