TGF-β signaling regulates epithelial permeability in Drosophila ovaries by modulating adhesion independent of actomyosin contractility

Epithelial morphogenesis and homeostasis rely on dynamic remodeling of cell-cell junctions. Tricellular junctions (TCJs) at cell vertices are key sites that control epithelial permeability and plasticity, yet how TCJs are remodeled remains unclear. In the follicular epithelium (FE) in Drosophila ovaries, TCJs open transiently in a process called patency to allow passage of yolk proteins for uptake by the oocyte. We investigated how a gradient of TGF-β signaling activity suppresses patency in a graded manner across the FE. We show that TGF-β signaling blocks patency in a cell-autonomous manner by strengthening E-Cadherin (E-Cad)-based adhesion through inducing E-Cad transcription and preventing its removal from cell vertices. In parallel, TGF-β signaling activates myosin II through Rho-Rok signaling. However, myosin II activity is dispensable for TGF-β-mediated suppression of patency. We show that TGF-β signaling controls TCJ remodeling in follicle cells primarily by reinforcing E-Cad-based adhesion, in part through upregulating p120-catenin. Our findings disentangle the roles of adhesion and actomyosin contractility in maintaining TCJ integrity and reveal how a tissue-scale morphogen gradient is translated into graded epithelial permeability.