BIOL2056 Lecture 19: From Cells to Tissue PDF

BIOL2056: Lecture 19 From cells to tissue: Cell Adhesion & communication 17 From cells to tissue: ECM 18 From cells to tissue: Cell Adhesion & communication 19 From cells to tissue: Cell Adhesion & communication 20 Model systems to study Cell Biology...

BIOL2056: Lecture 19 From cells to tissue: Cell Adhesion & communication 17 From cells to tissue: ECM 18 From cells to tissue: Cell Adhesion & communication 19 From cells to tissue: Cell Adhesion & communication 20 Model systems to study Cell Biology Dr Nicole Prior [email protected]  Learning outcomes: Lecture 19 From cells to tissue: Cell Adhesion & communication By the end of this session you should be able to: Describe the major superfamilies of proteins that are important in cell adhesion and how they function Cadherins Integrins Selectins Immunoglobulin superfamily members Compare the methods of cell adhesion in animal cells with plant cells  Junction structure Common features of junction complexes Transmembrane adhesion proteins Intracellular link to cytoskeleton Extracellular link to outside structures Cadherin and Integrin superfamilies Cadherins mediate cell-cell attachments Integrins mediate cell-matrix attachments Some cadherins link to actin forming adherens junctions other cadherins link to intermediate filaments to form desmosome junctions Tight junction structure Claudin: a four-pass transmembrane protein that constitutes TJ strands. Junctional adhesion molecules (JAMs): a class of cell–cell adhesion molecules with two Ig repeats that localize to TJs. Occludin: a four-pass transmembrane protein localized at TJs. ZO (zonula-occluding) family proteins: TJ- undercoating scaffolding proteins.  CadherinsCell-cell attachment Proteins - Found in all multicellular animals and Choanoflagellates - Not present in plants, fungi, bacteria or archaea. Important component of being an animal Choanoflagellates an exist as free-living individual organisms or as a colony. hought to be part of the group of protists from which animals evolved. resence of cadherin may have be important in this evolutionary process allowing multicellu  Cadherins me derived from the fact that they require Ca2+ to mediate cell-cell adhesion w can this be demonstrated? rtant during embryogenesis to stick cells together ely held together until the 8 cell stage – then compaction occurs and cells become tightly a cell junctions forming a chelating agent (EDTA) to remove Ca++ and cells can separate sembly when Ca++ is added back  Cadherins st cadherins identified were named based on the cell type they were discovered in adherin – nerve cells adherin – epithelia cells However not restricted to single types of cell – eg N-cadherin also found in fibroblasts adherin – placental cells hin a particular tissue there is diversity in the different cadherins present Embryonic mouse brain Cadherin distribution  Types of Cadherins Cadherin domain Extracellular region has multiple copies of the cadherin domain Intracellular region is more diverse Cadherins tend to form homodimers GPI anchor Over 180 different cadherins in humans Types of Cadherins Non-classical Cadherins Desmocollin – forms desmosome junctions Identified in Drosophila - Regulates epithelia growt Identified in Drosophila - Regulates cell polarity No transmembrane domain – attached via a glycophosphatidylinositol (GPI) anchor Phenotypes of Cadherin defects  Cadherin function Binding between individual cadherins is Strength comes from many such relatively weak links close together …Think of Velcro Why is Ca2+ important for cadherin function? Flexible hinge regions between the cadherin repeats Ca2+ binding to the hinge prevents it flexing Removal of Ca2+ also reduces binding affinity at N-terminus Destabilisation leads to proteolytic degradation  Cadherins play an important role in tissue organisation lassic experiment from the 1950’s (Townes & Holtfreter J. Exp. Zool. 128: 53-120) y amphibian embryo – mesoderm, neural plate and epidermal cells have been disagreggated and mixed cells are able to arrange themselves according to cell type and assemble into structure mophilic attachments between cadherins likely to be key in this reassembly  Development of the neural system Changes in Cadherin expression helps regulate neural tube development Chick embryo as neural tube separates from the ectoderm Cells lose E-cadherin and gain N-cadherin as the neural tube pinches off E-cadherin antibody N-cadherin antibody  Linking Cadherins with the cytoskeleton Catenins form a link between the intracellular cadherin domain and the actin filament Key role played by β catenin and/or γ catenin (plakoglobin) Adherens junctions have an additional related protein p120- catenin If the intracellular domain of cadherin is absent then cell adhesion is weakened The link to actin is important Adherens junction  β-catenin has an important role in Wingless/Wnt signalling Dual role of β-catenin : 1) Intracellular anchor protein at adherens junct 2) Transcriptional regulator in Wnt signalling Breakdown of adherens junction releases β-catenin to move from cytoplasm into the nucleus - there it can affect transcription and Wnt signalling regulates phosphorylation and degradation of β-catenin controlling its availability to form adherens junctions he absence of the Wnt signal, β-catenin is degraded ucho inhibits transcription of Wnt target genes Signalling and cell adhesion are lin resence of Wnt, β-catenin is stable laces Groucho and Wnt target genes are transcribed  Signal transmission roles of other Cadherins The 7TM structure suggests Flamingo may function as a GPCR Vascular endothelial cadherin (VE Cadherin) is required for endothelial cell survival Required for the response to Vascular Endothelial Growth Factor (VEGF) VEGF binds to a