lecture 3 - nonmuscle cells & cell locomotion
DESCRIPTION
LECTURE 3 - NONMUSCLE CELLS & CELL LOCOMOTION. Non-Contractile Bundles Lamellipodia Filopodia Surface Projections Non-Muscle Cells Circumferential belt Cortical attachment Stress fibers Cytokinesis Vesicle transport Cell Locomotion. Lamellipodium. Broad membrane protrusion - PowerPoint PPT PresentationTRANSCRIPT
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LECTURE 3 - NONMUSCLE CELLS & CELL LOCOMOTION
Non-Contractile Bundles Lamellipodia Filopodia Surface Projections
Non-Muscle Cells Circumferential belt Cortical attachment Stress fibers Cytokinesis Vesicle transport
Cell Locomotion
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LamellipodiumLamellipodium Broad membrane Broad membrane
protrusionprotrusion Moves forward Moves forward
from cellfrom cell Forms Forms focal focal
adhesionsadhesions Fills with cytosolFills with cytosol Rear of cell retracts Rear of cell retracts
toward process toward process
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LamellipodiumLamellipodium
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FilopodiaFilopodia Finger-like extensions of memb.Finger-like extensions of memb. Form Form focal adhesionsfocal adhesions on ventral surface on ventral surface Form Form rufflesruffles on dorsal surface on dorsal surface
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MicrovilliMicrovilli Microvilli and filopodia – internal actin bundlesMicrovilli and filopodia – internal actin bundles Actin linked by fimbrin, villin (intestine) and Actin linked by fimbrin, villin (intestine) and
spectrin (RBCs)spectrin (RBCs)
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NON-MUSCLE CELLS - PROTEINSNON-MUSCLE CELLS - PROTEINS
ActinActin Myosin type IMyosin type I
Assoc. w/ cell membAssoc. w/ cell memb Does Does notnot form thick filaments form thick filaments
Myosin type IIMyosin type II Forms prominent bundles w/ actinForms prominent bundles w/ actin Powers muscle contraction & cytokinPowers muscle contraction & cytokin
Myosin type VMyosin type V Cytoskeletal-memb. interactionsCytoskeletal-memb. interactions Transport of memb. vesiclesTransport of memb. vesicles
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CONTRACTILE BUNDLESCONTRACTILE BUNDLES
Prominent bundles of actin & myosin IIProminent bundles of actin & myosin II Located at points of cell contactLocated at points of cell contact Differ from non-contractile bundlesDiffer from non-contractile bundles Myosin II interspersed with actinMyosin II interspersed with actin
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CONTRACTILE BUNDLES - CONTRACTILE BUNDLES - EXAMPLESEXAMPLES
Circumferential beltCircumferential belt Cortical attachmentCortical attachment Stress fibersStress fibers CytokinesisCytokinesis Vesicle transportVesicle transport
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Circumferential beltCircumferential belt
Linker proteins to Linker proteins to cell adhesions mol. cell adhesions mol. in memb.in memb.
Forms junctional Forms junctional complex in epith.complex in epith.
Works like tension Works like tension cable – wound healcable – wound heal
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Cortical AttachmentsCortical Attachments
Network of actinNetwork of actin Attached by filaminAttached by filamin Strengthen memb.Strengthen memb. Help w/ memb. Help w/ memb.
transporttransport Myosin II acts as Myosin II acts as
small tension rodssmall tension rods
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Stress FibersStress Fibers
Static bundles of actinStatic bundles of actin Form radial & axial bund.Form radial & axial bund. Alternating patches of Alternating patches of
myosin & α-actininmyosin & α-actinin ContainContain
• TropomyosinTropomyosin• CaldesmonCaldesmon• Myosin LC kinase (SM)Myosin LC kinase (SM)
Attach at focal adhesionsAttach at focal adhesions
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CytokinesisCytokinesis
Contractile ringContractile ring Actin and myosin II Actin and myosin II
accumulate at equator accumulate at equator of dividing cellof dividing cell
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Vesicle TransportVesicle Transport
Actin & microtubule Actin & microtubule networksnetworks
Myosin I & VMyosin I & V Myosin carries cargoMyosin carries cargo Cytoplasmic streamingCytoplasmic streaming
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Vesicle TransportVesicle Transport
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CELL LOCOMOTIONCELL LOCOMOTION
SEQUENCESEQUENCE1.1. Extension of cell membraneExtension of cell membrane
2.2. Attachment to substratumAttachment to substratum
3.3. Forward flow of cytosolForward flow of cytosol
4.4. Retraction of rear of cellRetraction of rear of cell
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Protrusion of LamellipodiumProtrusion of Lamellipodium
Controlled Controlled polymerization of polymerization of actinactin
Actin cross-linkedActin cross-linked Memb. pushed Memb. pushed
forward by forward by polymerizationpolymerization
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Focal AdhesionsFocal Adhesions
Actin anchored to substratumActin anchored to substratum Develops into focal adhesionDevelops into focal adhesion Anchors cell to substratumAnchors cell to substratum Prevents lamella from retractingPrevents lamella from retracting
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Cell Body MovementCell Body Movement Unknown mechanismUnknown mechanism Translocate bulk contents of cellTranslocate bulk contents of cell Contraction of stress fibersContraction of stress fibers De-adhesion of focal adhesionsDe-adhesion of focal adhesions
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Gel-Sol TransformationGel-Sol Transformation
Transformation – disassembly and Transformation – disassembly and reassembly of actin networkreassembly of actin network
Process controlled by actin binding prot.Process controlled by actin binding prot.• Profilin – promotes polymerization (gel)Profilin – promotes polymerization (gel)• a-actin and filamin form gel-like networka-actin and filamin form gel-like network• Cofilin sever actin filaments (sol)Cofilin sever actin filaments (sol)
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Gel-Sol TransformationGel-Sol Transformation
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MyosinsMyosins Myosin I – leading edge – forwardMyosin I – leading edge – forward Myosin II –trailing edge - retractionMyosin II –trailing edge - retraction
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PolarityPolarity
Front and back polarityFront and back polarity Wound stimulates growth of Wound stimulates growth of
processesprocesses Stress fibers help close woundStress fibers help close wound Signal-transduction pathways control Signal-transduction pathways control
activationactivation Chemotactic mol. bind to cell-surface Chemotactic mol. bind to cell-surface
receptors and activate signalingreceptors and activate signaling CaCa2+2+ - high at leading, low at rear - high at leading, low at rear
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LOCOMOTION SUMMARYLOCOMOTION SUMMARY
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Dynamics SummaryDynamics Summary Alberts et al, 1994Alberts et al, 1994