Notch (LNR) domain | |||||||||
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Identifiers | |||||||||
Symbol | Notch | ||||||||
Pfam | PF00066 | ||||||||
InterPro | IPR000800 | ||||||||
SMART | SM00004 | ||||||||
PROSITE | PS50258 | ||||||||
OPM superfamily | 462 | ||||||||
OPM protein | 5kzo | ||||||||
Membranome | 19 | ||||||||
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Notch proteins are a family of type 1 transmembrane proteins that form a core component of the Notch signaling pathway, which is highly conserved in animals. The Notch extracellular domain mediates interactions with DSL family ligands, allowing it to participate in juxtacrine signaling. The Notch intracellular domain acts as a transcriptional activator when in complex with CSL family transcription factors. Members of this type 1 transmembrane protein family share several core structures, including an extracellular domain consisting of multiple epidermal growth factor (EGF)-like repeats and an intracellular domain transcriptional activation domain (TAD). Notch family members operate in a variety of different tissues and play a role in a variety of developmental processes by controlling cell fate decisions. Much of what is known about Notch function comes from studies done in Caenorhabditis elegans (C.elegans) and Drosophila melanogaster. Human homologs have also been identified, but details of Notch function and interactions with its ligands are not well known in this context.
Notch was discovered in a mutant Drosophila in March 1913 in the lab of Thomas Hunt Morgan. [2] This mutant emerged after several generations of crossing out and back-crossing beaded winged flies with wild type flies and was first characterized by John S. Dexter. [3] The most frequently observed phenotype in Notch mutant flies is the appearance of a concave serration at the most distal end of the wings, for which the gene is named, accompanied by the absence of marginal bristles. [4] [5] This mutant was found to be a sex-linked dominant on the X chromosome that could only be observed in heterozygous females as it was lethal in males and homozygous females. [2] The first Notch allele was established in 1917 by C.W. Metz and C.B. Bridges. [6] In the late 1930s, studies of fly embryogenesis done by Donald F. Poulson provided the first indication of Notch's role in development. [7] Notch-8 mutant males exhibited a lack of the inner germ layers, the endoderm and mesoderm, that resulted in failure to undergo later morphogenesis embryonic lethality. Later studies in early Drosophila neurogenesis provided some of the first indications of Notch's roll in cell-cell signaling, as the nervous system in Notch mutants was developed by sacrificing hypodermal cells. [8]
Starting in the 1980s researchers began to gain further insights into Notch function through genetic and molecular experiments. Genetic screens conducted in Drosophila led to the identification of several proteins that play a central role in Notch signaling, including Enhancer of split, [8] Master mind, Delta, [9] Suppressor of Hairless (CSL), [10] and Serrate. [11] At the same time, the Notch gene was successfully sequenced [12] [13] and cloned, [14] [15] providing insights into the molecular architecture of Notch proteins and led to identification of Notch homologs in Caenorhabditis elegans (C. elegans) [16] [17] [18] and eventually in mammals.
In the early 1990s Notch was increasingly implicated as the receptor of a previously unknown intercellular signal pathway [19] [20] in which the Notch intercellular domain (NICD) is transported to the nucleus where it acts as a transcription factor to directly regulate target genes. [21] [22] [23] The release of the NICD was found to be as a result of proteolytic cleavage of the transmembrane protein through the actions of the γ-secretase complex catalytic subunit Presenilin. This was a significant interaction as Presenilin is implicated in the development of Alzheimer's disease. [24] This and further research into the mechanism of Notch signaling led to research that would further connect Notch to a wide range of human diseases.
Drosophila contain a single Notch protein, C. elegans contain two redundant notch paralogs, Lin-12 [25] and GLP-1, [18] [26] and humans have four Notch variants, Notch 1-4. Although variations exist between homologs, there are a set of highly conserved structures found in all Notch family proteins. The protein can broadly be split into the Notch extracellular domain (NECD) and Notch intracellular domain (NICD) joined together by a single-pass transmembrane domain (TM).
The NECD contains 36 EGF repeats in Drosophila, [13] 28-36 in humans, and 13 and 10 in C. elegans Lin-12 and GLP-1 respectively. [27] These repeats are heavily modified through O-glycoslyation [28] and the addition of specific O-linked glycans has been shown to be necessary for proper function. The EGF repeats are followed by three cysteine-rich Lin-12/Notch Repeats (LNR) and a heterodimerization (HD) domain. Together the LNR and HD compose the negative regulatory region adjacent to the cell membrane and help prevent signaling in the absence of ligand binding.