receptor tyrosine kinase that requires VE cadherin as a cofactor  Integrins Comprised of 2 non-covalently associated glycoprotein subunits Transmembrane proteins - Short intracellular C-terminal - Large extracellular N-terminal domain Extracellular domain binds extracellular matrix proteins or cell surface ligands of other cells Intracellular domain links (usually via Talin) to the actin cytoske The role of integrins in hemidesmosomes  Cell adhesions via Integrins need to be dynamic Cells in animals can migrate and so cell adhesions need to be broken and reformed Allosteric regulation allows switching between active and inactive states As an integrin binds or detaches from a ligand, it affects conformation of both intra- and extracellular domains Incubation of integrins with an RGD peptide mimicking ligand causes a conformational change. RGD – inactive state. α and β chains are close and adhere +RGD – active state. Association between α and β chains is lost. Talin binding site on β chain is exposed  Outside-in activation of Integrins Binding of an extracellular ligand to an integrin results in binding to the cytoskeleton Transmission of a force via the cytoskeleton Inside-out activation of Integrins ntracellular regulatory molecules such as phosphoinositide (PIP2) activate Talin Causes strong binding of Talin to β integrin chain n turn this activates the extracellular domain of integrin to bind extracellular ligands PIP2 can be produced in response to extracellular signals. Complex crosstalk between different signalling processes  Consequences of defects in Integrins ns have 24 different Integrins – combinations of 8 different β chain and 18 different α chain s combinations eg α5β1 is a fibronectin receptor, α6β1 is a laminin receptor s in either the α or β subunits can lead to genetic disorders  Selectins Heterophilic binding – bind to molecules of a different type Cell surface carbohydrate binding proteins – lectins Mediate transient cell-cell adhesion in the bloodstream Control binding of white blood cells to the endothelial cells lining the blood vessels White blood cells move between the bloodstream and tissues – requires changes in cell adhesion Controlling where and when selectins and integrins are expressed regulates movement of white blood cells  Selectins At least 3 types of selectin L-selectin on white blood cells P-selectin on platelets and endothelial cells activated by an inflammatory response E-selectin on activated endothelial cells ymph organs endothelial cells express oligosaccharides recognised by L-selectin on lympho ses lymphocytes to bind and become trapped nflammation sites endothelial cells express selectins that recognise oligosaccharides on te blood cells and platelets  ICAMs, VCAMs and NCAMs CAMs – Intercellular Cell Adhesion Molecules VCAMS – Vascular Cell Adhesion Molecules NCAMs – Neural Cell Adhesion Molecules mbers of the immunoglobulin (Ig) superfamily Ms have an extracellular domain characteristic of antibodies ICAMs and VCAMs – heterophilic binding to integr NCAMs – homophilic binding  NCAMs Multiple forms of NCAM can be generated by alternative splicing NCAMs can have a high level of sialic acid chains making them negatively ch The negative charge can inhibit cell adhesion Cadherins and Ig superfamily proteins present in the same cell types Cadherins have stronger adhesion properties – important for tissue integrity NCAM likely to function in fine tuning of structures Cadherin mutations usually lethal but NCAM mutations have more subtle effe  Creation of a synapse Axon outgrowth relies on regulation of adhesion, chemotaxis and signal factors Ig superfamily members have a role Mutations in Drosophila Fascicilin2 (related to NCAM) have abnormal direction of axon growth Fascicilin3 functions in recognition of the target tissue by neuronal growth cones Fascicilin3 forms homophilic adhesions. Transient expression of Fascicilin3 in motor neurones allows synapse formation with muscle expressing Fascicilin3 Abnormal synapses can be made by ectopic Fascicilin3 expression Synapse formation is complex with many components Cadherins, Ig superfamily members, neuroligins and neurexins hold the pre- and postsynaptic membranes together Different ways cells stick together Different strengths of adhesion  How do Plant Cells Attach and Detach? Plants like animals are comprised of tissues and orga Leaf and petal abscission Fruit ripening  Plant Cell Walls Cellulose Hemicellulose Pectins Cell wall proteins Structural and mechanical support. Maintain and determine cell shape. Resist internal turgor pressure of cell. Control rate and direction of growth. Regulate diffusion through the apoplast. Carbohydrate storage. Defence. Precise organisation is somewhat speculative Source of signalling molecules. Cell adhesion is via cell wall components Cell adhesion at the middle lamella – pectin rich dom - Role in cell adhesion - Form a hydrated gel in the cell wall - Breakdown products, oligogalacturonides (OGAs) function as signalling molecules. Synthesis of cell wall components- Pectins There are different domains of pectin Homogalacturonan (HGA) Rhamnogalacturonan II (RGII) Rhamnogalacturonan I (RGI) Xylogalacturonan (XGA) Not much known about the enzymes needed for pectin synthesis Cell adhesion via cell wall components Daher and Braybrook (2015) How to let go: pectin and plant cell adhesion. Frontiers in Plant Science 6:523 Alberts Molecular Biology of the Cell 5th Ed. Chapter 19.  Defects in plant cell adhesion Defects in synthesis of plant cell wall polysaccharides can cause loss of cell adhesion  Lecture Summary ants and animals stick cells together in different way nimals – predominantly via protein interactions Cadherins Integrins Selectins Immunoglobulin superfamily members ants – predominantly via polysaccharides