Research Highlights 2014

Active Torque Generation by the Actomyosin Cell Cortex Drives left-right Symmetry Breaking

We show that chirally asymmetric flows occur in the cell cortex during cell division in C. elegans. These flows can be accounted for by a general hydrodynamic theory of gels in which active chiral processes take place. Our work suggests that active chiral flows generated in the actin cytoskeleton contribute to the left-right symmetry breaking of the C. elegans body plan.

S. R. Naganathan, S. Fürthauer, M. Nishikawa, F. Jülicher and S. W. Grill
eLife 2014;3:e04165 (2014)

[PDF 2,8 MB)]

Synchronization in Networks of Mutually Delay-Coupled Phase-Locked Loops

We study the synchronization of coupled electronic oscillators based on phase-locked loops. We show that delays in signal transmission between such oscillators can facilitate synchronization. Despite the high transmission speeds in electronic circuits, such delays can be significant at the high frequencies used in modern electronics.

A. Pollakis, L. Wetzel, D. J. Jörg, W. Rave, G. Fettweis and F. Jülicher
New J. Phys. 16, 113009 (2014)

[PDF (655 kB)]

The Balance of Prickle/Spiny-Legs Isoforms Controls the Amount of Coupling between Core and Fat PCP Systems

We study the dynamics of planar cell polarity in the developing fly wing. We show that the observed time-dependence of cell polarity patterns in wild type and several mutant conditions can be understood from a general hydrodynamic theory. We find that cell polarity reorientation is guided by both tissue shear and by coupling to the Fat planar polarity system. The latter is regulated by the Prickle/Spiny-Legs Isoforms.

M. Merkel, A. Sagner, F. S. Gruber, R. Etournay, C. Blasse, E. Myers, S. Eaton and F. Jülicher
Current Biololgy 24, 2111 (2014)

[PDF (18,1 MB)] 

Stress Distributions and Cell Flows in a Growing Cell Aggregate

We present a hydrodynamic theory of the mechanics and dynamics of spherical cell aggragates. Our work suggests that cells exhibit a radial pattern of cell polarity that is relevant to the cell density and stress profiles obtained when the cell aggregate is subject to a jump in external pressure.

M. Delarue, J.-F. Joanny, F. Jülicher and J. Prost
Interface Focus 4, 20140033 (2014)

[PDF (492 kB)]

Quantification of Surface Tension and Internal Pressure Generated by Single Mitotic Cells

Using an assay in which cells are compressed between two surfaces, we determine the active mechanical tension of the cell cortex of mitotic cells.

E. Fischer-Friedrich, A. A. Hyman, F. Jülicher, D. J. Müller and J. Helenius
Scientific Reports 4, 6213 (2014)

[PDF (705 kB)]

An Active Oscillator Model Describes the Statistics of Spontaneous Otoacoustic Emissions

The ears of mammals have the ability to amplify weak stimuli by active processes. A signature of this cochlear amplifier are spontaneous emissions that can be detected in the ear canal. Here we present a model of the mammalian cochlea that contains dynamic oscillators as active elements.We show that this model can account for the statistics of spontaneous emissions observed in humans.

F. Fruth, F. Jüicher, B. Lindner
Biophys J. 107, 817 (2014)
[PDF (1,6 MB)] 

Local Increases in Mechanical Tension Shape Compartment Boundaries by Biasing Cell Intercalations

We discuss the dynamics of tissues in the developing fly. Within a tissue compartment, cells can mix while cells of different tissue compartments do not mix. We show that local mechanical tension at a compartment boundary biases cell junction remodeling, thereby preventin cell mixing across compartment boundaries.

D. Umetsu, B. Aigouy, M. Aliee, S. Sui, S. Eaton, F. Jülicher and C. Dahmann
Current Biology 24, 1798 (2014)
[PDF (3,9 MB)] 

Active Phase and Amplitude Fluctuations of Flagellar Beating

Flagella are hair-like extensions of many cells that generate periodic movements and can propel microorganisms in a fluid. Here, we analyze the motion of a beating flagellum and quantify amplitude and phase fluctuations. We discuss these active fluctuations in the context of stochastic many-motor systems.

R. Ma, G. S. Klindt, I. H. Riedel-Kruse, F. Jülicher and B. Friedrich
Phys. Rev. Lett. 113, 048101 (2014)
[PDF (1,3 MB)] 

Multimotor Transport in a System of Active and inactive Kinesin-1 Motors

We study the collective effects of large groups of motor molecules of which a fraction is inactive. We show that interesting dynamic instabilities and bimodal velocity distributions can occur as a function of the fraction of inactive motors.

L. Scharrel, R. Ma, R. Schneider, F. Jülicher and S. Diez
Biophys. J. 107, 365 (2014)
[PDF (1 MB)] 

A Doppler Effect in Embryonic Pattern Formation

The segmented body plan of vertebrate animals is formed by a sequential process during development called somitogenesis. The subsequent formation of somites is organized by collective genetic oscillations in the unpatterned tissue. These cellular oscillations give rise to nonlinear wave patterns of gene activity. Here we analyze the dynamics of these waves and show that a Doppler effects contributes to the timing of segmentation.

