Transient opening of tricellular vertices controls paracellular transport through the follicle epithelium during Drosophila oogenesis

Paracellular permeability is regulated to allow solute transport or migration of cells across epithelial or endothelial barriers. However, how occluding junction dynamics controls paracellular permeability is poorly understood. Here we describe patency, a developmentally regulated process in Drosophila oogenesis, during which cell vertices in the follicle epithelium open transiently to allow paracellular transport of yolk proteins for uptake by the oocyte. We show that the sequential removal of E-Cadherin, N-Cadherin, NCAM/Fasciclin-2 and Sidekick from vertices precedes their basal-to-apical opening, while the subsequent assembly of tricellular occluding junctions terminates patency and seals the paracellular barrier. E-Cadherin-based adhesion is required to limit paracellular channel size, whereas stabilized adherens junctions, prolonged NCAM/Fasciclin-2 expression, impeded endocytosis, or increased actomyosin contractility prevent patency. Our findings reveal a key role of cell vertices as gateways controlling paracellular transport, and demonstrate that the dynamic regulation of adhesion and actomyosin contractility at vertices governs epithelial barrier properties.