In epithelial tissues, the polarisation of cells within the plane of the tissue helps to coordinate morphogenesis. The Dachsous (Ds) and Frizzled (Fz) signalling systems play key roles in establishing and maintaining this planar polarity but how these systems interact is unclear. Now, on p. , Seth Donoughe and Stephen DiNardo report that the ds and fz genes contribute separately to planar polarity in the Drosophila ventral epidermis. The cuticle of fly larvae is covered with denticles, protrusions that help the larvae move. To investigate how this polarised pattern of denticles is established, the researchers developed a semi-automated method that measures the orientation of individual denticles in the ventral epidermis. Their analyses of various mutants show that ds and fz contribute independently to polarity, that they act over spatially distinct domains, and that the Ds but not the Fz system polarises tissue equally well across small and large field sizes. These and other results provide new insights into the planar polarity machinery.
