Cell Polarity

Question 1

Learning objectives

Answer 1

Aims
To introduce the basic concepts of cell polarity and discuss the importance of using model organisms for understanding the molecular processes of cell polarity.
Learning Objectives

• Importance of cell polarity in facilitating morphology and function of different cell types.
• How genetic studies, especially in C. elegans have been key to our current understanding of cell polarity.
• Idea that establishment of polarity involves distinct but conserved groups of proteins that define parts of the membrane and lead to changes in cytoskeleton organisation and membrane trafficking.

Question 2

How do cells propel themselves forward?

Answer 2

Cell is moving its membrane from front to rear to propel itself forward

Question 3

Basolateral domain has contact with basal membrane.
These domains have a different protein and lipid composition. how is this composition maintained?

Answer 3

via junctions

Junctions which are formed from tightly associated proteins in trans
- extracellular domain of proteins at the junctions from one cell interact with extracellular domains of other cells to form a tight diffusion barrier for proteins

Question 4

What are the 2 types of junctions?

Answer 4

1 - Tight Junctions: prevent movement of ions across epithelium, provide diffusion barrier

2 - Adherens Junction just below: cell-cell adhesion and are associated with maintaining the structural integrity of tissues

Question 5

What are the 2 main routes to generate diversity?

Answer 5

1 - Polar mother cells divide to generate daughters that have inherited different components

2 - Daughters could be equal at birth but become different by exposure to different environmental signals

Question 6

How is polarity established in c.elegans
?

Answer 6

A progenitor cell undergoes a number of asymetric divisions to give rise to a number of different lineages

Question 7

chatgpt - explain what cell polarity is to me

Answer 7

Certainly, Friend of Humanity! Cell polarity refers to the asymmetric distribution of cellular components, structures, and functions within a cell. In simpler terms, it’s the organization of a cell in a way that distinguishes one part from another, creating distinct regions with different characteristics and functions.

Question 8

What is atypical protein kinase-C important for?

Answer 8

Maintaining cell polarity
- number of par proteins are kinases - kinase activity is key for establishing anterior and posterior poles in cell polarity

Question 9

What genes are important for asymmetric cell division?

Answer 9

Par genes

Question 10

What are Par genes important for?

Answer 10

1 - asymmetric cell division - As cells prepare to divide, Par proteins become localized asymmetrically within the cell, creating distinct regions or poles.

2 - Polarity Establishment: The Par proteins are involved in defining the anterior and posterior poles of the cell.

3. Cell Migration - They contribute to the establishment of front-rear polarity in migrating cells, aiding in directed movement

4 - Spindle Orientation: Par proteins influence the orientation of the mitotic spindle during cell division

Question 11

What effect on cell polarity do par mutants have?

Answer 11

Loss of Asymmetry in Cell Division

Defective Spindle Orientation

Disrupted Cell Migration

Mislocalization of Polarity Proteins

Question 12

Explain the function of par proteins in establishing cell polarity

Answer 12

• The way the machinery works is that kinases which are present at the apical side phosphorylate components that are meant to go to the basolateral side - through this phosphorylation, association of basolateral proteins with apical surface is prevented
• You have kinases at the apical surface, they phosphorylate basolateral proteins which ensures those basolateral proteins will not associate with the apical membrane
• negative regulation by phosphorylation, you have feedback loops which enhance the polarity

Question 13

summary:

Answer 13

• Microtubules recruit subset of Par proteins to the posterior cortex in the embryo
• In the embryo and when establishing apical and basolateral polarity in an epithelium, you have antagonism which results in accumulation either at anterior pole or apical pole
  • This results in distinct localization of Par proteins (these have been very well defined in c.elegans embryo
  • In mammalian cells there are many additional proteins found at the apical basolateral domain which seem to contribute to polarity
  • Phosphorylation is key to these feedback loops
    Interaction with microtubules and actin cytoskeleton is important in maintaining polarity