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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.