(A) Schematic of localisation of core planar polarity pathway protein complexes in cells of the Drosophila pupal wing. Proximal localisation of Stbm (orange) and distal localisation of Fz (green) at apicolateral cell junctions leads to trichome (grey) emergence from distal cell edges. (B and C) Evolution of symmetry breaking cluster formation. (B) Fmi homodimers are stabilised by Fz localisation on one side of the complex at junctions between neighbouring cells. (C) Stbm localises to the apposing cell edge and the cytoplasmic proteins Pk, Dsh and Dgo localise proximally and distally in the complex as shown. (D) Image of dorsal surface of a wild-type Drosophila wing, showing uniform distal orientation of trichomes. Proximal is left, and anterior is up. (E) Image of dorsal surface of wing from a pkpk-sple13 mutant fly, showing a swirled trichome pattern. (F) Confocal microscope image of Drosophila pupal wing epithelium, immunolabelled for Fmi (green, localised preferentially to proximodistal cell boundaries) and showing actin-rich trichomes (red, emerging from distal cell edges). (G and H) Confocal microscope image of a Drosophila pupal wing epithelium genetically mosaic for dshV26 mutant tissue, marked by loss of blue β-gal immunolabelling and outlined in white (G). Fmi (green) and Stbm (red, or white in H) are asymmetrically localised at proximodistal cell boundaries at the apicolateral cell junctions (left and right cell edges) in wild-type tissue, but lose this asymmetric localisation in mutant tissue. This shows that Dsh activity is required for planar polarisation of core pathway components such as Fmi and Stbm. (I–K) Molecularly asymmetric complexes (I) are sorted by feedback interactions (J) so that they all align in the same orientation (K). Complexes of opposite orientation are destabilised (red inhibitory symbols) and complexes of the same orientation are stabilised (black arrows).