Molecular Basis of Differential Gene Expression in Themouse Preimplantation Embryo

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Preimplantation development of the mammalianembryo consists of stages that include formation of thezygote, blastocyst formation and implantation of theembryo into the uterus. Depending on the animal, firstfew cleavages of the early embryo is fully supported bytranslation of maternal transcripts and use of maternalproteins. After this period, the preimplantation embryostarts to transcribe from its own genome and produceproducts, which are necessary for further development. Eventually, differential gene expression resultsin production of three cell types in the preimplantationembryo; an outer transporting polarized epithelium(trophoblast) and two cell types of primitive endoderm(hypoblast), and epiblast in the inner cell mass. Afterimplantation, the trophoblast and hypoblast give rise toextra-embryonic tissues and epiblast cells form primarily the embryo proper. Expression of maternal andembryonic transcripts and proteins, and differentialexpression of these products that lead to differentiationof embryonic cells are all highly coordinated events,which need to be temporally and spatially regulatedduring this period of development. In this review articlemechanisms and paradigms that may define and regulate these cellular activities leading to the first cellulardifferentiation of life are presented. Considering theabundance of research data on the preimplantationdevelopment of rodents, in this review we will mainlyfocus on the mouse model.