Apical-basal polarity regulates Collagen IV-dependent cell-cell adhesion in the Drosophila adipose tissue

E-Cadherin-based adherens junctions are the main type of junctional compartment in epithelia mediating cell-cell adhesion. The apical-basal cell polarity machinery positions adherens junctions at the apical-lateral border. The Drosophila adipose tissue, called the fat body, forms a monolayer in which cells adhere to each other through the binding of Integrin to pericellular Collagen IV concentrations. It is currently not known, how these atypical adhesion complexes form. Here we examine the epithelial apical-basal cell polarity network in the larval fat body. We find that this tissue displays an apical-basal cell polarity, with the apical proteins aPKC, Crumbs and Par-6 and the basolateral proteins Lgl and Dlg on opposite sides. Crumbs, aPKC, Scribble, and Lgl knockdown in the fat body leads to cell-cell-adhesion defects. We find that aPKC plays a key role in mediating cell-cell adhesion by regulating the formation of Collagen IV-Intercellular-Adhesion-Concentrations. We further show that during fat body remodeling, the steroid hormone Ecdysone regulates the loss of apical-basal polarity and Collagen IV-Intercellular-Adhesion-Concentrations to induce cell-cell dissociation and initiation of amoeboid swimming cell migration. Our work hence uncovers a novel role for the apical-basal polarity machinery in the Drosophila adipose tissue in regulating cell-cell adhesion via Collagen IV-Intercellular-Adhesion-Concentrations.