Lect2: Polarized Cells Flashcards
Basal side:
Lateral side:
Apical side:
Basal side:
- Side which connects to the basement membrane.
Lateral side:
- Side not touching the basement membrane or apical surface
Apical side:
- Side which interfaces with the lumen
Examples of polarized cells:
Basal vs Apical (hepatocytes, simple epithelium, proximal renal tubule, sertoli cells)
Dendritic vs Axonal
Migrating cells (migrating fibroblast)
Budding yeast
How can one study apical vs basal polarization?
MDCK cells form tight junctions. Can be placed on a extracellular matrix with a porous filter and a basal and apical medium on either side. If the cells formed tight gap junctions, then there will be a high resistance if measured by a voltometer (this is good)
What’s a methionine pulse experiment?
Pulse with radioactive methionine, for 10 minutes. Immunoprecipitate at different time points. See what the weight of your protein is. Has it been glycosylated yet?
Result from the loss of N terminus of LDL receptor:
It became predominately located apically, whereas it is normally located to the basolateral membrane. Tells us to things.
1: N terminus (which was inside the cytoplasm) is involved in basolateral sorting.
2: Loss of it did not result in an equilibrium. Instead, the apical side was favored. There must be another signal which guides to the apical side of the protein.
N-glycans help some proteins sort to the apical side (this is a soluble protein) what does this tell us?
Must be lectins which help in apical vs basal sorting.
Apical Surface:
- Sorting signals:
- Sorting mechanisms:
- Apical Surface (Based on lumenal facing factors):
1: Glycosylation (N and O)
2: glycosylphosphatidylinositol (GPI, a lipid anchor) group - Sorting mechanisms:
1: Partitioning into microdomains (lipid rafts, sorting lectins)
Basolateral Surface:
- Sorting signals:
- Sorting mechanisms:
- Sorting signals:
1: Tyrosine-based (YXXΦ)
2: Non-tyrosine based
3: Di-hydrophobic (ΦΦXΦΦ) - Sorting mechanisms:
Clustering by cytoplasmic coat proteins (AP(#), clathrin, etc.)
Possible mechanisms for polarized sorting:
1: All newly synthesized proteins go to BL first, then same are selectively sorted apically
2: Proteins are sorted directly to the apical or BL biosynthetic pathway
3: Proteins are retained in the BL or apical membranes through interactions with cytoskeleton
4: Protein are recycled to the BL or apical membranes
5: Proteins interact with the extracellular matrix
6: proteins interact with adjoining cells
AP-μ1B:
- What is the significance of μ?
- What does this protein do?
- What is the significance of μ?
It is the segment of an AP which binds the protein receptor. Not natively found in MDCK
- What does this protein do?
I guides proteins to the basal membrane, but it is not the only way to do so (does this through clathrin pit formation, as AP proteins do)
Basolateral proteins are inserted via the mammalian exocyst close to the ______.
tight junction
AP-μ1B:
- In what tissues is this highly expressed?
- In what tissues is this not expressed?
- In what tissues is this highly expressed?
Kidney, prostate, thyroid
- In what tissues is this not expressed?
Liver
Hepatocyte structure:
Important to note basolateral connects to capilleries for protein excretion
Three options for transport in the hepatocyte:
Transferrin receptor goes directly to the BL membrane.
5’ nucleotidase, a GPI-linked protein goes first to the BL membrane and then to the apical membrane where it localizes at steady-state.
Bile transporters and the multidrug resistance protein both multispanning membrane proteins go directly to the apical membrane.
Trafficking in neurons:
- Axon vs dendrite:
- Dendrite spines:
- Axon vs dendrite:
Axon = apical trafficking, dendrite = basolateral trafficking.
- Dendrite spines:
Provide additional proteins for binding and sequestering of products delivered to the dendrite
