Publications

The mechanical properties of the extracellular matrix dictate tissue behaviour. In epithelial tissues, laminin is a very abundant extracellular matrix component and a key supporting element. Here we show that laminin hinders the mechanoresponses of breast epithelial cells by shielding the nucleus from mechanical deformation. Coating substrates with laminin-111-unlike fibronectin or collagen I-impairs cell response to substrate rigidity and YAP nuclear localization. Blocking the laminin-specific integrin β4 increases nuclear YAP ratios in a rigidity-dependent manner without affecting the cell forces or focal adhesions. By combining mechanical perturbations and mathematical modelling, we show that β4 integrins establish a mechanical linkage between the substrate and keratin cytoskeleton, which stiffens the network and shields the nucleus from actomyosin-mediated mechanical deformation. In turn, this affects the nuclear YAP mechanoresponses, chromatin methylation and cell invasion in three dimensions. Our results demonstrate a mechanism by which tissues can regulate their sensitivity to mechanical signals.© 2023. The Author(s).

JTD Keywords: actin, cell migration, filaments, force transmission, localization, membrane, motility, proteins, yap, Integrin alpha-6-beta-4

During tumor progression, cancer-associated fibroblasts (CAFs) accumulate in tumors and produce an excessive extracellular matrix (ECM), forming a capsule that enwraps cancer cells. This capsule acts as a barrier that restricts tumor growth leading to the buildup of intratumoral pressure. Combining genetic and physical manipulations in vivo with microfabrication and force measurements in vitro, we found that the CAFs capsule is not a passive barrier but instead actively compresses cancer cells using actomyosin contractility. Abrogation of CAFs contractility in vivo leads to the dissipation of compressive forces and impairment of capsule formation. By mapping CAF force patterns in 3D, we show that compression is a CAF-intrinsic property independent of cancer cell growth. Supracellular coordination of CAFs is achieved through fibronectin cables that serve as scaffolds allowing force transmission. Cancer cells mechanosense CAF compression, resulting in an altered localization of the transcriptional regulator YAP and a decrease in proliferation. Our study unveils that the contractile capsule actively compresses cancer cells, modulates their mechanical signaling, and reorganizes tumor morphology.© 2023. The Author(s).

JTD Keywords: force, migration, yap, Tumor

Recent experimental evidence indicates a role for the intermediate filament vimentin in regulating cellular mechanical homeostasis, but its precise contribution remains to be discovered. Mechanical homeostasis requires a balanced bi-directional interplay between the cell's microenvironment and the cellular morphological and mechanical state-this balance being regulated via processes of mechanotransduction and mechanoresponse, commonly referred to as mechanoreciprocity. Here, we systematically analyze vimentin-expressing and vimentin-depleted cells in a swatch of in vitro cellular microenvironments varying in stiffness and/or ECM density. We find that vimentin-expressing cells maintain mechanical homeostasis by adapting cellular morphology and mechanics to micromechanical changes in the microenvironment. However, vimentin-depleted cells lose this mechanoresponse ability on short timescales, only to reacquire it on longer time scales. Indeed, we find that the morphology and mechanics of vimentin-depleted cell in stiffened microenvironmental conditions can get restored to the homeostatic levels of vimentin-expressing cells. Additionally, we observed vimentin-depleted cells increasing collagen matrix synthesis and its crosslinking, a phenomenon which is known to increase matrix stiffness, and which we now hypothesize to be a cellular compensation mechanism for the loss of vimentin. Taken together, our findings provide further insight in the regulating role of intermediate filament vimentin in mediating mechanoreciprocity and mechanical homeostasis.© 2023. The Author(s).

JTD Keywords: contributes, dynamics, focal adhesions, forces, mechanotransduction, migration, motility, organization, tissue, Intermediate-filaments

Neurotrophic factors are essential not only for guiding the organization of the developing nervous system but also for supporting the survival and growth of neurons after traumatic injury. In the central nervous system (CNS), inhibitory factors and the formation of a glial scar after injury hinder the functional recovery of neurons, requiring exogenous therapies to promote regeneration. Netrin-1, a neurotrophic factor, can initiate axon guidance, outgrowth, and branching, as well as synaptogenesis, through activation of deleted in colorectal cancer (DCC) receptors. We report here the development of a nanofiber-shaped supramolecular mimetic of netrin-1 with monomers that incorporate a cyclic peptide sequence as the bioactive component. The mimetic structure was found to activate the DCC receptor in primary cortical neurons using low molar ratios of the bioactive comonomer. The supramolecular nanofibers enhanced neurite outgrowth and upregulated maturation as well as pre- and postsynaptic markers over time, resulting in differences in electrical activity similar to neurons treated with the recombinant netrin-1 protein. The results suggest the possibility of using the supramolecular structure as a therapeutic to promote regenerative bioactivity in CNS injuries.

JTD Keywords: axon growth, axon guidance, cell-migration, colorectal-cancer, dcc, dopaminergic-neurons, force-field, functional recovery, netrin-1, neurite outgrowth, neuronal maturation, neurotrophic factor, neurotrophicfactor mimetic, synapsis, Axon growth, Coarse-grained model, Netrin-1, Neuronal maturation, Neurotrophic factor mimetic, Peptide amphiphile, Synapsis

Cancer progression is caused by genetic changes and associated with various alterations in cell properties, which also affect a tumor's mechanical state. While an increased stiffness has been well known for long for solid tumors, it has limited prognostic power. It is hypothesized that cancer progression is accompanied by tissue fluidization, where portions of the tissue can change position across different length scales. Supported by tabletop magnetic resonance elastography (MRE) on stroma mimicking collagen gels and microscopic analysis of live cells inside patient derived tumor explants, an overview is provided of how cancer associated mechanisms, including cellular unjamming, proliferation, microenvironment composition, and remodeling can alter a tissue's fluidity and stiffness. In vivo, state-of-the-art multifrequency MRE can distinguish tumors from their surrounding host tissue by their rheological fingerprints. Most importantly, a meta-analysis on the currently available clinical studies is conducted and universal trends are identified. The results and conclusions are condensed into a gedankenexperiment about how a tumor can grow and eventually metastasize into its environment from a physics perspective to deduce corresponding mechanical properties. Based on stiffness, fluidity, spatial heterogeneity, and texture of the tumor front a roadmap for a prognosis of a tumor's aggressiveness and metastatic potential is presented.© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.

JTD Keywords: brain, cancer, cells, collective migration, elastic energy, elastography, in vivo magnetic resonance elastography, invasion, medical imaging, solid stress, tissue fluidity, tumor mechanics, viscoelastic properties, Cancer, Extracellular-matrix, In vivo magnetic resonance elastography, Medical imaging, Tissue fluidity, Tumor mechanics

Ex vivo-loaded white blood cells (WBC) can transfer cargo to pathological foci in the central nervous system (CNS). Here we tested affinity ligand driven in vivo loading of WBC in order to bypass the need for ex vivo WBC manipulation. We used a mouse model of acute brain inflammation caused by local injection of tumor necrosis factor alpha (TNF-α). We intravenously injected nanoparticles targeted to intercellular adhesion molecule 1 (anti-ICAM/NP). We found that (A) at 2 h, >20% of anti-ICAM/NP were localized to the lungs; (B) of the anti-ICAM/NP in the lungs >90% were associated with leukocytes; (C) at 6 and 22 h, anti-ICAM/NP pulmonary uptake decreased; (D) anti-ICAM/NP uptake in brain increased up to 5-fold in this time interval, concomitantly with migration of WBCs into the injured brain. Intravital microscopy confirmed transport of anti-ICAM/NP beyond the blood-brain barrier and flow cytometry demonstrated complete association of NP with WBC in the brain (98%). Dexamethasone-loaded anti-ICAM/liposomes abrogated brain edema in this model and promoted anti-inflammatory M2 polarization of macrophages in the brain. In vivo targeted loading of WBC in the intravascular pool may provide advantages of coopting WBC predisposed to natural rapid mobilization from the lungs to the brain, connected directly via conduit vessels.

