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Cytoskeleton Adh/Junction/Coll
Lecture 62
78
Medical
Graduate
01/12/2009

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Term
What is the cytoskeleton and what does it do?
Definition
  • the stabilizing components of the cytosol
  • maintains external shape and internal structures
  • regulates internal and external movements
Term
What are the three major protein filaments from largest to smallest in diameter
Definition
  • Microtubules (25 nm)
  • Intermediate filaments (10 nm)
  • Actin filaments (5-9 nm)
Term
Accessory Proteins (AP)
Definition
Essential for the controlled assembly of cytoskeletal filaments.
Term
Motor Proteins (also AP)
Definition
Necessary for movement of organelles or the filaments themselves
Term
Actin
Definition
  • 2-stranded helical polymers
  • flexible aggregates of filaments organized in linear bundles, two dimensional networks, and three-dimensional gels
  • mostly beneath the plasma membrane
  • CELL SURFACE ORGANIZATION
  • actin anchoring junctions
Term
Microtubules
Definition
  • hollow cylinders
  • long, rigid, and straight hollow cylinders
  • one end attached to MTOC (centrosome or basal body)
  • CELL HIGHWAYS
Term
Intermediate Filaments
Definition
  • ropelike fibers
  • heterogeneous family of ropelike fibers spanning the cytoplasm from one cell-cell junction to another
  • also form the nuclear lamina
  • TISSUE STABILITY
  • Intermediate Filaments anchoring junctions
Term
Dynamic nature of cytoskeleton
Definition
  • not fixed streets, rather "ant trails"
  • actin and microtubule cytoskeleton reorganizes rapidly during mitosis
Term
Classes of Microtubules
Definition
Labile: Temporary according to need. Throughout cytoplasm
 
Stable: Form permanent parts of some cell components, e.g. centrioles, cilia and flagella
Term
Microtubule characteristics
Definition
  • microtubules are polymers of tubulin alpha and beta.
  • the wall of each microtubule consists of 13 protofilaments
  • microtubules have an inherent polarity, i.e. they have a dynamic (+) end and a more inert (-) end
  • the (-) end needs to be stabilized in a MTOC
  • growing and shrinking occurs at the (+) end
  • GTP binding to tubulin causes the microtubule to grow in a linear configuration
  • GTP hydrolysis causes the microtubule to depolymerize and shrink
Term
Microtubule Asosciated Proteins (MAPs)
Definition
  • involved in tubulin polymerization leading to stabilization of microtubules
  • thus, the formation of functionally differentiated cytoplasm is promoted, e.g. the axons of neurons
Term
Catastrophins
Definition
  • leads to the opposite reaction performed by MAPs
  • leads to microtubule destabilization (or catastrophe)
Term
MTOCs
Definition
  • Centrosome: Cell center MTOC
  • Basal bodies of cilia & flagella
Term
Axoneme
Definition
  • Motile core of cilia & flagella
  • built from microtubules and dyneins
  • all have a core of longitudinally arranged microtubules
  • 1. Clilia (9 peripheral doublets+ 2 central singlets pattern)
  • 2. Flagella (9 peripheral doublets + 2 central singlets pattern)
  • Basal body (a MTOC giving rise to a cilium or flagellum; it has a 9 peripheral triplets + 0 central pattern).
Term
Centrosome
Definition
The main microtubule organizing center (MTOC) located in the exact cell center
 
Composed of:
  • a pair of centrioles: 2 short cylinders at right angles to each other, composed of modified microtubules
  • the pericentriolar cloud or material, or centrosome matrix, containing gamma tubulin ring complexes;pericentriolar material provides the sites for the intitiation of the microtubule polymerization (nucleation)
  •  (-) ends of the microtubules are embedded in this
Term
Basal Body
Definition
  • A specialized centriole (MTOC) that gives rise to the axoneme of a cilium or a flagelum.
  •  
  • Has a 9 microtubular triplets radially arranged in a pinwheel fashion (9+0 axoneme pattern)
Term
Dynein Arms
Definition
  • form bridges between neighboring doublets
Term
Immotile Cilia Syndrome
Definition
  • caused by the genetic lack of dynein arms
Term
Difference between motions of cilia and flagella
Definition

