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#cell

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Public
Rxiv mechanobio

📰 "Fully three-dimensional force inference in intestinal organoids reveals ratchet-like bud stabilization"
biorxiv.org/content/10.1101/20 #Mechanical #Force #Cell

bioRxiv · Fully three-dimensional force inference in intestinal organoids reveals ratchet-like bud stabilizationThe intestinal epithelium in vertebrates has a characteristic architecture of protruding villi and receding crypts that enables nutrient absorption and cellular turnover. Intestinal organoids recapitulate its development and can be used as disease models, but the underlying mechanical processes are not fully understood yet. Here we combine advanced image processing and the bubbly vertex model for epithelial cell shape to achieve a fully three-dimensional reconstruction of cell shapes and forces during the development of mouse intestinal organoids. We show that the transition to budded morphologies is caused by a global increase in apical tension, which however is not maintained after budding, suggesting ratchet-like non-reversibility. We further demonstrate that luminal pressure decreases and basal line tensions increase during development, thus facilitating budding on the apical side, but at the same time mechanically stabilizing the system at the basal side, for example against cell extrusion. Our approach demonstrates how one can achieve a complete mechanical analysis of a complex tissue-like system. ### Competing Interest Statement The authors have declared no competing interest.
Public
Rxiv mechanobio

📰 "Rapid High-Resolution Analysis of Polysaccharide-Lignin Interactions via Proton-Detected Solid-State NMR with Application to Eucalyptus and Spruce"
biorxiv.org/content/10.1101/20 #Mechanical #Cell

bioRxiv · Rapid High-Resolution Analysis of Polysaccharide-Lignin Interactions via Proton-Detected Solid-State NMR with Application to Eucalyptus and SpruceThe plant secondary cell wall, a complex matrix composed of cellulose, hemicellulose, and lignin, is crucial for the mechanical strength and water-proofing properties of plant tissues, and serves as a primary source of biomass for biorenewable energy and biomaterials. Structural analysis of these polymers and their interactions within the secondary cell wall has been heavily relying on 13C-based solid-state NMR techniques. In this study, we explore the application of 1H-detected solid-state NMR techniques for rapid, high-resolution structural characterization of polysaccharides and lignin, demonstrated on the stems of hardwood eucalyptus and softwood spruce. We employed several strategies, including the use of synthesized 2D spectra to resolve central 1H resonances and the combined application of 3D hCCH and hCHH experiments for complete resonance assignment and unambiguous identification of lignin-carbohydrate interactions. Our findings emphasize the central role of acetylated three-fold xylan conformers, rather than two-fold, in stabilizing the carbohydrate-lignin interface, with glucuronic acid sidechains in eucalyptus glucuronoxylan colocalizing with lignin, revised cellulose-lignin interactions involving uncoated microfibril surfaces, and pectin-lignin interactions indicative of early-stage lignification. We also carefully evaluated the interference from tannins in softwood species. These results present a novel approach for rapid structural analysis of lignocellulosic biomaterials without the need for solubilization or extraction. ### Competing Interest Statement The authors have declared no competing interest.
Public
Rxiv mechanobio

📰 "PIP2-Tmie Interactions Drive Mammalian Hair Cell Slow Adaptation Independently of Myosin Motors"
biorxiv.org/content/10.1101/20 #Mechanical #Myosin #Cell

