Apical constriction

[2] During gastrulation in both invertebrates and vertebrates, apical constriction of a ring of cells leads to blastopore formation.

During Xenopus gastrulation, bottle cells are located in the dorsal marginal zone and apically constrict inwards to initiate involution of the blastopore.

Researchers have shown that the removal of bottle cells does not inhibit gastrulation, but simply makes it less efficient.

Because Shroom3 is an actin-binding protein and accumulates on the apical side, the most likely mechanism is that Shroom3 aggregates the actin meshwork, generating a squeezing force.

During Drosophila gastrulation, apical constriction of midline cells initiates invagination to create the ventral furrow.

Pulsed contractions of the actin meshwork are believed to be primarily responsible for reducing the apical surface area.

apical constriction in C. elegans
Two stages in the constriction of apical surfaces (blue) of a pair of cells in C. elegans .
apical constriction of bottle cells initiates invagination.
Constriction of the apical side of cells in an epithelial layer generates enough force initiate invagination. In gastrulation, the apically constricting cells are known as bottle cells. The bottle shape results when constriction of the apical side of the cell squeezes the cytoplasm, thus expanding the basal side.
Apical constriction mechanisms (red: filamentous actin. orange: myosin.)
apical constriction during neurulation.
Apical constriction of cells at the hingepoints of neural folds generates forces that participate in neural tube closure.