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Last Class: Cytoskeleton 1. Cytoskeleton components: Microtubules Actin Filaments Intermediate Filaments 2. The regulat PowerPoint Presentation
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Last Class: Cytoskeleton 1. Cytoskeleton components: Microtubules Actin Filaments Intermediate Filaments 2. The regulation of microtubules and Actin filaments 3. Molecular Motors 4. Cell behaviors related to cytoskeleton. Cell Adhesion on Extracellular Matrix (ECM).

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Presentation Transcript
slide1

Last Class: Cytoskeleton

  • 1. Cytoskeleton components:
    • Microtubules
    • Actin Filaments
    • Intermediate Filaments
  • 2. The regulation of microtubules and Actin
  • filaments
  • 3. Molecular Motors
  • 4. Cell behaviors related to cytoskeleton
slide3

Cells surrounded by ECM

(macromolecules consisting of proteins and polysacchrides)

Embryonic chick limb bud

slide4

Connective Tissue underlying an epithelium

Fibroblast, primary cell secreting ECM

slide5

Fibroblasts in Connective Tissue

With Collagen fibers

(SEM image of rat cornea, no elastic fiber existing, hyaluronan, proteoglycans and glycoproteins have been removed by enzymes and acids)

slide6
ECM
  • Glycosaminoglycans (GAGs) covalently linked to protein, proteoglycans forming gels
  • Fibrous proteins: collagen, elastin, fibronectin, Laminin.
slide7

The repeating disaccharide sequence of a GAG

Sulfate, carboxyl groups, negative charges

slide8
GAGs
  • Hyaluronan
  • Chondroitin sulfate and dermatan sulfate
  • Heparan sulfate
  • Keratan sulfate
slide9

The relative dimensions and volumes of different molecules

Very stiff and hydrophilic, can’t be packed

Negative charge->cation, Na+ ->water molecules->swelling pressure->compression resistent

slide10

The repeating sequence of hyoluronan

Single chain of 25,000 sugars; No sulfate

slide11

The linkage of GAG to protein, the assembly of proteoglycan

Start from a serine, 4 saccharide and GAG

Except hyalurona

slide12

Diversity of Proteoglycans

Membrane-bound ribosome-> endoplasmic reticulum ->golgi apparatus

slide13

Aggrecan aggregates

Non-covalently bound to hyaluronan chains

Just like decorin decorates collagen fibrils

proteoglycan functions
Proteoglycan functions
  • Constrain the range of embedded protein actions
  • Affect embedded protein activities
  • Control embedded protein release rate
  • Prevent embedded protein degradation
  • Control the local concentration of embedded proteins
  • Function as co-receptors
slide16

Fibrous Proteins:

Collagen, elastin, fibronectin, laminin

slide17

Collagen Molecules

Glycine, proline, hydroxyproline

Triple helix (three fibers interwined together)

slide18

Embryonic chick skin

Fibroblasts surrounded by collagen fibrils (high order polymers)

slide20

Crosslinking of collagen fibrils

Deaminated by lysyl oxidase to yield aldehyde groups, spontaneous covelent bond between aldehyde groups (about every 67 nm)

If crosslink is broken, collagen is easy to tear

slide24

Fibril-associated collagen helps the organization of fibrils to resist tensile force.

Collagen fibrils in the tadpole skin. Tendon and bone are different

slide25

Cells help the organization of collagen fibrils

Two embryonic chick hearts at the ends and collagen gel in the center

Hearts full of fibroblasts and heart muscle cells

slide27

Stretching of a network of elastin molecules

Elastin is highly hydrophobic

Mainly two features: hydrophobic and cross-linked segments

Hydrophobic segments provide elasticity

Cross-linking provides stability

slide28

Fibronectin (crucial for angiogenesis)

A glycoprotein dimer connected by disulfite bonds at one end

Can exist in soluble or fibrillar forms

slide29

Co-alignment of extracellular fibronectin fibrils and intracellular actin filament bundles

Red: fibronectin fibrils

Green: actin filament bundles

Not only important for adhesion, but also for migration

slide31

3 kinds of Basal Laminae

A thin, flexible mats underlying all epithelial cells and tubes

Not only for structural support and filtering, but also determine cellular functions

slide32

Basal Laminae in the cornea of a chick embryo

Usually synthesized by the cells seeded on it

Most laminar consists of type IV collagen, laminin and nidogen (enactin)

slide34

Function of Basal Laminae in neuromuscular junctions (besides the supporting or filtering functions)

Muscle cells: laminin; neuronal cells: agrin (heparan sulfate proteoglycan)

slide37

Cancer Cells and ECM Degradation

Matrix metalloproteinase, serine protease

Proteases bound on cell surface receptor

Controlling of protease activity: 1. local activation; 2. surface receptor binding; 3. inhibitor secretion

tPA: tissue-type plasminogen activator; uPA: urokinase-type plasminogen activator

slide38

ECM Receptors

Integrins

Transmembrane heterodimers

20 nm above cell surface, dependent on Ca2+ and Mg2+

Integrins couple ECM to cytoskeleton through cytosolic proteins, talin, a-atinin, paxillin, filamin, vinculin

slide41

Outside-in Signaling of integrins

FAK, a key molecule for integrin functions

FAK can bind to Talin which associates with integrin b subunit, to paxillin which associates with integrin a subunit

slide42

Matrix-dependent cell survival in the formation of proamniotic cavity

During embryonic development

slide44

Summary

  • 1. ECM components: glycosaminoglycans (GAGs) and fibrous proteins
  • GAGs: Hyaluronan; Chondroitin sulfate and dermatan sulfate; Heparan sulfate; Keratan sulfate
  • Fibrous proteins: collagen, elastin, fibronectin, laminin
  • 2. basal laminae
  • 3. Cell-ECM interaction, ECM degration
  • 4. ECM receptor, integrins