Biology subjects

Fischer-Friedrich, E.

Publications and source records attributed to Fischer-Friedrich, E..

12 recordsLinked to original sources

bioRxiv2026

Localized actin cortex perturbation generates cell-scale membrane tension gradients

Membrane tension is a key mechanical regulator of cell signaling, morphology, and division. Whether cells can sustain spatial gradients in membrane tension, or whether such asymmetries are rapidly dissipated by long-range tension propagation, remains actively debated. Here, we use the tension-sensitive fluorescent probe FliptR to directly measure in-plane membrane tension before and after localized optogenetic activation of RhoA in mitotic HeLa cells. We find that localized RhoA activation generates a sustained, cell-scale membrane tension gradient, with tension elevated on the non-activated side. This gradient depends on an intact actin and microtubule cytoskeleton and is accompanied by polarized cytoskeletal remodeling: cortical f-actin enrichment at the activation site and asymmetric microtubule growth on the opposite side. Tether-force measurements reveal enhanced membrane-cortex adhesion at the activated side, with no corresponding increase in in-plane tension, reconciling an apparent discrepancy between prior studies. A coarse-grained membrane chemical potential accounts for gradient maintenance through spatially heterogeneous membrane-cortex coupling. Together, our findings demonstrate that cells can actively generate and sustain spatially patterned mechanical states through localized cytoskeletal signaling.

biophysics↗

bioRxiv2025

A protein-DNA surface hydrogel mechanically protects the cell nucleus

The nuclear envelope protects the genome from mechanical stress during processes such as migration, division, and compression1-6, but how it buffers forces at the scale of DNA remains unclear. Here, we utilize optical tweezers to show that a multivalent protein-DNA co-condensate containing the nuclear envelope protein LEM27,8 and the DNA-binding protein BAF 9,10 shield DNA beyond its melting point at 65 pN11. Under load, their collective assembly induces an unconventional DNA stiffening effect that provides mechanical reinforcement, dependent on the intrinsically disordered region (IDR) of LEM2. At the nuclear surface, these components form an elastic surface hydrogel in which LEM2 IDR-IDR interactions contract the surface hydrogel relative to its relaxed state, introducing a pre-stress in the lamin network. Inside cells, this surface hydrogel model can recapitulate elastic properties of the nuclear envelope measured via AFM indentation experiments as well as nuclear morphology, using parameters obtained at the molecular scale by use of optical tweezers. Disruption of the surface hydrogel increases DNA damage and micronuclei formation during nuclear deformation. These findings reveal a load-bearing, mesoscale surface hydrogel that reinforces the nucleus and expands the functional repertoire of biomolecular condensates to include DNA protection under mechanical stress.

biophysics↗

bioRxiv2025

Regulation of plasma membrane tension through hydrostatic pressure and actin protrusion forces

The plasma membrane and its associated proteins form a critical signaling hub, mediating communication between the extracellular environment and the intracellular space. Previous research suggests that both membrane trafficking and signaling activity are influenced by mechanical tension in the plasma membrane. Despite its importance, the mechanisms by which cells regulate membrane tension remain poorly understood. Using the optical tension sensor FliptR and AFM-assisted tether force measurements, we investigate plasma membrane tension regulation in mitotic cells by measuring tension changes following cytoskeletal and cell shape perturbations. Our findings show that in both assays, reported tensions are critically influenced by the cytoskeleton, however, with partially deviating trends highlighting the conceptual differences between bare and apparent membrane tension. By integrating experimental data with theoretical modeling, we demonstrate that the actin cytoskeleton regulates bare membrane tension through two distinct mechanisms: (i) modulation of intracellular hydrostatic pressure and (ii) adjustment of polymerization forces in actin-rich finger-like protrusions. SIGNIFICANCE STATEMENTThe plasma membrane is a vital cell interface, facilitating communication with the environment. Mechanical tension in the membrane plays a crucial role in tuning this communication, yet its regulation remains poorly understood. This is partly due to the lack of precise measurement tools and the misleading use of membrane tether forces as proxies. In this study, we use advanced techniques -- FliptR tension sensors, AFM-based tether force measurements, and theoretical modeling -- to explore membrane tension in mitotically arrested cells. We find that the actin cytoskeleton regulates membrane tension via intracellular pressure control and polymerization forces in protrusions. Moreover, we show that tether forces do not reliably reflect in-plane membrane tension, making them unsuitable as direct reporters of membrane mechanics.

