Regensburg 2007 – scientific programme

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BP: Fachverband Biologische Physik

BP 24: Cell Mechanics (in vivo)

BP 24.7: Talk

Thursday, March 29, 2007, 11:45–12:00, H44

Active mechanical stabilization of the viscoplastic intracellular space of Dictyostelia cells by microtubule-actin crosstalk — •Doris Heinrich and Erich Sackmann — Department für Physik, Ludwig-Maximilians-Universität, Geschwister-Scholl-Platz 1, 80539 München, Germany

We investigated the micro-viscoelasticity of the intracellular space of Dictyostelium discoideum cells by evaluating the intracellular transport of magnetic force probes and their viscoelastic responses to force pulses of 20-700 pN. The role of the actin cortex, the microtubule (MT) aster and their crosstalk is explored by comparing the behaviour of wild type cells, myosin II null mutants, latrunculin A and benomyl treated cells. The MT coupled beads perform irregular local and long range directed motions which are characterized by measuring their velocity distributions (P(v)). The correlated motion of the MT and the centrosome are evaluated by microfluorescence of GFP-labeled MTs. P(v) can be represented by log-normal distributions with long tails and it is determined by random sweeping motions of the MTs and by intermittent bead transports parallel to the MTs. The viscoelastic responses are strongly non-linear and are mostly directed opposite or perpendicular to the force, showing that the cytoplasm behaves as an active viscoplastic body with time and force dependent drag coefficients. Force-balance is established by the mechanical coupling between the soft microtubules and the viscoelastic actin cortex, providing cells with high mechanical stability despite the softness of the cytoplasm.