cell motility and shape require microfilaments (f-actin), microtubules and intermediate
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Cell Motility and Shape require microfilaments (F-actin), microtubules and intermediate filaments. Not surprisingly, the actin skeleton is dynamic, not just the tracks. Fibroblasts migrate through tissues by extending forward, attaching to the substrate at focal adhesions and - PowerPoint PPT PresentationTRANSCRIPT
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Cell Motility and Shaperequire microfilaments (F-actin), microtubules and intermediatefilaments.
Not surprisingly, the actin skeleton isdynamic, not just the tracks.
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Fibroblasts migrate through tissues by extending forward, attaching to the substrateat focal adhesions and pulling along the tail.
Actin assembly anddisassembly is themechanism.
Actin is highly conserved.
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G actin assembles into F actin. ATP holds together the two lobes. Polymerizationcan be done in vitro. ATP is hydrolyzed but this is not required for assembly.F actin depolymerizes back to G actin.
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F actin has structural and functional polarity. Can’t be seen directly.Myosin (S1 heads) bind F actin assymetrically.
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The actin cytoskeleton is organized into bundles andnetworks to provide framework.
Cortical actin is netlike andcytosolic networks are meshes.
Cortical nets are attached to the membrane
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Actin crosslinkers:
Fascin in bundles,Filamin in networks
There are many otheractin crosslinkers, eachwith actin-binding domains.
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RBC, network provides flexible structure.
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HypotheticalJunctional complex
Know components
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Left: Platelets at restMiddle: Induced to spreadRight: Stellate pattern during clot retraction
All are actin based and coupled via ABPs tothe actin cytoskeleton
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Actin bundles support projections
Microvilli (epithelial) and filopodia (fibroblasts)
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-3 stepsNucl. Is marked by lag phaseElong by addition at both endsSS at the critical concentration
ATP is eventually hydrolyzedso that internal actin is ADP form
Growth is greater at + end
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Polar growth is demonstrated bydecorated nuclei
End growth differences due todifferences in Cc
Cc is measured by capping oneend and measuring C for growth
G actin ADP, Cc for bothends are equal
Treadmilling
Tools: cytochalasin D depolymerizesby bind plus ends (fungal alkaloid)Lantrunculin binds G actin and blkspolymerization (sponges)Phalloidin, binds F actin and blksDepolmerization (Death Angel)
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Summary
Cell dynamics are controlled by dynamicsin the actin cytoskeleton network
Cell shape changes by filament size and treadmilling
But shape changes can also occur by actin severing proteins