When pathways collide: collaboration and connivance among signalling proteins in development.

Signal transduction pathways interact at various levels to define tissue morphology, size and differentiation during development. Understanding the mechanisms by which these pathways collude has been greatly enhanced by recent insights into how shared components are independently regulated and how the activity of one system is contextualized by others. Traditionally, it has been assumed that the components of signalling pathways show pathway fidelity and act with a high degree of autonomy. However, as illustrated by the Wnt and Hippo pathways, there is increasing evidence that components are often shared between multiple pathways and other components talk to each other through multiple mechanisms.