BOVINE NUCLEAR TRANSFER EMBRYOS - OOCYTE ACTIVATION PRIOR TO BLASTOMERE FUSION

Successful bovine nuclear transfer (NT) embyro production requires pro per oocyte activation and transfer of a nucleus into this oocyte. Howe ver, the temporal relationship between these two events is unclear. Th e current study examined whether activation of the oocyte prior to fus ion would induce nuclear swelling while also affecting development to morula and blastocyst stage and finally development to offspring. Aged oocytes can be activated by a number of techniques including exposure to room temperature. In this study oocyte activation was induced thro ugh three different means: reduced temperature culture alone, reduced temperature culture and calcium ionophore, and naturally, through the fertilization process. Electrofusion was carried out after the activat ion stimulus. When used in the NT procedure, activation of oocytes pri or to fusion resulted in NT embryos that underwent nuclear swelling an d had a high developmental rate to morula and blastocyst stages. Also, these NT embryos developed to normal offspring when transferred to re cipient animals. The addition of a calcium ionophore treatment to the reduced temperature culture was not beneficial and resulted in less nu clear swelling. The use of enucleated fertilized oocytes as recipient cytoplasm for the new nucleus resulted in NT embryos developing to mor ula and blastocyst stages at the same rate as room temperature activat ed NT embryos. Therefore, improved embryo development can be obtained from NT embryos if the aged recipient oocyte is activated prior to the time of fusion. Also, offspring were obtained from these pre-activate d NT embryos. (C) 1994 Wiley-Liss, inc.