Biology subjects

Vos, B. E.

Publications and source records attributed to Vos, B. E..

12 recordsLinked to original sources

bioRxiv2026

Structural order emerges without mechanical order inside living cells

Intracellular organization is vital for cell function, and disruption of organelle positioning is connected to severe diseases, such as cancer. Given the small length scale of cells and the importance of Brownian motion, maintaining intracellular organization requires mechanical interactions to remain stable. Here, we test the common view that intracellular organization is reflected in intracellular mechanical properties. Using the recently introduced active mechanical fingerprint, we quantify intracellular mechanical properties and active forces to create mechanical maps of patterned RPE1 cells. The organization of actin, microtubules, the Golgi apparatus, the endoplasmic reticulum, and the nucleus reveals pronounced structural polarization across the cell population. To overcome limitations of simple averages, we use a Wasserstein barycenter to calculate an optimal intracellular organization that explains all measurements with minimal cellular distortion. To our surprise, and in contrast to previous reports, we find neither a statistically significant spatial mechanical pattern nor any relevant correlation between the tested structures and intracellular mechanical properties. While there is clear local mechanical anisotropy, the large heterogeneity of mechanical values outweighs any intracellular mechanical gradient. This is further supported by large cell-to-cell variability. Thus, despite having the same genome, cells function properly while their intracellular mechanical properties vary over two orders of magnitude.

biophysics↗

bioRxiv2026

Zebrafish embryos are robust to mechanical perturbations

The investigation of morphogenesis during organism development has massively benefited from the interaction between developmental biology and biophysics, which gave new quantitative insights into natures physical working principles. The process of zebrafish epiboly provides a beautiful model system as cells exhibit collective migration, meanwhile requiring symmetry breaking for gastrulation and the subsequent tissue differentiation. These elegantly robust processes are facilitated by both biochemical and mechanical cues. Here we test the hypothesis that the future body axis is robust against mechanical perturbations of tissue flow and tissue stress fields. For this, we trigger tissue flow by photoablation, which leads to an externally enforced symmetry breaking before natural symmetry breaking of gastrulation occurs. Using 3D light sheet microscopy, we obtained nuclei trajectories as a proxy for the migration of individual cells. Analyzing the derived tissue velocity field, we observed that epiboly is highly robust and mostly unaffected by ablation damage. However, the photoablation induced a convergent motion of cells towards an azimuthal angle resembling shield formation. We extensively characterized this convergent motion and checked if this tissue flow is able to reorient natural symmetry breaking during shield formation. While ablations can transiently disrupt or reorient the convergent motion, we cannot confirm any redirection of the location where the future body axis of the animal develops. The observations were also highly dependent on the developmental stage of the embryo, which cast a greater and more permanent impact, suggesting strong control exerted by factors other than mechanical signals. Significance statementMorphogenesis emerges from the interplay between biochemical patterning and mechanical forces, yet the extent to which mechanical cues influence embryo developmental remains unclear. Using zebrafish epiboly as model system, we imposed controlled mechanical perturbations through targeted photoablation and tracking resulting 3D cell movements. We show that although ablations generate transient convergent motions, epiboly is remarkably robust to externally induced tissue flows. Our findings indicate that the future body axis is strongly buffered against mechanical disturbances, highlighting the dominant role of developmental stage and non-mechanical cues in guiding development.

biophysics↗

bioRxiv2025

Direct mechanical communication of cellular to nuclear shape in oocytes

The mechanical properties of the cytoplasm and nucleoplasm are crucial for the correct and robust functioning of a cell and play a key role in understanding how mechanical signals are transferred to the nucleus. Here, we demonstrate remarkable shape mimicry between the cellular and nuclear shape of oocytes, following the externally applied deformation without direct contact between the cell cortex and the nucleus. This effect arises from a surprisingly soft and fluid-like nucleoplasm that is barely resisting any external strain, while the viscoelastic cytoplasm drives shape transmission. Comparative studies in jellyfish, starfish, and mouse oocytes reveal that lower cytoplasmic elasticity in jellyfish leads to reduced nuclear shape mimicry, highlighting the role of cytoplasmic mechanics in nuclear deformation. Significance StatementMechanosensing of the nucleus is, in addition to chemical signalling, an important factor in gene expression. Although nuclei are often thought to be rigid inclusions in the cytoplasm of a cell, we show that in oocytes nuclei are much more deformable. Using a combination of intranuclear, intracellular and extracellular measurements, we attribute our findings to a fine balance between the soft nucleoplasm surrounded by an elastic shell and the viscoelastic properties of the cytoplasm.

