MCB 252 Topic 18 Role of Actin in Cell MovementProf David Rivier MCB 252 Spring 2015 MCB 252 Cell Biology part 2 Topic 3 Role of Actin in Cell Movement Reading Lodish 17 0 17 2 Outline Actin Cytoskeleton A Properties and Dynamics of Actin B Role of Actin in Cell Movement C Regulation of Actin Assembly in Cells D Stable Actin Structures E Muscle Cells and Myosin Motors Actin Cytoskeleton Properties of Actin Actin assembly Role of ATP Treadmilling Role of actin in cell movement Actin is required for movement Actin assembly can drive movement Regulation of actin assembly in cells Proteins involved in actin assembly disassembly Turning the protein involved in assembly and disassembly ON and OFF Actin Polymerization Can Do Work G actin F actin released energy Released energy can do work Work can result in membrane extension Membrane extension requires work G actin F actin membrane extension Actin Stable Structures and Dynamic Structures How do we know that actin polymerization is required for migration Two experimental questions 1 Is actin polymerization necessary for movement 2 Is actin polymerization sufficient for movement How do we know that actin polymerization is required for migration Use toxins that disrupt actin function Actin destabilizers Cytochalasin fungal alkaloid binds end prevents subunit addition Latrunculin toxin from sponges binds G actin inhibits assembly into filaments Actin stabilizers Phalloidin cyclic peptide from poisonous mushroom binds and stabilizes actin filaments preventing depolymerization Need to know these drugs Effects of latrunculin on keratocyte migration Movie T18M1 latrunculin treated avi Lamellipoia are filled with branched F actin polymers Movie T18M2 1706 lamellipodium mov How do we know that actin polymerization is required for migration Two experimental questions 1 Is actin polymerization necessary for movement 2 Is actin polymerization sufficient for movement Lamellopodia are filled with branched actin polymers How do we know that polymerization can drive movement The answer comes in part from work with the bacterium Listeria monocytogenes Listeria monocytogenes Listeria Actin Comet Tails Listeria Movie T18M3 1703 comet tails mov How do we know that actin polymerization is required for migration Two experimental questions 1 Is actin necessary for movement 2 Is actin polymerization sufficient for movement Listeria Movie T18M4 Listeria in vitro mov Listeria movement in vitro Movement only requires Bactria plus Actin ATP and a few proteins that facilitate actin polymerization we ll talk about them later Conclusion Listeria can induce actin polymerization Does that tell us that polymerization is sufficient to drive motion Hypothesis Questions about Listeria movement in vitro No Motor Polymerization drives movement Motor required Polymerization necessary but not sufficient for movement Listeria ActA Protein Bacteria with a LOF allele in the gene that codes for ActA cannot move ActA is necessary for actin assembly How to test our two models Is ActA sufficient Is ActA the only Bacterial Protein needed for Movement Plastic Bead Purified ActA protein Actin Polymerization is Sufficient for Movement in vitro Movie T18M5 ActABead mov Actin Stable Structures and Dynamic Structures Lamellipodia are filled with branched F actin polymers
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