The diverse effects of mechanical loading on active hair bundles.

Hair cells in the auditory, vestibular, and lateral-line systems of vertebrates receive inputs through a remarkable variety of accessory structures that impose complex mechanical loads on the mechanoreceptive hair bundles. Although the physiological and morphological properties of the hair bundles in each organ are specialized for detecting the relevant inputs, we propose that the mechanical load on the bundles also adjusts their responsiveness to external signals. We use a parsimonious description of active hair-bundle motility to show how the mechanical environment can regulate a bundle's innate behavior and response to input.

Polarization of PAR proteins by advective triggering of a pattern-forming system.

In the Caenorhabditis elegans zygote, a conserved network of partitioning-defective (PAR) polarity proteins segregates into an anterior and a posterior domain, facilitated by flows of the cortical actomyosin meshwork. The physical mechanisms by which stable asymmetric PAR distributions arise from transient cortical flows remain unclear. We present evidence that PAR polarity arises from coupling of advective transport by the flowing cell cortex to a multistable PAR reaction-diffusion system.

Diffusive coupling can discriminate between similar reaction mechanisms in an allosteric enzyme system.

Background: A central question for the understanding of biological reaction networks is how a particular dynamic behavior, such as bistability or oscillations, is realized at the molecular level. So far this question has been mainly addressed in well-mixed reaction systems which are conveniently described by ordinary differential equations. However, much less is known about how molecular details of a reaction mechanism can affect the dynamics in diffusively coupled systems because the resulting partial differential equations are much more difficult to analyze.

Inward rotating spiral waves in glycolysis.

We report on the first observation of inward rotating spiral waves (antispirals) in a biochemical reaction-diffusion system. Experiments are performed with extracts from yeast cells in an open spatial reactor. By increasing the protein concentration of the extract we observe a transition from outward to inward propagating waves of glycolytic activity.

Critical asymmetry for giant diffusion of active Brownian particles.

We study the effect of an asymmetry on the transport properties of an active Brownian particle. We demonstrate the existence of a critical force or, more generally, of a critical asymmetry that separates parameter regimes of giant diffusion from those with reliable directed transport. We derive a condition for the critical asymmetry by means of an exact expression for the diffusion coefficient and by a simplified discrete picture.

An osmoregulatory basis for shape oscillations in regenerating hydra.

The freshwater polyp Hydra has considerable regeneration capabilities. A small fragment of tissue excised from an adult animal is sufficient to regenerate an entire Hydra in the course of a few days. During the initial stages of the regeneration process, the tissue forms a hollow sphere.

Wave instability induced by nonlocal spatial coupling in a model of the light-sensitive Belousov-Zhabotinsky reaction.

We study spatiotemporal patterns resulting from instabilities induced by nonlocal spatial coupling in the Oregonator model of the light-sensitive Belousov-Zhabotinsky reaction. In this system, nonlocal coupling can be externally imposed by means of an optical feedback loop which links the intensity of locally applied illumination with the activity in a certain vicinity of a particular point weighted by a given coupling function. This effect is included in the three-variable Oregonator model by an additional integral term in the photochemically induced bromide flow.

Drifting pattern domains in a reaction-diffusion system with nonlocal coupling.

Drifting pattern domains (DPDs), i.e., moving localized patches of traveling waves embedded in a stationary (Turing) pattern background and vice versa, are observed in simulations of a reaction-diffusion model with nonlocal coupling.