The canonical Wnt/beta-catenin signalling pathway.

Embryonic development of multicellular organisms is an incredibly complex process that relies heavily on evolutionarily conserved signalling pathways to provide crucial cell-cell communication. Typically, secreted signalling proteins such as Wnts, BMPs, and Hedgehogs released by one cell population will trigger concentration-dependent responses in other cells located some distance away. In adults, the same signalling pathways orchestrate tissue renewal in organs such as the intestine and skin, and direct tissue regeneration in many organs following injury. Strict regulation of these signalling pathways is critical, with insufficient or excess activity having catastrophic consequences including severe developmental defects or, later in life, cancer. This chapter deals with the beta-catenin-dependent branch of Wnt signalling (also referred to the canonical pathway).