Glossary of Cell Motility
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- What is cell motility?
- Directed Cell movement
- Why is cell motility important? 4 reasons
- 1) Wandering cells must get to sites of infection
2) Cells must migrate during embryology and normal development
3) Important in the repair of wounds (wound healing)
4) Important part of cancer spread throughout body (metastisis)
- Please look at p328 Diagram
- look at p 328 diagram
- Specific morphology defines junctional regions of cell membranes. For cell to cell adhesion there are 4 distinct areas what are they?
- 1) Tight junctions = Zonula Occuldens
2) Adhesion belts = Zonula Adherens (cadherins)
3) Desmosomes = macula adherens (cadherins)
4) Gap junctions = nexus = communicating junctions
- Specific morphology defines junctional regions of cell membranes. For cell to matrix adhesion there are 2 discinct facets. Name them.
- 1) Hemidesmosomes (integrins)
2) Focal attachements (integrins)
- What is a Non-junctional area?
- Where no structural entity is seen in the membranes but physiologically there is adherence by the membranes and biochemical adhesion molecules are present.
- Four families of of cell surface molecules involved in cell-to-cell adhesion.
- 1) Cadherins
2) Ig-like CAMs (Cell Adhesion Molecules)
4) Selectins (bind to carbohydrates on cell surface)
- Two types of Cell to matrix adhesion molecules:
2) Proteoglycan surface molecules
Also transmembrane surface molecules like syndycan and fibroglycan
- Most cell to cell junctional and nonjunctional adhesion invoves what protein and what type of interactions does it mediate?
- Cadherin usually mediates homophilic interactions.
- Most cell to matrix junctional and nonjunctional adhesion invoves what protein and what type of interactions does it mediate?
- Integrin usually mediates heterophilic interactions.
- Since the interaction of non junctional cell surface molecules is not enough to ensure cell adhesion, how do they adhere?
- Non junctional, cell to cell adhesion molecules initiate tissue specific cell-cell adhesions, which are then stabilized by the assembly of full blown intercellular juncitons.
- What are the 2 stages via which leukocyes exits a capillary and migrates to an area of infection?
- Extravasation and Diapedesis
- Process of attaching to the endothelial lining followed by migration of cell through the wall.
- Process of migrating or moving through the extracellular space to site of infection.
- What are the four steps of Extravasation?
- 1) Activation of endothelial cells.
4) Migration through wall.
- What occurs during the activation step of Extravasation? (3)
- Caused by cytokines from Ab-Ag interactioni or released by mast cells.
Causes exocytosis of P-selectin within seconds.
Also production of PAF (platelet activating factor) by endothelium.
- What occurs during the Trapping step of Extravasation? (3)
- P-selectine temporarily binds to selectin receptor on leukocyte.
Not very tightly bound, bonds easily break and cell rolls.
PAF activates PAF receptor on leukocyte that causes conformational change in integrin on surface of leukocyte.
- What occurs during the Adhesion step of Extravasation? (2)
- Tight adhesion of leukocyte to wall occurs when integrin of leukocyte binds to ICAM (intracellular adhesion molecule) of endothelial cell.
Leukocyte now tightly attached and cell thins and spreads out over capillary surface.
- What is Leukocyte Adhesion Deficiency?
- Improperly produced integrin and leukocytes can not effectively migrate out of blood vessel (can't bind). Patients suffer from life threatening infections.
- What occurs during the Migration step of Extravasation?
- Cell has lamella podia or pseudopodia that push between the adjacent cells.
Metalloproteases secreted by leukocyte breaks junctional complex. (allows leukocytes to reach between cells and grab the basal lamina)
Pseutopodia grabs on to basement membrane and pulls cells through into extracellular connective tissue space.
- What does E-cadherin do?
- For transmembrane linkage
- What are Focal contacts?
- Anchor bundles of microfilaments to the plasma membrane. (Integrin)
Cystolic side linked to cytoskeleton filaments of actin via linker proteins; talin, vinculin, and alpha actin.
Exterior side attaches to laminin, collagen IV, tenacin or fibronectin
- What is Integrin?
- Cell surface adhesion molecule.
Acts to bind cell to cell and cell to extracellular matrix.
Is a transmembrane protein.
- What is the structure of integrin?
- Consists of alpha and beta heterodimers. (14 types of alpha subunits, 8 types of beta subunits)
There are different mixes of subunits that bind to different extracellular materials to give it specificity for only certain substrates.
Alpha1 subunit binds to components of ECM.
Ex. Alpha1 Beta1 and Alpha2 Beta2 bind to type IV collagen. Alph6Beta1 binds to 2 regions on laminin. Alpha 5 Beta 1 binds to fibronectin. Beta2 subunit only binds to leukocytes (mediates only in cell-cell interactions)
- What kind binding does integrin have and what purpose might this bindgin have?
- Typically the various integrins have low binding affinites for their ligand.
It takes week bindings of nermerous integrin molecules to ECM gives cell firm hlod on to the ECM.
