@article{14795, abstract = {Metazoan development relies on the formation and remodeling of cell-cell contacts. Dynamic reorganization of adhesion receptors and the actomyosin cell cortex in space and time plays a central role in cell-cell contact formation and maturation. Nevertheless, how this process is mechanistically achieved when new contacts are formed remains unclear. Here, by building a biomimetic assay composed of progenitor cells adhering to supported lipid bilayers functionalized with E-cadherin ectodomains, we show that cortical F-actin flows, driven by the depletion of myosin-2 at the cell contact center, mediate the dynamic reorganization of adhesion receptors and cell cortex at the contact. E-cadherin-dependent downregulation of the small GTPase RhoA at the forming contact leads to both a depletion of myosin-2 and a decrease of F-actin at the contact center. At the contact rim, in contrast, myosin-2 becomes enriched by the retraction of bleb-like protrusions, resulting in a cortical tension gradient from the contact rim to its center. This tension gradient, in turn, triggers centrifugal F-actin flows, leading to further accumulation of F-actin at the contact rim and the progressive redistribution of E-cadherin from the contact center to the rim. Eventually, this combination of actomyosin downregulation and flows at the contact determines the characteristic molecular organization, with E-cadherin and F-actin accumulating at the contact rim, where they are needed to mechanically link the contractile cortices of the adhering cells.}, author = {Arslan, Feyza N and Hannezo, Edouard B and Merrin, Jack and Loose, Martin and Heisenberg, Carl-Philipp J}, issn = {1879-0445}, journal = {Current Biology}, number = {1}, pages = {171--182.e8}, publisher = {Elsevier}, title = {{Adhesion-induced cortical flows pattern E-cadherin-mediated cell contacts}}, doi = {10.1016/j.cub.2023.11.067}, volume = {34}, year = {2024}, } @article{14846, abstract = {Contraction and flow of the actin cell cortex have emerged as a common principle by which cells reorganize their cytoplasm and take shape. However, how these cortical flows interact with adjacent cytoplasmic components, changing their form and localization, and how this affects cytoplasmic organization and cell shape remains unclear. Here we show that in ascidian oocytes, the cooperative activities of cortical actomyosin flows and deformation of the adjacent mitochondria-rich myoplasm drive oocyte cytoplasmic reorganization and shape changes following fertilization. We show that vegetal-directed cortical actomyosin flows, established upon oocyte fertilization, lead to both the accumulation of cortical actin at the vegetal pole of the zygote and compression and local buckling of the adjacent elastic solid-like myoplasm layer due to friction forces generated at their interface. Once cortical flows have ceased, the multiple myoplasm buckles resolve into one larger buckle, which again drives the formation of the contraction pole—a protuberance of the zygote’s vegetal pole where maternal mRNAs accumulate. Thus, our findings reveal a mechanism where cortical actomyosin network flows determine cytoplasmic reorganization and cell shape by deforming adjacent cytoplasmic components through friction forces.}, author = {Caballero Mancebo, Silvia and Shinde, Rushikesh and Bolger-Munro, Madison and Peruzzo, Matilda and Szep, Gregory and Steccari, Irene and Labrousse Arias, David and Zheden, Vanessa and Merrin, Jack and Callan-Jones, Andrew and Voituriez, Raphaël and Heisenberg, Carl-Philipp J}, issn = {1745-2481}, journal = {Nature Physics}, publisher = {Springer Nature}, title = {{Friction forces determine cytoplasmic reorganization and shape changes of ascidian oocytes upon fertilization}}, doi = {10.1038/s41567-023-02302-1}, year = {2024}, } @inbook{13052, abstract = {Imaging of the immunological synapse (IS) between dendritic cells (DCs) and T cells in suspension is hampered by suboptimal alignment of cell-cell contacts along the vertical imaging plane. This requires optical sectioning that often results in unsatisfactory resolution in time and space. Here, we present a workflow where DCs and T cells are confined between a layer of glass and polydimethylsiloxane (PDMS) that orients the cells along one, horizontal imaging plane, allowing for fast en-face-imaging of the DC-T cell IS.