bioRxiv · PIP2-Tmie Interactions Drive Mammalian Hair Cell Slow Adaptation Independently of Myosin MotorsHair cells and their apically located stereocilia bundle are responsible for detecting sound and balance, by converting mechanical stimuli into electrical signals through the mechano-electric transduction (MET) channels, located at the lower end of the tip link connecting adjacent stereocilia. A long-studied regulation of the MET process is slow adaptation, which is hypothesized to contribute to the auditory systems remarkable dynamic range. Recent studies challenged the old model of slow adaptation which centered around myosin motors. We support a new model of slow adaptation that relies on phosphatidylinositol 4,5-bisphosphate (PIP2) interactions with the MET complex protein Tmie. First, we further support the hypothesized location of the slow adaptation mechanism at the lower end of the tip link by showing that slow adaptation is independent of myosin VIIa, located at the upper end of the tip link. Next, in both cochlear and vestibular hair cells, we demonstrate the reliance of slow adaptation on PIP2. Most strikingly, slow adaptation was rescued with exogenous PIP2 when myosin motors were inhibited, indicating the primary importance of PIP2. Finally, we suggest the importance of Tmie that binds PIP2 in the slow adaptation mechanism. These data support a new model of slow adaptation where PIP2 interactions with Tmie mediate slow adaptation in mammalian hair cells with myosin motors having a classic cargo transport role. ### Competing Interest Statement The authors have declared no competing interest.
Public
Rxiv mechanobio

📰 "Outer epidermal edges mediate cell-cell adhesion for tissue integrity in plants"
biorxiv.org/content/10.1101/20 #Mechanical #Cell

bioRxiv · Outer epidermal edges mediate cell-cell adhesion for tissue integrity in plantsCell-cell adhesion in plants is generally thought to be primarily mediated by the middle lamella, a supposedly thin adhesive layer of the cell wall. Here, we challenge this view. Through computational simulation we found that outer edges of cellular interfaces of the epidermis are hotspot for cell separating tensile stress. Characterization of the ultrastructure of those edges in planta revealed that they are locally thickened regions that harbor cellulose lamellae and pectin-based structural continuity across adjacent cells. We confirmed their dominant role for adhesion by studying mutants where those edges are defective and through direct mechanical testing. This reveals the key role of outer epidermal cell edges, rather than the middle lamella, in mediating cell-cell adhesion for tissue integrity in plants. ### Competing Interest Statement The authors have declared no competing interest.
Public
Rxiv mechanobio

📰 "Mechanical Stress dissipation in locally folded epithelia is orchestrated by calcium waves and nuclear tension changes"
biorxiv.org/content/10.1101/20 #Mechanical #Forces #Cell

bioRxiv · Mechanical Stress dissipation in locally folded epithelia is orchestrated by calcium waves and nuclear tension changesEpithelia are continuously exposed to a range of biomechanical forces such as compression, stretch and shear stress arising from their dynamic microenvironments and associated to their function. Changes in tension such as stretch are known to trigger cell rearrangements and divisions, and impact cellular transcription until mechanical stress is dissipated. How cells process, adapt and respond to mechanical stress is being intensively investigated. In here we focus on epithelial folding which is the fundamental process of transformation of flat monolayers into 3D functional tissues. By combining the innovative method for fold generation, live imaging, mechanobiology tools and chemical screening, we uncover the role of calcium waves on mechanical adaptation of folded epithelia that occurs at the tissue and nuclear level. Folding associated tensional load results in the nuclear flattening which is recovered in the time scale of minutes and is dependent on the calcium wave that spread outwards from the channel and across the epithelium. By creating a mutant overexpressing LBR that relaxed nuclear envelope, we demonstrated that despite presence of calcium waves, nuclear tension increase was essential to trigger nuclear shape recovery post folding through the activation of cellular contractility in the cPLA2 dependent manner. Overall our results identify the molecular mechanism for nuclear shape recovery and indicate that mechanical stress dissipation program is activated at the level of nuclei which serve as internal tension sensors. ### Competing Interest Statement The authors have declared no competing interest.
Public
Rxiv mechanobio

