Lecture 5 Cell adhesion and junctional complexes

What is the basement membrane made of?

Proteins which the epithelial cells secrete

Main components of the basement membrane/ basal lamina (type of matrix)?

Collagen IV, Laminin, Nidogen, Perlecan

Components of the Fibrillar matrix?

3D matrix composed of many fibres, also contains fibroblasts

Surrounds the mesenchyme which is basically connective tissue under the basal lamina.

Made of: Collagen I, Fibronectin, Elastin, Proteoglycans (proteins+carbs)

Name the diff types of junctions:

Tight junctions, Adherens junctions, Desmosomes, Hemidesmosomes

Role of tight junctions?

Found close to the apical surface, forms a ring around the cell and does not allow the passage of molecules.

Formed by the proteins: claudin and occludin

Role, Gap junctions?

These junctions form pores, fenestrations. Allows small molecules and ions to pass between cells: chemical and electrical coupling.

Role Adherens junctions?

These junctions are linked to the actin cytoskeleton.

Actin myosin forces can cause epithelial cells to bend!

Homophilic binding of E-cadherins, depends on calcium ions.

Role of focal adhesions?

Connects the cell to the ECM, also plays a huge role in movement. Helps maintain structure of cell, made of integrins which helps to do this

How was the first cell adhesion molecule discovered?

Masatoshi Takeichi, investigated amphibian embyronics, a cell on solution in petri dish in Japan clustered together and proliferated. Cell in the USA on a solution containing EDTA did not, because EDTA binds to the calcium, removing it from the cell and prevented the cells to stick together.

Cadherins are dependent on what?

Ca2+ ions, can cause E-Cadherins to bind together.

Cadherens are different on different cell types, and they are homophilic meaning they stick to only the same types.

Examples of other junctions not covered:

Neuronal synapse junctions and plasmodesmata, plant gap junctions + several others…

Desmosomes and hemidesmosomes under the EM?

Desmosomes—> like a railway track, dark areas between cells 500nm

Hemidesmosomes—> Like dark buttons (basal surface) at the cell ECM interface 100nm

The desmosomes are attached to what?

Intermediate filaments within the cell.

Pemphigus?

Auto immune disease, where the body attacks its own cells.

The composition of the ECM?

Made of both the basement membrane and its collagen IV and laminin as well as the fibrillar matrix and its collagen I and fibronectin.

Experiment to see the role of tight junctions?

2 mice cubs, one was control, other one knockout protein: claudin, as a result tight junctions were not made, purple dye was injected in both. Control did not look purple, the knockout mouse did, and after several hours body mass decreased due to water evaporating…