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The potential significance of binovular follicles and binucleate giant oocytes for the development of genetic abnormalities(Review)

机译：双卵泡和双核巨卵母细胞对遗传异常发生的潜在意义（综述）

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摘要

Normal development of a fertilizable female gamete emanates from a follicle containing only one oocyte that becomes haploid after first meiotic division. Binovular follicles including two oocytes and binucleate giant oocytes that are diploid after first meiosis constitute notable exceptions from this rule. Data provided by programmes of human-assisted reproduction on the occurrence of both phenomena have been reviewed to evaluate possible implications for the formation of genetic abnormalities. To exclude confusion with oocytes aspirated from two adjacent individual follicles, true binovularity has been defined as inclusion of two oocytes within a common zona pellucida or their fusion in the zonal region. A total of 18 conjoined oocytes have been reported and one of the oocyte was normally fertilized in seven cases. Simultaneous fertilization of both female gametes occurred only once. No pregnancy was achieved after transfer of an embryo from a binovular follicle. Binucleate giant oocytes have been observed sporadically but a few reports suggest an incidence of up to 0.3% of all gametes retrieved. Extensive studies performed by two independent centres demonstrated that giant oocytes are diploid at metaphase II, can undergo fertilization in vitro with formation of two or three pronuclei and develop into triploid zygotes and triploid or triploid/mosaic embryos. In summary, giant binucleate oocytes may be responsible for the development of digynic triploidy whereas the currently available data do not support a role of conjoined oocytes in producing dizygotic twins, mosaicism, chimaeras or tetraploidy. However, more information on the maturity and fertilizability of oocytes from binovular follicles is needed. Future studies should also evaluate a possible impact of pharmaceutical and environmental oestrogens on the formation of multiovular follicles.
机译：可受精的雌配子的正常发育来自仅包含一个卵母细胞的卵泡，卵母细胞在第一次减数分裂后变成单倍体。首次减数分裂后为二倍体的双卵泡（包括两个卵母细胞和双核巨卵母细胞）构成该规则的明显例外。已经审查了由人类辅助生殖计划提供的有关两种现象发生的数据，以评估对遗传异常形成的可能影响。为了排除与从两个相邻单个卵泡吸出的卵母细胞的混淆，真正的双头畸形被定义为在普通透明带内包含两个卵母细胞或它们在区域内的融合。据报道，总共有18个相连的卵母细胞，其中7例正常受精。两个雌配子同时受精仅发生一次。从双卵泡滤泡中移出胚胎后，没有怀孕。偶发地观察到双核巨卵母细胞，但是一些报告表明，这种现象的发生率高达所取回的所有配子的0.3％。由两个独立的中心进行的广泛研究表明，巨卵母细胞在中期II是二倍体，可以在体外受精并形成两个或三个原核，并发育成三倍体合子和三倍体或三倍体/镶嵌胚。总而言之，巨大的双核卵母细胞可能是导致二胎三倍体发育的原因，而目前可获得的数据并不支持结合的卵母细胞在产生双卵双胞胎，镶嵌，嵌合体或四倍体中的作用。但是，需要更多有关双卵泡卵母细胞的成熟度和受精能力的信息。未来的研究还应评估药物和环境雌激素对多卵泡卵泡形成的可能影响。

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