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 Broad membrane protrusion Moves forward from cell Moves forward from cell Forms focal adhesions Forms focal adhesions Fills with cytosol Fills with cytosol Rear of cell retracts toward process Rear of cell retracts toward process

Lamellipodium

Filopodia Finger-like extensions of memb. Finger-like extensions of memb. Form focal adhesions on ventral surface Form focal adhesions on ventral surface Form ruffles on dorsal surface Form ruffles on dorsal surface

Microvilli Microvilli and filopodia – internal actin bundles Microvilli and filopodia – internal actin bundles Actin linked by fimbrin, villin (intestine) and spectrin (RBCs) Actin linked by fimbrin, villin (intestine) and spectrin (RBCs)

NON-MUSCLE CELLS - PROTEINS Actin Actin Myosin type I Myosin type I Assoc. w/ cell memb Assoc. w/ cell memb Does not form thick filaments Does not form thick filaments Myosin type II Myosin type II Forms prominent bundles w/ actin Forms prominent bundles w/ actin Powers muscle contraction & cytokin Powers muscle contraction & cytokin Myosin type V Myosin type V Cytoskeletal-memb. interactions Cytoskeletal-memb. interactions Transport of memb. vesicles Transport of memb. vesicles

CONTRACTILE BUNDLES Prominent bundles of actin & myosin II Prominent bundles of actin & myosin II Located at points of cell contact Located at points of cell contact Differ from non-contractile bundles Differ from non-contractile bundles Myosin II interspersed with actin Myosin II interspersed with actin

CONTRACTILE BUNDLES - EXAMPLES Circumferential belt Circumferential belt Cortical attachment Cortical attachment Stress fibers Stress fibers Cytokinesis Cytokinesis Vesicle transport Vesicle transport

Circumferential belt Linker proteins to cell adhesions mol. in memb. Linker proteins to cell adhesions mol. in memb. Forms junctional complex in epith. Forms junctional complex in epith. Works like tension cable – wound heal Works like tension cable – wound heal

Cortical Attachments Network of actin Network of actin Attached by filamin Attached by filamin Strengthen memb. Strengthen memb. Help w/ memb. transport Help w/ memb. transport Myosin II acts as small tension rods Myosin II acts as small tension rods

Stress Fibers Static bundles of actin Static bundles of actin Form radial & axial bund. Form radial & axial bund. Alternating patches of myosin & α-actinin Alternating patches of myosin & α-actinin Contain Contain TropomyosinTropomyosin CaldesmonCaldesmon Myosin LC kinase (SM)Myosin LC kinase (SM) Attach at focal adhesions Attach at focal adhesions

Cytokinesis Contractile ring Contractile ring Actin and myosin II accumulate at equator of dividing cell Actin and myosin II accumulate at equator of dividing cell

Vesicle Transport Actin & microtubule networks Actin & microtubule networks Myosin I & V Myosin I & V Myosin carries cargo Myosin carries cargo Cytoplasmic streaming Cytoplasmic streaming

Vesicle Transport

CELL LOCOMOTION SEQUENCE 1.Extension of cell membrane 2.Attachment to substratum 3.Forward flow of cytosol 4.Retraction of rear of cell

Protrusion of Lamellipodium Controlled polymerization of actin Controlled polymerization of actin Actin cross-linked Actin cross-linked Memb. pushed forward by polymerization Memb. pushed forward by polymerization

Focal Adhesions Actin anchored to substratum Actin anchored to substratum Develops into focal adhesion Develops into focal adhesion Anchors cell to substratum Anchors cell to substratum Prevents lamella from retracting Prevents lamella from retracting

Cell Body Movement Unknown mechanism Unknown mechanism Translocate bulk contents of cell Translocate bulk contents of cell Contraction of stress fibers Contraction of stress fibers De-adhesion of focal adhesions De-adhesion of focal adhesions

Gel-Sol Transformation Transformation – disassembly and reassembly of actin network Transformation – disassembly and reassembly 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 Transformation

Myosins Myosin I – leading edge – forward Myosin I – leading edge – forward Myosin II –trailing edge - retraction Myosin II –trailing edge - retraction

Polarity Front and back polarity Front and back polarity Wound stimulates growth of processes Wound stimulates growth of processes Stress fibers help close wound Stress fibers help close wound Signal-transduction pathways control activation Signal-transduction pathways control activation Chemotactic mol. bind to cell-surface receptors and activate signaling Chemotactic mol. bind to cell-surface receptors and activate signaling Ca 2+ - high at leading, low at rear Ca 2+ - high at leading, low at rear

LOCOMOTION SUMMARY

Dynamics Summary Alberts et al, 1994