Armadillo/beta-catenin-dependent Wnt signalling is required for the polarisation of epidermal cells during dorsal closure in Drosophila

At the end of germband retraction, the dorsal epidermis of the Drosophila embryo exhibits a discontinuity that is covered by the amnioserosa. The process of dorsal closure (DC) involves a coordinated set of cell-shape changes within the epidermis and the amnioserosa that result in epidermal continuity. Polarisation of the dorsal-most epidermal (DME) cells in the plane of the epithelium is an important aspect of DC. The DME cells of embryos mutant for wingless or dishevelled exhibit polarisation defects and fail to close properly. We have investigated the role of the Wingless signalling pathway in the polarisation of the DME cells and DC. We find that the beta-catenin-dependent Wingless signalling pathway is required for polarisation of the DME cells. We further show that although the DME cells are polarised in the plane of the epithelium and present polarised localisation of proteins associated with the process of planar cell polarity (PCP) in the wing, e.g. Flamingo, PCP Wingless signalling is not involved in DC.