title: Improved development to blastocyst of ovine nuclear transfer embryos reconstructed during the presumptive S-phase of enucleated activated oocytes.
abstract: The timing of pronuclear formation and the initiation and duration of the DNA synthetic period (S-phase) were determined during the first cell cycle of electrically activated ovine oocytes matured in vivo. Reconstructed embryos were produced by electro-fusion-mediated nuclear transfer of unsynchronized single blastomeres. These were derived from embryos produced in vivo at the 16-cell stage (Day 4) and transferred to enucleated metaphase II oocytes at the time of activation or to enucleated activated oocytes during early, mid, and late stages of the presumptive S-phase. The frequency of development to blastocyst was greatest in embryos reconstructed during the presumptive S-phase of enucleated activated oocytes than in embryos reconstructed at the time of activation (mean 55.4% vs. 21.3%). No significant differences were observed when embryos were reconstructed during early, mid, or late stages of the presumptive S-phase (61.3%, 45.7%, and 57.7%, respectively). The results indicate that the use of enucleated activated oocytes as cytoplasts for embryo reconstruction can increase the frequency of development to blastocyst of embryos reconstructed from unsynchronized donor blastomeres.
authors.affiliation: AFRC Roslin Institute, Roslin, Midlothian, United Kingdom.
authors.forename: K H
authors.initials: KH
authors.lastname: Campbell
authors.forename: P
authors.initials: P
authors.lastname: Loi
authors.forename: P
authors.initials: P
authors.lastname: Cappai
authors.forename: I
authors.initials: I
authors.lastname: Wilmut
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000502:physiology*; D001757:Blastomeres / Q000502:physiology / Q000648:ultrastructure; D046508:Culture Techniques; D004247:DNA / Q000096:biosynthesis; D004558:Electric Stimulation; D004624:Embryo Transfer; D005260:Female; D053652:Nuclear Transfer Techniques; D009865:Oocytes / Q000648:ultrastructure*; D016196:S Phase; D012756:Sheep
chemical_list: D004247:DNA