ZO-1 Guides Tight Junction Assembly and Epithelial Morphogenesis via Cytoskeletal Tension-Dependent and -Independent Functions

Abstract

Formation and maintenance of tissue barriers require the coordination of cell mechanics and cell–cell junction assembly. Here, we combined methods to modulate ECM stiffness and to measure mechanical forces on adhesion complexes to investigate how tight junctions regulate cell mechanics and epithelial morphogenesis. We found that depletion of the tight junction adaptor ZO-1 disrupted junction assembly and morphogenesis in an ECM stiffness-dependent manner and led to a stiffness-dependant reorganisation of active myosin. Both junction formation and morphogenesis were rescued by inhibition of actomyosin contractility. ZO-1 depletion also impacted mechanical tension at cell-matrix and E-cadherin-based cell–cell adhesions. The effect on E-cadherin also depended on ECM stiffness and correlated with effects of ECM stiffness on actin cytoskeleton organisation. However, ZO-1 knockout also revealed tension-independent functions of ZO-1. ZO-1-deficient cells could assemble functional barriers at low tension, but their tight junctions remained corrupted with strongly reduced and discontinuous recruitment of junctional components. Our results thus reveal that reciprocal regulation between ZO-1 and cell mechanics controls tight junction assembly and epithelial morphogenesis, and that, in a second, tension-independent step, ZO-1 is required to assemble morphologically and structurally fully assembled and functionally normal tight junctions.

Cellular segregation in co-cultures driven by differential adhesion and contractility on distinct time scales

“…(45, 46) Note, in our study, adhesion differences were induced by tight junction disruption, which was also shown by previous work to decrease adhesion, in agreement with our data. (30, 47) Purely adhesionbased sorting was recently confirmed via simulations and experiments in direct relation to constant contractility. (18) On the other hand, differential contractility was found to aid sorting in an embryo and possibly dominate over adhesion.…”

“…(59) Nevertheless, in agreement with other work, it is reasonable to assume that the loss of tight junction integrity reduces intercellular adhesion on all relevant timescales. (30, 47) While ZO proteins do not directly bind to the other cell, their loss destabilizes the contact zone and influences the transmembrane proteins. (30, 60)…”

“…(30, 47) While ZO proteins do not directly bind to the other cell, their loss destabilizes the contact zone and influences the transmembrane proteins. (30, 60)…”

“…(59) Nevertheless, in agreement with other work, it is reasonable to assume that the loss of tight junction integrity reduces intercellular adhesion on all relevant timescales. (30,47) While ZO proteins do not directly bind to the other cell, their loss destabilizes the contact zone and influences the transmembrane proteins. (30,60) In general, the presented model system has the advantage of great experimental accessibility compared with in vivo experiments but lacks some physiological conditions, e.g., properties of the substrate.…”

“…(30,47) While ZO proteins do not directly bind to the other cell, their loss destabilizes the contact zone and influences the transmembrane proteins. (30,60) In general, the presented model system has the advantage of great experimental accessibility compared with in vivo experiments but lacks some physiological conditions, e.g., properties of the substrate. While the cell-substrate adhesion might be different, it is well suited to capture the general physics of cell-cell interactions that also governs sorting in vivo.…”