biophysics↗

bioRxiv2024

Mesenchymal-epithelial transition reduces proliferation but increases immune evasion in tumor spheroids

Mesenchymal-epithelial transition (MET) has been associated with secondary tumor outgrowth during metastasis but the underlying mechanism remains elusive. Using MET-inducible mesenchymal breast cancer cells, we investigated whether MET benefits tumor outgrowth by enhancing proliferation. We found that crowding inhibition of proliferation is present before and after MET, but mesenchymal cells gain a proliferative advantage through more effective escape from crowded cell islands. In 3D culture, proliferation is reduced upon MET with differential effects of focal-adhesion-signalling and actomyosin activity. In particular, inhibition of Src-signalling leads to increased growth after MET. Finally, in co-culture experiments, MET-induced tumor spheroids evade immune cell attack to a larger extent, likely due to more confined epithelial spheroid shape and changes in immunomodulatory molecules. Our data suggest that, contrary to previous assumptions in the field, MET might promote secondary tumor outgrowth not through a proliferation boost but through increased survival rate in the presence of immune cells.

cell biology↗

bioRxiv2024

Epithelial folding through local degradation of an elastic basement membrane plate

Epithelia are polarised layers of cells that line the outer and inner surfaces of organs. At the basal side, the epithelial cell layer is supported by a basement membrane, which is a thin polymeric layer of self-assembled extracellular matrix (ECM) that tightly adheres to the basal cell surface. Proper shaping of epithelial layers is an important prerequisite for the development of healthy organs during the morphogenesis of an organism. Experimental evidence indicates that local degradation of the basement membrane drives epithelial folding. Here, we present a coarse-grained plate theory model of the basement membrane that assumes force balance between i) cell-transduced active forces and ii) deformation-induced elastic forces. We verify key assumptions of this model through experiments in the Drosophila wing disc epithelium and demonstrate that the model can explain the emergence of outward epithelial folds upon local plate degradation. Our model accounts for local degradation of the basement membrane as a mechanism for the generation of epithelial folds in the absence of epithelial growth.

biophysics↗

bioRxiv2023

Epithelial-mesenchymal transition induces cell-cycle-dependent changes of cortical signalling

Epithelial-mesenchymal transition (EMT) is a key cellular transformation for many physiological and pathological processes ranging from cancer over wound healing to embryogenesis. Changes in cell migration, cell morphology and cellular contractility were identified as hallmarks of EMT. These cellular properties are known to be tightly regulated by the actin cytoskeleton. EMT-induced changes of actin-cytoskeletal regulation were demonstrated by previous reports of cell-cycle-dependent changes of actin cortex mechanics in conjunction with characteristic modifications of cortex-associated f-actin and myosin. However, at the current state, the changes of upstream actomyosin signalling that lead to corresponding mechanical and compositional changes of the cortex are not well understood. In this work, we show in breast epithelial cancer cells MCF-7 that EMT results in characteristic changes of the cortical signalling of Rho-GTPases Rac1, RhoA and RhoC and downstream actin regulators cofilin, mDia1 and Arp2/3. In the light of our findings, we propose that cell-cycle-dependent EMT-induced changes in cortical mechanics rely on two hitherto unappreciated signalling paths - i) a cell-cycle-dependent interaction between Rac1 and RhoC and ii) an inhibitory effect of Arp2/3 activity on cortical association of myosin II.

cell biology↗

bioRxiv2022

Hydrostatic pressure and lateral actomyosin tension control stretch and tension of the basement membrane in epithelia

