Epithelial Cells
Skin
Lung Alveoli & Bronchi
Kidney Tubules
Intestinal Villi
Bladder
Glandular Ducts
Basal lamina
Basal lamina
Basal lamina
Types of Epithelium
Simple Squamous/ Cuboidalcells wider than they are tallline body cavities e.g. peritoneum, hepatocytes
Columnarcells taller than they are widemucus secetingline the intestinal tract, kideny tubules, ducts of glands
Stratifieda) transitional - usually associated with cavities subject to expansion and contaction e.g. bladder
b) stratified squamous - subject to frequent renewal e.g. skin
Epithelial Cell Characteristics
Cell contactCell communication
Signal reception & transductionGeneration of ionic gradientsConstitutive secretion
Cell-matrix interactionsBasement membrane
Regulation of nutrient & water uptakeRegulated secretionProtection
TJ
D
GJ
Apical membrane• Glycosyl-phosphatidylinositol
linked (PI) proteins• Na+-dependent transporters•Hydrolases• Cl-channels• H+-ATPase
Lateral membrane• Cell adhesion molecules• Tight Junctions (TJ)• Adherens Junction (AJ)• Desmosomes (D)• Gap Junctions (GJ)
Baso-Lateral membrane• Anion transporters• Na+K+-ATPase• Growth factor receptors• Hormone & neurotransmitterreceptors
Basal membrane• Hemidesmosomes (HD)• Basement membrane receptors
HD
Apical Membrane
Lateral Membrane
Baso-Lateral Membrane
Basal Membrane
AJ
Cell Junctions
*
*
*
Tight Junctions
seal apical surfaces from lateral and basal surfaces
Tight Junction Molecules
Desmosomes
E-cadherin α,β,γ catenins
Important for strength and flexibilty
Cadherins
Basement membrane
Hemidesmosome
Anchoring to the basement membrane
Laminin 5
KidneySalivary Gland
BranchingMorphogenesis
Mesenchymal-EpithelialTransistion
BranchingMorphogenesis
mesenchyme determines epithelial differentiation
Kidney Organ Culture
Advantages of the Kidney Organ Culture Model
• Inducer and responder tissues remain separate until late stagesof development
• Isolation of metanephric mesenchyme and in vitro growth is possible
• Development occurs slowly, allowing characterization of all stages
• Polarization of epithelial cells can be studied, a characteristic shared by all epithelial cell regardless of mode of development
distal tubule
proximal tubule
podocytes
bowmans capsule
+/- Antibodies
Effect on tubule formation
Differential expression of genes expressed inuninduced and inducedmesenchyme
Loose mesenchyme Condensate Comma-shaped body S-shaped tubule
Stages in Epithelial Development in the Kidney and Important Factors
Induction/Proliferation Polarization
ureter loose condensate polarisation Tubulemesenchyme (comma-shaped body) (S-shaped
tubule)
Extracellular collagen I/IIIMatrix fibronectin/ tenascin-C
laminin α1laminin α5
++ +/- - -++ ++ ++
++ ++--
-
- - -Cell-Matrix Receptors
integrin α6dystroglycan + ++- -
Cell-Cell NCAMAdhesion syndecan-1
E-cadherin
++++ +
- - --
- - +++-
TranscriptionFactors
Pax2WT1
WNT4 BMP4FGF7
Growth Factors
++++ ++ ++ (++)
+ ++
- - - --
+ +
Laminin α1/ integrin α6β1, α-dystroglycan condensation and polarisation
Uvomorolin/ E-cadherin condensation
WNT4 required for condensation and epithelial cell formation
WT1 inhibits apoptosis of metanephric mesenchyme/ proliferationmaintains podocytes
Pax2 early ureteric bud formation and branching
BMP4 inhibits ureteric bud branching
FGF7 induces ureteric bud branching
Laminin Family
type IV collagen
laminin
perlecan
KEY:
nidogen
Laminin α1 Laminin α5Pan-Laminin
condensate
ureter
Comma shaped bodies
S-shaped tubule
ureter
Laminin α1
Pan Laminin Laminin α1
Protease Fragments of Laminin 1
E = elastaseP = pepsinT = trypsinC = cathepsin G
E8
E3
P1E1-x
Antibodies to laminin α1 (E8) inhibit epithelial cell development no polarization
E3 Data
α6β1
α dys α dys
α dysLam α1
α dys
α dys + Integrin α6
Integrin α6
Laminin 1G1-3
α6β1
Laminin 1G4-5
α1
α6β1 G1-3G4-5 α-dystroglycan
Laminin 1
Angiogenesis
-ingrowth of blood vessels
distal tubule
proximal tubule
podocytes
bowmans capsule
Podocytes produce laminin α5which is deposited in the glomerular basement membrane
Substrate for endothelial cell ingrowth
Laminin α5 knockout mouse
Podocytes proliferateNo glomerular basement membrane formation
Overexpression of transgene for a chimeric laminin α5 cannot rescue the phenotype
α5
Pan LM
Pan LM
LM α1
LM α1
Laminin α1 appears around forming epithelia Antibodies to laminin α1 (E8) inhibit epithelial cell development no polarization
control + anti-E8
24h
36h 72h 72h
Role of Laminins in Differentiation
Refs: Ekblom et al., 1980 PNAS USA 77, 485; Klein et al., 1989. Cell 55, 331
Kidneysalivary gland, lung organ cultures
Models for Investigating Protein Targeting
MDCK cell line = madin-Darby canine kidney epithelial cell line
Viral Model - polarized viral budding occurs in different viruses and various cell types
e.g. Influenza virus buds APICALLY in all epitheliaVesicular stomatitis virus (VSV) buds BASO-LATERALLY in all epithelia
- viral proteins are produced 100-1000 times in excess over endogenous plasma proteins
MDCK+ Influenza-haemaglutini (HA)+ VSV
20°C incubation
(accumulation of viral poteins in trans-golgi)
nitrocellulose 37°C incubation
Vesicles released into mediumIP with anti-viral tails
Differential sedimentation
Analysis of HA & VSV containing vesicles
Proteins common to HA & VSV vesicles are involved in vesicle buddingProteins specific for HA or VSV vesicles are involved in apical or baso-lateral targeting