Biology subjects

Rupprecht, J.-F.

Publications and source records attributed to Rupprecht, J.-F..

13 recordsLinked to original sources

bioRxiv2026

Encoding neuronal shape in the stochastic dynamics of branching processes

Cell shape critically influences function, yet how complex and reproducible morphologies emerge from stochastic cellular dynamics remains unclear. Here, we investigate dendritic morphogenesis of two classes of Drosophila mechanosensory neurons with contrasting architectures, combining in vivo live imaging, quantitative analysis, cytoskeletal perturbations, and computational modeling. We show that despite sharing similar local stochastic branching rules, the two classes exhibit divergent growth dynamics that cannot be explained by standard, diffusive growth models. This discrepancy arises because Class I neurons display subdiffusive branch dynamics over long timescales, unlike Class IV. Based on these findings, we develop a minimal model with only four parameters that separates short-and long-term branch behaviors, and successfully recapitulates growth dynamics and final morphologies in both classes. Cytoskeletal perturbations reveal a functional separation between actin, which drives short-term exploratory branch fluctuations and arbor expansion, and microtubules, which tune long-term branch diffusivity and determine class-specific morphology. Together, these results establish a parsimonious, generalizable framework linking local cytoskeletal regulation to global neuronal architecture and reveal how stochastic dynamics encode reproducible cell shapes.

biophysics↗

bioRxiv2025

Fibrillar adhesions are the primary integrin complexes shaped by matrix topography

Mechanisms of matrix topography recognition are poorly understood. Here, we show that 5{beta}1-integrin mediated fibrillar adhesions serve this function. While on planar substrates, their formation requires fibronectin secretion, tensins, and actomyosin contractility, these requirements are bypassed on nanotopographical features. While focal adhesions avoid these features, fibrillar adhesions rapidly align along pre-existing fibrous cell-derived matrix or electrospun nanofibers where they can then template fibronectin fibrils. Topography-induced fibrillar adhesions depend primarily on 5{beta}1-integrin clustering and disassemble upon cortical stiffening driven by myosin-II overactivation or increased membrane tension. We propose a generic theoretical model where the adhesion receptor favours the membrane and substrate planes to be tilted relative to each other. This model matches experimental observations of preferential 5{beta}1-integrin clustering along nanofibers and concave edges of large negative curvature along micro-ridges. These findings establish fibrillar adhesions as primary adhesion complexes that form independently of focal adhesions in response to matrix topography.

cell biology↗

bioRxiv2024

Titin-dependent biomechanical feedback tailors sarcomeres to specialised muscle functions in insects

Sarcomeres are the contractile units of muscles that enable animals to move. Insect muscles are remarkable examples because they use extremely different contraction frequencies (ranging from [~]1 to 1000 Hz) and amplitudes for flying, walking and crawling. This is puzzling because sarcomeres are built from essentially the same actin-myosin components. We show here that the giant protein titin is the key to this functional specialisation. I-band titin spans and determines the length of the sarcomeric I-band, and occurs in muscle-type-specific isoforms. Surprisingly, it also rules the length of the force-generating myosin filament in a force feedback mechanism, even though it is not present there. We provide evidence for this model and its validity beyond insects. SummaryHere we identified a mechanical mechanism that instructs sarcomeres to fulfill the specific needs of different muscle types.

developmental biology↗

bioRxiv2024

A multicellular actin star network underpins epithelial organization and connectivity

Epithelial tissues serve as physical barriers against various external pressures yet remarkably maintain structural stability. Various cellular apparatus including bicellular junction and actomyosin network contribute to the epithelial integrity, packing and remodelling. Although their role in morphogenetic and mechanical processes have been extensively studied during embryogenesis and disease development, their synergistic effects in maintaining tissue organization and connection remain poorly understood. In this study, we discovered a tissue-scale actomyosin network connected through bicellular junctions and manifested in the villi of adult murine intestinal tissue. Later we reproduced such supracellular structure in the differentiated compartment of ex vivo intestinal epithelium model. The self-organized actomyosin networks comprised individual actin nodes in each hexagonal cell at the epithelial base with six radial actin branches, presenting an actin star unit. The repeated units were connected through the bicellular junctions, forming a large, multicellular array covering the differentiated domains. Functionally, actin stars contribute to epithelial morphological stability by maintaining cell hexagonality and packing, thereby preserving the solid-like order of the epithelium. Laser ablation experiments validate a modified vertex theoretical model that connects the emergence of such solid-like order to the onset of tension along the actin star branches. Actin stars also acted as locks at the basal side minimizing protrusive activity in the epithelial layer, hindering cell migration and disorganization of the epithelial tissue. Altogether, the supracellular actin star network constitutes a basal biomechanical apparatus coordinating epithelial tissue stability and organization.

cell biology↗

bioRxiv2024

Inferring the location and orientation of cell divisions on time-lapse image sequences

