Polarity systems and the fat body. (A) Classical polarised cells: epithelial cells (apicobasal polarity), migrating cells (front-rear polarity) and neurons (dendrite-versus-axon polarity). (B) In a classical epithelial cell polarity and adhesion complexes define and maintain the polarity: Crumbs/aPKC/Par-6 at the apical side, E-Cadherin/Par-3 at the adherens junctions and Scribble/Dlg/Lgl the lateral side, with integrins and dystroglycans mediating adhesion to the extracellular matrix (ECM) at the lateral side. (C) The Drosophila larval fat body, as the equivalent of vertebrate adipocytes, comprises two single-layered sheets of cells surrounded by ECM sandwiched between body wall muscles and internal gastrointestinal organs. (D) In Drosophila larval fat body cells all complexes are localised to equivalent positions in an apical-like and basal-like region of the cells with two differences: cell–cell adhesion is mainly mediated via so-called CIVICs (collagen IV-intercellular concentrations). with only a small contribution from E-Cadherin, and the sheet of cells is surrounded by ECM, but with differing composition between apical-like and basal-like domains. (E) As in epithelial cells, Crumbs, aPKC, Scribble and Lgl a key to the assembly and maintenance of cell–cell adhesion in the larval fat body. The developmental disassembly of the fat body into individual cells at the beginning of pupal stages is triggered by ecdysone signalling leading to downregulation of polarity factors leading to loss of cell–cell adhesion via CIVICs.