Cilia: Beat-like

Flagella: Wave-like

Term
Motor Proteins
Definition
  • proteins that bind to a polarized  cytoskeletal filament and use energy from repeated ATP hydrolysis to move along it
  • 2 types: (Actin binding, Microtubule binding)
Term
Microtubule binding Motor molecules
Definition
  • Kinesin: movement towards the (+) end of the microtubule
  • cytoplasmic Dynein: movement towards the (-) end of the microtubule, i.e. towards the cell center. (closely related to the ciliary dynein)
  • locations of the ER and the Golgia are due to the movements induced by kinesin and dynein
Term
Functions of microtubules
Definition
  • organize the cells (centrosome)
  • form mitotic spindle
  • provide highways for organelle transport (intracellular movement, e.g. along axons)
  • cell motility (external movements: cilia flagella)
Term
Actin (micro) filament structure
Definition
  • two-stranded helical polymers composed of G-actin. Polymerized into F-actin
  • also have polarity
  • ATP binding
Term
Formins
Definition
  • mediate actin elongation on the plus end
Term
Cross Linking Proteins
Definition
The presence of fimbrin in the filopodia and alpha-actinin in the stress fibers/focal contacts is responsible for their respective properties, i.e. allowing or not Myosin II molecules in.
Term
Actin cross linking proteins
Definition
The bundles of actin responsible for the shape of microvilli is related to cross linking by Villin and Myosin-I
Term
Functions of Actin filaments
Definition
  • keep external cell shape (cortex)
  • muscle contraction
  • participation in anchoring junctions (Cell-cell & Cell-matrix)
  • microvilli formation
  • cleavage furrow in dividing cells
  • cell polarity
  • development of tubes
Term
Actin Binding Motor proteins
Definition
Myosin II (contraction);
other myosins I (intracellular organization)
III - XII (other e.g. delivery of melanosomes)
Term
Which filaments help display significant differences between cell types (Diagnosis of tumors)
Definition
Intermediate Filaments
Term
Intermediate Filaments Properties
Definition
  • rope-like
  • tetramers with no polarity
  • not dependent on ATP or GTP for polymerization, but still dynamic (phosphorylation)
  • assembly along entire length, i.e. along their length as well as ends
  • easily bent but difficult to break
  • integrate mechanically with MT and Actin MF
  • participate in anchoring junctions (cell-cell desmosomes & cell0matrix hemidesmosomes)
  • spanning the cytoplasm form one junction toanother --> tissue strength
Term
Classes of Intermediate Filaments
Definition
Keratins: Epithelia
Vimentin-like
  • Vimentin: Mesenchymal cells
  • Desmin: Muscle cells
  • Glial fibrillary acidic protein (GFAP): Astrocytes
Neurofilaments: Neurons
Lamins: Nuclear laminae
 
Term
Functions of intermediate filaments
Definition
  • Structural support against rupturing forces.
  • Nuclear lamins from the nuclear lamina
  • Immunologic markers for identification of cells and corresponding tumors
Term
Immunostain for what in a malignant tumor of uncertain nature indicates a mesenchymal derivation
Definition
Vimentin
Term
Cytochalasin B
Definition
  • Actin-specific drug
  • Prevents polymerization
Term

Phalloidin

Definition
  • Actin-specific drugs
  • Stabilizes filaments (leucocytes cannot move effectively)
Term
Colchicine
Definition
  • Microtubule specific drug
  • Prevents polymerization (gout treatment)
Term
Vinca Alkaloids
Definition
  • Microtubule specific drugs
  • Prevent polymerizaiton (preventing mitoses:antcancer drugs)
Term
Acrylamide
Definition
  • Intermediate Filament-Specific Toxins
  • Acrylamide: disassembly or rearrangement of IF (neurotoxin)
Term
Epidermolysis Bullosa Simplex
Definition
  • Blistering of the skin caused by a mutant keratin gene
Term
Secondary Cytoskeleton changes due to cell injury
Definition
  • Lou Gehrig's disease
  • Alzheimer disease
  • Alcoholic liver disease
  • HPV infection-->Koilocytosis
Term
Lou Gehrig's Disease (ALS)
Definition
Abnormal accumulation of neurofilaments in neurons
Term
Alzheimer's Disease
Definition
Neurofibrillary tangles containing microtubular associated proteins and neurofilaments.
Term
What type of filaments accumulate in liver cells injured by alcohol (alcoholic hyaline or Mallory bodies)
Definition
Keratin filaments
Term
HPV leads to this...
Definition
Koilocytosis: collaps of the keratin filaments
Term
Classification of cell junctions
Definition
Occluding: Tight junctions
 
