title: Timing factors affecting blastocyst development in equine somatic cell nuclear transfer.
abstract: In nuclear transfer (NT), exposure of donor cell chromatin to the ooplast cytoplasm may aid reprogramming; however, the length of exposure feasible is limited by the developmental life span of the oocyte. We examined the effect of duration of nucleus-cytoplasmic exposure before activation and of in vitro maturation (IVM) in equine NT. In experiment 1, 24 h IVM and a delay of 2, 5, or 8 h between reconstruction and activation yielded 4%, 15%, and 11% blastocysts, respectively. In experiment 2, a 5-h activation delay yielded 17% and 22% blastocysts with two donor cell lines. In experiment 3, using a 5-h activation delay, the blastocyst rate was significantly higher using oocytes after 20 h IVM than after 24 h IVM; however, only 28% of oocytes were in metaphase II (MII) at 20 h. In experiment 4, oocytes were denuded of cumulus at 20 h, and those in metaphase I (MI) were returned to culture for 3 h (20+3H treatment); blastocyst rates were 30% and 27%, respectively (8-h and 5-h delay to activation, respectively). Four live foals resulted from the transfer of 17 blastocysts (24%) produced using MII oocytes and a 5- or 8-h activation delay. Use of equine oocytes immediately after reaching MII, combined with a longer delay from reconstruction to activation, increased developmental competence after equine NT.
authors.affiliation: Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University , College Station, Texas, 77843.
authors.forename: Young-Ho
authors.initials: YH
authors.lastname: Choi
authors.forename: Isabel C
authors.initials: IC
authors.lastname: Velez
authors.forename: Beatriz
authors.initials: B
authors.lastname: Macías-García
authors.forename: Katrin
authors.initials: K
authors.lastname: Hinrichs
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000166:cytology*; D004624:Embryo Transfer / Q000662:veterinary; D047108:Embryonic Development; D005260:Female; D005307:Fertilization in Vitro / Q000662:veterinary; D006736:Horses; D008677:Metaphase; D053652:Nuclear Transfer Techniques / Q000662:veterinary*; D009865:Oocytes / Q000166:cytology*; D013997:Time Factors