Notch 

Notch signaling is evolutionarily conserved and operates in many cell types and at various stages during development. Notch signaling occurs via cell-cell communication, where transmembrane ligands on one cell activate transmembrane receptors on a juxtaposed cell.

Regulation of Notch signaling is critical to development and maintenance of most eukaryotic organisms. The Notch receptors (NOTCH1, 2, 3, and 4) and ligands (DLL1, 3, and 4, JAG1 and 2) are integral membrane proteins and direct cell-cell interactions are needed to activate signaling. Ligand-expressing cells activate Notch signaling through an unusual mechanism involving Notch proteolysis to release the intracellular domain from the membrane, allowing the Notch receptor to function directly as the downstream signal transducer.