Department Biological Physics
Frank Jülicher

for the Physics of Complex Systems
Nöthnitzer Straße 38
01187 Dresden

Tel. +49 351 871-1202
Fax. +49 351 871-1299
Curriculum Vitae
List of Publications
Research Interests

Theory of Biological Systems and Processes

The main focus of our research are theoretical approaches to understand dynamic processes in cells and tissues. Work on active cellular processes includes the study of cellular oscillations, cellular signaling and the cytoskeletal dynamics during cell division and cell motility. We furthermore study the biophysical basis of hearing. Finally, we investigate the biophysical properties and dynamics of tissues and epithelia. Based on the properties of individual cells and of cellular signaling systems, we are interested in the dynamics of developmental processes, for example wing development in the fruit fly.

Research topics include:

Active cellular processes
Cellular oscillations
Swimming of microorganisms
Cell locomotion

Physics of the cytoskeleton and of motor proteins
Active gels and fluids
Collective behaviors of motor proteins
Self-organization phenomena in the cytoskeleton

Physics of Cell Division

Tissues and developmental processes
Cellular packings in epithelia
Cellular rearrangements during growth and development
Morphogen signaling and morphogen gradient formation

Biophysics of hearing
Active mechanics of hair cells
Cochlear waves
Signal amplification by nonlinear oscillators

Research Highlights

Wnt-regulated Dynamics of Positional Information in Zebrafish Somitogenesis
L. Bajard, L. G. Morelli, S. Ares, J. Pécréaux, F. Jülicher and A. C. Oates
Development. 141 1381 (2014)
PDF (5,7 MB)]

Mechanically Driven Interface Propagation in Biological Tissues

We discuss the competition of two tissues with different homeostatic pressure in a continuum theory. We show that a tissue with larger homeostatic pressure invades the second tissue by a propagating interface and calculate the propagation velocity. This is a generalization of the Fisher-Kolmogorov wave taking in to account stress distributions and mechanics. Interestingly, we find both pulled and pushed fronts as a function of parameter values.

J. Ranft, M. Aliee, J. Prost, F. Jülicher and J.-F. Joanny
New J. Phys. 16 035002 (2014)
PDF (406 kb)]

General Theory for the Mechanics of Confined Microtubule Asters

We discuss the positioning of microtubule asters in confined geometries mediated by pushing and pulling forces on the boundary. Pulling forces can lead to robust centering and off-center positioning due to asymmetric districutions of force generators. This work applies to the positioning of mitotic spindles in the cell during symmetric and asymmetric cell divisions.

R. Ma, L. Laan, M. Dogterom, N. Pavin and F. Jülicher
New J. Phys. 16 013018 (2014)
PDF (885 kb)]

Cell-body Rocking is a Dominant Mechanism for Flagellar Synchronization in a Swimming Alga

We study the mechanisms of flagellar synchronization in the green algae Chlamydomonas. Using a combination of theory and experiment, we show that cell body rocking generated by nonsynchronous beats effectively produces an interaction between the two flagella that drives their synchronization.

V. F. Geyer, F. Jülicher, J. Howard, and B. M. Friedrich
Proc. Natl. Acad. Sci. USA, 110, 18058 (2013)
PDF (1,3 MB)]

Spatial Organization of the Cell Cytoplasm by Position-Dependent Phase Separation

The cell cytoplasm can undergo phase separation leading to the coexistence of drop-like objects with the remaining cytoplasm. Such phase separation generates droplets which concentrate certain components and provide specific chemical environments. We show how such phase separation can be used to segregate components in the cell cytoplams using a gradient of a regulator of phase separation. Such segregation plays an important role during asymmetric cell division. Cellular components can be distributed unequally to the two daughter cells.

C. F. Lee, C. P. Brangwynne, J. Gharakhani, A. A. Hyman and F. Jülicher
Phys. Rev. Lett. 111, 088101 (2013)
PDF (1,6 MB)]

XMAP215 Activity Sets Spindle Length by Controlling the Total Mass of Spindle Microtubules

During cell division, a bipolar spindle assembles from a large numbers of dynamic microtubules. We show that length of meiotic spindles, which is much bigger than the average microtubule length is set by mass balance via localized microtubule nucleation and global disassembly. We show that perturbing microtubule growth rate using mutants of microtubule growth promotor. The spindle length is proportional to microtubule growth rate which can be understood by our theory.

