Biology subjects

Gov, N. S.

Publications and source records attributed to Gov, N. S..

9 recordsLinked to original sources

bioRxiv2026

From biting to engulfment: curvature-actin coupling controls phagocytosis of soft, deformable targets

Phagocytosis is a core innate immune process that clears targets spanning a wide range of mechanical properties, yet the role of target mechanics in recognition and engulfment remains unclear. Here, we combine theoretical modeling and experiments to reveal how target stiffness governs distinct modes of phagocyte-target interaction. We develop a membrane-based simulation framework in which both the engulfing cell and its target are deformable and undergo large shape changes, while actin-driven protrusions are regulated by curvature-sensitive membrane complexes. The model predicts three mechanical regimes with increasing target stiffness: (i) biting (trogocytosis), where part of the target is extracted; (ii) pushing, where the target is displaced rather than engulfed; and (iii) complete engulfment. We validate these predictions in epithelial clearance of apoptotic targets in vivo and macrophage engulfment of Giant Unilamellar Vesicles (GUVs) and lymphoma cells. Together, our results identify target mechanics as a key regulator of clearance and cell-cell interactions. Significance statementPhagocytosis is essential for immune defence, yet the physical principles governing engulfment of deformable targets remain poorly understood. Most theoretical models assume rigid particles, appropriate for phagocytosis of bacteria or fungi. When phagocytes engage dying cells or antibody-opsonised cancer cells, these targets undergo substantial shape changes during phagocytosis. We develop a theoretical model to simulate cell-cell interactions, enabling a mechanistic exploration of phagocytosis of soft targets. We utilize a model in which cytoskeletal protrusive activity is guided by curvature-sensitive membrane complexes, and show that target membrane rigidity dictates whether targets are fully engulfed, pushed away, or partially bitten. These mechanically driven dynamic regimes are validated experimentally using artificial elastic beads, GUVs, and lymphoma cells, both in vivo and in vitro.

biophysics↗

bioRxiv2025

Phototactic Decision-Making by Micro-Algae

We study how simple eukaryotic organisms make decisions in response to competing stimuli in the context of phototaxis by the unicellular alga Chlamydomonas reinhardtii. While negatively phototactic cells swim directly away from a collimated light beam, when presented with two beams of adjustable intersection angle and intensities, we find that cells swim in a direction given by an intensity-weighted average of the two light propagation vectors. This geometrical law is a fixed point of an adaptive model of phototaxis and minimizes the average light intensity falling on the anterior pole of the cell. At large angular separations, subpopulations of cells swim away from one source or the other, or along the direction of the geometrical law, with some cells stochastically switching between the three directions. This behavior is shown to arise from a population-level distribution of photoreceptor locations that breaks front-back symmetry of photoreception.

biophysics↗

bioRxiv2025

Photometric Decision-Making During the Dawn Choruses of Cicadas

We report the first quantitative study of the onset of dawn choruses of cicadas in several natural habitats. A time-frequency analysis of the acoustical signals is used to define an order parameter for the development of collective singing. The ensemble of recordings reveals that the chorus onset times accurately track the changing sunrise times over the course of many weeks, occurring within civil twilight at a solar elevation of -3.8{degrees} {+/-} 0.2{degrees}. Despite day-to-day variations in the amplitude of fully developed choruses, the order parameter data collapse to a common sigmoidal curve when scaled by those amplitudes and shifted by the onset time, revealing a characteristic rise time of [~]60 s for a chorus to reach saturation amplitude. The results are used to obtain the cumulative distribution function of singing as a function of ground illumination, from which is obtained a generalized susceptibility which exhibits a narrow peak with a half-width of [~]12%. The variance of the order parameter exhibits a similar peak, suggesting that a generalized fluctuation-dissipation theorem holds for this system. A model of decision-making under ramps of a control parameter is developed and can achieve a quantitative match to the data. It suggest that sharpness of the susceptibility peak reflects cooperative decision-making arising from acoustic communication.

biophysics↗

bioRxiv2024

Confinement in fibrous environments positions and orients mitotic spindles

Accurate positioning of the mitotic spindle within the rounded cell body is critical to physiological maintenance. Adherent mitotic cells encounter confinement from neighboring cells or the extracellular matrix (ECM), which can cause rotation of mitotic spindles and, consequently, titling of the metaphase plate (MP). To understand the positioning and orientation of mitotic spindles under confinement by fibers (ECM-confinement), we use flexible ECM-mimicking nanofibers that allow natural rounding of the cell body while confining it to differing levels. Rounded mitotic bodies are anchored in place by actin retraction fibers (RFs) originating from adhesion clusters on the ECM-mimicking fibers. We discover the extent of ECM-confinement patterns RFs in 3D: triangular and band-like at low and high confinement, respectively. A stochastic Monte-Carlo simulation of the centrosome (CS), chromosome (CH), membrane interactions, and 3D arrangement of RFs on the mitotic body recovers MP tilting trends observed experimentally. Our mechanistic analysis reveals that the 3D shape of RFs is the primary driver of the MP rotation. Under high ECM-confinement, the fibers can mechanically pinch the cortex, causing the MP to have localized deformations at contact sites with fibers. Interestingly, high ECM-confinement leads to low and high MP tilts, which mechanistically depend upon the extent of cortical deformation, RF patterning, and MP position. We identify that cortical deformation and RFs work in tandem to limit MP tilt, while asymmetric positioning of MP leads to high tilts. Overall, we provide fundamental insights into how mitosis may proceed in fibrous ECM-confining microenvironments in vivo.