JTD Keywords: drug delivery, icam-1, inflammation, lung injury, messenger-rna, migration, model, nanoparticles, neutrophils, pharmacokinetics, t-cells, white bloodcells, Adhesion molecules, Brain, Drug delivery, Inflammation, Nanoparticles, Pharmacokinetics, White blood cells

Sprouting angiogenesis is a core biological process critical to vascular development. Its accurate simulation, relevant to multiple facets of human health, is of broad, interdisciplinary appeal. This study presents an in-silico model replicating a microfluidic assay where endothelial cells sprout into a biomimetic extracellular matrix, specifically, a large-pore, low-concentration fibrin-based porous hydrogel, influenced by chemotactic factors. We introduce a novel approach by incorporating the extracellular matrix and chemotactic factor effects into a unified term using a single parameter, primarily focusing on modelling sprouting dynamics and morphology. This continuous model naturally describes chemotactic-induced sprouting with no need for additional rules. In addition, we extended our base model to account for matrix sensing and degradation, crucial aspects of angiogenesis. We validate our model via a hybrid in-silico experimental method, comparing the model predictions with experimental results derived from the microfluidic setup. Our results underscore the intricate relationship between the extracellular matrix structure and angiogenic sprouting, proposing a promising method for predicting the influence of the extracellular matrix on angiogenesis.Copyright © 2023 Ferre-Torres, Noguera-Monteagudo, Lopez-Canosa, Romero-Arias, Barrio, Castaño and Hernandez-Machado.

JTD Keywords: angiogenesis, biomimmetic, chemotaxis, endothelial cells, filopodia, growth, in silico model, mathematical models, mechanisms, metalloproteinase, migration, morphogenesis, phase field, pore-size, simulation, Angiogenesis, Biomimmetic, Chemotaxis, Endothelial cells, Extracellular matrix, In silico model, Mathematical models, Phase field, Tip cells

The TGF-β1 transcription factor SMAD3 is epigenetically repressed in tumour-associated fibroblasts (TAFs) from lung squamous cell carcinoma (SCC) but not adenocarcinoma (ADC) patients, which elicits a compensatory increase in SMAD2 that renders SCC-TAFs less fibrotic. Here we examined the effects of altered SMAD2/3 in fibroblast migration and its impact on the desmoplastic stroma formation in lung cancer.We used a microfluidic device to examine descriptors of early protrusions and subsequent migration in 3D collagen gels upon knocking down SMAD2 or SMAD3 by shRNA in control fibroblasts and TAFs.High SMAD3 conditions as in shSMAD2 fibroblasts and ADC-TAFs exhibited a migratory advantage in terms of protrusions (fewer and longer) and migration (faster and more directional) selectively without TGF-β1 along with Erk1/2 hyperactivation. This enhanced migration was abrogated by TGF-β1 as well as low glucose medium and the MEK inhibitor Trametinib. In contrast, high SMAD2 fibroblasts were poorly responsive to TGF-β1, high glucose and Trametinib, exhibiting impaired migration in all conditions.The basal migration advantage of high SMAD3 fibroblasts provides a straightforward mechanism underlying the larger accumulation of TAFs previously reported in ADC compared to SCC. Moreover, our results encourage using MEK inhibitors in ADC-TAFs but not SCC-TAFs.© 2022. The Author(s).

JTD Keywords: cancer, cell, degradation, nintedanib, osteoblast migration, phenotype, progression, protrusion dynamics, smad3, Growth-factor-beta

Topographical patterns are a powerful tool to study directional migration. Grooved substrates have been extensively used as in vitro models of aligned extracellular matrix fibers because they induce cell elongation, alignment, and migration through a phenomenon known as contact guidance. This process, which involves the orientation of focal adhesions, F-actin, and microtubule cytoskeleton along the direction of the grooves, has been primarily studied on hard materials of non-physiological stiffness. But how it unfolds when the stiffness of the grooves varies within the physiological range is less known. Here we show that substrate stiffness modulates the cellular response to topographical contact guidance. We find that for fibroblasts, while focal adhesions and actin respond to topography independently of the stiffness, microtubules show a stiffness-dependent response that regulates contact guidance. On the other hand, both clusters and single breast carcinoma epithelial cells display stiffness-dependent contact guidance, leading to more directional and efficient migration when increasing substrate stiffness. These results suggest that both matrix stiffening and alignment of extracellular matrix fibers cooperate during directional cell migration, and that the outcome differs between cell types depending on how they organize their cytoskeletons.© 2023 The Authors.

JTD Keywords: actin, behavior, cell migration, contact guidance, cytoskeleton, fibroblasts, focal adhesions, matrix, microtubules, stiffness, stress fibers, topography, transduction, Contact guidance, Substrate stiffness, Topography

Surface curvature both emerges from, and influences the behavior of, living objects at length scales ranging from cell membranes to single cells to tissues and organs. The relevance of surface curvature in biology is supported by numerous experimental and theoretical investigations in recent years. In this review, first, a brief introduction to the key ideas of surface curvature in the context of biological systems is given and the challenges that arise when measuring surface curvature are discussed. Giving an overview of the emergence of curvature in biological systems, its significance at different length scales becomes apparent. On the other hand, summarizing current findings also shows that both single cells and entire cell sheets, tissues or organisms respond to curvature by modulating their shape and their migration behavior. Finally, the interplay between the distribution of morphogens or micro-organisms and the emergence of curvature across length scales is addressed with examples demonstrating these key mechanistic principles of morphogenesis. Overall, this review highlights that curved interfaces are not merely a passive by-product of the chemical, biological, and mechanical processes but that curvature acts also as a signal that co-determines these processes.© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.

JTD Keywords: biological systems, butterfly wing scales, cubic membranes, extracellular-matrix, geometry, mechanotransduction, membrane curvature, morphogenesis, neotissue growth, pattern-formation, soft materials, surface curvature, tissue-growth, Biological systems, Collective cell-migration, Surface curvature

Human induced pluripotent stem cell (hiPSC) technologies offer a unique resource for modeling neurological diseases. However, iPSC models are fraught with technical limitations including abnormal aggregation and inefficient maturation of differentiated neurons. These problems are in part due to the absence of synergistic cues of the native extracellular matrix (ECM). We report on the use of three artificial ECMs based on peptide amphiphile (PA) supramolecular nanofibers. All nanofibers display the laminin-derived IKVAV signal on their surface but differ in the nature of their non-bioactive domains. We find that nanofibers with greater intensity of internal supramolecular motion have enhanced bioactivity toward hiPSC-derived motor and cortical neurons. Proteomic, biochemical, and functional assays reveal that highly mobile PA scaffolds caused enhanced β1-integrin pathway activation, reduced aggregation, increased arborization, and matured electrophysiological activity of neurons. Our work highlights the importance of designing biomimetic ECMs to study the development, function, and dysfunction of human neurons.Copyright © 2022 Elsevier Inc. All rights reserved.

