Comparing the viability and in vitro maturation of cumulus-germinal vesicle break down (GVBD) oocyte complexes using two vitrification techniques in mice

Vitrification is assumed to be a promising method to cryopreserve humanoocytes but still needs optimizing.

The aim of this study was to improve the single step and step-wisevitrification effects on maturing mouse GVBD oocytes by ethylene glycol (EG) inconventional straws.

Oocytes with compact cumulus cells were cultured for 3hr inTCM199 supplemented with 10% fetal bovine serum (FBS) in 5% CO2 in air. GVBDoocytes were randomly allocated into three groups. (1) Control (non-vitrified group), (2)exposed to single-step vitrification (contained of EG 20%+0.5M sucrose), (3) exposedto step-wise vitrification (2%, 5%, 10%, 20%EG +0.5M sucrose). In vitrificationgroups,oocytes were thawed and underwent additional 21 hr maturation. Viability ofoocytes and maturation to MII stage were analyzed using inverted microscope andadditionally by staining of propidium iodide and Hoechst 33342.

All non-vitrified oocytes were viable after 24 hr; however, viability of vitrifiedsamples in single-step group was significantly lower than that of the step-wise andcontrol Groups. Also, the maturation rate in the step-wise group was significantly higher(p < 0.05) compared to single-step.

These results suggest that step-wise vitrification of GVBD oocytes ascompared to single step vitrification was better in the rate of survival and in vitromaturation of oocytes.