Dr Mahmood S Choudhery, PhD Assistant Professor Advance Center of Research in Biomedical Sciences...
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Transcript of Dr Mahmood S Choudhery, PhD Assistant Professor Advance Center of Research in Biomedical Sciences...
INTEGRATION OF CELLS INTO
TISSUESDr Mahmood S Choudhery, PhD
Assistant Professor
Advance Center of Research in Biomedical Sciences
Incharge Tissue Engineering Laboratory, Mayo Hospital Lahore, Pakistan
King Edward Medical University, Lahore, Pakistan
Learning objective
How cells attach to neighboring cells How cells communicate with other
cells and extracellular matrix (ECM) Types of different junctions Role of ECM in cell signaling
Levels of Organization in Living Things
Why cells integrate to
form tissues?
They need to perform specific functions more effectively
Permits the organism as a whole to move,
metabolize, reproduce, and carry out other essential
activities.
Integration of Cells into TissuesInvolves 2 processes
1. Cell Recognition
2. Cell Adhesion
Cell Adhesion……………
1.Cell-cell adhesion
2. Cell-matrix adhesion
Adhesion Receptors
Cells can adhere to each other by two ways
Cell Adhesion Molecules (CAMs)
Cell Adhesion Molecules (CAMs)………..
1. Are proteins (glycoproteins) 2. Involved in binding with other cells or with ECM3. Typically transmembrane proteins4. Cluster to form specialized cell junctions
Cell Adhesion Molecules……….. 4 Types
CadherinsImmunoglobulinsIntegrinsSelectins
TYPES OF INTERACTIONS
Between adhesion molecules Homophilic interactions Heterophilic interactions
Between cells Homotypic interactions Heterotypic interactions
What are Cis and Trans interactions?
SPECIALIZED CELL JUNCTIONS
Between cellsTight junctionsAdhesive/ Anchoring junctionsGap junctions
Between cells and matrixHemidesmosomesFocal Junctions
1. Cell Junctions- types based on localization
2. Cell junctions - types based on function
Adhering junctions:1. Tight junctions
2. Adhesive/ Anchoring junctions
3. Hemidesmosomes
4. Focal Junctions Communicating junctions:
1. Gap junctions
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1. Tight Junctions
Only found in epithelial cells Composed of 3 transmembrane protein families Prevent substances from moving through intercellular
spaces
2 typesa) Desmosomes
b) Adherens Junctions
2. Adhesive/ Anchoring junctions
Hold cells tightly together Connect a cell’s cytoskeleton to another cell
a) DESMOSOMES HOLD CELLS TOGETHER
1. Form links between cells2. Connect intermediate filaments of adjacent cells3. Composed of cadherins
Under the cell membrane, contractile fibers of microfilaments connect to cell membrane proteins called cadherins
b) Adherens Junctions
E- cadherin mediated adherens junctions Homophilic pairing of E- cadherins Adapter proteins (plakoglobin and α and βcatenins)
link cadherins to the belt of actin filaments.
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3. GAP JUNCTIONS
Gap junctions allow cells to exchange electrical and/or chemical signals
Composed of proteins that form channels that allow small molecules to pass.
Subunits of these channels are connexins that are assembled together to make connexons. The connexons from 2 cells join together to make a gap junction.
Gap Junctions
This channel is big enough to allow small molecules such as inorganic ions, and other small water soluble molecules (smaller than 1000kDa) to pass between the cells. However the channel is too small for proteins, nucleic acids or sugars to pass through.
Cell Communication Structures
Gap Junctions
desmosomedesmosomeGap Junctions:pairs of channelsconnect insides ofadjacent cells
Gap Junctions:pairs of channelsconnect insides ofadjacent cells
LiverLiver Plasma membrane(edge view)Plasma membrane(edge view)
Liver cellsLiver cells
Plasmodesmata
Plasmodesmataconnect insidesof adjacent cells
Plasma membrane(edge view)
Root cells
Cell wall(edge view)
Middle lamella(edge view)
RootRoot
Animals Plants
4. Hemidesmosome Connections between cell and ECM Composed of Integrins
What is ExtraCellular Matric (ECM)?
•Secreted by surrounding cells
EXTRACELLULAR MATRIX
1. Basal lamina
2. Interstitial Matrix
Two types of Extracellular Matrix
ECM COMPONENTS
1. Proteoglycans 2. Structural Proteins (Collagens and
Elastins) 3. Adhesive Glycoproteins (Fibronectins
and Laminins)
1. Proteoglycans: (Protein-polysaccharide complexes)
ECM components…………….
Composed of a core protein and GAGsHave net negative chargeTrap and store growth factors
2. Structural Glycoproteins (Collagens and Elastins)
ECM components…………….
3. Adhesive Glycoproteins (Fibronectins and Laminins)
Collagens are the main proteins of ECMElastin give elasticity to tissues
Fibronectin connect cells with collagen fibers in the ECM and integrin receptors on cell membraneLaminin found in the basal lamina
Role of Extracellular Matrix in Cell Signaling
Provides space where different ligands and growth factors are released
Act as a reservoir for various growth factors
Different proteins of ECM act as ligand for cell receptors
How Extracellular Matrix Components Mediate Cell Signaling?
Integrins are transmembrane receptors for extracellular matrix (ECM) proteins such as collagens, fibronectin, laminins and vitronectin.
The Extracellular Matrix Participates in Signaling
lntegrin adhesion receptor mediated signaling pathways that control diverse cell functions.
Recommended Books
• Molecular Cell Biology By Lodish 7th
• Molecular Biology of The Cell by Bruce Alberts