The Wnt's Tale

Wnt signaling represents one of the major intercellular signaling pathways during animal development. This chapter discusses the evolutionary diversification of canonical Wnt pathway in metazoans. It focuses on the complexity and the specific features of canonical Wnt signaling activities and of the Wnt and Fzd repertoires during early metazoan development. This analysis is presented from an atypical perspective, that is, starting from knowledge related to human, mouse, and chick and tracing it back up to prebilaterian animals such as cnidarians and sponges. The chapter compares the developmental functions of nuclear β-catenin in these several animal phyla in order to extract an essence of the basis of this pathway from an evolutionary point of view. Finally, it analyzes the composition of the Wnt and Fzd inventories in several metazoans to presume the complexity changes of these genes repertoires across animal evolution.