Biology subjects

Thijssen, K.

Publications and source records attributed to Thijssen, K..

3 recordsLinked to original sources

bioRxiv2026

A principal-stress rule for cell division in epithelia

Dense active materials, from cellular tissues to jammed and glassy systems, must continuously relieve internal mechanical stress to remain structurally stable as they are driven far from equilibrium. In epithelial tissues, this relief occurs through cell division, yet what sets the geometry of this structural remodeling event has, for over a century, been attributed to a purely geometric principle: Hertwigs rule, whereby cells divide along their long axis. We show that as epithelial tissues densify and cell shape anisotropy collapses, this geometric rule is superseded by a mechanical one in which dense epithelia relieve anisotropic stress by cells dividing along their principal axis, independent of the tissues isotropic stress state. Using direct force measurement and stress inference, we show that stress orientation, rather than cell shape, governs the axis of cell division across mechanically distinct systems, from fluid-like to jammed monolayers and structurally heterogeneous organoids, remaining predictive precisely where the classical geometric rule fails. This stress-oriented remodeling is reciprocally coupled to the materials mechanical state: anisotropic stress accelerates the underlying remodeling rate, while each remodeling event locally dissipates the stress that triggered it, closing a negative feedback loop. This "principal-stress rule" recasts epithelial cell division as a stress-relief mechanism intrinsic to dense active matter, providing a general mechanical framework linking internal stress, structural remodeling, and homeostasis in living materials.

biophysics↗

bioRxiv2024

Topological Excitations govern Ordering Kinetics in Endothelial Cell Layers

Many physiological processes, such as the shear flow alignment of endothelial cells in the vasculature, depend on the transition of cell layers between disordered and ordered phases. Here, we demonstrate that such a transition is driven by the non-monotonic evolution of nematic topological defects and the emergence of topological strings that bind the defects together, unveiling an intermediate phase of ordering kinetics in biological matter. We used time-resolved large-scale imaging and physical modeling to resolve the nature of the non-monotonic decrease in the number of defect pairs. The interaction of the intrinsic cell layer activity and the alignment field determines the occurrence of defect domains, which defines the nature of the transition. Defect pair annihilation is mediated by topological strings spanning multicellular scales within the cell layer. We propose that these long-range interactions in the intermediate ordering phase have significant implications for a wide range of biological phenomena in morphogenesis, tissue remodeling, and disease progression.

biophysics↗

bioRxiv2024

Cell aspect ratio is a mechanical winning strategy in microbial competition

Bacterial competition shapes community architecture, yet a universally conserved determinant remains elusive. We show that cell aspect ratio -a simple morphological feature- confers a competitive advantage. Using growth-based range expansion experiments, we show that longer bacteria conquer the expanding front, even when initially in minority. Using an agent-based model of dividing bacteria, to isolate the effect of aspect ratio, we reveal that the takeover mechanism is collective alignment: groups of locally aligned bacteria form "nematic arms" bridging the central region of the colony to the expanding front. Once at the front, bacteria align parallel to it and block shorter bacteria from access to nutrients and space. We confirm this observation with single-cell experiments and further generalise our findings by introducing a generic continuum model of alignment-dominated competition, explaining both experimental and cell-based model observations. Moreover, we extend our predictions to spherical range expansions and confirm the competitive advantage, even though the effect is less pronounced than in surface-attached colonies. Our results uncover a simple, yet hitherto overlooked, mechanical mechanism determining the outcome of bacterial competition, which is potentially ubiquitous among various bacteria. Current advances in genetic engineering enable aspect ratio tuning as a mechanism with broad implications for biofilm control.

biophysics↗