Spatial Confinement Causes Lifetime Enhancement and Expansion of Vortex Rings with Positive Filament Tension

We study the impact of spatial confinement on the dynamics of three-dimensional excitation vortices with circular filaments. In a chemically active medium we observe a decreased contraction of such scroll rings and even expanding ones, despite of their positive filament tension. We propose a kinematical model which takes into account the interaction of the scroll ring with a confining Neumann boundary. The model reproduces all experimentally observed regimes of ring evolution, and correctly predicts the results obtained by numerical simulations of the underlying reaction-diffusion equations

Discovering dynamics and parameters of nonlinear oscillatory and chaotic systems from partial observations

Despite rapid progress in live-imaging techniques, many complex biophysical and biochemical systems remain only partially observable, thus posing the challenge to identify valid theoretical models and estimate their parameters from an incomplete set of experimentally accessible time series. Here, we combine sensitivity methods and VoteFair popularity ranking to construct an automated hidden dynamics inference framework that can discover predictive nonlinear dynamical models for both observable and latent variables from noise-corrupted incomplete data in oscillatory and chaotic systems. After validating the framework for prototypical FitzHugh-Nagumo oscillations, we demonstrate its applicability to experimental data from squid neuron activity measurements and Belousov-Zhabotinsky (BZ) reactions, as well as to the Lorenz system in the chaotic regime.Comment: 37 pages, 18 figure

Dynamics, scaling behavior, and control of nuclear wrinkling

The cell nucleus is enveloped by a complex membrane, whose wrinkling has been implicated in disease and cellular aging. The biophysical dynamics and spectral evolution of nuclear wrinkling during multicellular development remain poorly understood due to a lack of direct quantitative measurements. Here, we combine live-imaging experiments, theory, and simulations to characterize the onset and dynamics of nuclear wrinkling during egg development in the fruit fly, Drosophila melanogaster, when nurse cell nuclei increase in size and display stereotypical wrinkling behavior. A spectral analysis of three-dimensional high-resolution data from several hundred nuclei reveals a robust asymptotic power-law scaling of angular fluctuations consistent with renormalization and scaling predictions from a nonlinear elastic shell model. We further demonstrate that nuclear wrinkling can be reversed through osmotic shock and suppressed by microtubule disruption, providing tunable physical and biological control parameters for probing mechanical properties of the nuclear envelope. Our findings advance the biophysical understanding of nuclear membrane fluctuations during early multicellular development.Comment: Main text: 10 pages, 3 figures. SI: 19 pages, 10 figures, 1 tabl

A novel technique to initiate and investigate scroll waves in thin layers of the photosensitive Belousov-Zhabotinsky reaction

While free scroll rings are non-stationary objects that either grow or contract with time, spatial confinement can have a large impact on their evolution reaching from significant lifetime extension (J.F. Totz, H. Engel, O. Steinbock, New J. Phys. 17, 093043 (2015)) up to formation of stable stationary and breathing pacemakers (A. Azhand, J.F. Totz, H. Engel, EPL 108, 10004 (2014)). Here, we explore the parameter range in which the interaction between an axis-symmetric scroll ring and a confining planar no-flux boundary can be studied experimentally in transparent gel layers supporting chemical wave propagation in the photosensitive variant of the Belousov-Zhabotinsky medium. Based on full three-dimensional simulations of the underlying modified complete Oregonator model for experimentally realistic parameters, we determine the conditions for successful initiation of scroll rings in a phase diagram spanned by the layer thickness and the applied light intensity. Furthermore, we discuss whether the illumination-induced excitability gradient due to Lambert-Beer’s law as well as a possible inclination of the filament plane with respect to the no-flux boundary can destabilize the scroll ring

Combinatorial patterns of graded RhoA activation and uniform F-actin depletion promote tissue curvature

ABSTRACT During development, gene expression regulates cell mechanics and shape to sculpt tissues. Epithelial folding proceeds through distinct cell shape changes that occur simultaneously in different regions of a tissue. Here, using quantitative imaging in Drosophila melanogaster, we investigate how patterned cell shape changes promote tissue bending during early embryogenesis. We find that the transcription factors Twist and Snail combinatorially regulate a multicellular pattern of lateral F-actin density that differs from the previously described Myosin-2 gradient. This F-actin pattern correlates with whether cells apically constrict, stretch or maintain their shape. We show that the Myosin-2 gradient and F-actin depletion do not depend on force transmission, suggesting that transcriptional activity is required to create these patterns. The Myosin-2 gradient width results from a gradient in RhoA activation that is refined through the balance between RhoGEF2 and the RhoGAP C-GAP. Our experimental results and simulations of a 3D elastic shell model show that tuning gradient width regulates tissue curvature.</jats:p

Topological braiding and virtual particles on the cell membrane

Significance Topological defects are robust particle-like structures that essentially determine the mechanics and dynamics of physical and biological matter. Examples range from vortices in quantum superfluids to the cores of spiral wave patterns in the brain. In biological systems, such defects play important roles as organizers of biochemical signaling patterns, cellular forces, and even cell death. Combining direct experimental observations with mathematical modeling and chemical perturbations, we investigated the dynamics of spiral wave defects on the surfaces of starfish egg cells. Our quantitative analysis showed that these defects exhibit complex braiding, pair creation, and annihilation dynamics, in agreement with predictions from a generic continuum theory. More broadly, these results suggest interesting parallels between information transport in living and quantum systems.</jats:p

Cell membrane buckling governs early-stage ridge formation in butterfly wing scales: code

Full Changelog: https://github.com/AnthonyMcDougal/buckling-scale-ridges/commits/v1.0.

Cell membrane buckling governs early-stage ridge formation in butterfly wing scales: data

This repository contains the raw data for: JF Totz, AD McDougal, L Wagner, S Kang, PTC So, J Dunkel, BD Wilts, and M Kolle, Cell membrane buckling governs early-stage ridge formation in butterfly wing scales, (forthcoming). The raw data is of a volumetric time series of scales growing on the wing of an individual Vanessa cardui pupa, collected with quantitative phase imaging. Additional details may be found in the Materials and Methods, as well as the SI, of the above publication. The companion code repository may be found on Zenodo: JF Totz, AD McDougal, L Wagner, S Kang, PTC So, J Dunkel, BD Wilts, and M Kolle. (Forthcoming). "Cell membrane buckling governs early-stage ridge formation in butterfly wing scales:code" (v1.0) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.8369163 Note that file A-40-01_11_04_34_set_115.mat was previously released in: AD McDougal, S Kang, Z Yaqoob, PTC So, and M Kolle, Data and analysis codes for “In vivo visualization of butterfly scale cell morphogenesis in Vanessa cardui.” Zenodo. https://doi.org/10.5281/zenodo.5532941. We include it here for completeness of this time series