NICD acts as a transcription factor that is released after ligand binding triggers its cleavage. It contains a nuclear localization sequence (NLS) that mediates its translocation to the nucleus, where it forms a transcriptional complex along with several other transcription factors. Once in the nucleus, several ankyrin repeats and the RAM domain interactions between the NICD and CSL proteins to form a transcriptional activation complex. [29] In humans, an additional PEST domain plays a role in NICD degradation. [30]
Notch family members play a role in a variety of developmental processes by controlling cell fate decisions. The Notch signaling network is an evolutionarily conserved intercellular signaling pathway that regulates interactions between physically adjacent cells. In Drosophila, notch interaction with its cell-bound ligands (delta, serrate) establishes an intercellular signaling pathway that plays a key role in development. This protein functions as a receptor for membrane bound ligands, and may play multiple roles during development. [31] A deficiency can be associated with bicuspid aortic valve. [32]
There is evidence that activated Notch 1 and Notch 3 promote differentiation of progenitor cells into astroglia. [33] Notch 1, then activated before birth, induces radial glia differentiation, [34] but postnatally induces the differentiation into astrocytes. [35] One study shows that Notch-1 cascade is activated by Reelin in an unidentified way. [36] Reelin and Notch1 cooperate in the development of the dentate gyrus, according to another. [37]
Jagged/Serrate protein | |||||||||
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Identifiers | |||||||||
Symbol | DSL | ||||||||
Pfam | PF01414 | ||||||||
InterPro | IPR026219 | ||||||||
Membranome | 76 | ||||||||
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Notch signaling is triggered via direct cell-to-cell contact, mediated by interactions between the Notch receptor protein in the signal receiving cell and a ligand in an adjacent signal transmitting cell. These type 1 single-pass transmembrane proteins fall into the Delta/Serrate/Lag-2 (DSL) family of proteins which is named after the three canonical Notch ligands. [19] Delta and Serrate are found in Drosophila while Lag-2 is found in C. elegans. Humans contain 3 Delta homologs, Delta-like 1, 3, and 4, as well as two Serrate homologs, Jagged 1 and 2. Notch proteins consist of a relatively short intracellular domain and a large extracellular domain with one or more EGF motifs and a N-terminal DSL-binding motif. EGF repeats 11-12 on the Notch extracellular domain have been shown to be necessary and sufficient for trans signaling interactions between Notch and its ligands. [38] Additionally, EGF repeats 24-29 have been implicated in inhibition of cis interactions between Notch and ligands co-expressed in the same cell. [39]
In order for a signaling event to occur, the Notch protein must be cleaved at several sites. In humans, Notch is first cleaved in the NRR domain by furin while being processed in the trans-Golgi network before being presented on the cell surface as a heterodimer. [40] [41] Drosophila Notch does not require this cleavage for signaling to occur, [42] and there is some evidence that suggests that LIN-12 and GLP-1 are cleaved at this site in C. elegans.
Release of the NICD is achieved after an additional two cleavage events to Notch. Binding of Notch to a DSL ligand results in a conformational change that exposes a cleavage site in the NECD. Enzymatic proteolysis at this site is carried out by a A Disintegrin and Metalloprotease domain (ADAM) family protease. This protein is called Kuzbanian in Drosophila, [43] [44] sup-17 in C. elegans, [45] and ADAM10 in humans. [46] [47] After proteolytic cleavage, the released NECD is endocytosed into the signal transmitting cell, leaving behind only a small extracellular portion of Notch. This truncated Notch protein can then be recognized by a γ-secretase that cleaves the third site found in the TM domain. [48]
Notch-2 (Neurogenic locus notch homolog protein 2) is a protein that in humans is encoded by the NOTCH2 gene. [49]
NOTCH2 is associated with Alagille syndrome [50] and Hajdu–Cheney syndrome. [51]
The Notch signaling pathway is a highly conserved cell signaling system present in most animals. Mammals possess four different notch receptors, referred to as NOTCH1, NOTCH2, NOTCH3, and NOTCH4. The notch receptor is a single-pass transmembrane receptor protein. It is a hetero-oligomer composed of a large extracellular portion, which associates in a calcium-dependent, non-covalent interaction with a smaller piece of the notch protein composed of a short extracellular region, a single transmembrane-pass, and a small intracellular region.
