RELATIONSHIP BETWEEN NUCLEAR REMODELING AND SUBSEQUENT DEVELOPMENT OFMOUSE EMBRYONIC NUCLEI TRANSFERRED TO ENUCLEATED OOCYTES

The present study was conducted to examine the relationship between nu clear remodeling and subsequent embryonic development in nuclear trans plant mouse embryos. Metaphase II oocytes were enucleated without stai ning and fused with transferred donor nuclei from two-, four-, or eigh t-cell embryos. Fusion and oocyte activation were performed by means o f electric fields. High rates of enucleation (89.1%), fusion (88.0-91. 6%), and activation (95.2-96.9%) were obtained using this system. Nucl ear remodeling was characterized by premature chromosome condensation (PCC), followed by various pronuclear-like formations upon oocyte acti vation. Development to blastocysts was obtained from both PCC (17.9%) and non-PCC (NPCC; 52.9%) embryos fused with the two-cell nuclei. Howe ver, development to term was obtained only in PCC embryos with a singl e pronucleus-like structure and a polar body (12.5%). In vitro develop ment of nuclear transplant embryos with four- and eight-cell nuclei wa s limited. All the NPCC embryos examined had tetraploid chromosome con stitutions, but chromosome constitutions of PCC embryos varied. Only 3 7.5% of the PCC embryos had diploid chromosome constitutions. The resu lts indicated that the development of nuclear transplant embryos is af fected by the types of nuclear remodeling and that oocyte activation i n relation to their chromosome constitutions. The results also indicat ed that the PCC of the donor nucleus in nonactivated cytoplasm is impo rtant for the development of the nuclear transplant embryos. (C) 1994 Wiley-Liss, Inc.