Comparative aspects of early lineage specification events in mammalian embryos – insights from reverse genetics studies

Abstract

Within the mammalian class, formation of the blastocyst is morphologically highly conserved among different species. The molecular and cellular events during preimplantation embryo development have been studied extensively in the mouse as model organism, because multiple genetically defined strains and a plethora of reverse genetics tools are available to dissect specific gene functions and regulatory networks. However, major differences in preimplantation developmental kinetics, implantation, and placentation exist among mammalians, and recent studies in species other than mouse showed, that even regulatory mechanisms of the first lineage differentiation events and maintenance of pluripotency are not always conserved. Here, we focus on the first and the second lineage segregation in mouse and bovine embryos, when the first differentiated cell types emerge. We outline their common features and differences in the regulation of these essential events during embryonic development with a glance at further species. In addition, we show how new reverse genetics strategies aid the study of regulatory circuits in embryos of domestic species, enhancing our overall understanding of mammalian preimplantation development.

Mild maternal hyperglycemia in INSC93S transgenic pigs causes impaired glucose tolerance and metabolic alterations in neonatal offspring

“…Despite differences in pig versus human placenta (epithelial-chorial vs hemochorial), transfer of relevant nutrients such as glucose, amino acids and at least partially of fatty acids takes place in both species (Litten-Brown et al, 2010). Decisive phases of early embryonic development are also similar, as major genome activation takes place between the 4-cell and 8-cell stage in pig and human compared with the 2-cell stage in mouse (Simmet et al, 2018). Also, in rodents, late phases of fetal development are generally not exposed to an altered maternal metabolism as their pups are born at a more immature state compared with pigs and humans (Litten-Brown et al, 2010).…”

Trophectoderm regeneration to support full-term development in the inner cell mass isolated from bovine blastocyst

“…The microenvironmental events associated with cell fate specification at the blastocyst stage described above have rarely been investigated in nonrodent species other than mice. However, crucial differences exist in the molecular mechanisms that regulate cell fate specification at the blastocyst stage among species (22)(23)(24). For example, OCT4, a representative basis of cell pluripotency, is not restricted to the ICM in human and bovine blastocysts, unlike that in mouse (25,26), suggesting that diverse regulatory mechanisms are applied in a speciesspecific developmental manner.…”

A New Toolbox in Experimental Embryology—Alternative Model Organisms for Studying Preimplantation Development

“…Due to its high efficiency and ease of use, CRISPR/Cas9 is currently the method of choice for creating genome alterations in animal models. Together with highly developed ARTs, an unlimited set of possible applications arises, making large animals a valuable and very accessible model for gaining a deeper understanding of mammalian preimplantation development ([ 107 ], reviewed in [ 108 ]).…”