Abstract
Author SummaryThe specification of the anterior-posterior body axis of the mouse embryo depends on migration of the anterior visceral endoderm (AVE) to a position that overlies the future head. By high-resolution imaging of intact embryos we show that movement of the AVE is a form of collective cell migration, as the migrating cells retain tight and adherens junctions while they migrate and exchange neighbors within the plane of the visceral endoderm epithelium. Using conditional knockouts, we find that the small GTPase Rac1 is absolutely required for specification of the anterior-posterior axis and acts cell-autonomously within the AVE to allow cells to extend long, dynamic lamellar projections that are required for movement. Rac1-mediated epithelial migration of the AVE is a crucial step in the establishment of the mammalian body plan, and Rac1 may be important for collective migration in general in mammalian tissues, including invading tumor cells.
Highlights
Between the time of implantation and gastrulation, the pluripotent cells of the mammalian epiblast become restricted to specific lineages in a series of inductive interactions that depend on both intercellular signals and highly orchestrated cell rearrangements
The specification of the anterior-posterior body axis of the mouse embryo depends on migration of the anterior visceral endoderm (AVE) to a position that overlies the future head
By high-resolution imaging of intact embryos we show that movement of the AVE is a form of collective cell migration, as the migrating cells retain tight and adherens junctions while they migrate and exchange neighbors within the plane of the visceral endoderm epithelium
Summary
Between the time of implantation and gastrulation, the pluripotent cells of the mammalian epiblast become restricted to specific lineages in a series of inductive interactions that depend on both intercellular signals and highly orchestrated cell rearrangements. One day after implantation (e5.5), the embryonic region that will give rise to the three germ layers of the mouse is a singlelayered cup-shaped columnar epithelium (the epiblast) that is surrounded by the squamous visceral endoderm (VE) epithelium. At this stage, the mouse embryo is elongated in its proximal-distal axis, where the site of connection to the uterine tissue defines the proximal pole. Migration of DVE/AVE cells converts the early proximal-distal asymmetry into the definitive anterior-posterior (AP) axis of the animal
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