THE EFFECT OF RECIPIENT OOCYTE VOLUME ON NUCLEAR TRANSFER IN CATTLE

This study compared the developmental potential of bovine nuclear tran sfer embryos with varying amounts of cytoplasm. Embryos formed from si ngle cytoplasts fused to blastomeres by a single electrical pulse or f rom double cytoplasts using a double electrical pulse resulted in reco nstituted embryos containing 75% and 150% of the original oocyte volum e. No differences in fusion, cleavage, or development rates to blastoc ysts were observed between the groups. Mean cell numbers 2 days after fusion were significantly lower in single-cytoplast clones. Cell numbe rs of resulting blastocysts were likewise significantly lower in singl e-cytoplast clones. Embryos formed by fusion of blastomeres with singl e cytoplasts using a single electrical pulse or from double cytoplasts using either a single or a double pulse resulted in reconstituted emb ryos containing 50%, 100% and 100% of the original oocyte volume. Agai n, no differences in fusion or cleavage rates were observed between gr oups, but the development to blastocysts at day 7 was significantly hi gher in double cytoplasts constructed with one fusion pulse than in si ngle cytoplasts (P < 0.05). Mean cell numbers 2 days after fusion were significantly lower in single-cytoplast clones (P < 0.05), but at the blastocyst stage, no statistically significant differences in cell nu mbers were observed. The results of this study show that cytoplasmic v olume plays a role in the development of nuclear transfer embryos. Whe n using crude enucleation methods such as oocyte bisection, normal cyt oplasmic volumes can be achieved by fusing double cytoplasts with embr yonic blastomeres. (C) 1998 Wiley-Liss, Inc.