JTD Keywords: differentiation, force-field, laminin, migration, nanostructures, peptide amphiphiles, spinal-cord, statistical-model, supramolecular materials, Coarse-grained model, Dynamics, Extracellular matrix, Ikvav, Ipsc-derived neurons, Laminin, Neuronal maturation, Peptide amphiphiles, Supramolecular motion, Supramolecular nanofibers

The directed migration of cellular clusters enables morphogenesis, wound healing and collective cancer invasion. Gradients of substrate stiffness direct the migration of cellular clusters in a process called collective durotaxis, but the underlying mechanisms remain unclear. Here we unveil a connection between collective durotaxis and the wetting properties of cellular clusters. We show that clusters of cancer cells dewet soft substrates and wet stiff ones. At intermediate stiffness-at the crossover from low to high wettability-clusters on uniform-stiffness substrates become maximally motile, and clusters on stiffness gradients exhibit optimal durotaxis. Durotactic velocity increases with cluster size, stiffness gradient and actomyosin activity. We demonstrate this behaviour on substrates coated with the cell-cell adhesion protein E-cadherin and then establish its generality on substrates coated with extracellular matrix. We develop an active wetting model that explains collective durotaxis in terms of a balance between in-plane active traction and tissue contractility and out-of-plane surface tension. Finally, we show that the distribution of cluster displacements has a heavy tail, with infrequent but large cellular hops that contribute to durotactic migration. Our study demonstrates a physical mechanism of collective durotaxis, through both cell-cell and cell-substrate adhesion ligands, based on the wetting properties of active droplets.

JTD Keywords: Adhesion, Dynamics, E-cadherin, Gradient, Migration, Model, Motility, Movements, Rigidity, Substrate stiffness

In response to different types and intensities of mechanical force, cells modulate their physical properties and adapt their plasma membrane (PM). Caveolae are PM nano-invaginations that contribute to mechanoadaptation, buffering tension changes. However, whether core caveolar proteins contribute to PM tension accommodation independently from the caveolar assembly is unknown. Here we provide experimental and computational evidence supporting that caveolin-1 confers deformability and mechanoprotection independently from caveolae, through modulation of PM curvature. Freeze-fracture electron microscopy reveals that caveolin-1 stabilizes non-caveolar invaginations-dolines-capable of responding to low-medium mechanical forces, impacting downstream mechanotransduction and conferring mechanoprotection to cells devoid of caveolae. Upon cavin-1/PTRF binding, doline size is restricted and membrane buffering is limited to relatively high forces, capable of flattening caveolae. Thus, caveolae and dolines constitute two distinct albeit complementary components of a buffering system that allows cells to adapt efficiently to a broad range of mechanical stimuli.© 2022. The Author(s).

JTD Keywords: cavin, cell-migration, cholesterol, extracellular-matrix, nanoscale organization, particle-size, polarization, size distribution, tension, Plasma-membrane

Biomolecular and physical cues of the extracellular matrix environment regulate collective cell dynamics and tissue patterning. Nonetheless, how the viscoelastic properties of the matrix regulate collective cell spatial and temporal organization is not fully understood. Here we show that the passive viscoelastic properties of the matrix encapsulating a spheroidal tissue of breast epithelial cells guide tissue proliferation in space and in time. Matrix viscoelasticity prompts symmetry breaking of the spheroid, leading to the formation of invading finger-like protrusions, YAP nuclear translocation and epithelial-to-mesenchymal transition both in vitro and in vivo in a Arp2/3-complex-dependent manner. Computational modelling of these observations allows us to establish a phase diagram relating morphological stability with matrix viscoelasticity, tissue viscosity, cell motility and cell division rate, which is experimentally validated by biochemical assays and in vitro experiments with an intestinal organoid. Altogether, this work highlights the role of stress relaxation mechanisms in tissue growth dynamics, a fundamental process in morphogenesis and oncogenesis.© 2022. The Author(s), under exclusive licence to Springer Nature Limited.

JTD Keywords: in-vitro, migration, morphogenesis, stiffness, Intestinal stem-cell

Mesenchymal condensation is a prevalent morphogenetic transition that is essential in chondrogenesis. However, the current understanding of condensation mechanisms is limited. In vivo, progenitor cells directionally migrate from the surrounding loose mesenchyme towards regions of increasing matrix adherence (the condensation centers), which is accompanied by the upregulation of fibronectin. Here, we focused on the mechanisms of cell migration during mesenchymal cell condensation and the effects of matrix adherence. Dendrimer-based nanopatterns of the cell-adhesive peptide arginine-glycine-aspartic acid (RGD), which is present in fibronectin, were used to regulate substrate adhesion. We recorded collective and single-cell migration of mesenchymal stem cells, under chondrogenic induction, using live-cell imaging. Our results show that the cell migration mode of single cells depends on substrate adhesiveness, and that cell directionality controls cell condensation and the fusion of condensates. Inhibition experiments revealed that cell-cell interactions mediated by N-cadherin (also known as CDH2) are also pivotal for directional migration of cell condensates by maintaining cell-cell cohesion, thus suggesting a fine interplay between cell-matrix and cell-cell adhesions. Our results shed light on the role of cell interactions with a fibronectin-depositing matrix during chondrogenesis in vitro, with possible applications in regenerative medicine. This article has an associated First Person interview with the first author of the paper.© 2022. Published by The Company of Biologists Ltd.

JTD Keywords: alpha-v-beta-3, arginine-glycine-aspartic acid, chondrogenesis, dynamics, expression, fibronectin, gastrulation, involvement, mechanisms, mesenchymal condensation, model, nanopatterned substrates, rgd, Arginine-glycine-aspartic acid, Cell migration, Chondrogenesis, Mesenchymal condensation, N-cadherin, Nanopatterned substrates, Rgd

Around 30-40% of patients with colorectal cancer (CRC) undergoing curative resection of the primary tumour will develop metastases in the subsequent years1. Therapies to prevent disease relapse remain an unmet medical need. Here we uncover the identity and features of the residual tumour cells responsible for CRC relapse. An analysis of single-cell transcriptomes of samples from patients with CRC revealed that the majority of genes associated with a poor prognosis are expressed by a unique tumour cell population that we named high-relapse cells (HRCs). We established a human-like mouse model of microsatellite-stable CRC that undergoes metastatic relapse after surgical resection of the primary tumour. Residual HRCs occult in mouse livers after primary CRC surgery gave rise to multiple cell types over time, including LGR5+ stem-like tumour cells2-4, and caused overt metastatic disease. Using Emp1 (encoding epithelial membrane protein 1) as a marker gene for HRCs, we tracked and selectively eliminated this cell population. Genetic ablation of EMP1high cells prevented metastatic recurrence and mice remained disease-free after surgery. We also found that HRC-rich micrometastases were infiltrated with T cells, yet became progressively immune-excluded during outgrowth. Treatment with neoadjuvant immunotherapy eliminated residual metastatic cells and prevented mice from relapsing after surgery. Together, our findings reveal the cell-state dynamics of residual disease in CRC and anticipate that therapies targeting HRCs may help to avoid metastatic relapse.© 2022. The Author(s), under exclusive licence to Springer Nature Limited.

