NUCLEAR TRANSPLANTATION OF ECTODERMAL CELLS IN PIG OOCYTES - ULTRASTRUCTURE AND RADIOGRAPHY

This study investigated the changes in nucleolar fine structure and th e synthesis of both heterogeneous nuclear RNA (hnRNA) and ribosomal RN A (rRNA) in pig reconstructed embryos obtained by electrofusion of a s ingle pig ectodermal cell to an enucleated metaphase-II oocyte. The nu cleolar morphological changes and the pattern of transcription were ex amined in the ectodermal cells before fusion and in the nuclear transf er reconstructed embryos 16-18 hr after fusion. Before fusion the ecto dermal cells exhibited a reticulated nucleolus with active RNA synthes is. In the reconstructed embryos, modifications of the nucleolar struc ture were observed, as assessed by the presence of either round-shaped , compact, dense nucleolar precursor bodies, or reticulated nucleoli. However, in both cases there was no RNA synthesis. Blebbing activity o f the nuclear envelope was not observed. These results indicate that t he nucleus of pig ectodermal cells exhibited either a complete or an i ncomplete remodelling when transferred to an enucleated metaphase-II o ocyte, with no detectable RNA synthesis. Cell-cycle synchronization of ectodermal cell donor nuclei may play an important role in nuclear re programming after fusion. (C) 1996 Wiley-Liss, Inc.