Ligands of the Delta/Serrate/lag-2 (DSL) family and their receptors, members of the lin-12/Notch family, mediate cell-cell interactions that specify cell fate in invertebrates and vertebrates. In Caenorhabditis elegans, two DSL genes, lag-2 and apx-1, influence different cell fate decisions during development [ (PUBMED:8575327) ]. Molecular interaction between Notch and Serrate, another EGF-homologous transmembrane protein containing a region of striking similarity to Delta, has been shown and the same two EGF repeats of Notch may also constitute a Serrate binding domain [ (PUBMED:1657403) (PUBMED:7716513) ].
The LIN-12/Notch signaling pathway and its regulation.
Annu Rev Cell Dev Biol. 1997; 13: 333-61
Display abstract
Notch, LIN-12, and GLP-1 are receptors that mediate a broad range of cell interactions during Drosophila and nematode development. Signaling by these receptors relies on a conserved pathway with three core components: DSL ligand, LNG receptor, and a CSL effector that links the receptor to its transcriptional response. Although key functional regions have been identified in each class of proteins, the mechanism for signal transduction is not yet understood. Diverse regulatory mechanisms influence signaling by the LIN-12/Notch pathway. Inductive signaling relies on the synthesis of ligand and receptor in distinct but neighboring cells. By contrast, lateral signaling leads to the transformation of equivalent cells that express both ligand and receptor into nonequivalent cells that express either ligand or receptor. This transformation appears to rely on regulatory feedback loops within the LIN-12/Notch pathway. In addition, the pathway can be regulated by intrinsic factors that are asymmetrically segregated during cell division or by extrinsic cues via other signaling pathways. Specificity in the pathway does not appear to reside in the particular ligand or receptor used for a given cell-cell interaction. The existence of multiple ligands and receptors may have evolved from the stringent demands placed upon the regulation of genes encoding them.
The Notch/Lin-12/Glp-1 receptor family mediates the specification of numerous cell fates during development in Drosophila and Caenorhabditis elegans. Studies on the expression, mutant phenotypes, and developmental consequences of unregulated receptor activation have implicated these proteins in a general mechanism of local cell signaling, which includes interactions between equivalent cells and between different cell types. Genetic approaches in flies and worms have identified putative components of the signaling cascade, including a conserved family of extracellular ligands and two cellular factors that may associate with the Notch Intracellular domain. One factor, the Drosophila Suppressor of Hairless protein, is a DNA-binding protein, which suggests that Notch signaling may involve relatively direct signal transmission from the cell surface to the nucleus. Several vertebrate Notch receptors have also been discovered recently and play important roles in normal development and tumorigenesis.
Interchangeability of Caenorhabditis elegans DSL proteins and intrinsic signalling activity of their extracellular domains in vivo.
Development. 1995; 121: 4275-82
Display abstract
Ligands of the Delta/Serrate/lag-2 (DSL) family and their receptors, members of the lin-12/Notch family, mediate cell-cell interactions that specify cell fate in invertebrates and vertebrates. In C. elegans, two DSL genes, lag-2 and apx-1, influence different cell fate decisions during development. Here we show that APX-1 can fully substitute for LAG-2 when expressed under the control of lag-2 regulatory sequences. In addition, we demonstrate that truncated forms lacking the transmembrane and intracellular domains of both LAG-2 and APX-1 can also substitute for endogenous lag-2 activity. Moreover, we provide evidence that these truncated forms are secreted and able to activate LIN-12 and GLP-1 ectopically. Finally, we show that expression of a secreted DSL domain alone may enhance endogenous LAG-2 signalling. Our data suggest ways that activated forms of DSL ligands in other systems may be created.
Sequence of C. elegans lag-2 reveals a cell-signalling domain shared with Delta and Serrate of Drosophila.
Nature. 1994; 368: 150-4
Display abstract
The lin-12 and glp-1 genes of Caenorhabditis elegans encode members of the Notch family of transmembrane proteins. Genetic studies indicate that the lin-12 and glp-1 proteins act as receptors in specific developmental cell interactions and that their functions are partially redundant. lin-12 glp-1 double mutants display certain embryonic defects not found in either single mutant. The phenotype of this double mutant is called Lag, and recessive mutations in either of the genes lag-1 or lag-2 can also result in the Lag phenotype, indicating that these two genes may participate in the same cell interactions that require lin-12 or glp-1. We report here that lag-2 encodes a predicted transmembrane protein of 402 amino acids. The predicted extracellular region of lag-2 is similar to amino-terminal regions of Delta and Serrate, two Drosophila proteins that are thought to function as ligands for Notch. The region of similarity includes sequences related to epidermal growth factor (EGF) repeats. We have isolated lag2(sa37), a dominant allele that shows specific genetic interactions with lin-12. The sa37 mutation causes a Gly-->Asp change in a conserved residue of an EGF motif. Because of its overall structure, its sequence similarity to Delta and Serrate, and its genetic interactions, we suggest that lag-2 encodes an intercellular signal for the lin-12 and glp-1 receptors.
Specific EGF repeats of Notch mediate interactions with Delta and Serrate: implications for Notch as a multifunctional receptor.
Cell. 1991; 67: 687-99
Display abstract
The neurogenic loci Notch and Delta, which both encode EGF-homologous transmembrane proteins, appear to function together in mediating cell-cell communication and have been shown to interact at the cell surface in vitro. To examine the role of the EGF repeats in this interaction, we performed an extensive deletion mutagenesis of the extracellular domain of Notch. We find that of the 36 EGF repeats of Notch, only two, 11 and 12, are both necessary and sufficient to mediate interactions with Delta. Furthermore, this Delta binding ability is conserved in the corresponding two repeats from the Xenopus Notch homolog. We report a novel molecular interaction between Notch and Serrate, another EGF-homologous transmembrane protein containing a region of striking similarity to Delta, and show that the same two EGF repeats of Notch also constitute a Serrate binding domain. These results suggest that Notch may act as a multifunctional receptor whose 36 EGF repeats form a tandem array of discrete ligand-binding units, each of which may potentially interact with several different proteins during development.
Metabolism (metabolic pathways involving proteins which contain this domain)
This information is based on mapping of SMART genomic protein database to KEGG orthologous groups. Percentage points are related to the number of proteins with DSL domain which could be assigned to a KEGG orthologous group, and not all proteins containing DSL domain. Please note that proteins can be included in multiple pathways, ie. the numbers above will not always add up to 100%.