Anchoring:
  • Actin filament association: Cell-cell: Adherens junctions; Cell-Matrix: Focal adhesions
  • Intermediate filament association: Cell-cell: Desmosomes; Cell-Matrix: Hemidesmosomes
Communicating (channel forming): Gap Junctions
Term
Tight junctions (zona occludens)
Definition
  • Outer leaflets of adjacent plasma membranes fuse to form a zone around the entire apical perimeter of the cells
  • restrict the mobility of membrane proteins and passage of molecules between cells
Term
Tight-junction proteins
Definition
  • Claudin
  • Occludin
Term
Functons of Anchoring Junctions
Definition
  • Link cytoskeleton of adjacent cells
  • Link cytoskeleton to extracellular matrix
Term
Actin Anchoring Junctions
Definition
  • Cell-cell: Zonula adherens (Adhesion belt; intermediate junction)
  • Cell-matrix: Focal contacts/Adhesion
Term
Intermediate Filament Anchoring Junctions
Definition
  • Cell-cell: Desmosome (macula adherens)
  • Cell-matrix: Hemidesmosome
Term
Muscular Dystrophy
Definition
dystrophin is either missing, decreased, or altered
Term
Pemphigus Vulgaris
Definition
  • Autoantibodies against desmoglein
  • Deposition of immunoglobulin along the plasma membranes of epidermal keratinocytes (Immunofluorescence) -->Severe blistering
  • separation in desmosomes
Term
What attaches cell to matrix in hemidesmosomes
Definition
  • Integrins attach cell to matrix
Term
Bullous Pemphigoid
Definition
  • Antibody against hemidesmosome binds at the dermoepidermal junction
  • Gross and microscopic appearance of subepiderma, non-acantholytic blisters
Term
Importance of Gap Junctions
Definition
  • Facilitate metabolic and electrical coupling between cells.
  • Coordinate activities in epithelia, smooth muscle, heart muscle
  • communication between oocyte and surrouonding granulosa cells. mutation-->infertility
Term
Components of ECM
Definition
  • Polysaccharides+/- Protein: GAGs and Proteoglycans
  • Fibrous & adhesive proteins: Collagen, Elastin, Fibronectin and Laminin
Term
Glycosaminoglycans (GAGs)
Definition
  • Long, unbranched polysaccharide chains composed of repeating disaccharide units
  • One of the two sugars is always an amino sugar, usuall sulfated (except in hyaluronic acid)
Term
Four main groups of GAGs
Definition
  • Hyaluronan: Most connective tissues
  • Chondroitin & Dermatan sulfate: Cartilage and skin (rel. to aging)
  • Heparan Sulfate: Basal laminae, cell surfaces
  • Keratan sulfate: Cornea and cartilage
Term
All GAGs are attached to a core protein except for which one?
Definition
hyaluran
Term
Functions of Proteoglycans
Definition
  • Binding messenger & secretory molecules
  • Structural and functional role in basal laminae: Selective sieves
  • Can be integral components of plasma membrane, acting e.g. as coreceptors
Term
Collagen
Definition
Most abundant protein in ECM and overall

Types
  • Fibril-forming (fibrillar): I, II, III, V, XI
  • Fibril-associated (lateral association): IX, XII
  • Network-forming: IV (basal laminae), VII (anchoring fibrils)
Term
Structure of Collagen
Definition
  • Fiber: seen by LM
  • Fibri: seen by EM
  • Collagen molecule: Tropocollagen
  • Cross banding pattern
  • Extremely rich in proline and glycine
Term
Diseases associated with collagen
Definition
Scurvy: Vit. C deficiency prevents proline hydroxylation
 
Mutations: I,II,III (Osteogenesis imperfecta, Chondrodysplasia, Ehlers-Danlos syndrome)
 
