Neurogenic locus Notch 4 <p> Notch cell surface receptors are large, single-pass type-1 transmembrane proteins found in a diverse range of metazoan species, from human to Caenorhabditis species. The fruit fly, Drosophila melanogaster, possesses only one Notch protein, whereas in C.elegans, two receptors have been found; by contrast, four Notch paralogues (designated N1-4) have been identified in mammals, playing both unique and redundant roles. </p> <p> The hetero-oligomer Notch comprises a large extracellular domain (ECD), containing 10-36 tandem Epidermal Growth Factor (EFG)-like repeats, which are involved in ligand interactions; a negative regulatory region, including three cysteine-rich Lin12-Notch Repeats (LNR); a single trans-membrane domain (TM); a small intracellular domain (ICD), which includes a RAM (RBPjk-association module) domain; six ankyrin repeats (ANK), which are involved in protein-protein interactions; and a PEST domain. Drosophila Notch also contains an OPA domain [<cite idref="PUB00053622"/>]. </p> <p> Notch signalling is an evolutionarily conserved pathway involved in a wide variety of developmental processes, including adult homeostasis and stem cell maintenance, cell proliferation and apoptosis [<cite idref="PUB00013432"/>]. Notch is activated by a range of ligands -the so-called DSL ligands (Delta/Seratte/LAG-2). Activation is also mediated by a sequence of proteolytic events: ligand binding leads to cleavage of Notch by ADAM proteases [<cite idref="PUB00053623"/>] at site 2 (S2) and presenilin-1/g-secretase at sites 3 (S3)and 4 (S4) [<cite idref="PUB00053638"/>].The last cleavage releases the Notch intracellular part of the protein (NICD) from the membrane and, upon release, the NICD translocates to the nucleus where it associates with a CBF1/RBJk/Su(H)/Lag1 (CSL) family of DNA-binding proteins. The subsequent recruitment of a co-activator mastermind like (MAML1) protein [<cite idref="PUB00053624"/>] promotes transcriptional activation of Notch target genes: well established Notch targets are the Hes and Hey gene families. </p><p> Aberrant Notch function and signalling has been associated with a number of human disorders, including Allagile syndrome, spondylocostal dysostosis, aortic valve disease, CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy), and T-cell Acute Lympho-blastic Leukemia (T-ALL); it has also been implicated in various human carcinomas [<cite idref="PUB00053625"/>, <cite idref="PUB00053626"/>]. </p> <p> Notch 4 is selectively expressed in vascular endothelium, and regulates vascular remodelling [<cite idref="PUB00053661"/>]. </p>