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