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SUMMARY:Active self-organization of the actin cytoskeleton driven by molec
 ular motors - Dr. Gijsje Koenderinck
DTSTART:20100507T130000Z
DTEND:20100507T140000Z
UID:TALK24738@talks.cam.ac.uk
CONTACT:Erika Eiser
DESCRIPTION:The aim of the Biological Soft Matter group at AMOLF is to und
 erstand the physical mechanisms that govern the (active) mechanics of cell
 s. We study in parallel two different model systems of cells. The first ap
 proach is to reconstitute artificial cells from purified cytoskeletal prot
 eins inside cell-sized PDMS microchambers or inside liposomes. We can thus
  dissect the roles of polymer physics\, motor proteins\, and active filame
 nt (de)polymerization. The second approach is to reconstitute artificial t
 issues by growing cells inside simplified extracellular matrices (collagen
  or fibrin gels)\, to study mechanosensing and mechanotransduction. Key te
 chnologies are optical microscopy and quantitative image analysis\, optica
 l tweezer manipulation\, and rheology.\nIn my seminar I will focus on the 
 active self-organization of contractile actin-myosin 2 networks. Myosin II
  motors assemble into bipolar filaments that slide polar actin filaments (
 F-actin) past each other as they walk to their plus end. We systematically
  adjust the myosin activity and processivity and the level of crosslinking
 \, to find out how molecular parameters change the emergent properties (st
 ructure and mechanics) of the model cytoskeleton. We show with fluorescenc
 e microscopy that the motors generate ring-like actin structures whose siz
 e and shape depends both on motor and crosslink density. Myosin accumulate
 s at the center of the actin rings\, at the plus ends of the actin filamen
 ts\, leading to polarity sorting of the actin filaments. Increasing crossl
 ink density enhances the network connectivity and thereby increases the co
 ntractility of the network\, leading to coarsening and eventually to macro
 scopic gel contraction. The structure and contractile dynamics in the reco
 nstituted system closely resemble observations in vivo. Using these data\,
  we are starting to build a model relating motor activity on a molecular s
 cale to whole-cell organization and mechanics.
LOCATION:Pippard Lecture Theatre\, Cavendish Laboratory
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