Influence of vitrification on mouse metaphase II oocyte spindle dynamics and chromatin alignment

ObjectiveTo evaluate influences of vitrification and warming of metaphase II (MII) mouse oocytes on survival, spindle dynamics, spindle morphology, and chromatin alignment on metaphase plates.DesignExperimental animal study.SettingUniversity animal laboratory.Animal(s)Eight-week-old B6D2F1 mice.Intervention(s)Denuded MII oocytes were used fresh (control), exposed to vitrification/warming solutions (Sol Expos), or vitrified and warmed (Vitr).Main Outcome Measure(s)Oocyte recovery and survival after warming and the influence of solution exposure and cryopreservation on spindle dynamics and chromatin alignment.Result(s)Cryopreservation of two or 10 oocytes per straw resulted in recovery (100% ± 0% and 95% ± 4%, respectively; mean ± SE) and survival (95% ± 2% and 98% ± 2%, respectively). Immediately after warming (Vitr), significantly fewer oocytes assessed with immunocytochemistry contained spindles, compared with control and Sol Expos. When oocytes were placed into a 37°C environment for 2 hours after exposure or warming, the ability to recognize spindles by immunocytochemistry was not significantly different between groups. Using live-cell time-lapse imaging with LC-Polscope, similar time-dependent spindle formation dynamics were observed. At 2 hours after collection or treatment, spindle morphology and length were not significantly different between the groups, nor was the incidence of aberrant alignment of chromatin on metaphase plates.Conclusion(s)Immediately after warming of vitrified MII oocytes, β-tubulin is depolymerized and chromatin remains condensed on the metaphase plate. Within a 2-hour period, β-tubulin repolymerizes, forming morphologically normal metaphase spindles with properly aligned chromatin.