Lecture 24 Flashcards

1
Q

What are the two types of cell interactions?

A
  1. cell- cell

2. cell- (extra)cellular matrix

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2
Q

Describe the key features of tissue adhesion

Hint: illustrate using epithelial and connective tissues as examples

A

Epithelial tissue: Cells are bound together into sheets (collagen), cells are anchored on the thin matrix mat of the basal lamina and the forces are born by intracellular cytoskeleton linked through adhesions.

Connective tissue is formed mainly by extracellular matrix with the cells secreting the matrix are distributed within it and forces are born through extracellular matrix

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3
Q

How does epithelial tissue respond to mechanical stress?

A

Mechanical stress is transmitted from cell-cell by cytoskeletal filaments anchored to cell-matrix and cell-cell adhesion sites

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4
Q

How does connective tissue respond to mechanical stress?

A

extracellular matrix directly bears mechanical stresses of tension and compression

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5
Q

What are the cell junctions anchoring the lateral side?

A

adherence junctions (actin filaments) and desmosomes (intermediate filaments)

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6
Q

What are the cell junctions anchoring the basal side?

A

actin linked cell matrix junctions and hemidesmosomes for intermediate filaments

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7
Q

Functional role of tight junctions

A

Tight junctions fence between plasma membrane domains to seal gaps between epithelial cells

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8
Q

adheren junctions

A

connects actin filament bundle between adjacent cells

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9
Q

desmosome

A

connects intermediate filaments between adjacent cells

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10
Q

actin-linked cell matrix junction

A

anchors actin filaments in cell to extracellular matrix

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11
Q

hemidesmosome

A

anchors intermediate filaments in a cell to extracellular matrix

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12
Q

What do anchoring junctions depend on?

A

transmembrane adhesion proteins

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13
Q

What are the two superfamilies of anchoring junctions?

A

Cadherins (cell-cell interactions)

Integrins (cell-matrix interactions)

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14
Q

Cadherins

A

Except prokaryotes, fungi, and plants cadherins form a diverse family of adhesion molecules in all animals and choanoflagellates. Cadherins need calcium for adhesion function. Anchoring of cell-cell junctions through cadherins are usually symmetrical and mediate homotypic (homophilic) adhesions.

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15
Q

Velcro principle of Cadherins

A

Cadherins mediate weak interactions, but many of these interactions typically have strong adhesion. To remodel cell junctions, individual interactions are easily broken

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16
Q

How do cadherins guide the organization of developing tissues?

A

Qualitative and quantitative differences in cadherin expression have different roles in mediating highly selective recognition in organization of developing tissues.

In 1950s, dissociated embryos reformed and many structures resembled the original embryo

17
Q

catenins

A

In adherens junctions, catenins link classical cadherins to actin cytoskeleton.

18
Q

Adherens junction assembly mechanism

A
  1. Cell-cell contact is initiated by membrane protrusions with small cadherin and catenin clusters
  2. Actin and cadherin recruitment expands junction with recruitment of more cadherins and catenins
  3. Actin remodeling and myosin recruitment expands adherens junction to form contractile actin and myosin bundles
19
Q

How do adherens junction respond to forces generated by actin cytoskeleton ?

A
  1. equalize actin contractility in neighboring cells
  2. coordinate actin usage in neighboring cells
  3. loosen adhesion after actin contraction
20
Q

In cell junctions, tissue remodeling depends on what?

A

coordination of actin-mediated contraction with cell-cell adhesion

21
Q

Diffusion through tight junctions

A

Paracellular diffusion of ions vary across epithelia

Tight junctions in small intestine 10, 000x more permeable to ions like Na+ than urinary bladder

22
Q

What are the two tight junction proteins?

A

claudin and occludin

23
Q

Claudins

A

Claudins can form ion-specific pores. The intracellular domains of claudins interact with ZO proteins. Claudins are important for structural assembly of tight junctions

24
Q

Occludins

A

limit junctional permeability

25
Q

Tricellulins

A

seals membrane where three cells meet