The shaping of epithelial tissues into functional organs often depend on asymmetries in mechanical tension present at the apical and basal sides of cells. Contraction of an actomyosin meshwork underlying the apical side of cells is known to generate apical tension. The basal side of cells is also associated with an actomyosin meshwork, but it is, in addition, connected to a specialized extracellular matrix, the basement membrane. However, how basal tension is generated, and the role of the basement membrane in this process, are not well understood. Here, using atomic force microscopy, we measure mechanical tension in the basal surface of the wing disc epithelium of Drosophila. We find that basal tension depends on both the actomyosin cytoskeleton and the basement membrane, and that it is proportional to lateral surface tension and hydrostatic pressure. Collagen IV turnover and mobility are slow indicating that the basement membrane can store elastic stresses. Our data suggest that elastic stresses in the basement membrane induced by basement membrane stretch are a key factor in the adjustment of basal tension. Hydrostatic pressure and lateral actomyosin contractility are two driving forces by which epithelial cells can maintain this basement membrane stretch.

biophysics↗

bioRxiv2022

Skin epithelial cells change their mechanics and proliferation upon Snail-mediated EMT signalling

Skin cancer is the most commonly occurring cancer in the USA and Germany, and the fourth most common cancer worldwide. Snail-dependent epithelial-mesenchymal transition (EMT) was shown to initiate and promote skin cancer. Previous studies could show that EMT changes actin cortex regulation and cellular mechanics in epithelial cells of diverse tissue origin. However, in spite of its potentially high significance in the context of skin cancer, the effect of EMT on cellular mechanics, mitotic rounding and proliferation has not been studied in skin epithelial cells so far. In this work we show that TGF-{beta}-induced partial EMT results in a transformation of the mechanical phenotype of skin epithelial cells in a cell-cycle dependent manner. Concomitantly, we looked at EMT-induced changes of cell proliferation. While EMT decreases proliferation in 2D culture, we observed an EMT-induced boost of cellular proliferation when culturing cells as mechanically confined aggregates of skin epithelial cells. This proliferation boost was accompanied by enhanced mitotic rounding and composition changes of the actin cortex. We give evidence that observed EMT-induced changes depend on the EMT-upregulated transcription factor Snail. Overall, our findings indicate that EMT-induced changes of cellular mechanics might play a currently unappreciated role in EMT-induced promotion of skin tumor proliferation. Significance statementThis study describes how epithelial-mesenchymal transition (EMT) alters the actin cytoskeleton, cellular mechanics and proliferation in a benign tumor model of skin epithelial cells. We show that corresponding EMT-induced phenotypes depend on the signalling of the transcription factor Snail. Our findings suggest that EMT-induced changes of cellular mechanics and proliferation might play a currently under-appreciated role in EMT-induced promotion of skin tumors.

biophysics↗

bioRxiv2020

EMT changes actin cortex rheology in a cell-cycle dependent manner

The actin cortex is a key structure for cellular mechanics and cellular migration. Accordingly, cancer cells were shown to change their actin cytoskeleton and their mechanical properties in correlation with different degrees of malignancy and metastatic potential. Epithelial-Mesenchymal transition (EMT) is a cellular transformation associated with cancer progression and malignancy. To date, a detailed study of the effects of EMT on the frequency-dependent viscoelastic mechanics of the actin cortex is still lacking. In this work, we have used an established AFM-based method of cell confinement to quantify the rheology of the actin cortex of human breast, lung and prostate epithelial cells before and after EMT in a frequency range of 0.02 - 2 Hz. Interestingly, we find for all cell lines opposite EMT-induced changes in interphase and mitosis; while the actin cortex softens upon EMT in interphase, the cortex stiffens in mitosis. Our rheological data can be accounted for by a rheological model with a characteristic time scale of slowest relaxation. In conclusion, our study discloses a consistent rheological trend induced by EMT in human cells of diverse tissue origin reflecting major structural changes of the actin cytoskeleton upon EMT. Significance statementThe actin cortex is a key structure for cellular mechanics and cellular migration. Correspondingly, migratory cancer cells were shown to change their mechanical properties to a softer phenotype. EMT is a cellular transformation associated with cancer progression and malignancy. To date, a detailed study of the effects of EMT on the mechanics of the actin cortex is still lacking. In this work, we provide such a study for human breast, lung and prostate epithelial cells in dependence of the cell cycle stage. We observe a softening of the actin cortex in interphase but stiffening in mitosis upon EMT. In conclusion, our study discloses a consistent mechanical trend induced by EMT in human cells of diverse tissue origin.

