slide set 12 Flashcards
for most cells, motility is guided by….
extracellular cues!
small G proteins
small G proteins control where actin polymerizes and the type of network formed
small G protein experiment
cells injected with constitutively active forms of small G proteins
cells were then stained for filamentous actin
constitutively active = consistently formed no matter what the cell needs
filopodia
- finger-like projections that extend from surface of cells
- G protein Cdc42 is activated on inner surface of the plasma membrane, which stimulates actin polymerization and bundling (parallel bundles)
Cdc42 activation
activated Cdc42 targets members of the WASp protein family
patients deficient in WASp have Wiskott-Aldrich syndrome (immune cells have abnormal actin-based motility
WASp activates formins and bundling proteins
lamellipodia
G protein Rac is activated at the cell periphery, which stimulates actin polymerization and sheet-like extensions (branched, dendritic network)
Rac also activates WASp proteins, which then activate Arp2/3
weird diagram
Rac
promotes branched actin network assembly AND inhibits myosin activity
stress fibers
- stress fibers are contractile bundles of actin filaments and myosin
- G protein Rho activation stimulates bundling of actin filaments with myosin II into stress fibers (and also clustering of integrins and other proteins to form focal adhesions)
- Rho activates formins and myosin
- Rho inactivates cofilin, so filaments are more stable