Analysis of the mechanism for chromatin remodeling in embryos reconstructed by somatic nuclear transfer

Biol Reprod. 2002 Sep;67(3):760-6. doi: 10.1095/biolreprod.101.000612.


The objective of the present study was to understand the molecular/biochemical nature of chromatin remodeling that occurs in the somatic nuclei transferred into oocytes. We produced the reconstructed mouse embryos by two different protocols of nuclear transfer. The nucleus of a cumulus cell was transferred into enucleated unfertilized oocytes (transferred before activation, TA protocol) or activated oocytes (activated before transfer, AT protocol). More than half (56.1%) of the embryos reconstructed using the TA protocol developed to the morula/blastocyst stage, whereas very few (1.0%) of the embryos reconstructed using the AT protocol reached the morula/blastocyst stage. These embryos were analyzed for the events associated with transcriptional regulation. Changes in transcriptional activity, nuclear accumulation of TATA box binding protein (TBP), and DNase I sensitivity were examined after nuclear transfer. In the embryos reconstructed by TA protocol, all of these events occurred in a manner similar to that in the control diploid parthenogenetic embryos. The transcriptional activity was silenced after nuclear transfer and resumed at the late 1-cell stage. TBP was displaced and subsequently accumulated at the early and the late 1-cell stage, respectively. DNase I sensitivity was increased and then decreased at the early and late 1-cell stage, respectively. In contrast, embryos reconstructed using the AT protocol did not show such changes in transcriptional activity, TBP accumulation, and DNase I sensitivity. These events would be necessary for differentiated nuclei to restore totipotency and are useful indices to evaluate successful chromatin remodeling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blastocyst
  • Cell Nucleus / metabolism
  • Chromatin / ultrastructure*
  • Cloning, Organism*
  • Cytochalasin B / pharmacology
  • Deoxyribonuclease I / pharmacology
  • Embryo, Mammalian / ultrastructure*
  • Embryonic and Fetal Development
  • Female
  • Mice
  • Mice, Inbred C57BL
  • Mice, Inbred DBA
  • Morula
  • Nuclear Transfer Techniques*
  • Oocytes / drug effects
  • Oocytes / ultrastructure*
  • TATA-Box Binding Protein / metabolism


  • Chromatin
  • TATA-Box Binding Protein
  • Cytochalasin B
  • Deoxyribonuclease I