Figure 1.

Signaling and responses to cell interactions. (A) At homotypic contacts of mesoderm cells, the PCP pathway can promote adhesion (green) because PAPC complexes form that have low PCP inhibitory activity. Eph receptor activation that promotes repulsion (red) is weak because coexpressed ephrins have low affinity. Consequently, the balance of cell responses favors adhesion (B). (C) At heterotypic contacts, free PAPC inhibits the PCP pathway. This PAPC activity requires Fz7-induced expression of Snail1. Eph receptors are strongly activated by high affinity ephrins expressed in ectoderm. Consequently, there is a balance of repulsion and adhesion that leads to formation of cleft contacts, characterized by interspersed stretches of adhesion and intercellular gaps (D).