Epithelia Polarity and Protein Trafficking Flashcards
What is polarity?
A difference in structure, composition or function between the two poles of a cell, such as apical/basolateral in an epithelial cell, axon/dendrites in a neuron.
In epithelial cells this also means location of a protein in a specific location (e.g., apical or basolateral) in the cellular membrane.
Are all cells polar?
Yes
What are the two distinct domains that epithelial cells develop?
Apical domain
Basolaterial domain
What are the steps taken to establish polarised epithelium?
1) Interactions between neighbouring cells and between cells and basement membrane
2) Adherens junctions form
3) Activation of small GTP proteins to form polarity complexes.
4) Formation of tight junctions
5) Positioning of the three protein polarity complexes (PAR / CRB / SCRIB)
What connects cells to basal lamina?
Hemidesmosomes
What is cell-cell interaction between?
Tight Junctions, Adherens Junction and Desmosomes
What occurs in order for the epithelial cells to form epithelium (e.g., during wound healing)?
Stem cells divide - new cells form contract with basal lamina though hemidesmosomes - then new cells form intercellular connections with neighbouring epithelial cells, helping to form an enlarged epithelium/fill gap.
What does the formation of adheren junctions initiate?
Epithelia formation
What makes the initial cell to cell contact in the formation of adherens junctions?
Nectin proteins
What does two e-cadherins on neighbouring cells form?
homodimer
What does the formation of a homodimer require?
Ca2+
What does the cytoplasmic tail of E-cadherin bind to?
Alpha Catenin
What links E-cadherin to actin cytoskeleton?
Alpha catenin
What does alpha catenin link to and what does the link form?
Alpha catenin links E-cadherin to actin cytoskeleton and also links nectin and cadherin complexes.
What are the small GTP binding proteins?
cdc42 and RAC1
what does aPKC do?
initiate enzyme activating and can phosphorylate target proteins
What are the three polarity complexes?
PAR (Partitioning defective)
CRB (Crumbs proteins)
SCRIB (Scribble proteins)
What are the three functions of a tight junction?
Barrier
Gate
Fence
What do tight junction components recruit?
Polarity protein complexes (PAR, CRB, SCRIB)
What is the position of PAR complex?
Apical near TJ
What is the positioning of the CRB complex?
Apical near TJ
What is the positioning of the SCRIB complex?
basolateral
What does the positioning of the protein polarity complexes create?
Polar epithelium
What has to be pulled apart for cell division?
Polarity complexes (then they are reformed so they have to be able to change rapidly)