UNSW Cell Biology

This lecture introduces the concept of cell adhesion. Unicellular organisms use to adhere to the environment, nutrition or pathogenesis. Multicellular organisms require adhesion for cells to adhere to each other and the extracellular matrix. Cell adhesion occurs through specific cellular specializations and molecules and has both static and dynamic functions. This topic will be revisited in lectures on extracellular matrix, cell cytoskeleton and signalling.

Lecture Text: Lecture Word Document (182 Kb)

Lab 5: Immunochemistry 

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• Transmembrane glycoproteins
• Normally permanent
• Except migrating cells and embryonic
• Changes with development
• Loose adhesion when mature or disease
• Erythrocytes, cancer

• Cadherins
• Immunoglobulin Superfamily
• Selectins
• Gap Junctions
• Integrins

• Contain 5 cadherin repeats
• Each comprising sandwich of beta sheets
• requires calcium ions to bind
• Homophilic binding through end element
  • Like with like
• Functional unit a dimer

• Vertebrates have 100+
• In addition to adhesion they also have role in immune system
• Contain varying number of Ig-related domains
• Comprising sandwich of beta sheets
• Held together by hydrophobic interactions

• G. Edelman
  • Nobel Prize in Physiology or Medicine in 1972
  • "for their discoveries concerning the chemical structure of antibodies"
• studying the nervous system
• Cell Adhesion Molecules (CAMs) family
  • Neuronal cell adhesion molecules (N-CAM)
  • N-CAM, Ng-CAM L-CAM, I-CAM

Neuronal cell adhesion molecules

(Image: Stress, cognitive impairment and cell adhesion molecules, Carmen Sandi, Nature Reviews Neuroscience 5, 917- (December 2004) doi:10.1038/nrn1555)

• Vertebrates have only in circulatory system
• Role in adhesion of leukocytes (blood cells) to endothelium (vessel wall)
• Cooperate with integrins and Ig-SF receptors
• Selectins 2 Heterophilic interactions
• Bind counterreceptors
• Glycosylated proteins
• Bind through C terminal lectin domain of selectin

• Mammals have genes for 18 alpha and eight beta integrins
• Role in cell adhesion to extracellular matrix (ECM) basement membranes
• Induction of cell polarization by adhesion
• Cell migration through ECM will discuss in ECM lecture

• Desmosomes (macula adherens)
• Adherens Junctions (zonula adherens)
• Septate Junctions
• Tight Junctions
• Gap Junctions

• Discovered by K.R. Porter in 1954
• intermediate filaments anchor the dense plaque that occurs under the membrane of each cell
• desmos = bond
• skin, lining of internal body cavity surfaces
• disappear when cells are transformed

• microfilaments anchor the plaque that occurs under the membrane of each cell
• plaques not as dense also occur as hemiform
• heart muscle, layers covering body organs, digestive tract
• transmembrane proteins
• Cadherin

Adherens Junctions

• Discovered by M.G. Farquhar and G.E. Palade in 1963
• zonula occludens
• Fusion of 2 plasma membranes acts as a “seal”
• Epithelia lining
• digestive system gut, ducts, cavities of glands, liver, pancreas capillary walls urinary bladder

• Discovered by J.P. Revel & M.J. Karnovsky in 1967
• allowing direct communication between cells (open & close)
• close membranes 2 - 3 nm apart
• connexins form hollow 1.5 nm diameter cylinders
• heart muscle, smooth muscle electrical and chemical integration as a single functional unit
• Also in embryonic development

• gap junction
• two hemichannels (connexons)
• each formed from 6 connexin molecules
• rapidly turned over

Tight Junction

seals neighbouring cells

Adherens Junction

joins actin bundles between cells

Desmosome

joins intermediate filaments between cells

Gap Junction

cell-cell communication, passage of small molecules

Hiemidesmosome

anchors cell intermediate filaments to to basal lamina (extracellular matrix)

• Mammals have genes for 18 alpha and eight beta integrins
• Role in cell adhesion to extracellular matrix (ECM)
• basement membranes
• Induction of cell polarization by adhesion
• Cell migration through ECM
• Mainly receptors for ECM proteins
• Fibronectin, laminin, collagen
• Some heterotypic binding Ig superfamily
• Interact with cell cytoskeleton signalling

• links the outside of the cell (ECM) through transmembrane proteins (integrins) with the cell cytoskeleton (actin microfilaments)
• extracellular matrix
• integrins
• actin cytoskeleton

Focal Adhesions (red) Actin microfilaments (green)

(Image: Christoph Moehl)

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Links: Current Course Outline 2008