Ingression is one of the many changes in the location or relative position of cells that takes place during the gastrulation stage of embryonic development.
[1] While the mechanisms of ingression are not fully understood, studies using the sea urchin as a model organism have begun to shed light on this developmental process, and will be the focus here.
The ingressing cells will then apically constrict and alter their cellular architecture through a dramatic reorganization of their cytoskeleton.
Lastly, these cells will modify their mode of motility and presumably gain affinity for the basal lamina which composes the lining of the blastocoel, the future migration substrate of the PMCs.
[3] In sea urchins, epithelial cells adhere to one another as well as the hyaline layer through classic cadherins and adherens junctions.
[2] Within birds and mammals, epiblast cells converge at the midline and ingress at the primitive streak.