Effect of telophase enucleation on bovine somatic nuclear transfer

Telophase enucleation has been proven to be an efficient method for prepari ng recipient cytoplasts in bovine embryonic nuclear transfer (2, 11). This research was designed to study in vitro development of bovine oocytes conta ining transferred somatic cell nuclei, reconstructed by using enucleated in vitro-matured oocytes 32 h of age at telophase Il stage as recipient cytop lasts, compared with those 24 h of age at metaphase II stage. Two protocols for donor cell injection were adopted, i.e., subzonal injection (SUZI) and intracytoplasmic injection (ICI). Bovine oviduct epithelial cells (BOECs) and bovine cumulus cells (BCCs) from an adult cow were used as nuclear dono rs for these experiments. In SUZI groups, the fusion rate of donor cells, b oth BOECs and BCCs, with MII enucleated oocytes were higher than those with TII enucleated oocytes (54% vs. 41% and 53% vs. 39%, respectively; P < 0.0 5), but the development rates to morula plus blastocyst stage in MII groups were lower than those in TII groups (22% vs. 39% and 21% vs. 41%, respecti vely; P < 0.05). In ICI groups, about 26% of enucleated MII oocytes injecte d with BOECs or BCCs cleaved and only small parts of them developed to blas tocyst stage (4% and 3%, respectively; P > 0.05). When BOECs or BCCs were i ntracytoplasmically injected into oocytes enucleated at TII stage, no blast ocyst was formed in either donor cell group and no cleavage occurred in BOE C group. Our data demonstrated that telophase enucleation is beneficial to early embryo development when bovine somatic nuclei are transferred by subz onal injection. However, ii is harmful when donor cells are directly inject ed into the cytoplast of the enucleated oocytes. (C) 2000 by Elsevier Scien ce Inc.