JTD Keywords: colonization, defines, human colon, mutations, plasticity, retrieval, stem-cells, subtypes, underlie, Animal, Animal cell, Animal experiment, Animal model, Animal tissue, Animals, Article, Cancer, Cancer growth, Cancer immunotherapy, Cancer inhibition, Cancer recurrence, Cancer staging, Cell, Cell adhesion, Cell migration, Cell population, Cell surface receptor, Cohort analysis, Colorectal cancer, Colorectal neoplasms, Colorectal tumor, Comprehensive molecular characterization, Controlled study, Crispr-cas9 system, Cytoskeleton, Disease exacerbation, Disease progression, Dynamics, Emp1 gene, Epithelial membrane protein-1, Extracellular matrix, Flow cytometry, Fluorescence intensity, Gene expression, Genetics, Human, Human cell, Humans, Immune response, Immunofluorescence, In situ hybridization, Marker gene, Metastasis potential, Mice, Minimal residual disease, Mouse, Neoplasm proteins, Neoplasm recurrence, local, Neoplasm, residual, Nonhuman, Pathology, Phenotype, Prevention and control, Protein, Receptors, cell surface, Single cell rna seq, Tumor, Tumor protein, Tumor recurrence

JTD Keywords: adhesion, attachment, growth, ligands, membrane, microcontact printing, migration, organoid-derived intestinal epithelia, receptor, tissue organization, Eph-ephrin, Stem-cells

Several factors present in the extracellular environment regulate epithelial cell adhesion and dynamics. Among them, growth factors such as EGF, upon binding to their receptors at the cell surface, get internalized and directly activate the acto-myosin machinery. In this study we present the effects of EGF on the contractility of epithelial cancer cell colonies in confined geometry of different sizes. We show that the extent to which EGF triggers contractility scales with the cluster size and thus the number of cells. Moreover, the collective contractility results in a radial distribution of traction forces, which are dependent on integrin β1 peripheral adhesions and transmitted to neighboring cells through adherens junctions. Taken together, EGF-induced contractility acts on the mechanical crosstalk and linkage between the cell-cell and cell-matrix compartments, regulating collective responses.Copyright © 2022 The Authors. Published by Elsevier GmbH.. All rights reserved.

JTD Keywords: actin, activation, actomyosin, adherens junctions, adhesion, e-cadherin, egf, maturation, mechanical regulation, micropatterning, migration, traction forces, transduction, transmission, Actomyosin, Adherens junctions, Collective contractility, Egf, Epidermal-growth-factor, Micropatterning, Traction forces

Cooperative behaviour of sperm is one of the mechanisms that plays a role in sperm competition. It has been observed in several species that spermatozoa interact with each other to form agglomerates or bundles. In this study, we investigate the effect of physical and biochemical factors that will most likely promote bundle formation in bull sperm. These factors include fluid viscosity, swim-up process, post-thaw incubation time and media additives which promote capacitation. While viscosity does not seem to influence the degree of sperm bundling, swim-up, post-thaw migration time and suppressed capacitation increase the occurrence of sperm bundles. This leads to the conclusion that sperm bundling is a result of hydrodynamic and adhesive interactions between the cells which occurs frequently during prolonged incubation times.Copyright © 2022 Morcillo i Soler, Hidalgo, Fekete, Zalanyi, Khalil, Yeste and Magdanz.

JTD Keywords: acrosome reaction, adhesion, bundling, capacitation, cell-cell interaction, cooperation, cooperative behaviour, fertilization, mammals, membrane, motility, progesterone, sperm competition, sperm migration, sperm selection, Bovine spermatozoa, Bundling, Cell-cell interaction, Cooperative behaviour, Sperm competition, Sperm migration, Sperm selection, Spermatozoa

Upon the initiation of collective cell migration, the cells at the free edge are specified as leader cells; however, the mechanism underlying the leader cell specification remains elusive. Here, we show that lamellipodial extension after the release from mechanical confinement causes sustained extracellular signal-regulated kinase (ERK) activation and underlies the leader cell specification. Live-imaging of Madin-Darby canine kidney (MDCK) cells and mouse epidermis through the use of Förster resonance energy transfer (FRET)-based biosensors showed that leader cells exhibit sustained ERK activation in a hepatocyte growth factor (HGF)-dependent manner. Meanwhile, follower cells exhibit oscillatory ERK activation waves in an epidermal growth factor (EGF) signaling-dependent manner. Lamellipodial extension at the free edge increases the cellular sensitivity to HGF. The HGF-dependent ERK activation, in turn, promotes lamellipodial extension, thereby forming a positive feedback loop between cell extension and ERK activation and specifying the cells at the free edge as the leader cells. Our findings show that the integration of physical and biochemical cues underlies the leader cell specification during collective cell migration.Copyright © 2022 Elsevier Inc. All rights reserved.

JTD Keywords: activation, c-met, contact inhibition, focal adhesions, heparan-sulfate, mechanical forces, morphogenesis, rho, stress fibers, Collective cell migration, Erk, Feedback regulation, Fret, Growth-factor receptor, Hgf, Lamellipodia, Leader cell specification, Signal transduction, Traction force, Wound healing

Growing evidence suggests that the physical properties of the cellular microenvironment influence cell migration. However, it is not currently understood how active physical remodelling by cells affects migration dynamics. Here we report that cell clusters seeded on deformable collagen-I networks display persistent collective migration despite not showing any apparent intrinsic polarity. Clusters generate transient gradients in collagen density and alignment due to viscoelastic relaxation of the collagen networks. Combining theory and experiments, we show that crosslinking collagen networks or reducing cell cluster size results in reduced network deformation, shorter viscoelastic relaxation time and smaller gradients, leading to lower migration persistence. Traction force and Brillouin microscopy reveal asymmetries in force distributions and collagen stiffness during migration, providing evidence of mechanical cross-talk between cells and their substrate during migration. This physical model provides a mechanism for self-generated directional migration on viscoelastic substrates in the absence of internal biochemical polarity cues.; Cell clusters mechanically reorganize viscoelastic collagen networks, resulting in transient gradients in collagen density, alignment and stiffness that promote spontaneous persistent migration.

JTD Keywords: Cell-migration, Design, Invasion, Limits, Mechanics, Microscopy, Morphogenesis, Motility, Rear, Rigidity

Chemically responsive polymers are macromolecules that respond to local variations of the chemical composition of the solution by changing their conformation, with notable examples including polyelectrolytes, proteins, and DNA. The polymer conformation changes can occur in response to changes in the pH, the ionic strength, or the concentration of a generic solute that interacts with the polymer. These chemical stimuli can lead to drastic variations of the polymer flexibility and even trigger a transition from a coil to a globule polymer conformation. In many situations, the spatial distribution of the chemical stimuli can be highly inhomogeneous, which can lead to large spatial variations of polymer conformation and of the rheological properties of the mixture. In this paper, we develop a theory for the flow of a mixture of solute and chemically responsive polymers. The approach is valid for generic flows and inhomogeneous distributions of polymers and solutes. To model the polymer conformation changes introduced by the interactions with the solute, we consider the polymers as linear elastic dumbbells whose spring stiffness depends on the solute concentration. We use Onsager's variational formalism to derive the equations governing the evolution of the variables, which unveils novel couplings between the distribution of dumbbells and that of the solute. Finally, we use a linear stability analysis to show that the governing equations predict an equilibrium phase separation and a distinct shear-induced phase separation whereby a homogeneous distribution of solute and dumbbells spontaneously demix. Similar phase transitions have been observed in previous experiments using stimuli-responsive polymers and may play an important role in living systems. (C) 2022 The Society of Rheology.

JTD Keywords: Coil-globule transition, Constitutive equation, Dilute-solutions, Dumbbell model, Dynamics, Macromolecules, Nonequilibrium thermodynamics, Polyelectrolytes, Polymer migration, Polymer phase separation, Polymers, Predictions, Rheology, Shear-induced phase separation, Solute-polymer interactions, Stress, Viscoelasticity

Van der Waals layered ferroelectrics, such as CuInP2S6 (CIPS), offer a versatile platform for miniaturization of ferroelectric device technologies. Control of the targeted composition and kinetics of CIPS synthesis enables the formation of stable self-assembled heterostructures of ferroelectric CIPS and nonferroelectric In4/3P2S6 (IPS). Here, we use quantitative scanning probe microscopy methods combined with density functional theory (DFT) to explore in detail the nanoscale variability in dynamic functional properties of the CIPS-IPS heterostructure. We report evidence of fast ionic transport which mediates an appreciable out-of-plane electromechanical response of the CIPS surface in the paraelectric phase. Further, we map the nanoscale dielectric and ionic conductivity properties as we thermally stimulate the ferroelectric-paraelectric phase transition, recovering the local dielectric behavior during this phase transition. Finally, aided by DFT, we reveal a substantial and tunable conductivity enhancement at the CIPS/IPS interface, indicating the possibility of engineering its interfacial properties for next generation device applications.