We propose a two-stage supervised framework for characterizing cell divisions in 2D and 3D time-lapse microscopy. First, we recast division detection as a semantic segmentation task on image sequences. Second, a local regression model estimates the orientation and distance between daughter cells for each event. We validate this framework using image sequences of avian neuroepithelium and mouse gastruloids. Our results demonstrate that high performance is achieved with efficient architectures, namely a U-Net for segmentation and a CNN for regression, that are optimized through systematic hyperparameter exploration. We find that integrating temporal context via multiple consecutive frames significantly boosts segmentation accuracy. We achieve F1 scores exceeding 94% (2D+t) and 90% (3D+t), with orientation accuracy approaching the uncertainty limit of manual annotation. We provide the full codebase and training workflow, specifically designed for datasets where traditional tracking is challenging.

biophysics↗

bioRxiv2023

E-cadherin-dependent phosphorylation of EGFR governs a homeostatic feedback loop controlling intercellular junction viscosity and collective migration modes.

Actomyosin tension has been shown to be a ubiquitous driver of tissue morphogenesis1, 2. The Rho pathway, a prominent regulatory network influencing cortical tension, plays a central role in both tissue reorganisation and cell migration3-6. While viscous dissipation in the actin network is commonly regarded as a constant passive parameter in cell migration in both 2D and 3D contexts, there is limited knowledge concerning the regulation of dissipative forces arising from viscous drag between cells during collective rearrangement. Here, we found that the phosphorylation of Epithelial Growth Factor Receptor (EGFR) downstream of de novo E-cadherin adhesion7, 8 orchestrates a feedback loop, thereby governing intercellular viscosity via the Rac pathway regulating actin dynamics. Our findings highlight how the E-cadherin-dependent EGFR activity controls the migration mode of collective cell movements independently of intercellular tension. Combining molecular cell biology, micropatterning, and in silico simulation, our work suggests the existence of a regulatory loop by which cells can tune junctional actin viscosity, with implications for the phenomenology of morphogenetic movements.

cell biology↗

bioRxiv2022

Alcanivorax borkumensis Biofilms Enhance Oil Degradation By Interfacial Tubulation

Alcanivorax borkumensis are prominent actors in oil spill bioremediation; however, the interfacial dynamics of their biofilms and its role in oil degradation remain unclear. Longitudinal tracking of biofilm-covered oil microdroplets using microfluidics reveals a spontaneous morphological transition from a thick biofilm phenotype to a thin dendritic phenotype optimized for high oil consumption rates. We show experimentally that biofilm dendrites emerge from aster-like nematic defects in the thin biofilms. We develop a theoretical model that elucidates the transition between phenotypes, linking tubulation to decreased interfacial tension and increased cell hydrophobicity, which we verify experimentally. We demonstrate positional control over the nematic defects on the droplets using microfluidics, causing the biofilm to dimple the droplets. Our results reveal how A. borkumensis biofilms utilize topological defects to increase oil access to achieve superior oil consumption rates, which may be a general strategy in oil-consuming bacteria. ONE SENTENCE SUMMARYA. borkumensis adapt their interfacial properties over time to evolve their biofilm phenotype and increase their oil consumption

biophysics↗

bioRxiv2022

Enhanced cell viscosity as a marker of premature senescence induced by lamin A/C alterations

Lamin A/C is a well-established key contributor to nuclear stiffness and its role in nucleus mechanical properties has been extensively studied. However, its impact on whole cell mechanics has been poorly addressed, even less so in terms of measurable physical parameters. In the present study, microfluidic experiments combined with theoretical analyses were performed to provide a quantitative estimation of the whole cell mechanical properties. This allowed the characterization of mechanical cell changes induced by lamin A/C alterations resulting from Atazanavir treatment or lipodystrophy-associated LMNA R482W pathogenic variant. Results unveil an increase in the long-time viscosity as a signature of cells affected by lamin A/C alterations. In addition, they show that the whole cell response to mechanical stress is driven not only by the nucleus but also by the nucleo-cytoskeleton links and the microtubule network. This enhanced cell viscosity assessed by our microfluidic device could represent a useful diagnosis marker for lamin-related diseases.

biophysics↗

bioRxiv2022

Two-point optical manipulation reveals mechanosensitive remodeling of cell-cell contacts in vivo

Biological tissues acquire reproducible shapes during development through dynamic cell behaviors. These events involve the remodeling of cell contacts driven by active cytoskeletal contractile forces. However how cell-cell contacts remodel remains poorly understood because of lack of tools to directly apply forces at cell-cell contacts to produce their remodeling. Here we develop a dual-optical trap manipulation method to impose different force patterns on cell-cell contacts in the early epithelium of the Drosophila embryo. Through different push and pull manipulations at the edges of junctions, the technique allows us to produce junction extension and junction shrinkage. We use these observations to constrain and specify vertex-based models of tissue mechanics, incorporating negative and positive mechanosensitive feedback depending on the type of remodeling. We show that Myosin-II activity responds to junction strain rate and facilitates full junction shrinkage. Altogether our work provides insight into how stress produces efficient deformation of cell-cell contacts in vivo and identifies unanticipated mechanosensitive features of their remodeling. Significance statementThe highly organized tissues and organs that form our body emerge from internal dynamic activities at the cellular level. Among such activities, cell shape changes and cell rearrangement, cell extrusion and cell division sculpt epithelial tissues into elongated sheets, tubes and spherical cavities. Remodeling of cell-cell contacts, powered by actomyosin contractility, is key to all these transformations. Although much is known about the molecular machinery and biochemical signals that regulate remodeling of cell contacts, there is a lack of approaches to directly probe the mechanics of cell contacts and therefore assess their ability to resist or deform in response to mechanical loads. We developed an experimental technique to manipulate and exert contractile and extensile forces to cell-cell junctions. Our results lead to a specific physical model of junctional mechanics, with implications in the modeling of collective cell behavior in epithelial tissues.

