Complex networks orchestrate epithelial–mesenchymal transitions

Abstract
Epithelial–mesenchymal transition (EMT) is an essential process during morphogenesis. Dissecting the signalling strategies that orchestrate EMT have shown that a complex signalling network, which controls adhesion, motility, survival and differentiation, also regulates the initiation and execution of EMT during embryonic development. Epithelial–mesenchymal transition is an indispensable mechanism during morphogenesis, as without mesenchymal cells, tissues and organs will never be formed. However, epithelial-cell plasticity, coupled to the transient or permanent formation of mesenchyme, goes far beyond the problem of cell-lineage segregation. Understanding how mesenchymal cells arise from an epithelial default status will also have a strong impact in unravelling the mechanisms that control fibrosis and cancer progression.