JTD Keywords: copper indium thiophosphate, diffusion, elastic band method, ferroelectrics, ionic conductor, migration, nanoscale, phase transition, piezoresponse force microscopy, scanning dielectric microscopy, transition, Copper indium thiophosphate, Initio molecular-dynamics, Scanning dielectric microscopy

While chemokines were originally described for their ability to induce cell migration, many studies show how these proteins also take part in many other cell functions, acting as adaptable messengers in the communication between a diversity of cell types. In the nervous system, chemokines participate both in physiological and pathological processes, and while their expression is often described on glial and immune cells, growing evidence describes the expression of chemokines and their receptors in neurons, highlighting their potential in auto- and paracrine signalling. In this study we analysed the role of nociception in the neuronal chemokinome, and in turn their role in axonal growth. We found that stimulating TRPV1(+) nociceptors induces a transient increase in CCL21. Interestingly we also found that CCL21 enhances neurite growth of large diameter proprioceptors in vitro. Consistent with this, we show that proprioceptors express the CCL21 receptor CCR7, and a CCR7 neutralizing antibody dose-dependently attenuates CCL21-induced neurite outgrowth. Mechanistically, we found that CCL21 binds locally to its receptor CCR7 at the growth cone, activating the downstream MEK-ERK pathway, that in turn activates N-WASP, triggering actin filament ramification in the growth cone, resulting in increased axonal growth.

JTD Keywords: axonal growth, ccl21, ccr7, mek-erk, Actin dynamics, Axonal growth, Ccl21, Ccr7, Cell-migration, Central-nervous-system, Chemokine, Ligands, Mek-erk, Microglia, Neurons, Neuropathic pain, Nociception, Phosphorylation, Regeneration

Emerging evidence points to coordinated action of chemical and mechanical cues during brain development. At early stages of neocortical development, angiogenic factors and chemokines such as CXCL12, ephrins, and semaphorins assume crucial roles in orchestrating neuronal migration and axon elongation of postmitotic neurons. Here we explore the intrinsic mechanical properties of the developing marginal zone of the pallium in the migratory pathways and brain distribution of the pioneer Cajal-Retzius cells. These neurons are generated in several proliferative regions in the developing brain (e.g., the cortical hem and the pallial subpallial boundary) and migrate tangentially in the preplate/marginal zone covering the upper portion of the developing cortex. These cells play crucial roles in correct neocortical layer formation by secreting several molecules such as Reelin. Our results indicate that the motogenic properties of Cajal-Retzius cells and their perinatal distribution in the marginal zone are modulated by both chemical and mechanical factors, by the specific mechanical properties of Cajal-Retzius cells, and by the differential stiffness of the migratory routes. Indeed, cells originating in the cortical hem display higher migratory capacities than those generated in the pallial subpallial boundary which may be involved in the differential distribution of these cells in the dorsal-lateral axis in the developing marginal zone.

JTD Keywords: atomic force microscopy, cajal-retzius cells, cortical development, marginal zone, mechanical cues, Atomic force microscopy, Cajal-retzius cells, Central-nervous-system, Cortical development, Cortical hem, Developing cerebral-cortex, Expression, Growth, Marginal zone, Mechanical cues, Mouse, Neuronal migration, Nogo receptor, Olfactory ensheathing cells, Tangential migration, Traction force microscopy

During development, organs reach precise shapes and sizes. Organ morphology is not always obtained through growth; a classic counterexample is the condensation of the nervous system during Drosophila embryogenesis. The mechanics underlying such condensation remain poorly understood. Here, we characterize the condensation of the embryonic ventral nerve cord (VNC) at both subcellular and tissue scales. This analysis reveals that condensation is not a unidirectional continuous process but instead occurs through oscillatory contractions. The VNC mechanical properties spatially and temporally vary, and forces along its longitudinal axis are spatially heterogeneous. We demonstrate that the process of VNC condensation is dependent on the coordinated mechanical activities of neurons and glia. These outcomes are consistent with a viscoelastic model of condensation, which incorporates time delays and effective frictional interactions. In summary, we have defined the progressive mechanics driving VNC condensation, providing insights into how a highly viscous tissue can autonomously change shape and size.

JTD Keywords: actomyosin, central nervous system, drosophila, glia, mechanics, morphogenesis, neuron, ventral nerve cord, Collagen-iv, Contraction, Forces, Gene, Glial-cells, Migration, Morphogenesis, Quantification, System, Tissue, Viscolelastic model

Endothelial coverage of an exposed cardiovascular stent surface leads to the occurrence of restenosis and late-stent thrombosis several months after implantation. To overcome this difficulty, modification of stent surfaces with topographical or biochemical features may be performed to increase endothelial cells’ (ECs) adhesion and/or migration. This work combines both strategies on cobalt-chromium (CoCr) alloy and studies the potential synergistic effect of linear patterned surfaces that are obtained by direct laser interference patterning (DLIP), coupled with the use of Arg-Gly-Asp (RGD) and Tyr-Ile-Gly-Ser-Arg (YIGSR) peptides. An extensive characterization of the modified surfaces was performed by using AFM, XPS, surface charge, electrochemical analysis and fluorescent methods. The biological response was studied in terms of EC adhesion, migration and proliferation assays. CoCr surfaces were successfully patterned with a periodicity of 10 µm and two different depths, D (≈79 and 762 nm). RGD and YIGSR were immobilized on the surfaces by CPTES silanization. Early EC adhesion was increased on the peptide-functionalized surfaces, especially for YIGSR compared to RGD. High-depth patterns generated 80% of ECs’ alignment within the topographical lines and enhanced EC migration. It is noteworthy that the combined use of the two strategies synergistically accelerated the ECs’ migration and proliferation, proving the potential of this strategy to enhance stent endothelialization.

JTD Keywords: adhesion, bare-metal, biofunctionalization, biomaterials, cell adhesive peptides, cobalt-chromium alloy, direct laser interference patterning (dlip), endothelial cell migration, functionalization, matrix, proliferation, selectivity, shear-stress, surfaces, Direct laser interference patterning (dlip), Drug-eluting stents, Endothelial cell migration

The dizzying life of the homeostatic intestinal epithelium is governed by a complex interplay between fate, form, force and function. This interplay is beginning to be elucidated thanks to advances in intravital and ex vivo imaging, organoid culture, and biomechanical measurements. Recent discoveries have untangled the intricate organization of the forces that fold the monolayer into crypts and villi, compartmentalize cell types, direct cell migration, and regulate cell identity, proliferation and death. These findings revealed that the dynamic equilibrium of the healthy intestinal epithelium relies on its ability to precisely coordinate tractions and tensions in space and time. In this review, we discuss recent findings in intestinal mechanobiology, and highlight some of the many fascinating questions that remain to be addressed in this emerging field.Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.

JTD Keywords: crypt fission, designer matrices, differentiation, growth, gut, migration, model, scaffold, tissue mechanics, Cell migration, Cell proliferation, Ex vivo study, Human tissue, Intestine epithelium, Monolayer culture, Organoid, Review, Stem-cell, Tension, Traction therapy

The extracellular matrix mechanical properties regulate processes in development, cancer, and fibrosis. Among the distinct mechanical properties, the vast majority of research has focused on the extracellular matrix's elasticity as the primary determinant of cell and tissue behavior. However, both cells and the extracellular matrix are not only elastic but also viscous. Despite viscoelasticity being a universal feature of living tissues, our knowledge of the influence of the extracellular matrix's viscoelasticity in cell behavior is limited. This mini-review describes some of the recent findings that have highlighted the role of the extracellular matrix's viscoelasticity in cell and tissue dynamics.

