Proteolysis and developmental signal transduction.

Regulated proteolysis is a critical feature of many intercellular signalling pathways that control cell-fate specification and tissue patterning during metazoan development. The roles of proteolysis in three different pathways, the Toll, Hedgehog, and Notch pathways, are described to illustrate the importance of specific protein cleavages in both extracellular ligand-receptor interactions and intracellular signal transduction. An emerging principle is the use of proteolysis to control the maturation and activation of receptors, to limit the spatial diffusion of their ligands, and to modulate the subcellular localization or transcriptional activity of DNA-binding factors in response to receptor-ligand interactions at the cell surface.