Biology subjects

Camley, B. A.

Publications and source records attributed to Camley, B. A..

8 recordsLinked to original sources

bioRxiv2025

Using endocytosis to switch between chemoattraction and chemorepulsion

White blood cells can be guided to targets by chemoattractant signals, but this response is complicated, including guidance toward and away from inflammation sites. We model how cells can switch between being attracted and repelled by a chemical signal. We study experiments on malignant B cell lines, which find that depending on their environment, B cells can either be attracted or repelled by signals like CCL19. The presence of chemorepulsion is also dependent on whether the receptors for CCL19 can be internalized via endocytosis. We develop a stochastic model of receptor-ligand binding and internalization where bound receptors drive a nonlinear feed-forward loop of intracellular signaling molecules, which determine the cell's direction. We recapitulate key experimental results: changing CCL19 concentration or inhibiting receptor internalization can switch the cell's direction. Our model implies that cells can navigate toward a target concentration of a signal, regulating that target by receptor internalization. We propose experiments to test this idea.

cell biology↗

bioRxiv2025

Protein diffusion controls how single cells respond to electric fields

Cells sense and respond to electric fields, using these fields as a guidance cue in wound healing and development. This sensing is done by redistribution of charged membrane proteins on the cells surface ("sensors") via electrophoresis and electroosmotic flow. If membrane proteins have to physically rearrange on the cells surface, how quickly can a cell respond to an applied signal? What limits the cells ability to respond? Are galvanotaxing cells, like chemotaxing cells, limited by stochasticity from the finite number of molecules? Here, we develop a model for the response dynamics of galvanotaxing cells and show that, for weak enough field strengths, two relevant timescales emerge: the time for the cells sensors to rearrange, which depends on their diffusion across the cell, and the time for the cells orientation to respond to an applied field, which may be very different. We fit this model to experimental measurements on the recently-identified sensor galvanin (TMEM154) in neutrophil-like HL-60 cells, finding that given the dynamics of a cell responding to an applied field, we can predict the dynamics of the cell after the field is turned off. This fit constrains the noise of the galvanotaxis process, demonstrating that HL-60 is not limited by the stochasticity of finite sensor number. Our model also allows us to explain the effect of media viscosity on cell dynamics, and predict how cells respond to pulsed DC fields. These results place constraints on the ability to guide cells with pulsed fields, predicting that a field on half of the time is no better than a field that is always on with half the magnitude.

cell biology↗

bioRxiv2024

Confinement, jamming, and adhesion in cancer cells dissociating from a collectively invading strand

When cells in a primary tumor work together to invade into nearby tissue, this can lead to cell dissociations--cancer cells breaking off from the invading front--leading to metastasis. What controls the dissociation of cells, and whether they break off singly or in small groups? Can this be determined by cell-cell adhesion or chemotactic cues given to cells? We develop a physical model for this question, based on experiments that mimic aspects of cancer cell invasion using microfluidic devices with microchannels of different widths. Experimentally, most dissociation events ("ruptures") involve single cells breaking off, but we observe some ruptures of large groups ([~] 20 cells) in wider channels. The rupture probability is nearly independent of channel width. We recapitulate the experimental results with a phase field cell motility model by introducing three different cell states (follower, guided, and high-motility metabolically active leader cells) based on their spatial position. These leader cells may explain why single-cell rupture is the universal most probable outcome. Our simulation results show that cell-channel adhesion is necessary for cells in narrow channels to invade, and strong cell-cell adhesion leads to fewer but larger ruptures. Chemotaxis also influences the rupture behavior: Strong chemotaxis strength leads to larger and faster ruptures. Finally, we study the relationship between biological jamming transitions and cell dissociations. Our results suggest unjamming is necessary but not sufficient to create ruptures.

cell biology↗

bioRxiv2023

Secreted footprints let cells switch between confined, oscillatory, and exploratory migration

For eukaryotic cells to heal wounds, respond to immune signals, or metastasize, they must migrate, often by adhering to extracellular matrix. Cells may also deposit extracellular matrix components, leaving behind a footprint that influences their crawling. Recent experiments showed that some epithelial cells on micropatterned adhesive stripes move persistently in regions they have previously crawled over, where footprints have been formed, but barely advance into unexplored regions, creating an oscillatory migration of increasing amplitude. Here, we explore through mathematical modeling how footprint deposition and cell responses to footprint combine to allow cells to develop oscillation and other complex migratory motions. We simulate cell crawling with a phase field model coupled to a biochemical model of cell polarity, assuming local contact with the deposited footprint activates Rac1, a protein that establishes the cells front. Depending on footprint deposition rate and response to the footprint, cells on micropatterned lines can display many types of motility, including confined, oscillatory, and persistent motion. On two-dimensional substrates, we predict a transition between cells undergoing circular motion and cells developing an exploratory phenotype. Small quantitative changes in a cells interaction with its footprint can completely alter exploration, allowing cells to tightly regulate their motion, leading to different motility phenotypes (confined vs exploratory) in different cells when deposition or sensing is variable from cell to cell. Consistent with our computational predictions, we find in earlier experimental data evidence of cells undergoing both circular and exploratory motion. Significance StatementRecent experiments showed that epithelial cells modify and sense their local environment, creating a footprint that guides their own motion. Here, we explore how these deposited footprints regulate cell motility. We can recapitulate earlier experimental results with a model that assumes the footprint activates proteins that establish the cell front. We find that cells can use their footprints to change how they explore their surroundings, and that small changes in sensing or depositing footprint can switch the cell from being trapped to being able to explore new environments easily. We find both behaviors in experimental data, suggesting that cells can exhibit multiple crawling behaviors depending on how they deposit and respond to their foot-print.

