TGF-β signaling modulates adhesion and actomyosin contractility to pattern epithelial permeability in Drosophila ovaries.

Epithelial morphogenesis and homeostasis depend on dynamic remodeling of cell-cell junctions. Tricellular junctions (TCJs) control epithelial permeability and plasticity, yet how TCJs are remodeled remains unclear. In the Drosophila ovarian follicular epithelium, TCJs open transiently in a process called patency to allow passage of yolk proteins for uptake by the oocyte. Here we investigated how a TGF-β signaling gradient represses patency along the follicular epithelium. We show that TGF-β signaling blocks patency cell-autonomously by strengthening E-Cadherin (E-Cad)-based adhesion through inducing E-Cad transcription and preventing E-Cad removal from vertices. Elevated E-Cad levels alone are not sufficient to block patency, implying that additional TGF-β-dependent mechanisms stabilize E-Cad at vertices. We identify p120-catenin upregulation as a mechanism that may contribute to strengthened adhesion. In parallel, TGF-β signaling activates myosin II through Rho-Rok signaling. However, myosin II activity is dispensable for TGF-β-mediated patency suppression. Thus, our findings suggest that TGF-β signaling controls TCJ remodeling in follicle cells primarily by reinforcing E-Cad-based adhesion, disentangling the roles of adhesion and actomyosin contractility in maintaining TCJ integrity and revealing how a morphogen gradient spatially patterns epithelial permeability.