BIOL2056 Lecture 18: From Cells to Tissue - Cell Adhesion & Communication PDF

BIOL2056: Lecture 18 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 18 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 18 From cells to tissue: Cell Adhesion & communication By the end of this session you should have: Broad understanding of cell adhesion with other cells and ECM Understanding of different forms of adhesion junctions Understanding of the biological role of adhesion  The ECM of plant cells primary cell wall is flexible allowing cell expansion and remodelling Multicomponent structureCellulose Hemicelluloses pectin Pectins Arabinogalactans Cell wall proteins cellulose hemicellulose e secondary cell wall is rigid providing strength Predominantly Cellulose Hemicellulose Lignin  Plant primary cell wall Cellulose microfibril (1-4)-D-glucan Pectin Homogalacturonan Rhamnogalacturonan Arabinan Galactan Structural Hemicelluloses Xyloglucan, xylan, glucomannan protein Arabinoxylan, callose (1-3) -D-glucan  Cellulose Cellulose is composed of a polymer of glucose Cellulose synthase rosettes  Hemicellulose Crosslink cellulose microfibrils Xyloglucans Xylan Galactoglucomannan Glucuronoxylan Arabinoxylan Mannan Glucomannan Xyloglucan can account for up to 20% of the primary wall dry weight. Xyloglucan has a backbone composed of 1,4-linked β-D- Glcp residues. Up to 75% of these residues are substituted at O6 with mono-, di-, or triglycosyl side chains. Pectic polysaccharides Pectin crosslinks to form macromolecular structures Methylation prevents crosslinking Pectin methylesterases (PMEs) can demethylate pectin which is then available for crosslinking via Ca++ bridges  Plant secondary cell wall Secondary cell walls predominantly cellulose, hemicellulose and lignin S1, S2 and S3 layers have different orientations of the cellulose microfibrils Secondary cell wall deposition results in a rigid cellular structure  The bacterial ECM apsule is composed of high molecular weight polysaccharides Strongly adhered to the cell wall: caps Weakly adhered – slime layer / biofil  Some bacteria produce a biofilm trix produced by the organism drated extracellular polymeric substances – polysaccharides, proteins, nucleic acids, lipids vide mechanical stability to the biofilm diate cohesion to surfaces and form a network that immobilises the cells s as an external digestive system – keeps extracellular enzymes in close proximity to cells  Quick Summary Animals Glycosaminoglycans (GAGs) Proteoglycans - proteins with GAGs covalently attached Proteins such as collagen, elastin, fibronectin and laminin Plants Primary cell wall - cellulose, hemicellulose, pectin and cell wall proteins Secondary cell wall - cellulose, hemicellulose and lignin BacteriaCapsule composed of high molecular weight polysaccharides, capsule or slim layer Cell adhesion  Animal tissue composition The epithelium layer delimits org Need tight connections between epithelial cells to prevent leakage form an organised multicellular structure cells need to form a structure Cells can directly adhere to each other e.g. an epithelium...or …be bound by secreted extracellular materials  Cell junctions Types of Adhesion Cell-cell Cell-extracellular matrix Three types of cell junctions: 1. Occluding junctions: seal cells together into sheets (forming an impermeable barrier) 2. Anchoring junctions: attach cells (and their cytoskeleton) to other cells or extracellular matrix (providing mechanical support) 3. Communicating junctions: allow exchange of chemical/electrical information between cells Junctions and epithelial function More than 60% of cell types in vertebrates are epithelial Function to enclose and partition the animal body Common organisation – anchored to the underlying tissue via the basal lamina on one side (basal) - Free of attachment at the other side (apical) Epithelial cells are polar Act as selectively permeable barriers – fluid on the outside cannot readily permeate the epithelial membrane Requires occluding junctions (vertebrates – tight junctions)  Occluding junctions Seals gaps between epithelia cells to create an impermeable or selectively permeable barrier Adsorption of glucose from the gut Specialised absorptive epithelial cells Express Na+ glucose symporter on the apical face Passive glucose carrier protein expressed on basal an lateral faces This only works because of the tight junctions The tight junctions may function to help partition the transporters as well as prevent uncontrolled fluid flow  Anchoring junctions Cell-cell adhesions and cell-matrix adhesions Transmit stresses, tethered to cytoskeletal filaments inside the cell.  Adherens Junctions mportant role determining shape of multicellular structures Form an indirect link between actin cytoskeletons Allows coordination of cell activities Zonula adherens or adhesion belt Found below the apical face of epithelial cells Encircles each cell in the sheet The actin network links via caherins forming a linked network Myosin motor proteins can make this contractile and thus able to reshape Heart muscle Intercalated disks are regions of contractile cell attachment and function to co-ordinate the contraction of the  Adherens Junctions The Adhesion Belt allows reshaping of sheets of epithelial cells Formation of the neural tube  Desmosome junctions ar to Adherens junctions but link to intermediate filaments, not actin vide mechanical strength d in vertebrates but absent in Drosophila ent in mature vertebrate epithelia  Desmosomes form regions that stick cells together Desmosome The intermediate filament is dependent on cell type. Keratin – most epithelia cells Desmin – heart muscle emphigus (Autoimmune disease) Antibodies against desmosomal cadherin proteins ---> Weakened cell adhesions Causes leakage of body fluids into loosened epithelium (blistering of skin) Have a look online for pictures if you wan  Channel-forming junctions Create a link between cytoplasms of different cells TEM and freeze fracture images  Gap Junctions and Plasmodesmata ight junctions block the passage of small molecules ap junctions in contrast create passageways between cells lasmodesmata in plants; gap junctions in animals Fluorescent molecules llow exchange of small molecules between cells  Functions of Gap Junctions In tissues with electrically excitable cells gap junctions couple cells allowing rapid spread of action potentials Important in escape responses in fish and insects Vertebrates – gap junctions in heart muscle and smooth muscle cells in the intestine synchronises contraction Provide connections between cells allowing movement and coordinated sharing of signals Eg liver cells allowing a response to signals from nerve terminals that contact only some cells  Structure of a Gap Junction Each channel complex made of individual connexin subunits Complexes of protein subunits constitute the gap junction channels Can be homomeric or heteromeric Either connexin or innexin subunits Assemble into homotypic or heterotypic channels Structurally similar but unrelated Both present in vertebrates (mainly connexins) Only innexins in Drosophila and Caenorhabditis  Structure of a Gap Junction The combination of connexons determines function and permeability Most cell types express more than one type of connexin Adjacent cells can express different connexins Gap-junction plaques can rapidly assemble and disassemble Gap junction assembly and disassembly New connexons added at the periphery via exocytosis Old connexons removed from the centre – How?  Mutations in connexin genes cause several disorders exin 26 – mutation leads to death of cells in the organ of Corti (electrically active sensory epithelium) Congential deafness nnexin mutations can also cause – cateracts and demyelinating disease in peripheral nerves  Signal-relaying junctions Allow signals to be relayed between cells across the plasma membranes at the site of cell-cell contact Similar in principle to Channel-forming junctions More complex structures Typically include anchorage proteins alongside proteins mediating signal transduction Summary of the different types of cell junctions  Next lecture What proteins are found in junction complexes? How do the junction proteins interact?  Further reading material hts et al., (2012) Holding tight: Cell junctions and cancer spread. Trends Cancer Res. 8 61-6 k et al., (2009) Cell Communication and Signalling 7:4