Plenarvorträge - DPG-Tagungen

Arbeitskreis Biologische Physik Montag
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phys. J. (2004), in press.
AKB 12 Active Systems: Complex Cellular Processes
Zeit: Montag 14:30–16:30 Raum: H40
Hauptvortrag AKB 12.1 Mo 14:30 H40
Active Polymer Networks in Biological Cells — •Josef Käs,
Claudia Brunner, Jochen Guck, Falk Wottawah, Stefan
Schinkinger, Karla Mueller, Timo Betz, Bjoern Stuhrmann,
Daniel Koch, Allen Ehrlicher, Michael Goegler, and David
Smith — Fakultaet fuer Physik und Geowissenschaften, Universitaet
Leipzig
Cells signify the next fundamental challenge to soft matter physics
since they require establishing the physics of networks of active nanoelements.
All eukaryotic cells depend in their internal structure and organization
on a highly dynamic and active polymer network, the cytoskeleton.
Our results demonstrate that switchable nano-sized motors
can regulate the structural strength and assembly of such polymer networks.
These active mechano-sensitive networks generate motion driven
by nano-muscles and polymerization. Scanning force microscopy allows
us a precise spatial characterization of the resulting active forces. Lasers
provide optomolecular control over these active motions. In neurons weak
optical gradient forces can determine the growing nerve’s leading edge’s
direction, speed, branching, and contact to other neurons. Moreover,
these intracellular networks are closely related to cellular differentiation
and thus, cell elasticity measurements with our new laser trap, the optical
cell stretcher, provide an unparalleled cell marker distinguishing
malignant cells as well as stem cells from other cells.
Hauptvortrag AKB 12.2 Mo 15:00 H40
Dynamic Phenomena and Force Generation in Cells — •Frank
Jülicher — Max-Planck Institut für Physik komplexer Systeme,
Nöthnitzerstr. 38, 01187 Dresden
Living cells exhibit a remarkable variety of active behaviors. Material
is transported within the cell, cells divide and a lot of cells can swim or
crawl along substrates. The molecular basis of such behaviors are highly
specialized protein molecules which transduce the chemical energy of a
fuel molecule, ATP, to mechanical work and motion. A prototype system
are molecular motors of the cytoskeleton which generate forces and motion
along linear filaments. The activity on the molecular level leads to
complex dynamic behaviors as a result of the interaction of many interacting
components. The cytoskeleton on larger scales thus represents a
gel-like soft material which is far from thermal equiligrium due to internal
active processes. The physical properties and the dynamics of such
active gels can be described by a hydrodynamic theory. These concepts
can be used to obtain a phenomenological descriptoin of dynamic cellular
phenomena such as cell locomotion.
Hauptvortrag AKB 12.3 Mo 15:30 H40
Symmetriebrechung in einem mulitzellulären System am Besipiel
der Hydra — •Albrecht Ott 1 , Jordi Soriano 1 und Cyril
Colombo 2 — 1 Universität Bayreuth, EP1, NW1, 95440 Bayreuth, Germany
— 2 Institut Curie, Paris, France
Die Hydra hat erstaunliche Regenerationsfähigkeiten. Sie kann sich
nach Dissoziation in einzelne Zellen aus einem ungeordneten Zellball neu
formieren. Dabei bildet sie zunächst einen Zellball, dann wird die Achse
des Tieres festgelegt. Wir untersuchen diesen Prozess der Achsenfindung.
Wir zeigen das eine wohlregulierte mechanische Pumpbewegung des Balles
offenbar Information über die Achsenfindung überträgt. Unsere Beobachtung
ergänzt molekularbiologische Studien, die auf die Wichtigkeit
der Adhesionsregulierung hinweisen. Sie erklärt ebenfalls, wie eine kleine
Gruppe von fünf bis zehn irreversibel differenzierten Zellen den Prozess
der Achsenfindung entscheiden und mitteilen kann. Wir untersuchen
die Expression des Gens ks1 durch insitu Hybridisierung. Ks1 wird als
repräsentativ für das genetische Kopfprogramm der Hydra angesehen.
Erste Ergebnisse weisen auf ein fluktuierendes Expressionsmuster dieses
Gens auf dem Zellball hin, die Grössenverteilung skaliert. Wir etablieren
einen Zusammenhang mit der kürzlich in der Hydra nachgewiesenen
WNT-Signalkaskade her. Wir schlagen vor das genetische Fluktuationen
die Symmetrie brechen.
Hauptvortrag AKB 12.4 Mo 16:00 H40
Investigating Cell Division and Cell Protrusion by AFM —
•Manfred Radmacher — Institut für Biophysik, Universität Bremen
We have used an AFM to investigate the mechanical properties of
the cells cytoskeleton during dynamical processes like cell migration and
division. Actin is in the case of fibroblasts cells the major cellular components
responsible for the cellular stiffness. Stiffness is increased further by
myosin II creating cortical tension. When myosin function is diminished
by inhibiting the myosin light chain kinase a decrease in stiffness can be
observed. This is congruent with importance of both actin and myosin in
processes like cell migration and cell division. In cell division for instance
a rapid and large increase in stiffness is observed in the region where the
cleavage furrow will form. This is congruent with results from cellular
biology and supports the equatorial stiffening model of cytokinesis which
has been one out of several models suggested.
AKB 13 Active Systems: Structure and Pattern Formation
Zeit: Montag 17:00–18:00 Raum: H40
Hauptvortrag AKB 13.1 Mo 17:00 H40
Membranes with Rotating Motors — •Peter Lenz — Fachbereich
Physik, Philipps-Universität Marburg, 35032 Marburg, Germany
We study collections of rotatory motors confined to 2-dimensional manifolds.
These systems show a non-trivial collective behavior since the rotational
motion leads to a repulsive hydrodynamic interaction between
motors. While for high rotation speed motors might exhibit crystalline
order, they form at low speed a disordered phase where diffusion is enhanced
by velocity fluctuations. These effects should be experimentally
observable for motors driven by external fields and for dipolar biological
motors embedded into lipid membranes in a viscoelastic solvent.
Hauptvortrag AKB 13.2 Mo 17:30 H40
Models for Pattern Formation in Cell Biology — •Walter Zimmermann
— Theoretische Physik Universität des Saarlandes, 66041
Saarbrücken
During polymerization of the biological filaments microtubules or
actin, during filament transport by motor proteins or for interacting ionchannels
in biomembranes various types of spatiotemporal patterns occur.
Compared to the huge variety of patterns occuring in the unanimate
world, for these examples often conservation laws lead to new universality
classes of patterns und with rather surprising patterns. The effects of the
excluded volume interaction between filaments and the related nematic
ordering lead also additional pattern formation processes. An overview
about these effects and models will be given.