Abstract

The Wnt family of secreted ligands act through many receptors to stimulate distinct intracellular signalling pathways in embryonic development, in adults and in disease processes. Binding of Wnt to the Frizzled family of receptors and to low density lipoprotein receptor-related protein 5 (LRP5) or LRP6 co-receptors stimulates the intracellular Wnt–β-catenin signalling pathway, which regulates β-catenin stability and context-dependent transcription. This signalling pathway controls many processes, such as cell fate determination, cell proliferation and self-renewal of stem and progenitor cells. Intriguingly, the transmembrane receptor Tyr kinases Ror2 and Ryk, as well as Frizzled receptors that act independently of LRP5 or LRP6, function as receptors for Wnt and activate β-catenin-independent pathways. This leads to changes in cell movement and polarity and to the antagonism of the β-catenin pathway.