Dermatitis herpetiformis: Antibodies against anchoring fibrils (cross reacting antibodies against gluten).
Term
Elastin Structure
Definition
  • Like collagen rich in proline and glycine, but not glycosylated and without hydroxylsine
  • Cross linking of basic molecule (tropoelastin) similar to collagen.
  • The elastin core is covered by sheath of microfibrils (incl. Fibrillin)
Term
Marfan Syndrome
Definition
  • Fibrillin gene mutation
  • elastic tissue defects
Term
Adhesive glycoproteins
Definition
  • Fibronectin
  • Laminin
  • Responsible for linking ECM components to each other and to cells
Term
Functions of Basal Laminae
Definition
  • Scaffolding
  • Separation: Mechanical
  • Suppor: Cell polarity
  • Filtration barrier
Term
Diseases associated with the basal lamina (BL)
Definition
  • Alport's Syndrome: Missing BL components
  • Goodpasture's Syndrome: Antibodies against BL components
Term
Dystropohin
Definition
links actin to the extracellular matrix via a glycoprotein complex.
Term
Gap Junctions
Definition
  • permits ions, and small molecules (less than 1000 daltons) to pass from cell-to-cell, through their central channel
Term
Connexon
Definition
  • separate the opposing plasma membranes by a 2-4 nm gap in gap junctions
  • each connexon consists of six identical protein subunits (connexins) arranged radially around a central channel
Term
Collagen Cross-banding Pattern
Definition
  • The cross-banding is the result of the arrangement of tropocollagen molecules comprising the fibril
  • the collagen polecule (tropocollagen) is a rod-shaped molecule measuring 300nm in length.
  • the typical cross-banded repeat every 67 nm along the collagen fibril is due to the staggered parallel arrnagement of the tropocollagen molecules, and their ability to permit heavy metal stains from penetrating the fibril
Term

Intracellular Events

(Major Events in Synthesis of Collagen)

Definition

a. Preprocollagen synthesis (Pro-alpha chain)

b. Hydroxylation of selected prolines and lysines

c. Glycosylation (of selected hydroxylysines)

d. Procollagen formation (triple helix)

e. Secretion of procollagen

Term

Extracellular Events

(Major Events in Synthesis of Collagen)
Definition

f. Cleavage of procollagen to form tropocollagen (collagen molecules)

g. Self-assembly of tropocollagen into a fibril

i. Covalent bond formation = cross-links (Fig. 3)

Term
Fibronectin
Definition

A large adhesive glycoprotein that has domains specialized for binding itself, collagen, fibrin, proteoglycans and cell surfaces (via the integrins).

The fibronectin receptor (an integrin) is a transmembrane glycoprotein that links fibronectin (in ECM) with cytoskeleton (in cell). Fibronectin molecules assemble into fibrils only on the surface of certain cells.

There is also a plasma fibronectin that functions in blood clotting, wound healing and phagocytosis.

Term
Laminin
Definition

A cross-shaped glycoprotein with several functional domains.  It is abundantly present in the basal laminae, and links on the one hand  epithelial cells to the basal lamina and on the other hand ECM basal lamina components such as collagen type IV and heparan sulfate.

Term
Basal Lamina
Definition

a) A specialized region of extracellular matrix (ECM) that appears as a 40120 nm thick filamentous mat-like structure.  It is produced by the cells that rest upon it.  These include all epithelial cell sheets and tubes, individual muscle cells, fat cells and Schwann cells.  

b) Composed of type IV collagen, laminin, nidogen (also called entactin), and proteoglycans (mostly of the large heparan sulfate proteoglycan perlecan linked to core proteins). These molecules form bonds between themselves as well as with the overlying cell plasma membrane (integrin binds to Type IV collagen and laminin. The latter also binds to dystroglycan).

 

c) Morphologically characterized by two zones; the lamina rara (lamina lucida) lying next to the plasma membrane, and a denser meshwork of material, the lamina densa, lying adjacent to the reticular lamina of the connective tissue.  

d) Basal lamina is distinguished from basement membrane

Term
Basement Membrane
Definition
  • Consists of the basal lamina plus the undelrying reticular lamina
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