Fig. 5. Stages of cell-cell contact formation. (A) Migrating cells without cell contact protrude lamellipodia and filopodia at the leading edge of the cell. (B) Initial cell contacts at the tips of thin cellular protrusions result in the formation of primordial, spot-like adherens junctions or puncta, which are positive for E-cadherin, ZO-1 and JAM-A. (C) On further maturation of cell-cell contacts, the spot-like junctions fuse into a linear pattern; the cells start to polarize and proteins specifically enriched at adherens junctions (E-cadherin) or TJs (ZO-1, JAM A) start to segregate; (D) In fully polarized cells, proteins specific for AJs and TJs are completely segregated, and adherens junctions and TJs can be distinguished at a structural level. The figure is based on previous studies (Yonemura et al., 1995; Adams et al., 1996; Ando-Akatsuka et al., 1999).