Vitrification and slow cryopreservation differentially affects oocyte survival, development and cytoskeleton status

Backgroud: Oocyte cryopreservation is critical in assisted reproduction techniques. However, the effect of cryopreservation on the oocyte has not been widely explored yet. Currently a thorough understanding of oocyte cryobiology is urgently required due to its far lag behind the forces propelling the clinical application of oocyte cryopreservation. Methods: In this study, we used two different ways including vitrification freezing and slow freezing to cryopreserve the mouse oocytes and elucidated how the cyro-procedures affected the survival, development potential and cytoskeleton of oocytes. The development of oocytes was evaluated on the formation of 2-cell and blastocyst. The cytoskeleton was determined by the immunostaining for the biomarker of Spindle and chromosome. Results: The comparison between two different freezing methods indicated that the survival rate of oocyte at MII stage did not show significant difference between two methods, while the survival rate at GV stage was higher by vitrification than slow freezing. The development potential of oocytes cryopreserved at MII stage was different between two methods in the blastocyst ratio. Significant difference was found in ratio of mature oocyte, fertilized oocyte and blastocyst between two methods. Furthermore, the oocyte cytoskeleton status was better by vitrification freezing than slow freezing method. Besides, the comparison between the oocyte at two different stages only showed difference in mature oocyte ratio and cytoskeleton status by slow freezing method. Conclusion: This study may explain why the oocyte cryopreservation success rate is as yet far from satisfactory and why cryopreserved oocytes should be treated differently from their fresh siblings. A fresh look at the characteristic features of oocytes after cryopreservation may work as a stimulus to further improvement of oocyte cryopreservation.