Tight and adherens junctions are specialized sites of cell-cell interaction in epithelia and endothelia, and are involved in barrier, adhesion, and signaling functions. These functions are orchestrate Show more
Tight and adherens junctions are specialized sites of cell-cell interaction in epithelia and endothelia, and are involved in barrier, adhesion, and signaling functions. These functions are orchestrated by a highly organized meshwork of macromolecules in the membrane and cytoplasmic compartments. In this review, we discuss the structural organization and functions of the major cytoplasmic scaffolding and adaptor proteins of vertebrate apical junctions (ZO proteins, afadin, PLEKHA7, cingulin, paracingulin, polarity complex proteins, and a few others), focusing on their interactions with cytoskeletal and signaling proteins. Furthermore, we discuss recent results highlighting how mechanical tension, protein-protein interactions and post-translational modifications regulate the conformation and function of scaffolding proteins, and how spontaneous phase separation into biomolecular condensates contributes to apical junction assembly. Using a sequence-based algorithm, a large fraction of cytoplasmic proteins of apical junctions are predicted to be phase separating proteins (PSPs), suggesting that formation of biomolecular condensates is a general mechanism to organize cell-cell contacts by clustering proteins. Show less
The establishment and maintenance of epithelial cell-cell junctions is crucially important to regulate adhesion, apico-basal polarity and motility of epithelial cells, and ultimately controls the arch Show more
The establishment and maintenance of epithelial cell-cell junctions is crucially important to regulate adhesion, apico-basal polarity and motility of epithelial cells, and ultimately controls the architecture and physiology of epithelial organs. Junctions are supported, shaped and regulated by cytoskeletal filaments, whose dynamic organization and contractility are finely tuned by GTPases of the Rho family, primarily RhoA, Rac1 and Cdc42. Recent research has identified new molecular mechanisms underlying the cross-talk between these GTPases and epithelial junctions. Here we briefly summarize the current knowledge about the organization, molecular evolution and cytoskeletal anchoring of cell-cell junctions, and we comment on the most recent advances in the characterization of the interactions between Rho GTPases and junctional proteins, and their consequences with regards to junction assembly and regulation of cell behavior in vertebrate model systems. The concept of "zonular signalosome" is proposed, which highlights the close functional relationship between proteins of zonular junctions (zonulae occludentes and adhaerentes) and the control of cytoskeletal organization and signaling through Rho GTPases, transcription factors, and their effectors. Show less