S. B. Reber, J. Baumgart, P. O. Widlund, A. Pozniakovsky, J. Howard, A. A. Hyman and F. Jülicher
Nature Cell Biol. 15, 1116 (2013)
PDF (4,6 MB)]

Active Chiral Processes in Thin Films

Active fluids exhibit unconventional behaviors such as the generation of spontaneous movements and flows, driven e.g. by the action of molecular motors in cells. The interactions between motors and filaments can amplify chiral asymmetries of helical filaments and lead to relative rotations and chiral flows. Active chiral processes are most striking near surfaces. We develop a thin film theory of chiral active processes which could be relevant for the emergence of chiral flows in the actin cytoskeleton in cells.

S. Fürthauer, M. Strempel, S. W. Grill and F. Jülicher
Phys. Rev. Lett. 110, 048103 (2013)
[PDF (340 kB)]

Anomalous Behaviour of the Diffusion Coefficient in Thin Active Films

We study the diffusion of a smaller tracer particle in a fluctuating active gel. In a passive fluid, the diffusion coefficient depends on the particle radius as well as on the fluid viscosity. Here we show that in an active fluid, the diffusion coefficient can exhibit unconventional properties and can depend on the system size rather than the particle size. Such anomalous behavior of the diffusion coefficient results from close to a Frederiks transition.

A. Basu, J.-F. Joanny, F. Jülicher and J. Prost
New J. Phys. 14, 115001 (2012)
[PDF (565 kB)]

Positioning of Microtubule Organizing Centers by Cortical Pushing and Pulling Forces

During cell division, the mitotoc spindle is positioned in the cell near the cell center. Interactions between microtubule ends with the cell boundaries are important for this positioning. Growing microtubules can push against the cell boundary while microtubules interacting with dynein molecular motors at the cell boundary can be subject to pulling. Here we show that pulling forces exerted by dynein motors can provide a robust and stable centering mechanism.

N. Pavin, L. Laan, R. Ma, M. Dogterom and F. Jülicher
New J. Phys. 14, 105025 (2012)
[PDF (1,5 MB)]

Cortical Dynein Controls Microtubule Dynamics to Generate Pulling Forces that Position Microtubule Asters

L. Laan, N. Pavin, J. Husson, G. Romet-Lemonne, M. van Duijn, M. Preciado López,
R. D. Vale, F. Jülicher, S. L. Reck-Peterson and M. Dogterom
Cell 148, 502 (2012)
[PDF (1,9 MB)]

Active Chiral Fluids

Motor molecules interacting with filaments of the cytoskeleton can induce relative sliding of two filaments. In addition, because of the helical structure of filaments, relative filament rotation can occur. Such active chiral processes can give rise to novel and unconventional material properties in active chiral gels. We present a general hydrodynamic theory of active fluids which takes into account chiral processes. We show that active antisymmetric stresses as well as active contributions to angular momentum fluxes occur and we discuss generic terms that arise due to the existence of torque dipoles in an active medium.

S. Fürthauer, M. Strempel, S. W. Grill and F. Jülicher
Eur. Phy. J. E 35, 89 (2012)
[PDF (1,5 MB)]

Flagellar Synchronization Independent of Hydrodynamic Interactions

Inspired by the coordinated beating of the flagellar pair of the green algae Chlamydomonas, we study theoretically a simple, mirror-symmetric swimmer, which propels itself at low Reynolds number by a revolving motion of a pair of spheres. We show that perfect synchronization between these two driven spheres can occur due to the motion of the swimmer and local hydrodynamic friction forces. Hydrodynamic interactions, though crucial for net propulsion, contribute little to synchronization for this free-moving swimmer.

B. M. Friedrich and F. Jülicher
Phys. Rev. Lett. 109, 138102 (2012)
[PDF (446 kB)]

A General Theoretical Framework to Infer Endosomal Network Dynamics from Quantitative Image Analysis

Cells internalize many different molecules including nutrients and signaling ligands. After internalization by endocytosis, these molecules are sorted and further processes in endosomal networks. We present a general theory to understand the emergent properties of the endosome network resulting from the interactions of individual endosomes. Using quantitative image analysis, we determine cargo-distributions in the network. We estimate key kinetic parameters of the network and show that endosome fusion plays a particularly important role for shaping endosomal networks leading to power-laws in the cargo distributions.

L. Foret, J. E. Dawson, R. Villasenor, C. Collinet, A. Deutsch, L. Brusch, M. Zerial, Y. Kalaidzidis and F. Jülicher
Curr. Biol. 22, 1381 (2012)
[PDF (1 MB)]

Establishment of Global Patterns of Planar Polarity during Growth of the Drosophila Wing Epithelium

Many epithelia exhibit large scale polarity patterns in the plane of the tissue. An important model system is the wing of the fruit fly where this polarity is reflected in the aligned patterns of wing hairs. In order to study how this pattern emerges during development, we quantify patterns of planar cell polarity proteins in the wing imaginal disk which is the wing precursor in the larvae. We find that planar cell polarity patterns emerge at early stage and that they are guided by the activity of three organizer regions including two compartment boundaries.

