The oocyte spindle is preserved by 1,2-propanediol during slow freezing

ObjectiveTo investigate the specific changes in oocyte spindle subjected to severe challenges of low temperature, as well as to examine the effect of cryoprotectants in preserving oocyte spindle during cryopreservation.DesignIn vitro experimental study.SettingAcademic research laboratory.Animal(s)B6D2F1 (C57BL/6 X DBA/2) mice.Intervention(s)Mouse oocytes were cryopreserved using a slow freezing method in a sodium-depleted medium with 1.5 mol/l 1,2-propanediol (PROH) and 0.3 M sucrose. To examine the spindle, oocytes were fixed before, during, and after cryopreservation, and oocytes were analyzed by immunocytochemistry and confocal microscopy.Result(s)The MII spindle was preserved during the slow freezing, because the cryoprotectant PROH was found to support the organization of MII spindle in resisting the subzero temperature. In contrast, the MII spindle was disassembled gradually during the thawing process with or without PROH. Most of the oocytes were able to recover the MII spindle after thawing, but a portion of thawed oocytes could not sustain the meiotic spindle because of parthenogenetic activation.Conclusion(s)1,2-Propanediol can support the organization of MII spindle to defy the subphysiologic temperature; however, the PROH cannot sustain oocyte spindle structure after the subsequent thawing process.