Lecture 3

Question 1

Connective vs. Epithelial Tissue

Answer 1

• Epithelial tissue: Cells directly connected to each other with minimal extracellular matrix
• Connective tissue: Cells dispersed through extracellular matrix

Question 2

Epithelial structure

Answer 2

• Tight junction: seals gap between epithelial cells
• Adherens junction: Connects actin filament bundle in one cell with another
• Desmosome: Connects intermediate filaments in one cell to another
• Gap junction: Allows passage of water soluble molecule from cell to cell
• Hemidesmosome: anchors intermediate filaments in cell to extracellular matrix
• Cell-cell junction mediated by cadherins
• Cell-extracellular mediated by integrins

Question 3

Cadherins

Answer 3

• Transmembrane proteins expressed by both cells
• Stick to specific cadherin on other cells
• Interactions require Ca++
• Homophilic interactions
• Indirectly link actin cytoskeleton between adjacent cells in epithelial tissue

Question 4

Adhesion Belts

Answer 4

• Adhesion belt contraction pulls cells to form a tube
• Express different cadherins to establish new interactions and ensure neural tube closure

Question 5

Tight Junctions

Answer 5

• Define domain of the cell
• Apical domain: Surface, cavity, or organ
• Basal domain: Faces inside of the body
• Basal and lateral grouped in basolateral domain
• Maintained by tight junctions
• Occludins and claudins form tight junctions -> homophilic interactions with extracellular domains
• Limit diffusion in extracellular space
• Prevent membrane proteins from moving between apical and basolateral domain
• Active transporters: move glucose into epithelial cell on apical domain
• Passive carriers in basolateral allow glucose to diffuse our of epithelial cell into tissue/blood

Question 6

Integrin

Answer 6

• Mediate cell-cell matrix junctions
• Anchor actin filaments to extracellular matrix

Question 7

Polarity cues establish cell cohesion

Answer 7

• Adherens junction form first
• Provide polarity cues to define apical from basolateral
• PAR, CRUMB signal apical side -> stimulate by cdc42
• Scribble inhibit PAR, signal to basolateral