Abstract
From fertilization to onset of gastrulation, a mammalian embryo goes through several rounds of cellular morphogenesis resembling phenomena of epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET), collectively referred to as EMTs. How these EMT events play a role in shaping the three-dimensional (3-D) architecture of the developing embryo is not well-understood. In this review, we present a model in which cellular morphogenesis, represented primarily by dynamic changes in its epithelialization status, is the driving force of embryonic 3-D organization. This is achieved through the integration of three key components of mammalian early development, the pluripotency regulation, morphogenetic signaling, and biomechanical force anisotropy. Although cells in an early embryo do not exhibit full mesenchymal characteristics, our model underscores the importance of investigating molecular regulation of epithelial cell polarity and partial EMT/MET in understanding mammalian early development.
Highlights
After fertilization, a mammalian embryo undergoes several rounds of early cleavages before acquisition of apicobasal polarity through compaction and segregation of inner and outer cells through asymmetric divisions (Humiecka et al, 2017)
The epithelialized epiblast subsequently goes through an epithelial-mesenchymal transition (EMT) process during gastrulation, generates the mesoderm and definitive endoderm, and lays down the foundation of the three-germ layer and three-dimensional (3-D) mammalian body plan
The fourth stage is the “pluripotency exit.”. Cells at this stage are on the verge of differentiation (Thakurela et al, 2019) and are characterized by a progressive reduction of the core pluripotency factors such as OCT4, NANOG and SOX2
Summary
We present a model in which cellular morphogenesis, represented primarily by dynamic changes in its epithelialization status, is the driving force of embryonic 3-D organization. This is achieved through the integration of three key components of mammalian early development, the pluripotency regulation, morphogenetic signaling, and biomechanical force anisotropy. Cells in an early embryo do not exhibit full mesenchymal characteristics, our model underscores the importance of investigating molecular regulation of epithelial cell polarity and partial EMT/MET in understanding mammalian early development
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