cell adhesion and junctional complexes

what are the two types of extracellular membrane (ECM)

basement membrane/basal lamina

fibrillar matrix

basement membrane

thin 2D sheet on which the epithelial cells adhere

fibrillar matrix

3D matrix composed of various fibres

cells are loosely packed

contains proteins and fibroblasts

basal membrane location

underlies epithelia and surrounds some non-epithelial cells

basal membrane contains which proteins

• Collagen IV

• Laminin

• Nidogen

• Perlecan

fibrillar matrix contains

• collagen I

• fibronectin

• elastin

• proteoglycans

types of junctional complexes

occluding junction (tight)

cell-cell anchoring junction (adherens and desmosomes)

channel forming junctions (gap)

cell matrix anchoring junction (focal adhesions and hemidesmosomes)

which basal adhesions hold cells to the basement membrane

focal adhesions

hemidesmosomes

desmosomes and hemidesmosomes are connected to

intermediate filaments

desmosomes located at

cell-cell contacts

hemidesmosomes located at

cell-ECM interface

cadherins form

homophilic interactions meaning they can only attach to same type of cell

epidermolysis bullosa

caused by mutation in intermediate filaments or desmosomal factors

tight junctions are found

close to the apical surface

tight junction function

prevents passage of molecules in both apical and basal directions

form a ring around the cell

fully sealed and always found close to apical surface

acts as a physical barrier

tight junctions are formed by

claudin and occludin

pemphigus

when autoantibodies are produced against desmosomes

gap junctions function

create a pore which can open to allow the passage of molecules and ions (which maintain the membrane potential of neurons) between cells 

important for chemical and electrical signalling

adheren junctions are linked to

actin

When actin myosin filaments interact and generate contractile forces

apical surface constricts causing cell to change shape

sheet of cells become more rounded

Focal adhesions link the actin cytoskeleton to the ECM

via integrins

Focal adhesions form transiently during cell movement

cell movement is a dynamic process

filopodia contains

actin fibres

what do the actin fibres in filopodia enable

navigation of space

movement

what would happen if cells did not have junctions

cancer

cells can lose attachment to each other and squeeze through endothelium cells, leave circulation and become malignant through metastasis

which junctions have homophilic interactions

desmosomes

gap junctions

tight junctions

adheren junctions