A revised network of inhibitory interactions between polarity factors. (A) A diagram showing how the recruitment of RhoGAP19D to the lateral membrane by E-cadherin adhesion complexes restricts Cdc42 activity to the apical domain. This adds a new inhibitory interaction to the network of interactions between apical and lateral polarity factors. (B) A model of the changes in rhogap19d mutant cells that lead to the invasive phenotype. In the absence of RhoGAP19D, active Cdc42 localizes along the lateral domain as well as the apical domain and activates Gek to induce lateral actomyosin contractions. Lateral Cdc42-GTP also alters the conformation of Par-6/aPKC so that it is competent to bind to Crumbs. This primed Par-6/aPKC then diffuses until it binds to apical Crumbs, which activates aPKC’s kinase activity, resulting in expansion of the apical domain and a dome-shaped apical surface.