biophysics↗

bioRxiv2024

Membrane tension regulation is required for wound repair

Disruptions of the eukaryotic plasma membrane due to chemical and mechanical challenges are frequent and detrimental, and thus need to be repaired to maintain proper cell function and avoid cell death. However, the cellular mechanisms involved in wound resealing and restoration of homeostasis are diverse and contended. Here, we show that clathrin-mediated endocytosis is induced at later stages of plasma membrane wound repair following the actual resealing of the wound. This compensatory endocytosis occurs near the wound, predominantly at sites of previous early endosome exocytosis which is required in the initial stage of membrane resealing, suggesting a spatio-temporal co-ordination of exo- and endocytosis during wound repair. Using cytoskeletal alterations and modulation of membrane tension and membrane area, we identify membrane tension as a major regulator of the wounding-associated exo- and endocytic events that mediate efficient wound repair. Thus, membrane tension changes are a universal trigger for plasma membrane wound repair modulating the exocytosis of early endosomes required for resealing and subsequent clathrin-mediated endocytosis acting at later stages to restore cell homeostasis and function.

cell biology↗

bioRxiv2023

Intracellular mechanical fingerprint reveals cell type specific mechanical tuning

Living cells are complex entities that perform various tasks with astonishing robustness. While the direct dependence of biological processes on controlled protein expression is well established, we have only begun to understand how intracellular mechanical characteristics guide and support biological function. This is in stark contrast to the expected functional role that intracellular mechanical properties should have for many core cellular functions such as organization, homeostasis, and transport. From a mechanical point of view, cells are complex viscoelastic materials that are continuously driven out of thermodynamic equilibrium, which makes both a physical measurement and mathematical modeling of their properties difficult. Here, we define a "mechanical fingerprint" that can not only characterize the intracellular mechanical state, but also carve out the mechanical differences between cell types with the potential to relate these to proper cell function. By analyzing the frequency-dependent viscoelastic properties and intracellular activity of cells using microrheology, we distilled the complex active mechanical state into just 6 parameters that comprise the mechanical fingerprint. The systematic investigation of the fingerprint illustrates a parameter tuning that could be related to functional cellular requirements. However, the full potential of the mechanical fingerprint is given by a statistical analysis of its parameters across all investigated cell types, which suggests that cells can modify mechanical parameters in a correlated way to position their intracellular mechanical properties within a well-defined phase-space that is spanned between activity, mechanical resistance, and fluidity. This paves the way for a systematic study of the interdependence of biological function and intracellular active mechanics.

biophysics↗

bioRxiv2022

Primordial germ cells adjust their protrusion type while migrating in different tissue contexts in vivo

In both physiological processes and disease contexts, migrating cells have the ability to adapt to conditions in their environment. As an in vivo model for this process, we use zebrafish primordial germ cells that migrate throughout the developing embryo. When migrating within an ectodermal environment, the germ cells form fewer and smaller blebs as compared with their behavior within mesodermal environment. We find that cortical tension of neighboring cells is a parameter that affects blebbing frequency. Interestingly, the change in blebbing activity is accompanied by the formation of more actin-rich protrusions. These alterations in cell behavior that correlate with changes in RhoA activity could allow the cells to maintain dynamic motility parameters, such as migration speed and track straightness, in different settings. In addition, we find that the polarity of the cells can be affected by stiff structures positioned in their migration path.

cell biology↗

bioRxiv2021

Pressure drives rapid burst-like collective migration from 3D cancer aggregates

Collective migration of cells is a key behaviour observed during morphogenesis, wound healing and cancer cell invasion. Hence, understanding the different aspects of collective migration is at the core of further progress in describing and treating cancer and other pathological defects. The standard dogma in cell migration is that cells exert forces on the environment to move and cell-cell adhesion-based forces provide the coordination for collective migration. Here, we report a new collective migration mechanism that is independent of pulling forces on the extra-cellular matrix (ECM), as it is driven by the pressure difference generated inside model tumours. We observe a striking collective migration phenotype, where a rapid burst-like stream of HeLa cervical cancer cells emerges from the 3D aggregate embedded in matrices with low collagen concentration (0.5 mg ml-1). This invasion-like behaviour is recorded within 8 hours post embedding (hpe), and is characterised by high cell velocity and super-diffusive collective motion. We show that cellular swelling, triggered by the soft matrix, leads to a rise in intrinsic pressure, which eventually drives an invasion-like phenotype of HeLa cancer aggregates. These dynamic observations provide new evidence that pressure-driven effects need to be considered for a complete description of the mechanical forces involved in collective migration and invasion.

biophysics↗

bioRxiv2021

Designing a high-resolution, LEGO-based microscope for an educational setting

Microscopy is an essential tool in many fields of science. However, due to their costs and fragility, the usage of microscopes is limited in classroom settings and nearly absent at home. In this article we present the construction of a microscope using LEGO(R) bricks and low-cost, easily available lenses. We demonstrate that the obtained magnification and resolution are sufficient to resolve micrometer-sized objects and propose a series of experiments that explore various biophysical principles. Finally, a study with students in the age range of 9 to 13 shows that the understanding of microscopy increases significantly after working with the LEGO microscope.

