Multiplying embryos: experimental monozygotic polyembryony in mammals and its uses

Abstract

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.

Cloning and Embryo Splitting in Mammalians: Brief History, Methods, and Achievements

“…Embryo splitting is the in vitro stimulation of the natural process of producing identical twins with artificial SCNT [ 2 ]. For the first time, Solter and Magrath (1983) developed nuclear transfer technology in the mammalian embryo.…”

Generation of Monogenetic Cattle by Different Techniques of Embryonic Cell and Somatic Cell Cloning – Their Application to Biotechnological, Agricultural, Nutritional, Biomedical and Transgenic Research – A Review

“…The simplest example of this type of bisection is the isolation of blastomeres from very early-stage (2-to 4-cell) embryos that have been deprived of their zonae pellucidae. Most often, however, bisection is performed at advanced stages of preimplantation development, such as late morula or blastocyst (Ozil, 1983;Velásquez et al, 2017;Casser et al, 2019). At these stages of embryogenesis, embryos exhibit complete compaction, with the formation of gap junctions between blastomeres, and as a result, the embryos do not break apart into several pieces when they are cut microsurgically.…”

“…However, this technique is rather invasive because during the microsurgical embryo splitting at the compact morula or blastocyst stage, some of the embryonic cells are destroyed and eliminated. Particularly severe may be cell losses within the inner cell mass, which have a significant role in reducing the developmental potential of the obtained blastocyst "halves" (Skrzyszowska and Smorąg, 1989;Casser et al, 2019). Little information is known about how the bisection procedure affects the transcriptional activity of the genes in embryo "halves".…”

Unexpected Reproductive Effect of Prolonged Oral Administration of Silver Nanoparticles in Laboratory Mice

“…Вместе с тем удвоенная рождаемость может указывать и на повышенное рождение однояйцевых близнецов (наиболее интересная гипотеза, по мнению авторов). Из экспериментов известно [15], что у млекопитающих для достижения полиэмбрионии (для искусственного разделения групп клеток зародыша на разных стадиях его развития) достаточно выполнить о тделение бластомеров друг от друга путем химического растворения блестящей оболочки (zona pellucida) или механически разделять морулу или бластоцисту, например, микро-лезвием на примерно равные по количеству клеток части. Если AgNP или материал их покрытия каким-то образом ослабляют структурные связи между гликопротеинами блестящей оболочки, вызывая ее преждевременный распад на 2-3-й день после оплодотворения, или препятствуют формированию клеточных контактов при образовании морулы (бластоцисты), то появление однояйцевых близнецов в таком эксперименте становится объяснимым.…”