Biology subjects

Tweedy, L.

Publications and source records attributed to Tweedy, L..

8 recordsLinked to original sources

bioRxiv2026

ChemoTrack: A comprehensive dataset linking single-cell migration trajectories to precisely defined chemotactic signals

Chemotaxis drives cell migration in processes ranging from wound healing to embryonic development and cancer metastasis, yet its quantitative understanding remains limited because responding cells change and degrade attractant gradients, and existing datasets are too small and imprecise to capture stochastic behaviour. We present ChemoTrack, a publicly accessible resource comprising 2 million measurements from 500,000 migration tracks, in which the chemoattractant gradient and concentration experienced by every cell at the time of observation are precisely determined. The dataset includes microscopy images and trajectories spanning a full range of biologically relevant chemotactic conditions. Analysis shows that cells steer according to absolute differences in active receptor number, not fractional receptor occupancy, and maximal chemotaxis is not predicted by half-maximal receptor occupancy. By combining scale, precision and accessibility, ChemoTrack shifts quantitative description of eukaryotic chemotaxis from experimental conditions to the instantaneous chemical signal experienced by individual cells, enabling future mathematical and mechanistic analyses.

Cell Biology↗

bioRxiv2025

Macrophage chemotaxis steered by complex self-generated gradients of complement C5a

Macrophages rely on efficient chemotaxis to locate sites of infection and tissue damage. One general strategy that enhances chemotactic accuracy is the use of self-generated gradients, where cells locally deplete attractants to create or sharpen guidance cues. Here we show that mouse bone marrow-derived macrophages (BMDMs) migrate toward the complement component C5a using this strategy. Cells actively deplete C5a from their surroundings, establishing local gradients as fresh attractant diffuses inward. We visualized this process in real time with fluorescent C5a and reproduced its dynamics using computational models. C5a depletion is mediated primarily by C5aR1-dependent endocytosis. This mechanism produces complex responses, with different C5a concentrations inducing temporally distinct waves of migration, and maximal chemotaxis occurring below 10 nM C5a. As expected, increasing C5a concentrations recruit more cells. In contrast, human macrophages inactivate C5a mainly through carboxypeptidase-mediated enzymatic degradation, yielding a higher optimal concentration ([~]30 nM) and distinct migratory dynamics. Both species also deplete externally imposed C5a gradients, sharpening them and enhancing guidance. These findings identify C5a degradation as a critical mechanism by which macrophages extract directional information from their environment. Self-generated gradient formation, despite different mechanisms across species, emerges as a conserved and versatile strategy for immune navigation.

immunology↗

bioRxiv2024

CYRI-B loss promotes enlarged mature focal adhesions and restricts microtubule and ERC1 access to the cell leading edge

CYRI proteins promote lamellipodial dynamics by opposing Rac1-mediated activation of the Scar/WAVE complex. This activity also supports resolution of macropinocytic cups, promoting internalisation of surface proteins, including integrins. Here, we show that CYRI-B also promotes focal adhesion maturation and dynamics. Focal adhesions in CYRI-B-depleted cells show accelerated maturation and become excessively large. We probed the composition of these enlarged focal adhesions, using a Bio-ID screen, with paxillin as bait. Our screen revealed changes in the adhesome suggesting early activation of stress fibre contraction and depletion of the integrin internalisation mediator ERC1. Lack of CYRI-B leads to more stable lamellipodia and accumulation of polymerised actin in stress fibres. This actin acts as a barrier to microtubule targeting for adhesion turnover. Thus, our studies reveal an important connection between lamellipodia dynamics controlled by CYRI-B and microtubule targeting of ERC1 to modulate adhesion maturation and turnover.

cell biology↗

bioRxiv2023

How Should Eukaryotic Chemotaxis be Measured?

Chemotaxis and directed cell migration are fundamentally important to eukaryotic biology. To understand the mechanisms that drive such complex processes, informative and robust measurements are essential, but the field does not always agree what these should be. Here we identify the most dependable measures of chemotactic steering and the underlying cell migration, and provide tools to test them. Some widely-used metrics can end up misleading, in particular "cos 8" for directional accuracy. We suggest that chemotactic efficiency should be used as a primary metric. Mean squared displacement and directional autocorrelation can be used to unpick different models of random and directed cell migration. Transition matrices are another useful tool for understanding migration mechanisms and avoiding artefacts, and provide a graphical illustration of how well cells maintain each direction. Unexpectedly, the choice of start and end points of tracks strongly affects the measurements and can seriously bias the measured results. This is particularly clear when cells are not homogeneously distributed at the start of an assay. To support straightforward adoption of these methods, we provide a suite of tools as a plugin for the open-source ImageJ program, and describe how they can be used to understand complex scenarios like self-generated chemotactic gradients.

