The visceral endoderm (VE) is an epithelium of approximately 200 cells
encompassing the early post-implantation mouse embryo. At embryonic day
5.5, a subset of around 20 cells differentiate into morphologically
distinct tissue, known as the anterior visceral endoderm (AVE), and
migrate away from the distal tip, stopping abruptly at the future
anterior. This process is essential for ensuring the correct orientation
of the anterior-posterior axis, and patterning of the adjacent embryonic
tissue. However, the mechanisms driving this migration are not clearly
understood. Indeed it is unknown whether the position of the future
anterior is pre-determined, or defined by the movement of the migrating
cells. Recent experiments on the mouse embryo, carried out by Dr.
Shankar Srinivas (Department of Physiology, Anatomy and Genetics) have
revealed the presence of multicellular ‘rosettes’ during AVE migration.
We are developing a comprehensive vertex-based model of AVE migration.
In this formulation cells are treated as polygons, with forces applied
to their vertices. Starting with a simple 2D model, we are able to mimic
rosette formation by allowing close vertices to join together. We then
transfer to a more realistic geometry, and incorporate more features,
including cell growth, proliferation, and T1 transitions. The model is
currently being used to test various hypotheses in relation to AVE
migration, such as how the direction of migration is determined, what
causes migration to stop, and what role rosettes play in the process.