JTD Keywords: behavior, cell adhesion, cell mechanics, cell migration, deformability, extracellular matrix, extracellular matrix mechanics, fluidity, forces, hydrogels, mechanobiology, mechanotransduction, tissue mechanics, viscoelasticity, viscosity, Cell adhesion, Cell mechanics, Cell migration, Extracellular matrix, Extracellular matrix mechanics, Fluidity, Mechanobiology, Mechanotransduction, Migration, Tissue mechanics, Viscoelasticity, Viscosity

(Following spinal cord injury, olfactory ensheathing cell (OEC) transplantation is a promising therapeutic approach in promoting functional improvement. Some studies report that the migratory properties of OECs are compromised by inhibitory molecules and potentiated by chemical concentration differences. Here we compare the attachment, morphology, and directionality of an OEC-derived cell line, TEG3 cells, seeded on functionalized nanoscale meshes of Poly(l/dl-lactic acid; PLA) nanofibers. The size of the nanofibers has a strong effect on TEG3 cell adhesion and migration, with the PLA nanofibers having a 950 nm diameter being the ones that show the best results. TEG3 cells are capable of adopting a bipolar morphology on 950 nm fiber surfaces, as well as a highly dynamic behavior in migratory terms. Finally, we observe that functionalized nanofibers, with a chemical concentration increment of SDF-1α/CXCL12, strongly enhance the migratory characteristics of TEG3 cells over inhibitory substrates.

JTD Keywords: cell migration, cxcl12, electrospinning, gradients, pla nanofibers, sdf-1alpha, Cell migration, Cxcl12, Electrospinning, Gradients, Olfactory ensheathing cells, Pla nanofibers, Sdf-1alpha

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. In many solid tumors, collective cell invasion prevails over single-cell dissemination strategies. Collective modes of invasion often display specific front/rear cellular organization, where invasive leader cells arise from cancer cell populations or the tumor stroma. Collective invasion involves coordinated cellular movements which require tight mechanical crosstalk through specific combinations of cell–cell interactions and cell–matrix adhesions. Cancer Associated Fibroblasts (CAFs) have been recently reported to drive the dissemination of epithelial cancer cells through ECM remodeling and direct intercellular contact. However, the cooperation between tumor and stromal cells remains poorly understood. Here we present a simple spheroid invasion assay to assess the role of CAFs in the collective migration of epithelial tumor cells. This method enables the characterization of 3D spheroid invasion patterns through live cell fluorescent labeling combined with spinning disc microscopy. When embedded in extracellular matrix, the invasive strands of spheroids can be tracked and leader/follower organization of CAFs and cancer cells can be quantified.

JTD Keywords: 3d spheroid invasion, cancer associated fibroblasts, collective migration, dissemination, epithelial cancer cells, leader/follower cells, 3d spheroid invasion, Cancer associated fibroblasts, Collective invasion, Collective migration, Epithelial cancer cells, Leader/follower cells

© 2020 Elsevier Inc. Severe asthma is associated with an increased airway smooth muscle (ASM) mass and altered composition of the extracellular matrix (ECM). Studies have indicated that ECM-ASM cell interactions contribute to this remodeling and its limited reversibility with current therapy. Three-dimensional matrices allow the study of complex cellular responses to different stimuli in an almost natural environment. Our goal was to obtain acellular bronchial matrices and then develop a recellularization protocol with ASM cells. We studied equine bronchi as horses spontaneously develop a human asthma-like disease. The bronchi were decellularized using Triton/Sodium Deoxycholate. The obtained scaffolds retained their anatomical and histological properties. Using immunohistochemistry and a semi-quantitative score to compare native bronchi to scaffolds revealed no significant variation for matrixial proteins. DNA quantification and electrophoresis revealed that most DNA was 29.6 ng/mg of tissue ± 5.6, with remaining fragments of less than 100 bp. Primary ASM cells were seeded on the scaffolds. Histological analysis of the recellularizations showed that ASM cells migrated and proliferated primarily in the decellularized smooth muscle matrix, suggesting a chemotactic effect of the scaffolds. This is the first report of primary ASM cells preferentially repopulating the smooth muscle matrix layer in bronchial matrices. This protocol is now being used to study the molecular interactions occurring between the asthmatic ECMs and ASM to identify effectors of asthmatic bronchial remodeling.

JTD Keywords: 2d, airway smooth muscle cells, asthma, decellularization, disease, elastin, extracellular matrix, lung scaffolds, migration, peptide, recellularization, tissues, Airway smooth muscle cells, Asthma, Culture-systems, Decellularization, Extracellular matrix, Recellularization

During collective migration of epithelial cells, the migration direction is aligned over a tissue-scale expanse. Although the collective cell migration is known to be directed by mechanical forces transmitted via cell-cell junctions, it remains elusive how the intercellular force transmission is coordinated with intracellular biochemical signaling to achieve collective movements. Here, we show that intercellular coupling of extracellular signal-regulated kinase (ERK)-mediated mechanochemical feedback yields long-distance transmission of guidance cues. Mechanical stretch activates ERK through epidermal growth factor receptor (EGFR) activation, and ERK activation triggers cell contraction. The contraction of the activated cell pulls neighboring cells, evoking another round of ERK activation and contraction in the neighbors. Furthermore, anisotropic contraction based on front-rear polarization guarantees unidirectional propagation of ERK activation, and in turn, the ERK activation waves direct multicellular alignment of the polarity, leading to long-range ordered migration. Our findings reveal that mechanical forces mediate intercellular signaling underlying sustained transmission of guidance cues for collective cell migration.

JTD Keywords: Collective cell migration, EGFR, ERK/MAPK, FRET, Front-rear polarity, Intercellular signal transfer, Mathematical model, Mechanochemical feedback, Mechanotransduction, wave propagation

The isotropic or anisotropic organization of biological extracellular matrices has important consequences for tissue function. We study emergent anisotropy using fibroblasts that generate varying degrees of matrix alignment from uniform starting conditions. This reveals that the early migratory paths of fibroblasts are correlated with subsequent matrix organization. Combined experimentation and adaptation of Vicsek modelling demonstrates that the reorientation of cells relative to each other following collision plays a role in generating matrix anisotropy. We term this behaviour ‘cell collision guidance’. The transcription factor TFAP2C regulates cell collision guidance in part by controlling the expression of RND3. RND3 localizes to cell–cell collision zones where it downregulates actomyosin activity. Cell collision guidance fails without this mechanism in place, leading to isotropic matrix generation. The cross-referencing of alignment and TFAP2C gene expression signatures against existing datasets enables the identification and validation of several classes of pharmacological agents that disrupt matrix anisotropy.

JTD Keywords: Biomaterials – cells, Cell migration, Self-assembly, Tissues

In many solid tumors, collective cell invasion prevails over single-cell dissemination strategies. Collective modes of invasion often display specific front/rear cellular organization, where invasive leader cells arise from cancer cell populations or the tumor stroma. Collective invasion involves coordinated cellular movements which require tight mechanical crosstalk through specific combinations of cell–cell interactions and cell–matrix adhesions. Cancer Associated Fibroblasts (CAFs) have been recently reported to drive the dissemination of epithelial cancer cells through ECM remodeling and direct intercellular contact. However, the cooperation between tumor and stromal cells remains poorly understood. Here we present a simple spheroid invasion assay to assess the role of CAFs in the collective migration of epithelial tumor cells. This method enables the characterization of 3D spheroid invasion patterns through live cell fluorescent labeling combined with spinning disc microscopy. When embedded in extracellular matrix, the invasive strands of spheroids can be tracked and leader/follower organization of CAFs and cancer cells can be quantified.

