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

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

LamellipodiumLamellipodium

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

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)

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

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

CONTRACTILE BUNDLES - CONTRACTILE BUNDLES - EXAMPLESEXAMPLES

Circumferential beltCircumferential belt Cortical attachmentCortical attachment Stress fibersStress fibers CytokinesisCytokinesis Vesicle transportVesicle transport

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

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

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

CytokinesisCytokinesis

Contractile ringContractile ring Actin and myosin II Actin and myosin II

accumulate at equator accumulate at equator of dividing cellof dividing cell

Vesicle TransportVesicle Transport

Actin & microtubule Actin & microtubule networksnetworks

Myosin I & VMyosin I & V Myosin carries cargoMyosin carries cargo Cytoplasmic streamingCytoplasmic streaming

Vesicle TransportVesicle Transport

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

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

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

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

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)

Gel-Sol TransformationGel-Sol Transformation

MyosinsMyosins Myosin I – leading edge – forwardMyosin I – leading edge – forward Myosin II –trailing edge - retractionMyosin II –trailing edge - retraction

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

LOCOMOTION SUMMARYLOCOMOTION SUMMARY

Dynamics SummaryDynamics Summary Alberts et al, 1994Alberts et al, 1994