biophysics↗

bioRxiv2020

Binding dynamics of α-actinin-4 in dependence of actin cortex tension

Mechano-sensation of cells is an important prerequisite for cellular function, e.g. in the context of cell migration, tissue organisation and morphogenesis. An important mechano-chemical-transducer is the actin cytoskeleton. In fact, previous studies have shown that actin cross-linkers, such as -actinin-4, exhibit mechanosensitive properties in its binding dynamics to actin polymers. However, to date, a quantitative analysis of tension-dependent binding dynamics in live cells is lacking. Here, we present a new technique that allows to quantitatively characterize the dependence of cross-linking lifetime of actin cross-linkers on mechanical tension in the actin cortex of live cells. We use an approach that combines parallel plate confinement of round cells, fluorescence recovery after photo-bleaching, and a mathematical mean-field model of cross-linker binding. We apply our approach to the actin cross-linker -actinin-4 and show that the cross-linking time of -actinin-4 homodimers increases approximately twofold within the cellular range of cortical mechanical tension rendering -actinin-4 a catch bond in physiological tension ranges.

biophysics↗

bioRxiv2019

EMT-induced cell mechanical changes enhance mitotic rounding strength

To undergo mitosis successfully, most animal cells need to acquire a round shape to provide space for the mitotic spindle. This mitotic rounding relies on mechanical deformation of surrounding tissue and is driven by forces emanating from actomyosin contractility. Cancer cells are able to maintain successful mitosis in mechanically challenging environments such as the increasingly crowded environment of a growing tumor, thus, suggesting an enhanced ability of mitotic rounding in cancer. Here, we show that epithelial mesenchymal transition (EMT), a hallmark of cancer progression and metastasis, gives rise to cell-mechanical changes in breast epithelial cells. These changes are opposite in interphase and mitosis and correspond to an enhanced mitotic rounding strength. Furthermore, we show that cell-mechanical changes correlate with a strong EMT-induced change in the activity of Rho GTPases RhoA and Rac1. Accordingly, we find that Rac1 inhibition rescues the EMT-induced cortex-mechanical phenotype. Our findings hint at a new role of EMT in successful mitotic rounding and division in mechanically confined environments such as a growing tumor.

biophysics↗

bioRxiv2019

3D microenvironment stiffness regulates tumor spheroid growth and mechanics via p21 and ROCK

Mechanical properties of cancer cells and their microenvironment contribute to breast cancer progression. While mechanosensing has been extensively studied using two-dimensional (2D) substrates, much less is known about it in a physiologically more relevant 3D context. Here we demonstrate that breast cancer tumor spheroids, growing in 3D polyethylene glycol-heparin hydrogels, are sensitive to their environment stiffness. During tumor spheroid growth, compressive stresses of up to 2 kPa built up, as quantitated using elastic polymer beads as stress sensors. Atomic force microscopy (AFM) revealed that tumor spheroid stiffness increased with hydrogel stiffness. Also, constituent cell stiffness increased in a ROCK- and F-actin-dependent manner. Increased hydrogel stiffness correlated with attenuated tumor spheroid growth, a higher proportion of cells in G0/G1 phase and elevated levels of the cyclin-dependent kinase inhibitor p21. Drug-mediated ROCK inhibition reversed not only cell stiffening upon culture in stiff hydrogels but also increased tumor spheroid growth. Taken together, we reveal here a mechanism by which the growth of a tumor spheroid can be regulated via cytoskeleton rearrangements in response to its mechanoenvironment. Thus, our findings contribute to a better understanding of how cancer cells react to compressive stress when growing under confinement in stiff environments and provide the basis for a more in-depth exploration of the underlying mechanosensory response.

bioengineering↗