Department of Clinical Embryology, Kasturba Medical College Manipal, Manipal Academy of Higher Education, Manipal, 576 104, India.
Dipartimento di Biologia, Università di Napoli "Federico II", Complesso Universitario di Monte S Angelo, Napoli, Italy.
Cryobiology. 2020 Apr;93:49-55. doi: 10.1016/j.cryobiol.2020.02.012. Epub 2020 Feb 27.
This study investigated if in vitro maturation (IVM) before or after vitrification would be more successful for prepubertal oocytes. To mimic prepubertal conditions in an experimental setup, oocytes were collected from healthy 14, 21 and 28day old Swiss albino mice. The germinal vesicle (GV) stage oocytes and in vitro matured MII oocytes were subjected to vitrification-warming. Both structural (meiotic spindle morphology, mitochondrial integrity, cortical granules) and functional (sperm zona binding, fertilization) characteristics were assessed in oocytes after warming. This study demonstrated that IVM was more detrimental to prepubertal oocytes than to young adults. Further, vitrification of the IVM oocytes resulted in an increase in the number of abnormal meiotic spindles, a change in the cortical distribution pattern, a reduction in sperm zona binding and the fertilization rate. Importantly, oocyte integrity was better when prepubertal oocytes were vitrified before, rather than after, IVM. The above observations support GV stage vitrification for prepubertal oocytes requiring fertility preservation. Understanding the mechanisms behind the differing outcomes for oocytes from immature females will help in refining current protocol, thereby retaining the oocytes' maximum structural and functional integrity Further investigation is necessary to determine whether human prepubertal oocytes also behave in a similar way. It is to be noted here, with great emphasis, that a major limitation of this study is that the oocytes' abilities were tested only until fertilisation, as a consequence of which the study cannot reveal the developmental potentials of the embryos beyond fertilisation.
本研究旨在探讨体外成熟（IVM）在玻璃化之前或之后对未成年卵母细胞是否更有效。为了在实验设置中模拟未成年状态，从健康的 14、21 和 28 天大的瑞士白化小鼠中收集卵母细胞。GV 期卵母细胞和体外成熟的 MII 卵母细胞均进行玻璃化-复温。在复温后评估卵母细胞的结构（减数分裂纺锤体形态、线粒体完整性、皮质颗粒）和功能（精子透明带结合、受精）特征。本研究表明，IVM 对未成年卵母细胞的损害比对年轻成年卵母细胞更大。此外，IVM 卵母细胞的玻璃化导致异常减数分裂纺锤体数量增加、皮质分布模式改变、精子透明带结合和受精率降低。重要的是，当需要生育力保存时，未成年卵母细胞在 IVM 之前而不是之后进行玻璃化，卵母细胞的完整性更好。上述观察结果支持 GV 期玻璃化用于需要生育力保存的未成年卵母细胞。了解不成熟雌性卵母细胞产生不同结果的机制将有助于改进当前方案，从而保持卵母细胞的最大结构和功能完整性。需要进一步研究以确定人类未成年卵母细胞是否也以类似的方式表现。需要特别强调的是，本研究的一个主要限制是，仅在受精时测试卵母细胞的能力，因此该研究无法揭示受精后胚胎的发育潜力。
