Experimental and Theoretical Evidence for Bidirectional Signalling via Core Planar Polarity Protein Complexes in Drosophila

Summary In developing tissues, sheets of cells become planar polarised, enabling coordination of cell behaviours. It has been suggested that ‘signalling’ of polarity information between cells may occur either bidirectionally or monodirectionally between the molecules Frizzled (Fz) and Van Gogh (Vang). Using computational modelling we find that both bidirectional and monodirectional signalling models reproduce known non-autonomous phenotypes derived from patches of mutant tissue of key molecules, but predict different phenotypes from double mutant tissue, which have previously given conflicting experimental results. Furthermore, we re-examine experimental phenotypes in the Drosophila wing, concluding that signalling is most likely bidirectional. Our modelling suggests that bidirectional signalling can be mediated either indirectly via bidirectional feedbacks between asymmetric intercellular protein complexes, or directly via different affinities for protein binding in intercellular complexes, suggesting future avenues for investigation. Our findings offer insight into mechanisms of juxtacrine cell signalling and how tissue-scale properties emerge from individual cell behaviours.