📰 "The role of hydrodynamics in the synchronisation of {\it Chlamydomonas} flagella"
arxiv.org/abs/2504.02680 #Physics.Bio-Ph #Mechanical #Q-Bio.Cb #Cell

arXiv logo
arXiv.orgThe role of hydrodynamics in the synchronisation of {\it Chlamydomonas} flagellaWhile hydrodynamic coupling has long been considered essential for synchronisation of eukaryotic flagella, recent experiments on the unicellular biflagellate model organism {\it Chlamydomonas} demonstrate that -- at the single cell level -- intracellular mechanical coupling is necessary for coordination. It is therefore unclear what role, if any, hydrodynamic forces actually play in the synchronisation of multiple flagella within individual cells, arguably the building block of large scale coordination. Here we address this question experimentally by transiently blocking hydrodynamic coupling between the two flagella of single {\it Chlamydomonas}. Our results reveal that in wild type cells intracellularly-mediated forces are necessary and sufficient for flagellar synchronisation, with hydrodynamic coupling causing minimal changes in flagellar dynamics. However, fluid-mediated ciliary coupling is responsible for the extended periods of anti-phase synchronisation observed in a mutant with weaker intracellular coupling. At the single-cell level, therefore, flagellar coordination depends on a subtle balance between intracellular and extracellular forces.
Public
Rxiv mechanobio

📰 "Influence of erythrocyte density on aggregability as a marker of cell age: Dissociation dynamics in extensional flow"
arxiv.org/abs/2409.08877 #Physics.Bio-Ph #Mechanical #Dynamics #Cell

arXiv.orgInfluence of erythrocyte density on aggregability as a marker of cell age: Dissociation dynamics in extensional flowBlood rheology and microcirculation are strongly influenced by red blood cell (RBC) aggregation. The aggregability of RBCs can vary significantly due to factors such as their mechanical and membrane surface properties, which are affected by cell aging in vivo. In this study, we investigate RBC aggregability as a function of their density, a marker of cell age and mechanical properties, by separating RBCs from healthy donors into different density fractions using Percoll density gradient centrifugation. We examine the dissociation rates of aggregates in a controlled medium supplemented with Dextran, employing an extensional flow technique based on hyperbolic microfluidic constrictions and image analysis, assisted by a convolutional neural network (CNN). In contrast to other techniques, our microfluidic experimental approach highlights the behavior of RBC aggregates in dynamic flow conditions relevant to microcirculation. Our results demonstrate that aggregate dissociation is strongly correlated with cell density and that aggregates formed from the denser fractions of RBCs are significantly more robust than those from the average cell population. This study provides insight into the effect of RBC aging in vivo on their mechanical properties and aggregability, underscoring the importance of further exploration of RBC aggregation in the context of cellular senescence and its potential implications for hemodynamics. Additionally, it suggests that this technique can complement existing methods for improved evaluation of RBC aggregability in health and disease.
Public
Rxiv mechanobio

📰 "Extending the range of sizes of monodisperse core-shell hydrogel capsules from composite jet breakup by combined electrical and mechanical actuation"
arxiv.org/abs/2503.21333 #Physics.Flu-Dyn #Mechanical #Cell

arXiv.orgExtending the range of sizes of monodisperse core-shell hydrogel capsules from composite jet breakup by combined electrical and mechanical actuationThe production of monodisperse particles or droplets is a longstanding issue across various fields, from aerosol science to inkjet printing. In bioengineering, submillimeter cell laden hydrogel capsules have proven valuable for developing in vitro tissue models. A common practical approach for producing such droplets relies on the Plateau Rayleigh instability to break up a liquid compound jet in air. However, while the droplet size is closely linked to nozzle dimensions, achieving high monodispersity suitable for quantitative biological assays remains challenging due to coalescence events associated with the beads on a string morphology of viscoelastic jets. Here, a microfluidic strategy is introduced, combining electrical and mechanical actuation to enhance control and versatility over jet breakup. By fine tuning the excitation frequency to select specific modes and applying an electric potential to regulate coalescence, a phase diagram is established, enabling the generation of monodisperse droplets over a broad size range. Notably, a previously hidden effect of the electric field on jet behavior is uncovered and quantitatively characterized. Finally, after crosslinking the compound droplets, capsules with a hydrogel envelope and a core composed of a cell suspension are formed in conditions compatible with cell proliferation, which lay the groundwork for quantitative high precision biological assays.
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