JTD Keywords: 3D spheroid invasion, Cancer associated fibroblasts, Collective migration, Epithelial cancer cells, Leader/follower cells

Integrins, and integrin-mediated adhesions, have long been recognized to provide the main molecular link attaching cells to the extracellular matrix (ECM) and to serve as bidirectional hubs transmitting signals between cells and their environment. Recent evidence has shown that their combined biochemical and mechanical properties also allow integrins to sense, respond to and interact with ECM of differing properties with exquisite specificity. Here, we review this work first by providing an overview of how integrin function is regulated from both a biochemical and a mechanical perspective, affecting integrin cell-surface availability, binding properties, activation or clustering. Then, we address how this biomechanical regulation allows integrins to respond to different ECM physicochemical properties and signals, such as rigidity, composition and spatial distribution. Finally, we discuss the importance of this sensing for major cell functions by taking cell migration and cancer as examples.

JTD Keywords: Cell migration, Extracellular matrix, Integrins, Mechanotransduction, Single-molecule biophysics

There is emerging evidence that molecules, receptors, and signaling mechanisms involved in vascular development also play crucial roles during the development of the nervous system. Among others, specific semaphorins and their receptors (neuropilins and plexins) have, in recent years, attracted the attention of researchers due to their pleiotropy of functions. Their functions, mainly associated with control of the cellular cytoskeleton, include control of cell migration, cell morphology, and synapse remodeling. Here, we will focus on their roles in the hippocampal formation that plays a crucial role in memory and learning as it is a prime target during neurodegeneration.

JTD Keywords: PlexinD1, Sema3E, Neuropilins, Neuronal migration, Synapse formation

Directed cell migration is essential for many biological processes, such as embryonic development or cancer progression. Cell contractility and adhesion to the extracellular matrix are known to regulate cell locomotion machinery. However, the cross-talk between extrinsic and intrinsic factors at the molecular level on the biophysical mechanism of three dimensional (3D)-directed cell migration is still unclear. In this work, a novel physiologically relevant in vitro model of the extracellular microenvironment is used to reveal how the topological anisotropy of the extracellular matrix synergizes with actomyosin contractility to modulate directional cell migration morphodynamics. This study shows that cells seeded on polarized 3D matrices display asymmetric protrusion morphodynamics and in-vivo-like phenotypes. It is found that matrix anisotropy significantly enhances cell directionality, but strikingly, not the invasion distance of cells. In Rho-inhibited cells, matrix anisotropy counteracts the lack of actomyosin-driven forces to stabilize cell directionality suggesting a myosin-II-independent mechanism for cell guidance. Finally, this study shows that on isotropic 3D environments, cell directionality is independent of actomyosin contractility. Altogether, this study provides novel quantitative data on the biomechanical regulation of directional cell motion and shows the important regulatory role of matrix anisotropy and actomyosin forces to guide cell migration in 3D microenvironments.

JTD Keywords: Anisotropy, Directed cell migration, Extracellular matrices, Migration modes, Three dimensional microenvironments

The interaction of cells with their natural environment influences a large variety of cellular phenomena, including cell adhesion, proliferation, and migration. The complex extracellular matrix network has challenged the attempts to replicate in vitro the heterogeneity of the cell environment and has threatened, in general, the relevance of in vitro studies. In this work, we describe a new and extremely versatile approach to generate native-like extracellular matrices with controlled morphologies for the in vitro study of cellular processes. This general approach combines the confluent culture of fibroblasts with microfabricated guiding templates to direct the three-dimensional growth of well-defined extracellular networks which recapitulate the structural and biomolecular complexity of features typically found in vivo. To evaluate its performance, we studied fundamental cellular processes, including cell cytoskeleton organization, cell-matrix adhesion, proliferation, and protrusions morphodynamics. In all cases, we found striking differences depending on matrix architecture and, in particular, when compared to standard two-dimensional environments. We also assessed whether the engineered matrix networks influenced cell migration dynamics and locomotion strategy, finding enhanced migration efficiency for cells seeded on aligned matrices. Altogether, our methodology paves the way to the development of high-performance models of the extracellular matrix for potential applications in tissue engineering, diagnosis, or stem-cell biology.

JTD Keywords: Biomimetics, Cell migration, Engineered cell-derived matrices, Extracellular matrix, In vitro model

Directed cell migration is a complex process that involves front-rear polarization, characterized by cell adhesion and cytoskeleton-based protrusion, retraction, and contraction of either a single cell or a cell collective. Single cell polarization depends on a variety of mechanochemical signals including external adhesive cues, substrate stiffness, and confinement. In cell ensembles, coordinated polarization of migrating tissues results not only from the application of traction forces on the extracellular matrix but also from the transmission of mechanical stress through intercellular junctions. We focus here on the impact of mechanical cues on the establishment and maintenance of front-rear polarization from single cell to collective cell behaviors through local or large-scale mechanisms.

JTD Keywords: Cell forces, Cell polarity, Collective cell migration, Mechanobiology, Micropatterning, Substrate stiffness

In the mammalian telencephalon, part of the progenitor cells transition from multipolar to bipolar morphology as they invade the mantle zone. This associates with changing patterns of radial migration. However, the molecules implicated in these morphology transitions are not well known. In the present work, we analyzed the function of FoxP2 protein in this process during telencephalic development in vertebrates. We analyzed the expression of FoxP2 protein and its relation with cell morphology and migratory patterns in mouse and chicken developing striatum. We observed FoxP2 protein expressed in a gradient from the subventricular zone to the mantle layer in mice embryos. In the FoxP2 low domain cells showed multipolar migration. In the striatal mantle layer where FoxP2 protein expression is higher, cells showed locomoting migration and bipolar morphology. In contrast, FoxP2 showed a high and homogenous expression pattern in chicken striatum, thus bipolar morphology predominated. Elevation of FoxP2 in the striatal subventricular zone by in utero electroporation promoted bipolar morphology and impaired multipolar radial migration. In mouse cerebral cortex we obtained similar results. FoxP2 promotes transition from multipolar to bipolar morphology by means of gradiental expression in mouse striatum and cortex. Together these results indicate a role of FoxP2 differential expression in cell morphology control of the vertebrate telencephalon.

JTD Keywords: Radial migration, Bipolar morphology, Striatum, Cortex

Evidence of guest migration in α-cyclodextrin-octylamine (α-CD-OA) inclusion compound (IC) generated via plasmonic heating of gold nanoparticles (AuNPs) has been studied. In this report, we demonstrate local effects generated by laser-mediated irradiation of a sample of AuNPs covered with inclusion compounds on surface-derivatized glass under liquid conditions by atomic force microscopy (AFM). Functionalized AuNPs on the glass and covered by the ICs were monitored by recording images by AFM during 5 h of irradiation, and images showed that after irradiation, a drastic decrease in the height of the AuNPs occurred. The absorption spectrum of the irradiated sample showed a hypsochromic shift from 542 to 536 nm, evidence suggesting that much of the population of nanoparticles lost all of the parts of the overlay of ICs due to the plasmonic heat generated by the irradiation. Mass spectrometry matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) performed on a sample containing a collection of drops obtained from the surface of the functionalized glass provided evidence that the irradiation lead to disintegration of the ICs and therefore exit of the octylamine molecule (the guest) from the cyclodextrin cavity (the matrix).