Teneurins are a family of phylogenetically conserved single-pass transmembrane glycoproteins expressed during pattern formation and morphogenesis. The name refers to "ten-a" and "neurons", the primary site of teneurin expression. Ten-m refers to tenascin-like protein major.
Neurogenic locus notch homolog protein 3(Notch 3) is a protein that in humans is encoded by the NOTCH3 gene.
Argos is a secreted protein that is an inhibitor of the epidermal growth factor receptor (EGFR) pathway in Drosophila melanogaster. Argos inhibits the EGFR pathway by sequestering the EGFR ligand Spitz. Argos binds the epidermal growth factor domain of Spitz, preventing interaction between Spitz and EGFR. Argos does not directly interact with EGFR. Argos represents the first example of ligand sequestration as a mechanism of inhibition in the ErbB (EGFR) family.
In molecular biology, heat shock factors (HSF), are the transcription factors that regulate the expression of the heat shock proteins. A typical example is the heat shock factor of Drosophila melanogaster.
Jagged1 (JAG1) is one of five cell surface proteins (ligands) that interact with four receptors in the mammalian Notch signaling pathway. The Notch Signaling Pathway is a highly conserved pathway that functions to establish and regulate cell fate decisions in many organ systems. Once the JAG1-NOTCH (receptor-ligand) interactions take place, a cascade of proteolytic cleavages is triggered resulting in activation of the transcription for downstream target genes. Located on human chromosome 20, the JAG1 gene is expressed in multiple organ systems in the body and causes the autosomal dominant disorder Alagille syndrome (ALGS) resulting from loss of function mutations within the gene. JAG1 has also been designated as CD339.
Faint little ball (flb) is a Drosophila gene that encodes the Drosophila epidermal growth factor receptor (DER) homolog. The gene is also called torpedo and Ellipse. The gene is located at 3-26 of the Drosophila melanogaster genome. It is named faint little ball because when the gene is mutated the embryo forms a ball of dorsal hypoderm. flb is necessary for several processes to occur during embryonic development, specifically in central nervous system development. It is expressed as quickly as 4 hours after fertilization of the egg. The peak of expression of the flb gene is between 4–8 hours into development. In all processes that are facilitated by flb the same signal transduction pathway is used. Drosophila EGF receptor is involved in the development of embryos as well as larvae/pupae's wings, eyes, legs and ovaries.
Presenilin-1(PS-1) is a presenilin protein that in humans is encoded by the PSEN1 gene. Presenilin-1 is one of the four core proteins in the gamma secretase complex, which is considered to play an important role in generation of amyloid beta (Aβ) from amyloid-beta precursor protein (APP). Accumulation of amyloid beta is associated with the onset of Alzheimer's disease.
Neurogenic locus notch homolog protein 1(Notch 1) is a protein encoded in humans by the NOTCH1 gene. Notch 1 is a single-pass transmembrane receptor.
Neurogenic locus notch homolog 4(Notch 4) is a protein that in humans is encoded by the NOTCH4 gene located on chromosome 6.
Neurogenic locus notch homolog protein 2 is a protein that in humans is encoded by the NOTCH2 gene.
Protein numb homolog is a protein that in humans is encoded by the NUMB gene. The protein encoded by this gene plays a role in the determination of cell fates during development. The encoded protein, whose degradation is induced in a proteasome-dependent manner by MDM2, is a membrane-bound protein that has been shown to associate with EPS15, LNX1, and NOTCH1. Four transcript variants encoding different isoforms have been found for this gene.
Delta-like protein 1 is a protein that in humans is encoded by the DLL1 gene.
Jagged-2 is a protein that in humans is encoded by the JAG2 gene.
Delta-like 4 is a protein that in humans is encoded by the DLL4 gene.
Protein deltex-1 is a protein that in humans is encoded by the DTX1 gene.
A polyglutamine tract or polyQ tract is a portion of a protein consisting of a sequence of several glutamine units. A tract typically consists of about 10 to a few hundred such units.
Slit-Robo is the name of a cell signaling protein complex with many diverse functions including axon guidance and angiogenesis.
Hugo J. Bellen is a professor at Baylor College of Medicine and an investigator emeritus at the Howard Hughes Medical Institute who studies genetics and neurobiology in the model organism, Drosophila melanogaster, the fruit fly.
Iva Susan Greenwald is an American biologist who is Professor of Cell and Molecular Biology at Columbia University. She studies cell-cell interactions and cell fate specification in C. elegans. She is particularly interested in LIN-12/Notch proteins, which is the receptor of one of the major signalling systems that determines the fate of cells.