cell biology↗

bioRxiv2022

Competition between chemoattractants causes unexpected complexity and can explain negative chemotaxis

Negative chemotaxis, where eukaryotic cells migrate away from repellents, is important throughout biology, for example in nervous system patterning and resolution of inflammation. However, the mechanisms by which molecules repel migrating cells are unknown. Here, we use a combination of modelling and experiments with Dictyostelium cells to show that competition between different ligands that bind to the same receptor leads to effective chemorepulsion. 8-CPT-cAMP, widely described as a simple chemorepellent, is inactive on its own, and only repels cells if it interacts with the attractant cAMP. If cells degrade either competing ligand, the pattern of migration becomes more complex; cells may be repelled in one part of a gradient but attracted elsewhere, leading to populations moving in different directions in the same assay, or converging in an arbitrary place. More counterintuitively still, two chemicals can each attract cells on their own, but repel cells when combined together. We have thus identified a new mechanism that drives reverse chemotaxis, verified by mathematical models and experiments with real cells, and important anywhere several ligands compete for the same receptors.

cell biology↗

bioRxiv2022

The Scar/WAVE complex drives normal actin protrusions without the Arp2/3 complex, but proline-rich domains are required

Cell migration requires the constant modification of cellular shape by reorganization of the actin cytoskeleton. The pentameric Scar/WAVE regulatory complex (WRC) is the main catalyst of pseudopod and lamellipodium formation. Its actin nucleation activity has been attributed to its ability to combine monomeric actin and Arp2/3 complex through the VCA domain of Scar/WAVE, while other regions of the complex are typically thought to mediate spatial and temporal regulation and have no direct role in actin polymerization. Here we show that the Scar/WAVE with its VCA domain deleted can still induce the formation of morphologically normal actin protrusions. Equivalent results are seen in B16-F1 mouse melanoma cells and Dictyostelium discoideum cells. This actin polymerization occurs independently of the Arp2/3 complex, whose recruitment to the leading edge is greatly reduced by the loss of the VCA domain. We also expressed Scar/WAVE with VCA and polyproline domains both deleted. In Dictyostelium cells, these were only active if WASP (which contains its own proline-rich domain) was available. Similarly, in B16-F1 cells both Abi and WAVE proline-rich domains needed to be deleted before the function of the WRC was lost. Thus we conclude that proline-rich domains play a central role in actin nucleation. Our data demonstrate a new actin nucleation mechanism of the WRC that is independent of its VCA domain and the Arp2/3 complex. We also show that proline-rich domains are more fundamental than has been thought. Together, these findings suggest a new mechanism for WRC action.

cell biology↗

bioRxiv2019

Seeing around corners: Cells create chemotactic gradients to solve mazes and respond to distant cues in complex environments.

Chemotaxis, in which cells steer using chemical gradients, drives fundamental biological processes like embryogenesis, metastasis and immune responses. Self-generated chemotaxis, where cells break down abundant attractants to create gradients, is an important but under-studied aspect of physiological navigation. Here we show that self-generated gradients allow cells to navigate arbitrarily complex paths and, remarkably, make accurate choices about pathways they have not yet encountered. This enables cells to solve microfluidic mazes, even with initially homogeneous environments and distant correct destinations. We combine computational models and experiments to understand how cells anticipate environmental features, and how decision accuracy is determined by path complexity, attractant diffusibility and cell speed. This permits mazes that are easy or hard for cells to resolve, despite similar appearances. Counterintuitively, slowly-diffusing attractants can generate a "mirage", making cells prefer dead ends over correct paths. In vivo environments resemble complex mazes, and only self-generated gradients realistically explain cell behaviour.

cell biology↗

bioRxiv2017

LPP3 mediates self-generation of chemotactic LPA gradients by melanoma cells

Melanoma cells steer out of tumours using self-generated lysophosphatidic acid (LPA) gradients. The cells break down LPA, which is present at high levels around the tumours, creating a dynamic gradient that is low in the tumour and high outside. They then also migrate up this gradient, creating a complex and evolving outward chemotactic stimulus. Here we introduce a new assay for self-generated chemotaxis, and show that raising LPA levels causes a delay in migration rather than loss of chemotactic efficiency. Knockdown of the lipid phosphatase LPP3 - but not its homologues LPP1 or LPP2 - diminishes the cells ability to break down LPA. This is specific for chemotactically active LPAs, such as the 18:1 and 20:4 species. Inhibition of autotaxin-mediated LPA production does not diminish outward chemotaxis, but loss of LPP3-mediated LPA breakdown blocks it. Similarly, in both 2D and 3D invasion assays, knockdown of LPP3 diminishes melanoma cells ability to invade. Our results demonstrate that LPP3 is the key enzyme in melanoma cells breakdown of LPA, and confirm the importance of attractant breakdown in LPAmediated cell steering.

cancer biology↗