Notch signalling regulates a diverse array of cell fate decisions in multiple tissues during both development and homeostasis, including lineage commitment, differentiation, cell cycle progression, and maintenance and self-renewal of stem cells. The canonical Notch cascade operates in a cell–cell contact-dependent manner, and is initiated when ligands expressed by a signal-sending cell ligate receptors expressed on a signal-receiving cell. In mammals, there are four Notch receptors (NOTCH1, NOTCH2, NOTCH3 and NOTCH4 (NOTCH1–4)) and five ligands of the Delta–Serrate–Lag (DSL) family (jagged 1 (JAG1), JAG2, delta-like 1 (DLL1), DLL3 and DLL4). Structurally, the Notch receptors are single-pass transmembrane heterodimers consisting of an extracellular ligand-binding domain and an intracellular domain comprising a transmembrane region and an intracellular portion that mediates signalling upon receptor ligation. Notch receptors contains multiple epidermal growth factor (EGF)-like repeats, which are important for ligand binding, as well as a negative regulatory region (NRR) that contains a smaller number of LIN12-NOTCH repeats and the heterodimerization domain. 
The NRR ensures that Notch signalling is inactive in the absence of interactions with DSL ligands1.  The NRR prevents ligand-independent Notch activity. Before transport to the cell surface an S1 cleavage mediated by furin-like convertase occurs in the Golgi within the HDD, which is thought to be important for the generation of the mature receptor, although the precise function is unclear. The intracellular domain contains the recombining binding protein suppressor of hairless (RBPJ) association molecule (RAM), ankyrin repeats (ANK) that contain nuclear localization signals (NLSs) in NOTCH1–3 (the NLS domain in NOTCH4 is not well defined), a transactivation domain (TAD) and a polypeptide enriched in proline, glutamate, serine and threonine (PEST) sequence important for degradation of the receptor.  Interaction between NOTCH1–4 and ligand jagged1 (JAG1), JAG2 or delta-like 1 (DLL1), DLL3 or DLL4 results in an S2 cleavage in the extracellular portion close to the transmembrane domain mediated by disintegrin and metalloproteinase domain-containing protein (ADAM) metalloproteinases. This removes the ligand binding domain, leaving the intracellular portion anchored to the plasma membrane. Subsequently, an S3 cleavage in the transmembrane domain mediated by the γ?secretase complex liberates the intracellular.


1.Nowell CS, Radtke F. Nat Rev Cancer. 2017;17(3):145–159.