8: Actin in Non-Striated Muscle, Intermediate filaments, and cell adhesion

Question 1

What does actin and myosin do in non-skeletal muscles?

Answer 1

• cytokinesis
• smooth muscle
• vesicle transport
• cytoplasmic streaming
• cell migration

Question 2

contractile ring/adherens/stress fibres belts is similar to

Answer 2

sarcomere (rolled up)

Question 3

what is the difference between sarcomeres and contractile rings/adheren belts

Answer 3

unstable = depolymerizing to shrink the ring in cytokinesis

not Ca2+

Question 4

smooth muscle contraction is

Answer 4

non voluntary + persistent (arteries, moving digestive tract)

Question 5

How is smooth muscle different from striated muscles?

Answer 5

not coated in troponin and tropomyosin

induced slower but persistent bc myosin binding site of actin not blocked

Question 6

What is the regulator of smooth muscle contraction?

Answer 6

ca2+ (external and released from SR) activates kinase activates myosin regulatory light chains alters myosin conformation via calmodulin (CaM) = contraction

Question 7

How does vesicle transport work with actin filaments?

Answer 7

• myosin 5 bound vesicles are carried along actin filaments
• can transport many types of vesicles and mRNA
• actin (+) end leads to the bud and (+) end actin inside the bud with formin for poly.

Question 8

when is vesicle transport used

Answer 8

budding yeast cells - transport mRNA, organelles, proteins into new bud by myosin walking along cortical actin also organizes Mts

Question 9

What is cytoplasmic streaming?

Answer 9

• found in large cells (plants)
• cytoplasm constantly moves around periphery of the cell for increase diffusion effectivity
• cortical actin network filaments surround moving cytoplasm

Question 10

Where does cell migration occur

Answer 10

embryos

Question 11

What are the actin structures involved in cell migration?

Answer 11

filopodia: fingerlike projection actin bundles

lamelipodia: large branched and networked actin pushing membrane forward by poly

stress fibers: bundles of actin connected to substrate/EXM on which it is moving (focal adhesion) by binding to integrins

Question 12

What are integrins

Answer 12

transmembrane PM proteins that hold stress fibres to connect to extracellular matrix during cell migration

Question 13

what is chemotaxis?

Answer 13

movement of cells due to high [] of chemoattractant

Question 14

receptors and g-proteins are found

Answer 14

around entire cell periphery

Question 15

What are the steps of cell migration/movement?

Answer 15

1. focal adhesion (cell stuck to substrate) and between focal adhesions are stress fibers and activate G-proteins on moving side to make actin
2. lamellipodium extension
3. new adhesion of lamellipodium + new stress fiber + integrins
4. translocation by cell body by actin/myosin movement, moving towards new adhesion
5. deadhesion

Question 16

proteins involved in cell migration?

Answer 16

Ras superfamily of small GTPases (ie Rho proteins)
- Cdc42 (arp2/3)
- Rac (arp2/3)
- Rho (formin)

active in GTP form

Question 17

In a dominant active Rho cell..

Answer 17

a lot of unbranched microfilaments bc of formin activation = long actin bundles -> stress fibers

Question 18

In a dominant active Cdc42 cell…

Answer 18

a lot of filapodia made (membrane protrusions)

Question 19

In a dominant active Rac cell…

Answer 19

membrane “ruffles” and is extending in all directions at once (lamelipodia everywhere)

Question 20

What is a wound closure assay? What does it study?

Answer 20

scratch confluent cells to see if the cells are migratory if they move into the wound

but they must have all of Rac, Cdc42, and Rho

Question 21

What are the steps of activation of GTPase proteins for cell migration?

Answer 21

1. growth factor binds to cell surface receptor which adds GTP to Cdc42 and Rac
2. Cdc42 activates WASp and Rac -> Arp2/3 -> actin polymerization -> filopodia forms
3. Cdc42 also activates Par6 -> gives cell polarity
4. Rac activates WAVE -> Arp2/3 -> actin poly -> lamellipodia
5. Rac + cell surface protein activates Rho-GTP -> forming activated and RacGTP inactivated -> actin poly -> strip finer forms
6. Rho kinase activates myosin

Question 22

adult cells do not

Answer 22

undergo cell migration

Question 23

Cdc42 important in

Answer 23

polarity AND coordinating actin and microtubules

Question 24

what does Par6 do?

Answer 24

• gets activated by Par 6
• induces MT growth and kinesis+dynein activation which will help MT bring proteins and monomers for actin formation at direction of polarization

Question 25

intermediate filaments are not

and have no

Answer 25

globular

no ATP or GTP

no polarity

no known motor proteins

less dynamic

Question 26

basic subunit of intermediate filament is

Answer 26

non polar tetramer linear subunit

Question 27

intermediate filament has

Answer 27

great tensile strength

Question 28

role of intermediate filament is

Answer 28

cell and tissue integrity

Question 29

What are the main types of intermediate filament?

Answer 29

1. keratins: epithelial cells
2. desmin: muscle cells
3. vimentin: mesenchymal (migrating) cells
4. neurofilaments: neural axons
5. lamins: nucleus (membrane)

Question 30

What are intermediate filament associated proteins?

Answer 30

proteins that can bind to intermediate filaments but only for organization

Question 31

intermediate filament do not have proteins for

Answer 31

motors, caps, or severing

Question 32

What are plectin?

Answer 32

intermediate filament protein that links them to MT

Question 33

An example of vimentin use is

Answer 33

ventimin links ankryin in RBC to plasma membrane

Question 34

types of lamins?

Answer 34

A B C support nuclear membrane

B lamins are ubiquitous and linked to inner NM by prenylation covalent bond

A and B form LINC complexes link lamins to internal cytoskeleton cytoplasm

Question 35

how are IFs disassembled in mitosis?

Answer 35

N terminal domain of lamin A phosphorylated at serine (induces disassembly and prevents reassembly)

Question 36

If there is a keratin mutation?

Answer 36

Transgenic mice carrying a mutant keratin gene exhibit skin blistering – weak skin integrity
(loss of dermis)

Question 37

What proteins are in IF junctions?

Answer 37

desmosomes (cell-cell adhesions) and hemidesmosomes (btw cell and extracellular matrix) of epithelial cells