Fig. 1. Schema of the experiments. (A) Injection of mouse cumulus cell nuclei (black) into GV nucleus, GV cytoplasm, GV intact or GV enucleated oocytes. (B) Cumulus cells were permeabilized with streptolysin O (SLO, 40 minutes), washed and incubated for 45 minutes in HEPES-CZB medium containing an ATP-generating system with or without (control) GV oocyte cytoplasmic lysate. Intact and treated cumulus cells were examined for the intensity of histone H3 methylation at lysine 9 (Me-H3-K9). GV nuclei were removed from the GV oocyte lysate before use (a). Scale bar: 35-40 µm. (b,c) Hoechst-stained GV nucleus at high magnification. Scale bar: 20 µm. The lower figure indicated fibroblasts treated as above, their membrane resealed and cultured for 1, 2, 3 or 4 weeks. These cells were then collected to examine Oct4 and nuclear lamin A (LMNA) using RT-PCR. (C) Cumulus cells were treated with GV oocyte cytoplasmic lysate and transferred into enucleated MII oocytes. The oocytes were activated and cultured until the blastocyst stage to examine Oct4 and Cdx2 immunoreactivities. Some embryos were transferred to pseudopregnant surrogate mothers to obtain cloned pups.