Limb and fin morphogenesis start with the formation of the apical ectodermal ridge (AER), an epithelial signalling centre that coordinates appendage development. Wnt signalling is required for AER induction and several extracellular matrix (ECM) components are necessary for proper limb formation. Mahendra Sonawane and colleagues (p. 320) set out to explore the mechanisms regulating ECM synthesis and the role of Wnt signalling during appendage development – using the zebrafish median fin as a model. They observe that cell morphology in the distal part of the AER is distinct from the rest of the appendage epithelium, and that these differences in morphology correlate with a gradient of Wnt. Mechanistically, canonical Wnt signalling modulates cell shape with spatiotemporal precision by regulating the expression of the ECM component laminin α5, which signals via integrin α3 to influence cell morphology. Finally, the authors show that those mechanisms are conserved in the pectoral fin. This study uncovers a novel mechanism in which canonical Wnt signalling controls laminin synthesis to regulate epithelial cell shapes and tissue morphology during vertebrate appendage development.