104EFFECT OF HATCHING STATUS ON VITRIFICATION OF CLONED BOVINE BLASTOCYSTS

Abstract

Bovine blastocysts produced by nuclear transplantation have mechanical slits in their zonae pellucidae, and therefore initiate hatching earlier than the non-manipulated embryos. The present study was undertaken to examine whether the hatching stage of cloned blastocysts is among the factors influencing their survival after vitrification and warming. Cloned bovine blastocysts were produced by using adult ear fibroblast cells as reported previously (Parnpai et al., 2002, Theriogenology 57, 443), except that fused couplets were co-cultured with bovine oviductal epithelial cells in mSOFaa medium supplemented with 0.1% linoleic acid-albumin (LAA)+0.2% BSA (Hochi et al., 1999, Theriogenology 52, 497–504). Hatching blastocysts harvested on Day 7 were classified into one of three groups according to the ratio of extruding embryonic diameter from zona (D2) to embryonic diameter inside the zona (D1); category-A: D2/D1=0.01–0.70; category-B: D2/D1=0.71–1.00; category-C: D2/D1=1.01–1.70. The blastocysts were first exposed to 10% DMSO+10% ethylene glycol in TCM199+20% FCS for 2min, and then equilibrated in 20% DMSO+20% ethylene glycol+0.5M sucrose with or without 10% Ficoll in TCM199+20% FCS for 30s. One to three blastocysts were placed on a Cryotop sheet (Kitazato Supply Co., Tokyo, Japan) and vitrified in liquid nitrogen. The samples were warmed in 0.5M sucrose solution for 2min and transferred into TCM199+20% FCS in five steps (5min per step). The post-warm survival of the blastocysts was assessed by in vitro culture for 24h. When Ficoll-free vitrification solution was used, post-warm survival rate of the category-A blastocysts (77%, 23/30) was not significantly different (ANOVA test) from those of category-B and category-C blastocysts (74%, 20/27; and 80%, 24/30; respectively). Inclusion of 10% Ficoll in the vitrification solution did not improve (ANOVA test) the post-warm survival rates of cloned blastocysts (category-A: 65%, 22/34; category-B: 54%, 15/28; category-C: 59%, 19/32). Groups of fresh nonsurgical embryos, vitrified with or without Ficoll, yielded 66.7% (4/6), 66.7% (2/3) and 40.0% (2/5), respectively, of recipients pregnant at 48 days of gestation. In conclusion, cloned bovine blastocysts, regardless of their hatching stages, were relatively resistant to cryopreservation by vitrification. (Supported by Thailand Research Fund and R&D Fund of Suranaree University of Technology.)