1. INTEGRATION OF CELLS INTO TISSUES
Dr shazia tufail
Assistant Professor
Anatomy
King Edward Medical University, Lahore, Pakistan

2. Learning objective How cells attach to neighboring cells
Extarcellular Matrix and Molecules that make up ECM
Role of ECM in cell signaling and intercellular communication

3. Levels of Organization in Living Things

4. Cells in tissues can adhere directly to one another (cell-cell adhesion) through specialized integral membrane protein called cell adhesion molecules (CAMs)
Cells in animal tissues also adhere indirectly (cell-matrix adhesion) through the binding of adhesion receptors in the plasma membrane to components of the surrounding extracellular matrix (ECM); A complex interdigitating meshwork of proteins and polysaccharides screted by cells into the spaces between them
CAMs and ECM can bind cell together, and transfer of information between the exterior and interior cells.
Cell Junctions are relatively stable, ultrastructurally (ie in EM) distinct sites where cells are joined to each other or the extracellular matrix.
Adhesion molecules are one component of adhering junctions
Adhesion Molecules are cell surface molecules that stick to each other to allow cell-cell or cell-ECM adhesion

7. Cell-cell adhesions can be tight and long lasting or relatively weak and transient.

8. Molecules of Extracellular Matrix
"the substance between cells" and the "material in the intercellular space“
Structure and support to cells
Specific functions depending on types of cells it is associated
It is involved in signal transduction and intercellular communication
The constituent materials in this structure can vary widely;
a. in plants…….cellulose,
b. arthropods and fungi….. chitin
b. in animals…proteins, and carbohydrates (mineral in bones).
Secreted by the surrounding cells.

9. Molecular Components of Extracellular Matrix
Proteoglycans
Are proteins that are heavily glycosylated
The basic proteoglycan unit consists of a "core protein" with one or more covalently attached to glycosaminoglycans chain(s)
point of attachment is a Serine residue to which the GAG is joined
Ser-Gly-X-Gly- (where X can be any amino acid residue, but Proline)
Proteoglycans may also help to trap and store growth factors within the ECM
Protein component of proteoglycans is synthesized by ribosomes while Glycosylation of the occurs in the Golgi apparatus
Heparin Sulfate………..development, angiogenesis, blood coagulation
Chondroitin sulfate cartilage, tendons, ligaments and walls of aorta
Karatan sulfate………. cornea, cartilage, bones and horns of animals

10. 2. Fibers Collagen most abundant protein in the ECM ,
produced as procollagen which is then cleaved by proteases to allow extracellular assembly
give structural support
Disorders such epidermolysis bullosa are due to genetic defects in collagen-encoding genes
Fibrillar (Type I, II, III, V, XI)
Facit (Type IX, XII, XIV)
Short chain (Type VIII, X)
Basement membrane (Type IV)
Other (Type VI, VII, XIII)

11. Elastin
give elasticity to tissues, allowing them to stretch when needed and then return to their original state
Present in blood vessels, lungs, skin
Synthesized by fibroblasts and smooth muscle cells
Are highly insoluble
Disorders such as cutis laxa and Williams syndrome are associated with deficient or absent elastin fibers in the ECM

12. 3. Multi-adhesive matrix proteins
Fibronectin
Are glycoproteins that connect cells with collagen fibers in the ECM, allowing cells to move through the ECM.
Help at the site of tissue injury by binding to platelets during blood clotting and facilitating cell movement to the affected area during wound healing.
Laminin …. are proteins found in the basal laminae of virtually all animals

13. ECM participate in cell signalling
The Extracellular Matrix Participates in Signaling and Intercellular Communication
ECM participate in cell signalling
Extracellular matrix proteins interact CAMs and influence cell survival, gene transcription, cytoskeletal organization, cell motility, and cell proliferation.
Thus, outside-in and inside out signaling involves numerous interconnected pathways.

14. Extracellular Matrix Components Mediate Cell Signalling Via Integrins
Integrins are transmembrane receptors that mediate the attachment between a cell and ECM.
In signal transduction, integrins pass information about the chemical composition and mechanical status of the ECM into the cell.

15. Cell Junctions Types 1. Anchoring Junctions Desmosomes Hemidesmosomes
Adherens Junctions
2. Communicating (Gap) Junctions
3. Tight Junctions

20. Anchoring protein is plectin
Integrin binds with laminin

22. Animal cells communicate by gap junctions
Gap Junctions Connect Animal Cells
an animal cell may contain hundreds of gap junctions connecting to the neighboring cells.
Gap Junctions are too samll for proteins, but small molecules such as ATP, metabolic intermediates. Amino acids and co-enzymes can pass through them

24. Plant cells Communicate by Plasmodesmata
Instead of gap junctions, plants have plasmodesmata, which are membrane-lined bridges spanning the thick cell walls that separate plant cells from one another.
A typical plant cell have several thousand plasmodesmata