Figure 8. AVE cells insert basal projections between neighboring cells to move forward.

(A) Individual confocal sections of a migrating snail-like AVE cell (dark blue cell from Video S1). The basal section shows a long lamella with two projections at its end (arrow); the projection is not visible apically. The distance between the apical and basal optical sections is 8 µm. (B) Individual confocal sections of an AVE cell (yellow cell from Video S1) that has arrived at the embryonic/extra-embryonic border. The cell shape became cuboidal. The basal surface was marked by retracting protrusions (arrow) that are not visible in the apical plane. The distance between the apical and basal optical sections is 14 µm. Scale bar = 30 µm. (C) Individual confocal section of an AVE cell from Video S1, oriented to show the apical-basal profile of the cell. The long projection is on the basal side. (D) Schematic of the shape changes of the cells with long lamellar projections. At e5.5, AVE cells are columnar. During migration, cells acquire a snail-like morphology with a round cell body and a highly elongated lamella ended by two lateral horn-like protrusions. At the end of migration, the cells become cuboidal.