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Protein Polymers, Crawling Cells, and Comet Tails 00:00:00 Cell motility 00:00:26 Four types of biological motors 00:01:58 Cell structure depends on protein filaments 00:03:06 Actin filament structure 00:04:36 Actin filament polymerization 00:05:25 Most cells in the human body are bacteria 00:06:58 Actin-based motility of the intracellular bacterial pathogen Listeria monocytogenes 00:09:49 00:10:54 Listeria monocytogenes actin-rich clouds and tails in cytoplasmic extract 00:11:24 00:12:15 What do we understand? 00:13:25 What don t we understand? 00:14:12 Force generation by protein polymerization: Thermodynamics 00:15:21 What can we do? 00:17:10 What can we do? 00:17:45 Movement of L. monocytogenes in cytoplasmic extracts 00:17:47 High-resolution tracking 00:19:44 Trajectories of 1000 bacteria 00:21:02 Trajectories of 1000 bacteria 00:21:03 Speeds vary significantly among genetically identical individuals 00:21:34 00:22:08 For each individual, speed and actin density both fluctuate 00:22:35 Cross-correlations between speed and actin density fluctuations 00:23:01 What can we do? 00:23:58 Movement of ActA-coated beads 00:24:08 Movement of ActA-coated beads in cytoplasmic extract 00:24:36 Symmetry is broken by variations in actin dynamic behavior 00:25:07 Elastic Brownian ratchet model 00:25:50 Stochastic model for symmetry-breaking based on the elastic Brownian ratchet 00:26:11 The simple 2-D stochastic model reproduces qualitative aspects of symmetry-breaking 00:26:32 Actin polymerization distorts vesicles 00:26:49 00:27:24 Movement of ellipsoidal beads 00:28:37 Two preferred orientations 00:29:16 What can we do? 00:29:48 How will we dissect the molecular basis of these complex mechanics? 00:29:57 Listeria monocytogenes ActA site-directed mutagenesis 00:30:23 Mechanical phenotype 1: Change in path persistence 00:30:48 Mechanical phenotype 2: Skidding 00:31:31 What about cell crawling? 00:32:38 Symmetry-breaking in fish skin cells 00:33:51 Conclusions 00:34:57 Acknowledgements 00:35:32