biophysics↗

bioRxiv2022

Mechanical stress driven by rigidity sensing governs epithelial stability

Epithelia act as a barrier against environmental stress and abrasion and in vivo they are continuously exposed to environments of various mechanical properties. The impact of this environment on epithelial integrity remains elusive. By culturing epithelial cells on 2D hydrogels, we observe a loss of epithelial monolayer integrity through spontaneous hole formation when grown on soft substrates. Substrate stiffness triggers an unanticipated mechanical switch of epithelial monolayers from tensile on soft to compressive on stiff substrates. Through active nematic modelling, we find unique patterns of cell shape texture called nematic topological defects that underpin large isotropic stress fluctuations at certain locations thereby triggering mechanical failure of the monolayer and hole opening. Our results show that substrate stiffness provides feedback on monolayer mechanical state and that topological defects can trigger stochastic mechanical failure, with potential application towards a mechanistic understanding of compromised epithelial integrity in bacterial infection, tumor progression and morphogenesis.

biophysics↗

bioRxiv2020

Adhesion-mediated heterogeneous actin organization governs apoptotic cell extrusion

Apoptotic extrusion is crucial in maintaining epithelial homeostasis and has implications in diseases of epithelial tissues. Current literature supports that epithelia respond to extrusion to maintain their integrity by the formation of a supracellular actomyosin ring (purse-string) in the neighbors that encompasses the dying cells. However, little is known about whether other types of actin structures could contribute to extrusion as well as how forces generated by mechanosensitive proteins in the cells are integrated. Here, we found that during extrusion, a heterogeneous actin network composed of lamellipodia protrusions and discontinuous actomyosin cables, was reorganized in the neighboring cells and was the main factor driving extrusion forwards. The early presence of basal lamellipodia protrusion participated both in basal sealing of the extrusion site and in orienting the actomyosin purse-string at the later stage of extrusion. These sequential events are essential in ensuring a successful extrusion in apicobasal direction. The co-existence of these two mechanisms is determined by the interplay between the cell-cell and cell-substrate adhesions. A theoretical model integrates the role of these cellular mechanosensitive components to explain why a dual-mode mechanism, which combined lamellipodia protrusion and purse-string contractility, leads to more efficient extrusion than a single-mode mechanism. We anticipate that our approach will be useful to provide mechanistic insight into epithelial homeostasis, morphogenetic events and tumorigenesis.

cell biology↗

bioRxiv2018

Shaping the zebrafish myotome by differential friction and active stress

Organ formation is an inherently biophysical process, requiring large-scale tissue deformations. Yet, understanding how complex organ shape emerges during development remains a major challenge. During fish embryogenesis, large muscle segments, called myotomes, acquire a characteristic chevron morphology, which is believed to play a role in swimming. The final myotome shape can be altered by perturbing muscle cell differentiation or by altering the interaction between myotomes and surrounding tissues during morphogenesis. To disentangle the mechanisms contributing to shape formation of the myotome, we combine single-cell resolution live imaging with quantitative image analysis and theoretical modeling. We find that, soon after its segmentation from the presomitic mesoderm, the future myotome spreads across the underlying tissues. The mechanical coupling between the myotome and the surrounding tissues is spatially varying, resulting in spatially heterogeneous friction. Using a vertex model, we show that the interplay of differential spreading and friction is sufficient to drive the initial phase of myotome shape formation. However, we find that active stresses, generated during muscle cell differentiation, are necessary to reach the acute angle of the myotome observed in wildtype embryos. A final ingredient for formation and maintenance of the chevron shape is tissue plasticity, which is mediated by orientated cellular rearrangements. Our work sheds a new light on how a spatio-temporal sequence of local cellular events can have a non-local and irreversible mechanical impact at the tissue scale, leading to robust organ shaping.

biophysics↗

bioRxiv2018

Myosin filaments reversibly generate large forces in cells

We present high resolution experiments performed on elementary contractile units in cells that challenge our current understanding of molecular motor force generation. The key features are the development of a force per motor considerably larger than forces measured in single molecule experiments, a force increase followed by relaxation controlled by a characteristic displacement rather than by a characteristic force, the observation of steps at half the actin filament period even though a large number of motors are at work in an elementary contractile unit. We propose a generic two-state model of molecular motor collections with hand-over-hand contractions and we find that these unexpected observations are spontaneously emerging features of a collective motor behavior.

biophysics↗