Open pulled straws for vitrification of mature mouse oocytes preserve patterns of meiotic spindles and chromosomes better than conventional straws

Vitrification of oocytes has been applied recently for humans, but remains elusive. The microtubules of oocytes are vulnerable to cryoprotectants and thermal changes. Using mouse oocytes, the effects of vitrification in open pulled straws (OPS) were investigated on survival, the meiotic spindle, and chromosomes and compared with conventional straws. Mature oocytes were all ocated to four groups for exposure to cryoprotectants, vitrification in con ventional straws, or vitrification in OPS. They were diluted in stepwise su crose solutions. Oocytes without treatments mere used as controls. The surv iving oocytes were stained for meiotic spindles and chromosomes, After dilu tion, all of the oocytes exposed to cryoprotectants survived. Vitrification sometimes resulted in lysis so that survival using OPS (62%) was significa ntly (P < 0.05) smaller than that using conventional straws (81%). Oocytes exposed to cryoprotectants or vitrified exhibited serious disturbances of m icrotubules immediately post-dilution, After 1 h incubation, the microtubul es could repolymerize so that the OPS group had significantly (P < 0.05) mo re normal spindles (78%) than did the conventional straw group (21%). The f ormer also tended to have more compact chromosomes (87%) than did the latte r (78%). OPS for vitrification of oocytes achieve more rapid cooling, warmi ng, and dilution and so reduce spindle injury. However, the lower survival rate in OPS needs improvement.