Epithelia II

Question 1

List the types of cell junctions and the proteins associated w/ those junctions

Answer 1

1. Tight junctions: occludins and claudins
2. adherence junctions: cadherins linked to intracellular actin cytoskeleton. Also important in intracellular signaling.
3. Desmosomes: different cadherins linked to intracellular intermediate filaments. Also important in intracellular signaling

Question 2

Describe how cells adhere to the basal lamina

Answer 2

Proteins called integrins link the epithelial cells to the basal lamina. These integrins are linked to either actin filaments (desmosomes) or intermediate filaments (hemidesmosomes)

Question 3

Describe the protein components of the basal lamina

Answer 3

1. collagen IV
2. laminin
3. different tissues have different protein compositions in their basal lamina, providing tissue-specific regulation of development, morphology, and functions of tissues.

Question 4

List the key features of stem cells

Answer 4

1. capable of division/ remain in the cell cycle
2. self renewal (mitosis)
3. produce pluripotent/multipotent daughter cells
4. control of division + differentiation

Also note that transit amplifying cells exist. These cells are special cells arising from stem cells, which divide a finite # of times while differentiating (think intestinal crypt)

Question 5

List the signaling systems for stem cells

Answer 5

1. sonic hedgehog (SHH)
2. Wnt
3. FGF (RTK)
4. TGF-Beta
5. Notch

All of these pathways contain:

1. a secreted protein ligand
2. cell signaling pathways
3. most alter gene expression at DNA and RNA levels

Question 6

Describe and give an example of how a small # of growth factors can regulate many stem cell populations

Answer 6

A small number of factors is able to regulate almost all stem cell populations because epigenetic changes allows stem cells to respond differently to the same growth signals.

For example, the Wnt signaling pathway is important in inhibiting cell growth in the colon. Mutations in this pathway lead to FAP. But the Wnt pathway is important in lung tissue too. Loss of Wnt ligand leads to increased lung cancer, but not colon cancer.