Transformation of Pluripotency States during Morphogenesis of Mouse and Human Epiblast

Abstract

The pluripotent status of a cell in vivo is spatio-temporally regulated within embryogenesis and is determined by the processes of self-renewal, endless proliferation, and differentiation into all cell types of the body. Initially, the concept of pluripotency status was proposed for characterization of teratocarcinoma cells, and then this concept was applied to the embryonic cells of the preimplantation mouse embryo. Mouse and human pluripotent stem cells (PSCs) are formed during the preimplantation period and are present in the embryo until the beginning of gastrulation. The differentiation of the inner cell mass of the blastocyst (ICM) into a hypoblast and an epiblast, which develops into the embryo itself, is one of the main events in early mammalian development. Continuous and dynamic transformation of pluripotency states in development coincides with the morphogenetic processes that are involved in the formation and maturation of the epiblast. Thus, blastocyst ICM cells differ in epigenetic and transcription patterns from their daughter cells forming the peri/postimplantation epiblast. With the onset of gastrulation movements, the maturation of epiblast cells ends with their differentiation into cells of three germ layers. This review considers the historical aspects of the study of cell pluripotency, various sources of PSCs, and mechanisms and signaling pathways that support self-renewal and pluripotency in PSCs cultures. In addition, the authors summarize and conceptualize data on morphogenetic processes that are involved in the formation of naive ICM cells in vivo and the subsequent maturation of mouse and human epiblast cells associated with the transformation of their pluripotency states.