D. Soroldoni, D. J. Jörg, L. G. Morelli, D. L. Richmond, J. Schindelin, F. Jülicher and A. C. Oates
Science 345, 222 (2014)
[PDF (623 kB)] Supplementary Material

Centrosomes are Autocatalytic Droplets of Pericentriolar Material Organized by Centrioles

Centrosomes are located at the poles of mitotic spindles during cell division. They assemble around centrioles and can occur in different sizes. We propose that centrosome properties can be understood as a liquid like phase that assembles by an autiocatalytic reaction. The centrioles are active nucleators of centrosome assembly by starting the autocatalyic process by their catalytic activity. Our theory can quantitatively account for the observed assembly dynamics of centrosomes in normal and perturbed conditions.

D. Zwicker, M. Decker, S. Jaensch, A. A. Hyman and F. Jülicher
Proc. Natl. Acad. Sci. USA 111, E2636 (2014)
[PDF (1,2 MB)]

Active Elastic Thin Shell Theory for Cellular Deformations

Cell shape is governed by the mechanics of the action cytoskeletion together with cell- cell adhesion. The actin cytoskeleton forms athin layer near the cell membraje called cell cortex. The cell cortex is an active material in which contractile stresses are generated by motor molecules. At short times the cortex is an elastic solid which at longer times exhibits viscous material properties. We develop a theory of active and elastic thin shells in order to calculate shapes of cells at short times after forced detachment of cell-cell adhesion.

H. Berthoumieux, J.-L. Maître, C.-P. Heisenberg, E. K. Paluch, F. Jülicher and G. Salbreux
New J. Phys. 16 065005 (2014)
[PDF (950 kB)]

Motor Regulation Results in Distal Forces that Bend Partially Disintegrated Chlamydomonas Axonemes into Circular Arcs

We investigate the mechanics of microtubule doublets interacting with dynein motors that can lead to circular configurations of filaments. We show that these shapes can be understood as the consquence of a dependence of the motor detachmenht rate by forces acting normal to filaments. This mechanism of motor regulation could have an important role in beating cilia such as those of swimming algea.

V. Mukundan, P. Sartori, V. F. Geyer, F. Jülicher and J. Howard
Biophys J., 106, 2434 (2014)
[PDF (1 MB)]

Pulsatory Patterns in Active Fluids

The regulation of active stresses by diffusing regulatory molecules provides a simple example for mechano-chemical pattern formation. In such systems, flows are generated by gradients of active stresses which lead to the transport of regulators. The regulators themselves organize the profiles of active stress. We show that two diffusing regulators, one which upregulates and one which downregulates stress can lead to oscillating spatial patterns and waves.

K. V. Kumar, J. S. Bois, F. Jülicher and S. W. Grill
Phys. Rev. Lett. 112, 208101 (2014)
[PDF (721 kB)]

Transduction Channels' Gating can Control Friction on Vibrating Hair-Cell Bundles in the Ear

Hair bundles are the sensory organelles of auditory hair cells. We study the mechanical response of hair bundles to mechanical stimuli of different velocity. We show that the hair bundle exhibits a friction that is due to dissipation associated with the opening and closing of mechanosensitive ion channels. This channel friction can be larger than the friction due to motion in the viscous environment of the hair bundle.

V. Bormuth, J. Barral, J.-F. Joanny, F. Jülicher and P. Martin
Proc. Natl. Acad. Sci. USA, 111, 7185 (2014)
[PDF (1,1 MB)]

Synchronization Dynamics in the Presence of Coupling Delays and Phase Shifts

We study the synchronization of dynamic oscillators in spatially extended systems. Oscillatiors are coupled to their neighbors with a time delay. We show that for sufficiently large time delay long wavelength modes can relax faster than certain short wavelength modes.

D. J. Jörg, L. G. Morelli, S. Ares and F. Jülicher
Phys. Rev. Lett. 112, 174101 (2014)
[PDF (328 kB)]

Growth Control by a Moving Morphogen Gradient during Drosophila Eye Development

We study the spatial profile of cell division in the developing eye of the fly. We show that the observed pattern of tissue growth can be understood as the result of a growth control mechanism mediated by a moving morphogen profile. Our work shows that the very different proliferation patterns in the wing an the eye can be understood by a common simple principle. Cell growth and division is stimulated by the relative rate of increase of a morphogen induced signal.

O. Wartlick, F. Jülicher and M. Gonzales-Gaitan
Development 141 1884 (2014)
[PDF (4,8 MB)]

Wnt-regulated Dynamics of Positional Information in Zebrafish Somitogenesis

All vertebrate animals generate the segmented body plan and the precursors of vertebra by a dynamic oscillatory process that involves genetic wave patterns. We study the influence of Wnt signaling on the dynamics of the wavefront. We show that the segment size can be varied by varying the speed of the wave front while leaving the clock period unchanged.

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 035002 (2014)
[PDF (406 kb)]