Presentation on theme: "Notch receptor activation and function. Lz Notch signaling completely changes the way that cells respond to other signaling pathways Flores et al., Cell."— Presentation transcript:
Lz Notch signaling completely changes the way that cells respond to other signaling pathways Flores et al., Cell 103:75-85 (2000) R7 Photoreceptor D-Pax2 Cone cell
Question: What are Notch receptors normally used for? Answer: Lateral Specification – Required to generate two distinct cell types in the correct ratio and configuration – e.g. spacing of neurons vs epidermal cells. Inductive Signaling – Induces differentiation of a new cell fate in response to Notch activation – e.g. induction of wing margin tissue in a fruit fly. Cellular Migration – e.g. Axonal pathfinding in flies Cell Division – e.g. Mitosis in the C. elegans male gonad. Cell Adhesion – e.g. Adhesion between the Oocyte and Follicle cells in Drosophila. Mesenchymal/Epithelial Transitions – e.g. maintenance of epithelial tissues in Drosophila Cell Survival/Death – e.g. Regulates cell death in the developing fly eye
Question: Maybe Notch receptors control everything? Answer: Probably involved in most biological processes in complex animals. Development: We know from temperature sensitive mutants of Notch in both flies and worms that Notch receptors are required for development of every tissue (blood vessels, nervous system, white blood cells, epithelial tissues, etc.). Diseases: Cancer (Notch oncogenes and Anti- Oncogenes/Tumor Suppressor Genes: Dementia caused by mutations in Presenilin (PS) genes and in Notch3).
Notch: A large Transmembrane Receptor/Transcription factor that regulates development of every tissue in complex animals. First analyzed in Drosophila (~1930s). Extracellular domains: Mammalian Notch 1, 2, 3 and 4 contain 36, 36, 34 and 29 highly conserved EGF-like repeats respectively. EGF-like repeats are ~40 amino acids in length and contain 6 cysteine residues (forming 3 C-C bonds). Three LNR repeats (Lin-12, Notch Repeats) are also present in the Notch extracellular domain. LNR repeats are cysteine-rich domains found only in Notch family receptors (Note that Lin-12 is a C. elegans Notch receptor). EGF Repeats LNR Repeats
Notch: A large Transmembrane Receptor/Transcription factor. The Ram23 domain is ~50 amino acids in length. It binds to a CSL DNA-binding protein (CSL = CBF-1, Suppresser of Hairless, and Lag-1 which are the mammalian, fly and worm versions of this protein) – see below. Cdc10 repeats are ~33 amino acids in length and bind to a number of proteins involved in chromatin remodeling such as Mastermind, Lag-3/Sel-8, or EMB-5, and also to Deltex. Ram23 domainCdc10/ankyrin repeats NLSPEST Sequences
Notch: A large Transmembrane Receptor/Transcription factor. Each domain of Notch is important for at least one function: -Receptor Trafficking/Processing or Activation -Receptor Signaling -Receptor Regulation (+ or -)
Notch is made as a very large single-chain precursor that must be glycosylated and cleaved before it appears on the cell surface. Glycosylation of Notch starts in the ER and is finished in the Golgi. Cleavage to generate the mature heterodimeric form on the plasma membrane occurs in the Golgi. This cleavage reaction at site 1 (S1) is carried out by a Furin protease. Furin Protease S1 cleavage
Question: What is Notch? Answer: A Receptor, an Adhesion Molecule, and a Transcription factor. Question: How is Notch regulated? Answer: Just about every way that you can imagine: Synthesis Folding Glycosylation Processing Subcellular localization Ligand Activation Proteolytic cleavage at activation Endocytosis Translocation to the Nucleus Binding to partners DNA binding/Transcription Degradation
Hes genes CSL/RBPJk The Notch IC (intracellular domain) switches on genes that were repressed by CSL/RBPJk/Su(H) through conversion of a repressor complex into a transcriptional activation complex.
Prior to Notch activation, the CSL protein was sitting on DNA in a complex with Ski-interacting protein (SKIP) and a transcriptional co- repressor termed SMRT. The CSL-Skip-SMRT complex represses gene expression and therefore CSL was repressing expression of a set of genes prior to Notch activation. Once Notch IC arrives in the nucleus, it binds to the CSL-Skip complex, displacing SMRT and recruiting transcription activating proteins such as Mastermind, Lag- 3/Sel-8, and/or EMB-5. Consequently, Notch activation turns on the genes that were repressed by CSL. Many of these Notch target genes are themselves transcription factors that regulate differentiation (e.g. HES).
Notch receptors and ligands (Human) Notch 1 2537 aa EGF-like repeats LNR RAM TAD Pest Notch 2 2445 aa Notch 3 2281 aa Notch 4 1979 aa Lin/Notch repeats RAM domain PEST domain Transactivation domain Anky Ankyrin repeats Nuclear localization signal TAD Anky LNR RAM LNR Pest TAD LNR RAM LNR Pest Anky LNR RAM Pest Anky LNR RAM LNR Pest Anky vWF DSL Delta/Serrate domain vWF Von Willebrand Factor cysteine-rich domain Jagged 1 1033 aa vWF DSL Jagged 2 1053 aa Delta-like 1 706 aa DSL Delta-like 3 591 aa Delta-like 4 658 aa DSL