scientific communication and education↗

bioRxiv2021

Intracellular softening and fluidification reveals a mechanical switch of cytoskeletal material contributions during division

The life and death of an organism depends largely on correct cell division. While the overall biochemical signaling and morphological processes during mitosis are well understood, the importance of mechanical forces and material properties is only just starting to be discovered. Recent studies of global cell stiffening during cell division may imply an understanding of the cytosol mechanics that is mistaken. Here we show that in contrast to the stiffening process in the cell cortex, the interior of the cell undergoes a softening and fluidification that is accompanied by a decrease of active forces driving particle mobility. Using optical tweezers-based microrheology we capture the complex active and passive material state of the cytoplasm using only six relevant parameters. We demonstrate that the softening occurs because of a surprising role switch between microtubules and actin, where the intracellular, actin-based mechanics is largely controlled by a formin-mediated network.

biophysics↗

bioRxiv2020

Molecular packing structure of fibrin fibers resolved by X-ray scattering and molecular modeling

Fibrin is the major extracellular component of blood clots and a proteinaceous hydrogel used as a versatile biomaterial. Fibrin forms branched networks of polymeric fibers, built of laterally associated double-stranded protofibrils. This multiscale hierarchical structure is crucial for the extraordinary mechanical resilience of blood clots. Yet, the structural basis of clot mechanical properties remains largely unclear due, in part, to the unresolved molecular packing structure of fibrin fibers. Here we quantitatively assess the packing structure of fibrin fibers by combining Small Angle X-ray Scattering (SAXS) measurements of fibrin networks reconstituted under a wide range of conditions with computational molecular modeling of fibrin oligomers. The number, positions, and intensities of the Bragg peaks observed in the SAXS experiments were reproduced computationally based on the all-atom molecular structure of reconstructed fibrin protofibrils. Specifically, the model correctly predicts the intensities of the reflections of the 22.5 nm axial repeat, corresponding to the half-staggered longitudinal arrangement of fibrin molecules. In addition, the SAXS measurements showed that protofibrils within fibrin fibers have a partially ordered lateral arrangement with a characteristic transverse repeat distance of 13 nm, irrespective of the fiber thickness. These findings provide fundamental insights into the molecular structure of fibrin clots that underlies their biological and physical properties.

biophysics↗

bioRxiv2019

Revealing the molecular origins of fibrin’s elastomeric properties by in situ X-ray scattering

Fibrin is an elastomeric protein forming highly extensible fiber networks that provide the scaffold of blood clots. Here we reveal the molecular mechanisms that explain the large extensibility of fibrin networks by performing in situ small angle X-ray scattering measurements while applying a shear deformation. We simultaneously measure shear-induced alignment of the fibers and changes in their axially ordered molecular packing structure. We show that fibrin networks exhibit distinct structural responses that set in consecutively as the shear strain is increased. They exhibit an entropic response at small strains (<5%), followed by progressive fiber alignment (>25% strain) and finally changes in the fiber packing structure at high strain (>100%). Stretching reduces the fiber packing order and slightly increases the axial periodicity, indicative of molecular unfolding. However, the axial periodicity changes only by 0.7%, much less than the 80% length increase of the fibers, indicating that fiber elongation mainly stems from uncoiling of the natively disordered C-peptide linkers that laterally bond the molecules. Upon removal of the load, the network structure returns to the original isotropic state, but the fiber structure becomes more ordered and adopts a smaller packing periodicity compared to the original state. We conclude that the hierarchical packing structure of fibrin fibers, with built-in disorder, makes the fibers extensible and allows for mechanical annealing. Our results provide a basis for interpreting the molecular basis of haemostatic and thrombotic disorders associated with clotting and provide inspiration to design resilient bio-mimicking materials.

biophysics↗

bioRxiv2018

Automated Tracking of Biopolymer Growth and Network Deformation with TSOAX

Studies of how individual semi-flexible biopolymers and their network assemblies change over time reveal dynamical and mechanical properties important to the understanding of their function in tissues and living cells. Automatic tracking of biopolymer networks from fluorescence microscopy time-lapse sequences facilitates such quantitative studies. We present an open source software tool that combines a global and local correspondence algorithm to track biopolymer networks in 2D and 3D, using stretching open active contours. We demonstrate its application in fully automated tracking of elongating and intersecting actin filaments, detection of loop formation and constriction of tilted contractile rings in live cells, and tracking of network deformation under shear deformation.

cell biology↗