Origin, Early Patterning, and Fate of the Mouse Epiblast

This chapter presents the latest findings regarding the origin, early patterning, and the fate of the epiblast in the mouse embryo, and attempts to complement earlier reviews. An important aspect of the establishment of the epiblast lineage, no doubt critical in the regulation of its differentiation, is the role of chromatin modifications in the regulation of gene expression. Fate mapping by clonal analysis in the early gastrula has demonstrated that the developmental fates and morphogenetic movements of cell populations in different regions of the epiblast are predictable during gastrulation. Major decisions about lineage allocation are made during gastrulation when the single-layered epiblast is transformed into the three primary germ layers of the embryo: the endoderm, the mesoderm, and the ectoderm. Molecular interactions continuously define the organizer during the cell movements of gastrulation. Active cell migration drives the unilateral movements of the anterior visceral endoderm. Eomesodermin is required for mouse trophoblast development and mesoderm formation.