Abstract
This study investigates the remodeling of a bovine donor nucleus after fusion with a parthenogenetically activated oocyte and its developmental ability following embryo transplant in cows. Recipient ooplasts were prepared by enucleating in vitro-matured oocytes after culturing for 24-27 h. These enucleated oocytes were activated with an ethanol treatment and then electrically fused with a 16-cell stage donor blastomere at 0, 6, or 12 h after activation. Nuclei that were fused 0 h after activation (0-h nuclei) and fixed 2 h later had a significantly higher (P<0.05) frequency of abnormal karyomorphism (26%) than the 6-h nuclei (2%). Sixty-five percent of the 6-h nuclei showed nuclear remodeling, i.e., nucleus swelling, whereas corresponding 12-h nuclei showed only 8%. Development into the blastocyst stage was significantly higher (P<0.05) in the 6 h group (10%) than that occurring in both the 0 h and 12 h groups (2% and 2%). Eight blastocysts obtained from embryos fused 6 h after activation were nonsurgically transferred to 6 recipient cows (1-2 embryos each), with 4 recipients becoming pregnant and 3 producing a single healthy offspring. Results indicate that an activated bovine ooplast has the ability to reprogram a donor nucleus.
