Cell polarity

Question 1

Cell polarity ?

Question 2

Mechanisms that Establish Cell Polarity

Answer 2

1. Polarity Complexes and Their Interactions:

• The Par complex localizes at the apical side, helping to establish the initial polarity cues.
• The Crumbs complex reinforces the apical domain.
• The Scribble complex antagonizes Crumbs to ensure basolateral identity.

2. Interplay of Determinants:

• Extracellular Signals: Neighboring cells and extracellular matrix interactions influence polarity.
• Intracellular Pathways: GTPases (like Cdc42 and RhoA) regulate cytoskeletal dynamics and vesicle trafficking.
  Feedback Loops: Once polarity is established, molecular feedback ensures maintenance.

Tight Junctions and Adhesion Molecules:

They physically separate cellular regions and allow differential localization of proteins.
Integrins: Link the cytoskeleton to the extracellular matrix, aiding in polarity maintenance.

Cytoskeletal and Organelle Positioning:

Microtubules provide a scaffold for vesicle transport.
Actin filaments define cellular shape and influence endocytosis.

Question 3

Sorting in Epithelial Cells:

Answer 3

Golgi Apparatus: Acts as a central hub for sorting cargo based on specific signals.
Endosomes: Help in recycling and directing proteins to the appropriate membrane domain.
Lipid Rafts: Specialized membrane microdomains that aid in sorting proteins to the apical surface.

Question 4

Neuronal Polarity and Sorting:

Answer 4

In neurons, polarity is crucial for differentiating axons from dendrites.
Selective transport of proteins and vesicles ensures proper neuronal function

Neurons are highly polarized cells, meaning different parts have specialized functions. The two main parts of a neuron are:

Dendrites (Input) – Receive signals from other neurons.
Axon (Output) – Sends electrical signals to other neurons, muscles, or glands.
This polarity is essential for proper communication in the nervous system because it ensures that information flows in one direction—from dendrites to axons.

How is Neuronal Polarity Maintained?
- Microtubules: Act as “highways” to transport materials between the cell body, dendrites, and axon.
- Polarity Proteins (Par, Crumbs, Scribble Complexes): Help distinguish between axons and dendrites.
- Tau Protein: Stabilizes microtubules in the axon, ensuring proper transport.

Question 5

Defects in Polarity and Their Role in Disease : cancer

Answer 5

Cancer (Epithelial-Mesenchymal Transition - EMT)

Loss of polarity disrupts cell-cell adhesion, allowing tumor cells to migrate and invade other tissues.
Example: Metastasis in carcinoma due to loss of epithelial polarity.

Normally, epithelial cells have apico-basal polarity and strong cell-cell adhesion.
In cancer, epithelial cells lose their polarity and transition into mesenchymal cells, which have front-rear polarity (migratory behavior).
This allows cancer cells to invade tissues and metastasize (spread to other organs).

–> EMT is a normal and essential biological process in certain situations
In cancer, EMT is hijacked by tumor cells, allowing them to:
- Lose polarity and adhesion (detach from their original site).
- Gain migratory abilities (move through tissues and blood vessels).
- Invade distant organs (forming metastatic tumors).

Question 6

Defects in Cell Polarity : Pancreatitis

Answer 6

The pancreas contains polarized acinar cells that secrete digestive enzymes directionally into ducts.
In pancreatitis, polarity defects cause mislocalized enzyme secretion, leading to:
- Autodigestion of the pancreas (enzymes digest the pancreas itself).
- Inflammation and cytokine release, worsening tissue damage.

Question 7

Defects in Cell Polarity : Alzheimer’s Disease and Neuronal Polarity

Answer 7

Neurons rely on polarity to transport signals correctly (axon-dendrite distinction).
In Alzheimer’s, tau proteins become hyperphosphorylated, leading to:
- Disrupted microtubules, impairing intracellular transport.
- Neuronal dysfunction and cell death, contributing to memory loss.