Weak binding may help cells in the process of migrating.
With multiple forms of integrin, some may be inactiveated to adjust the amount of binding necessary.
- There is some evidence that integren needs to be ________ to work properly.
Ex. Integrin on platelets unable to bind to fibrinogen to participate in clotting.
It must bind to collagen or thrombin first, which activates integrin to bind to fibrinogen.
- Glanzmann's disease
- Lack of Beta3 integrin casues excessive bleeding due to lack of clotting.
- What regulates inactivation of integrins?
- Intracelluar signalling.
i.e. Phosphorylation of integrin on cytosolic side is thought to prevent integrin from binding to fibronectin thus allowing the cells to round up and undergo mitosis.
- How are integrins involved in cancer?
- Result in metastasis via phosphorylation inactivating integrin. The conformational change releases talin and the subsequent release of its attachment to the cytoskeleton. This allows the cancer cells to round up and migrate.
- What is diapedesis and what are the two types of it?
- -Means "cell walking"
- 2 types of it:
Slow moving- Occurs in fibroblasts and growth cones of neurons
Fast moving- Occurs in leukocytes and macrophages.
Can see cytoplasmic streaming.
Both types have the same basic steps only the speeed of which it occurs is different.
- 4 Basic steps of cell walking
- 1. Extension of lamellapodia (podosomes)
2. Adhesion by focal attachements to adhesion molecules and collagen fibers in ECM.
3. Cytoplasm flows forward.
4. Retraction with footprint.
- What are the functions of focal adhesions (3)?
- Attach cell to substratum
Give cell point to pull against or to move toward
Prevent leading edge of lemella or pseudopodia from retracting.
It is necessary to have proper extracellular adhesion molecules present in order for diapedesis to occur.
- What are lamellapodia or podosomes?
- Sheetlike networks of microfilaments that move outward to extend the cytoplasm in cell motility.
- What occurs during the cytoplasm flows forward stage of diapedesis?
- Actin fiber extension occurs and the cytoskeletal framework shifts forward.
Cytplasm of cell flows into lamellapodia in direction of chemotaxic signals (ECF and NCF) released by mast cells, etc.
Cytoplasm changes from (a gel to a sol) readily flow into the expanding process.
- What occurs during the retraction with footprint stage of diapedesis?
- Trailing edge thins and forms retraction fiber.
This "snaps" leaving footprint or bit of membrane and cytoplams at focal attachement point.
- How does cell membrane move forward? (3 hypotheses)
- 1. Cytoskeletal elements, actin filaments are bound to membrane wall by myosin I - micro filaments grow, polymerize under influence of profilin to push membrane ahead of it
2. Myosin I with plasma membrane attached to it, the microfilaments are extended without profilin but still push membrane forward.
3. Myosin I attaches plasma membrane to cytoskeleton and myosin I moves forward within the membrane to shift microfilaments forward. (Rapid shif of cytoplams from gel to sol thought to be caused by increased osmotic pressure in forward edge)
- What is intrinsic to all 3 mechanisms of the cell membrane moving forward?
- The nucleus and all other organelles are attached to the cytoskeleton and are moved forward with the framework.
- How does the cell know which direction to go? (2)
- Chemotaxtic factors (mast cells)
Calcium concentration gradients.
- Give five examples of how formation of tissues and organs can be regulated by interaction with the extracellular matrix.
- 1. Cells help create order in ECM via integrins.
2. Organ formation
3. Reconstruction of regenerating myoneural junctions dependant on basal lamina
4. Laminin has been shown to regulate neuronal outgrowth.
5. Fibronectin promotes migration.
- 1. Cells help create order in ECM via integrins
- -Typically when acell is attached to ECM it forms stress fibers=bundes of actin filaments within cytoplasm.
-These stress filaments disappear when cells round up and become motile.
-Integrins mediate interaction between the cytoskeleton and the ECM to bring order to the ECM and arrangement cell.
-Cell tugs on ECM fibers to bring into orientation
-New cells in this organized matrix very quickly align their cytoskeleton and the arrangement is propagated throuhgout the forming tissue.
- 2. Organ formation
- - Basal lamina is essential for differentiation and formation of salivary gland
- The forming endoderm, mesoderm and basal lamina must interact to form the mature gland.
- 3. Reconstruction of regenerating myoneural junctions dependent on basal lamina
- -myoneural junction = neuralmuscular junction = type of synapse where nerve transmits its impulse to skeletal muscle cell.
-basal lamina surrounds muscle cell
-synaptic regions contain special forms of collagen IV and laminin.
- 4. Laminin has been shown to regulate neuronal outgrowth
- Grown cones select specific ECM molecules to migrate on
e.g. laminin substrate over collagen IV.
- 5. Fibronectin promotes migration
- -In mesenchyme for cells to migrate during development
-Fibronectin also incorporated into blood clots
-Promotes migration of epithelial cells across wound
-In addition promotes infilitration of fibroblasts into the clot from surrounding CT to repair gap and form scar tissue.
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