Fig. 8.

A model for the molecular control of protrusive activity during dorsal intercalation. Early, as intercalating cells begin to adopt a polarized, wedge-shaped morphology, protrusive activity is broadly distributed at the cell periphery. As intercalation proceeds, protrusions focus medially and basolaterally to produce a single, extending tip. As cell bodies translocate, cells migrate past one another and intercalation completes. The GEF UNC-73, which is broadly distributed, activates CED-10 and MIG-2, but only in regions devoid of CRML-1, which inhibits UNC-73 at lateral edges. Accumulation of CRML-1 at the contralateral edges of intercalating cells may promote protrusive downregulation as intercalation completes.