biophysics↗

bioRxiv2022

Migration and division in cell monolayers on substrates with topological defect

Collective movement and organization of cell monolayers are important for wound healing and tissue development. Recent experiments highlighted the importance of liquid crystal order within these layers, suggesting that +1 topological defects have a role in organizing tissue morphogenesis. We study fibroblast organization, motion and proliferation on a substrate with micron-sized ridges that induce +1 and -1 topological defects using simulation and experiment. We model cells as selfpropelled deformable ellipses that interact via a Gay-Berne potential. Unlike earlier work on other cell types, we see that density variation near defects is not explained by collective migration. We propose instead that fibroblasts have different division rates depending on their area and aspect ratio. This model captures key features of our previous experiments: the alignment quality worsens at high cell density and, at the center of the +1 defects, cells can adopt either highly anisotropic or primarily isotropic morphologies. Experiments performed with different ridge heights confirm a new prediction of this model: suppressing migration across ridges promotes higher cell density at the +1 defect. Our work enables new mechanisms for tissue patterning using topological defects.

cell biology↗

bioRxiv2022

Picking winners in cell-cell collisions: wetting, speed, and contact

Groups of eukaryotic cells can coordinate their crawling motion to follow cues more effectively, stay together, or invade new areas. This collective cell migration depends on cell-cell interactions, which are often studied by colliding pairs of cells together. Can the outcome of these collisions be predicted? Recent experiments on trains of colliding epithelial cells suggest that cells with a smaller contact angle to the surface or larger speeds are more likely to maintain their direction ("win") upon collision. When should we expect shape or speed to correlate with the outcome of a collision? We build a model for two-cell collisions within the phase field approach, which treats cells as deformable objects. We can reproduce the observation that cells with high speed and small contact angles are more likely to win with two different assumptions for how cells interact: (1) velocity-aligning, in which we hypothesize that cells sense their own velocity and align to it over a finite timescale, and (2) front-front contact repolarization, where cells polarize away from cell-cell contact, akin to contact inhibition of locomotion. Surprisingly, though we simulate collisions between cells with widely varying properties, in each case, the probability of a cell winning is completely captured by a single summary variable: its relative speed (in the velocity-aligning model) or its relative contact angle (in the contact repolarization model). Both models are currently consistent with reported experimental results, but they can be distinguished by varying cell contact angle and speed through orthogonal perturbations.

cell biology↗

bioRxiv2020

Rules of Contact Inhibition of Locomotion for Cells on Suspended Nanofibers

Contact inhibition of locomotion (CIL), in which cells repolarize and move away from contact, is now established as a fundamental driving force in development, repair, and disease biology. Much of what we know of CIL stems from studies on 2D substrates that fail to provide an essential biophysical cue - the curvature of extracellular matrix fibers. We discover rules controlling outcomes of cell-cell collisions on suspended nanofibers, and show them to be profoundly different from the stereotyped CIL behavior known on 2D substrates. Two approaching cells attached to a single fiber do not repolarize upon contact but rather usually migrate past one another. Fiber geometry modulates this behavior: when cells are attached to two fibers, reducing their freedom to reorient, only one of a pair of colliding cells repolarizes on contact, leading to the cell pair migrating as a single unit. CIL outcomes also change when one cell has recently divided and moves with high speed- cells more frequently walk past each other. In collisions with division in the two-fiber geometry, we also capture rare events where a daughter cell pushes the non-dividing cell along the fibers. Our computational model of CIL in fiber geometries reproduces the core qualitative results of the experiments robustly to model parameters. Our model shows that the increased speed of post-division cells may be sufficient to explain their increased walk-past rate. Our results suggest that characterizing cell-cell interactions on flat substrates, channels, or micropatterns is not sufficient to predict interactions in a matrix - the geometry of the fiber can generate entirely new behaviors. SignificanceWhen cells heal a wound or invade a new area, they coordinate their motion. Coordination is often studied by looking at what happens after pairs of cells collide. Post-collision, cells often exhibit contact inhibition of locomotion- they turn around and crawl away from the point where they touched. Our knowledge of repolarization on contact comes from studies on flat surfaces, unlike cells in the body, which crawl along fibers. We discover that cells on single fibers walk past one another- but that cells in contact with multiple fibers stick to one another and move as pairs. This outcome changes to walk-past after cell division. Our experiments and models reveal how the environment regulates cell-cell coordination after contact.

cell biology↗

bioRxiv2019

Leader cells in collective chemotaxis: optimality and tradeoffs

Clusters of cells can work together in order to follow a signal gradient, chemotaxing even when single cells do not. Cells in different regions of collectively migrating neural crest streams show different gene expression profiles, suggesting that cells may specialize to leader and follower roles. We use a minimal mathematical model to understand when this specialization is advantageous. In our model, leader cells sense the gradient with an accuracy that depends on the kinetics of ligand-receptor binding while follower cells follow the clusters direction with a finite error. Intuitively, specialization into leaders and followers should be optimal when a few cells have more information than the rest of the cluster, such as in the presence of a sharp transition in chemoattractant concentration. We do find this - but also find that high levels of specialization can be optimal in the opposite limit of very shallow gradients. We also predict that the best location for leaders may not be at the front of the cluster. In following leaders, clusters may have to choose between speed and flexibility. Clusters with only a few leaders can take orders of magnitude more time to reorient than all-leader clusters.

biophysics↗