biophysics↗

bioRxiv2023

Polarization and motility of one-dimensional multi-cellular trains

Collective cell migration, whereby cells adhere to form multi-cellular clusters that move as a single entity, play an important role in numerous biological processes, such as during development and cancer progression. Recent experimental work focused on migration of one-dimensional cellular clusters, confined to move along adhesive lanes, as a simple geometry in which to systematically study this complex system. One-dimensional migration also arises in the body when cells migrate along blood vessels, axonal projections and narrow cavities between tissues. We explore here the modes of one-dimensional migration of cellular clusters ("trains"), by implementing cell-cell interactions in a model of cell migration that contains a mechanism for spontaneous cell polarization. We go beyond simple phenomenological models of the cells as self-propelled particles, by having the internal polarization of each cell depend on its interactions with the neighboring cells, that directly affect the actin polymerization activity at the cells leading edges. Both Contact Inhibition of Locomotion (CIL) and Cryptic Lamellipodia (CL) interactions between neighboring cells are introduced. We find that this model predicts multiple motility modes of the cell trains, that can have several different speeds for the same polarization pattern. Comparing to experimental data we find that MDCK cells are poised along the transition region where CIL and CL roughly balance each other, where collective migration speed is most sensitive to the values of the cell-cell interaction strength.

biophysics↗

bioRxiv2022

Emergent oscillations during cellular directional decision-making on junctions

Motile cells inside living tissues often encounter junctions, where their path branches into several alternative directions of migration. We present a theoretical model of cellular polarization for cells migrating along one-dimensional lines, arriving at a symmetric Y-junction and extending protrusions along the different paths that emanate from the junction. The model predicts the spontaneous emergence of deterministic oscillations between competing protrusions, whereby the cellular polarization and growth alternates between the competing protrusions. The oscillations are modified by cellular noise, but remain as a dominant feature which affects the time it takes the cell to migrate across the junction. These predicted oscillations in the cellular polarization during the directional decision making process at the junction are found experimentally for two different cell types, non-cancerous endothelial and cancerous glioma cells, migrating on patterned network of thin adhesive lanes with junctions.

biophysics↗

bioRxiv2021

The geometry of decision-making

Choosing among spatially-distributed options is a central challenge for animals, from deciding among alternative potential food sources or refuges, to choosing with whom to associate. Using an integrated theoretical and experimental approach (employing immersive virtual reality), we consider the interplay between movement and vectorial integration during decision-making regarding two, or more, options in space. In computational models of this process we reveal the occurrence of spontaneous and abrupt "critical" transitions (associated with specific geometrical relationships) whereby organisms spontaneously switch from averaging vectorial information among, to suddenly excluding one, among the remaining options. This bifurcation process repeats until only one option--the one ultimately selected--remains. Thus we predict that the brain repeatedly breaks multi-choice decisions into a series of binary decisions in space-time. Experiments with fruit flies, desert locusts, and larval zebrafish reveal that they exhibit these same bifurcations, demonstrating that across taxa and ecological context, there exist fundamental geometric principles that are essential to explain how, and why, animals move the way they do.

animal behavior and cognition↗

bioRxiv2021

Dynamics on the web: spiders use physical rules to solve complex tasks in mate search and competition

A long-standing question in animal behaviour is how organisms solve complex tasks. Here we explore how the dynamics of animal behaviour in the ubiquitous tasks of mate-search and competition can arise from a physics-based model of effective interactions. Male orb-weaving spiders of the genus Trichonephila are faced with the daunting challenge of entering the web of a much larger and potentially cannibalistic female, approaching her, and fending off rival males. The interactions that govern the dynamics of males within the confined two-dimensional arena of the females web are dominated by seismic vibrations. This unifying modality allows us to describe the spiders as interacting active particles, responding only to effective forces of attraction and repulsion due to the female and rival males. Our model is based on a detailed analysis of experimental spider trajectories, obtained during the approach of males towards females, and amidst their interactions with rival males of different sizes. The dynamics of spider particles that emerges from our theory allows us to explain a puzzling relationship between the density of males on the web and the reproductive advantages of large males. Our results provide strong evidence that the simple physical rules at the basis of our model can give rise to complex fitness related behaviours in this system.

animal behavior and cognition↗

bioRxiv2021

Modelling cellular spreading and emergence of motility in the presence of curved membrane proteins and active cytoskeleton forces

Eukaryotic cells adhere to extracellular matrix during the normal development of the organism, forming static adhesion as well as during cell motility. We study this process by considering a simplified coarse-grained model of a vesicle that has uniform adhesion energy with a flat substrate, mobile curved membrane proteins and active forces. We find that a high concentration of curved proteins alone increases the spreading of the vesicle, by the self-organization of the curved proteins at the high curvature vesicle-substrate contact line, thereby reducing the bending energy penalty at the vesicle rim. This is most significant in the regime of low bare vesicle-substrate adhesion. When these curved proteins induce protrusive forces, representing the actin cytoskeleton, we find efficient spreading, in the form of sheet-like lamellipodia. Finally, the same mechanism of spreading is found to include a minimal set of ingredients needed to give rise to motile phenotypes.

biophysics↗