A. Sagner, M. Merkel, B. Aigouy, J. Gaebel, M. Brankatschk, F. Jülicher and S. Eaton
Curr. Biol. 22, 1296 (2012)
[PDF (401 kB)]

Topology and Dynamics of the Zebrafish Segmentation Clock Core Circuit

The verterate body has a segmented organization. During embryo development, these segments form sequentially by a dynamic process that involves genetic cellular oscillations in individual cells. Here we discuss the organization of the genetic work that governs these oscillations. We present a simplified dynamic model of gene regulation that involves two negative feedback loops of gene regulation. Transcription is regulated by different dimers of gene products. Our model can account for wild type behaviors and the effects of several mutants.

C. Schröter, S. Ares, L. G. Morelli, A. Isakova, K. Hens, D. Soroldoni, M. Gajewski, F. Jülicher, S. J. Maerkl,
B. Deplancke and A. C. Oates
PloS Biol 10, e1001364 (2012)
[PDF (843 kB)]

A mean-field Approach to Elastically Coupled Hair Bundles

The sensory cells of the ear, called hair cells, are active elements that can amplify weak mechanical stimuli. This amplification is based on the properties of dynamic oscillators. Here we study the behaviors of noisy oscillating hair bundles that are mechanically coupled. Our analytical approach elucidates the origin of noise reduction and reveals the importance of a new collective degree of freedom for the collective behaviours.

K. Dierkes, F. Jülicher and B. Lindner
Eur. Phys. J. E 35, 37 (2012)
[PDF (1,1 MB)]

Tissue Dynamics with Permeation

Animal tissues are complex assemblies of cells, extracellular matrix and permeating interstitial fluid. We develop a two-component continuum description of tissue dynamics taking into account a cell phase and an interstitial fluid. Cell growth requires absorption of the fluid while apoptosis releases interstitial fluid such that mass is conserved. Friction between the interstitial fluid and the cell phase leads to a  Darcy-like relation for the fluid velocity and introduces a new characteristic length scale.

J. Ranft, J. Prost, F. Jülicher and J.-F. Joanny
Eur. Phys. J. E 35, 46 (2012)
[PDF (723 kB)]

Collective Modes of Coupled Phase Oscillators with Delayed Coupling

We derive a general continuum theory that describes long wavelength modes of coupled oscillator with time delays in the coupling. We use our approach to investigate phase profiles of genetic oscillators in the segmentation clock which generates the segmented pattern of the vertebrate body plan. In this system, genetic oscillations together wit a moving front gives rise to wave like-collective modes. We discuss the influence of time delays on the phase profile of oscillators.

S. Ares, L. G. Morelli, D. J. Jörg, A. C. Oates and F. Jülicher
Phys. Rev. Lett. 108, 204101 (2012)
[PDF (229 kB)]

Physical Mechanisms Shaping the Drosophila Dorsoventral Compartment Boundary

In many tissues, cells are organized in distinct compartments separated by sharp boundaries. We study physical mechanisms that contribute to the morphology of compartment boundaries in the developing wing of the fly. In addition to increased cell bond tension at the boundary we show that a bias of cell division by cell elongation has a significant effect to reduce interface roughness.

M. Aliee, J.-C. Röper, K. P. Landsberg, C. Pentzold, T. J. Widmann, F. Jülicher and C. Dahmann
Curr. Biol. 22, 1 (2012)
[PDF (1,6 MB)]

The Taylor–Couette Motor:
Spontaneous Flows of Active Polar Fluids Between two Coaxial Cylinders

We discuss the behaviors of a polar or nematic active fluid confined between concentric cylinders and show that this system can behave as a rotatory motor. In the absence of an external torque, the fluid can generate a flow field with broken chiral symmetry which then results in the cylinders rotating relative to each other at a particular rate. If an external torque is applied the rotation rate changes and the system performs mechanical work. The relationship between rotation rate and the applied torque characterizes the mechanical properties of this motor.

S. Fürthauer, M. Neef, S. W. Grill, K. Kruse and F. Jülicher
New. J. Phys. 14, 023001 (2012)
[PDF (655 kB)]

Highlights 2011
Highlights 2010
Highlights 2009
Highlights 2008
Highlights 2007
The European Physical Journal E
Last updated: 14 April 2014