JTD Keywords: Cyclodextrin inclusion compound, Gold nanoparticles, Guest migration, Plasmonic heating

Olfactory ensheathing cell (OEC) transplantation emerged some years ago as a promising therapeutic strategy to repair injured spinal cord. However, inhibitory molecules are present for long periods of time in lesioned spinal cord, inhibiting both OEC migration and axonal regrowth. Two families of these molecules, chondroitin sulphate proteoglycans (CSPG) and myelin-derived inhibitors (MAIs), are able to trigger inhibitory responses in lesioned axons. Mounting evidence suggests that OEC migration is inhibited by myelin. Here we demonstrate that OEC migration is largely inhibited by CSPGs and that inhibition can be overcome by the bacterial enzyme Chondroitinase ABC. In parallel, we have generated a stable OEC cell line overexpressing the Nogo receptor (NgR) ectodomain to reduce MAI-associated inhibition in vitro and in vivo. Results indicate that engineered cells migrate longer distances than unmodified OECs over myelin or oligodendrocyte-myelin glycoprotein (OMgp)-coated substrates. In addition, they also show improved migration in lesioned spinal cord. Our results provide new insights toward the improvement of the mechanisms of action and optimization of OEC-based cell therapy for spinal cord lesion.

JTD Keywords: Olfactory ensheathing cells, Traction force microscopy, Chondroitin sulphate proteoglycans, Cell migration, Nogo receptor ectodomain

Calcium signaling participates in different cellular processes leading to cell migration. TRPV4, a non-selective cation channel that responds to mechano-osmotic stimulation and heat, is also involved in cell migration. However, the mechanistic involvement of TRPV4 in cell migration is currently unknown. We now report that expression of the mutant channel TRPV4-121AAWAA (lacking the phosphoinositide-binding site 121KRWRK125 and the response to physiological stimuli) altered HEK293 cell migration. Altered migration patterns included periods of fast and persistent motion followed by periods of stalling and turning, and the extension of multiple long cellular protrusions. TRPV4-WT overexpressing cells showed almost complete loss of directionality with frequent turns, no progression, and absence of long protrusions. Traction microscopy revealed higher tractions forces in the tail of TRPV4-121AAWAA than in TRPV4-WT expressing cells. These results are consistent with a defective and augmented tail retraction in TRPV4-121AAWAA- and TRPV4-WT-expressing cells, respectively. The activity of calpain, a protease implicated in focal adhesion (FA) disassembly, was decreased in TRPV4-121AAWAA compared with TRPV4-WT-expressing cells. Consistently, larger focal adhesions were seen in TRPV4-121AAWAA compared with TRPV4-WT-expressing HEK293 cells, a result that was also reproduced in T47D and U87 cells. Similarly, overexpression of the pore-dead mutant TRPV4-M680D resumed the TRPV4-121AAWAA phenotype presenting larger FA. The migratory phenotype obtained in HEK293 cells overexpressing TRPV4-121AAWAA was mimicked by knocking-down TRPC1, a cationic channel that participates in cell migration. Together, our results point to the participation of TRPV4 in the dynamics of trailing adhesions, a function that may require the interplay of TRPV4 with other cation channels or proteins present at the FA sites.

JTD Keywords: Calcium, Calpain, Focal adhesion, Migration, Traction forces, TRPV4

It is known that cells respond strongly to microtopography. However, cellular mechanisms of response are unclear. Here, we study wild-type fibroblasts responding to 25 μm2 posts and compare their response to that of FAK-/- fibroblasts and fibroblasts with PMA treatment to stimulate protein kinase C (PKC) and the small g-protein Rac. FAK knockout cells modulated adhesion number and size in a similar way to cells on topography; that is, they used more, smaller adhesions, but migration was almost completely stalled demonstrating the importance of FAK signaling in contact guidance and adhesion turnover. Little similarity, however, was observed to PKC stimulated cells and cells on the topography. Interestingly, with PKC stimulation the cell nuclei became highly deformable bringing focus on these surfaces to the study of metastasis. Surfaces that aid the study of cellular migration are important in developing understanding of mechanisms of wound healing and repair in aligned tissues such as ligament and tendon.

JTD Keywords: Adhesion, Cell migration, Cell morphology, Focal adhesion kinase, Microstructures

Abstract Fundamental biological processes including morphogenesis and tissue repair require cells to migrate collectively. In these processes, epithelial or endothelial cells move in a cooperative manner coupled by intercellular junctions. Ultimately, the movement of these multicellular systems occurs through the generation of cellular forces, exerted either on the substrate via focal adhesions (cell–substrate forces) or on neighboring cells through cell–cell junctions (cell–cell forces). Quantitative measurements of multicellular forces and kinematics with cellular or subcellular resolution have become possible only in recent years. In this chapter, we describe some of these techniques, which include particle image velocimetry to map cell velocities, traction force microscopy to map forces exerted by cells on the substrate, and monolayer stress microscopy to map forces within and between cells. We also describe experimental protocols to perform these measurements. The combination of these techniques with high-resolution imaging tools and molecular perturbations will lead to a better understanding of the mechanisms underlying collective cell migration in health and disease.

JTD Keywords: Collective cell migration, Monolayer stress microscopy, Traction force microscopy

Newly generated olfactory receptor axons grow from the peripheral to the central nervous system aided by olfactory ensheathing cells (OECs). Thus, OEC transplantation has emerged as a promising therapy for spinal cord injuries and for other neural diseases. However, these cells do not present a uniform population, but instead a functionally heterogeneous population that exhibits a variety of responses including adhesion, repulsion, and crossover during cell–cell and cell–matrix interactions. Some studies report that the migratory properties of OECs are compromised by inhibitory molecules and potentiated by chemical gradients. Here, we demonstrated that rodent OECs express all the components of the Nogo receptor complex and that their migration is blocked by myelin. Next, we used cell tracking and traction force microscopy to analyze OEC migration and its mechanical properties over myelin. Our data relate the decrease of traction force of OEC with lower migratory capacity over myelin, which correlates with changes in the F-actin cytoskeleton and focal adhesion distribution. Lastly, OEC traction force and migratory capacity is enhanced after cell incubation with the Nogo receptor inhibitor NEP1-40.

JTD Keywords: Ensheathing glia, Traction force, microscopy, Migration, Myelin-associated inhibitors

In this work, we propose an easy method to produce highly tunable gradients of covalently bound proteins on topographically modified poly(methyl methacrylate). We used a rnicrofluidic approach to obtain linear gradients with high slope (0.5 pmol.cm(-2).mm(-1)), relevant at the single-cell level. These protein gradients were characterized using fluorescence microscopy and surface plasmon resonance. Both experimental results and theoretical modeling on the protein gradients generated have proved them to be highly reproducible, stable up to 7 days, and easily tunable. This method enables formation of versatile cell culture platforms combining both complex biochemical and physical cues in an attempt to approach in vitro cell culture methods to in vivo cellular microenvironments.

JTD Keywords: Cell-migration, Microfluidic channel, Surface, Streptavidin, Molecules, Topography, Mechanisms, Generation, Responses, Guidance

For a monolayer sheet to migrate cohesively, it has long been suspected that each constituent cell must exert physical forces not only upon its extracellular matrix but also upon neighboring cells. The first comprehensive maps of these distinct force components reveal an unexpected physical picture. Rather than showing smooth and systematic variation within the monolayer, the distribution of physical forces is dominated by heterogeneity, both in space and in time, which emerges spontaneously, propagates over great distances, and cooperates over the span of many cell bodies. To explain the severe ruggedness of this force landscape and its role in collective cell guidance, the well known mechanisms of chemotaxis, durotaxis, haptotaxis are clearly insufficient. In a broad range of epithelial and endothelial cell sheets, collective cell migration is governed instead by a newly discovered emergent mechanism of innately collective cell guidance - plithotaxis.

JTD Keywords: Positional information, Drosophila embryo, Sheet migration, Dpp gradient, Cells, Force, Morphogenesis, Transition, Identification, Proliferation