Strabismus is asymmetrically localised and binds to Prickle and Dishevelled duringDrosophilaplanar polarity patterning

Planar polarity decisions in the wing of Drosophila involve the assembly of asymmetric protein complexes containing the conserved receptor Frizzled. In this study, we analyse the role of the Van Gogh/strabismus gene in the formation of these complexes and cell polarisation. We find that the Strabismus protein becomes asymmetrically localised to the proximal edge of cells. In the absence of strabismus activity, the planar polarity proteins Dishevelled and Prickle are mislocalised in the cell. We show that Strabismus binds directly to Dishevelled and Prickle and is able to recruit them to membranes. Furthermore, we demonstrate that the putative PDZ-binding motif at the C terminus of Strabismus is not required for its function. We propose a two-step model for assembly of Frizzledcontaining asymmetric protein complexes at cell boundaries. First, Strabismus acts together with Frizzled and the atypical cadherin Flamingo to mediate apicolateral recruitment of planar polarity proteins including Dishevelled and Prickle. In the second phase, Dishevelled and Prickle are required for these proteins to become asymmetrically distributed on the proximodistal axis.