Casser Ellen, Israel Steffen, Boiani Michele
Max Planck Institute for Molecular Biomedicine, Muenster, Germany.
Int J Dev Biol. 2019;63(3-4-5):143-155. doi: 10.1387/ijdb.190016mb.
Monozygotic (MZ) polyembryony is a strategy to increase the output of a single zygote, thereby producing more offspring from a limited number of oocytes. However, MZ twins and multiples (multiplets) of mammals occur rarely in nature, while their generation has been more successful experimentally. In this work, we review some of the methodological, biological and field aspects of experimental MZ polyembryony in mammals. First attempts of mechanical bisection of 2-cell stage rodent embryos provided a proof-of-principle for the survival and independent development of both blastomeres. Subsequently, experiments in other species, particularly sheep and bovine, allowed 2 methods of embryo multiplication to become routine: the separation or biopsy of blastomeres from cleavage-stage embryos and the bisection of morulae and blastocysts. We discuss how the preferable stage of bisection and the success rate can be species-specific. The scope that profited most from experimental MZ polyembryony is the production of additional copies of elite livestock individuals, the reduction of interindividual variation in test groups and the possibility of investigating discordant phenotypic traits in the same genomic background, for instance, comparing an affected twin with its healthy co-twin. By contrast, the original motivation for experimental polyembryony - efficiently generating more offspring out of the same zygote - has not been fulfilled yet. Although embryo splitting leads to an increase in quantity, there is a loss of embryo quality, thus, there is no real gain from artificially generated embryos (yet) in the field of medically assisted reproduction. In conclusion, mammalian zygotes have the regulative capacity to be polyembryonic, but this is not obligate.
单合子（MZ）多胚胎发育是一种增加单个受精卵产出的策略，从而从有限数量的卵母细胞中产生更多后代。然而，哺乳动物的MZ双胞胎和多胞胎在自然界中很少出现，而它们的产生在实验中更为成功。在这项工作中，我们回顾了哺乳动物实验性MZ多胚胎发育在方法学、生物学和领域方面的一些情况。对2细胞期啮齿动物胚胎进行机械二分的首次尝试为两个卵裂球的存活和独立发育提供了原理证明。随后，在其他物种，特别是绵羊和牛身上进行的实验，使两种胚胎增殖方法成为常规操作：从卵裂期胚胎中分离或活检卵裂球，以及对桑葚胚和囊胚进行二分。我们讨论了二分的最佳阶段和成功率如何因物种而异。从实验性MZ多胚胎发育中获益最大的领域是生产优良家畜个体的额外副本、减少测试组中的个体间变异，以及在相同基因组背景下研究不一致的表型特征的可能性，例如，将患病双胞胎与其健康的同卵双胞胎进行比较。相比之下，实验性多胚胎发育的最初动机——从同一个受精卵高效地产生更多后代——尚未实现。虽然胚胎分割导致数量增加，但胚胎质量有所下降，因此，在医学辅助生殖领域（目前）人工产生的胚胎并没有真正的收益。总之，哺乳动物的受精卵具有多胚胎发育的调节能力，但这并非必然。
