Effect of meiotic status, cumulus cells and cytoskeleton stabilizer on the developmental competence of ovine oocytes following vitrification

Abstract

This study was conducted to determine the effect of meiotic status, cumulus cells and cytoskeleton stabilizer on ovine oocyte vitrification. Oocytes at various developmental stages including GV (germinal vesicle), GVBD (GV breakdown), MI (metaphase I) and MII (metaphase II) were vitrified using open pulled straw (OPS) method. After warming, the survival rates were determined based on the morphological appearance and 3′,6′-diacetyl fluorescein staining. The developmental potential of treated oocytes was evaluated by their ability to undergo successful in vitro fertilization (IVF) and support embryo development in culture after in vitro maturation. In the first experiments, we evaluated the effect of meiosis status on oocytes vitrification. Survival rates of oocytes after warming were not different among all groups. However, significantly higher proportion of cleavages and blastocysts were obtained from vitrified MII oocytes than those from vitrified immature oocytes. Next, we selected MII oocytes to determine the influence of cumulus cells on vitrification and the results showed that survival rates were not affected by the absence of cumulus cells. Furthermore, the cleavage rates and blastocyst rates were not different with or without cumulus cells. Lastly, we examined the effect of cytoskeleton stabilizer on MII oocyte vitrification. Compared with the vehicle treated controls, pretreatment with Taxol significantly improved the survival rates (81.91% vs. 66.00%), cleavage rates ((52.29% vs.34.25%) and blastocyst rates (9.72% vs. 4.86%). Pretreatment of MII oocytes with another cytoskeleton stabilizer Cytochalansin B had no effect on oocyte survival and in vitro embryo development. Collectively, the meiotic status affected the developmental potential of oocytes after vitrification. MII stage oocytes showed better resistance to cryopreservation compared with the oocytes at immatured stages. Taxol treatment prior to vitrification was beneficial to vitrified/warmed ovine matured oocytes.