Cell Polarity-Dependent Regulation of Cell Allocation and the First Lineage Specification in the Preimplantation Mouse Embryo.

During the first few days in the mouse preimplantation embryo, two types of cells, polar and apolar cells are generated from spherical totipotent blastomeres. Sequential morphogenetic events, polarization, compaction, and asymmetric division, are essential for the generation of the first distinct cell populations, polar and apolar cells, which establish the outer/inner configuration within the embryo. This leads to position-dependent activation of the Hippo signaling pathway and lineage-specific gene expression to form the trophectoderm and inner cell mass in a blastocyst. It is still unknown how each morphogenetic event is initiated and how it influences subsequent events. In this chapter, we briefly review the two classic models of mouse preimplantation development and discuss recent studies providing novel insights into the self-organizing ability of the preimplantation mouse embryo. Advances in live cell imaging and mathematical modeling contribute a greater understanding to lineage specification and cell fate commitment at the single cell level. Differential molecular and mechanistic characteristics created by the presence and absence of the apical domain in polar and apolar cells, respectively, dictate cell allocation, divisional orientation, and differential activation of the Hippo signaling pathway.