}, author = {Leithner, Alexander F and Merrin, Jack and Sixt, Michael K}, booktitle = {The Immune Synapse}, editor = {Baldari, Cosima and Dustin, Michael}, isbn = {9781071631348}, issn = {1940-6029}, pages = {137--147}, publisher = {Springer Nature}, title = {{En-Face Imaging of T Cell-Dendritic Cell Immunological Synapses}}, doi = {10.1007/978-1-0716-3135-5_9}, volume = {2654}, year = {2023}, } @article{13342, abstract = {Motile cells moving in multicellular organisms encounter microenvironments of locally heterogeneous mechanochemical composition. Individual compositional parameters like chemotactic signals, adhesiveness, and pore sizes are well known to be sensed by motile cells, providing individual guidance cues for cellular pathfinding. However, motile cells encounter diverse mechanochemical signals at the same time, raising the question of how cells respond to locally diverse and potentially competing signals on their migration routes. Here, we reveal that motile amoeboid cells require nuclear repositioning, termed nucleokinesis, for adaptive pathfinding in heterogeneous mechanochemical microenvironments. Using mammalian immune cells and the amoebaDictyostelium discoideum, we discover that frequent, rapid and long-distance nucleokinesis is a basic component of amoeboid pathfinding, enabling cells to reorientate quickly between locally competing cues. Amoeboid nucleokinesis comprises a two-step cell polarity switch and is driven by myosin II-forces, sliding the nucleus from a ‘losing’ to the ‘winning’ leading edge to re-adjust the nuclear to the cellular path. Impaired nucleokinesis distorts fast path adaptions and causes cellular arrest in the microenvironment. Our findings establish that nucleokinesis is required for amoeboid cell navigation. Given that motile single-cell amoebae, many immune cells, and some cancer cells utilize an amoeboid migration strategy, these results suggest that amoeboid nucleokinesis underlies cellular navigation during unicellular biology, immunity, and disease.}, author = {Kroll, Janina and Hauschild, Robert and Kuznetcov, Arthur and Stefanowski, Kasia and Hermann, Monika D. and Merrin, Jack and Shafeek, Lubuna B and Müller-Taubenberger, Annette and Renkawitz, Jörg}, issn = {1460-2075}, journal = {EMBO Journal}, publisher = {Embo Press}, title = {{Adaptive pathfinding by nucleokinesis during amoeboid migration}}, doi = {10.15252/embj.2023114557}, year = {2023}, } @article{14361, abstract = {Whether one considers swarming insects, flocking birds, or bacterial colonies, collective motion arises from the coordination of individuals and entails the adjustment of their respective velocities. In particular, in close confinements, such as those encountered by dense cell populations during development or regeneration, collective migration can only arise coordinately. Yet, how individuals unify their velocities is often not understood. Focusing on a finite number of cells in circular confinements, we identify waves of polymerizing actin that function as a pacemaker governing the speed of individual cells. We show that the onset of collective motion coincides with the synchronization of the wave nucleation frequencies across the population. Employing a simpler and more readily accessible mechanical model system of active spheres, we identify the synchronization of the individuals’ internal oscillators as one of the essential requirements to reach the corresponding collective state. The mechanical ‘toy’ experiment illustrates that the global synchronous state is achieved by nearest neighbor coupling. We suggest by analogy that local coupling and the synchronization of actin waves are essential for the emergent, self-organized motion of cell collectives.}, author = {Riedl, Michael and Mayer, Isabelle D and Merrin, Jack and Sixt, Michael K and Hof, Björn}, issn = {2041-1723}, journal = {Nature Communications}, publisher = {Springer Nature}, title = {{Synchronization in collectively moving inanimate and living active matter}}, doi = {10.1038/s41467-023-41432-1}, volume = {14}, year = {2023}, } @article{14274, abstract = {Immune responses rely on the rapid and coordinated migration of leukocytes. Whereas it is well established that single-cell migration is often guided by gradients of chemokines and other chemoattractants, it remains poorly understood how these gradients are generated, maintained, and modulated. By combining experimental data with theory on leukocyte chemotaxis guided by the G protein–coupled receptor (GPCR) CCR7, we demonstrate that in addition to its role as the sensory receptor that steers migration, CCR7 also acts as a generator and a modulator of chemotactic gradients. Upon exposure to the CCR7 ligand CCL19, dendritic cells (DCs) effectively internalize the receptor and ligand as part of the canonical GPCR desensitization response. We show that CCR7 internalization also acts as an effective sink for the chemoattractant, dynamically shaping the spatiotemporal distribution of the chemokine. This mechanism drives complex collective migration patterns, enabling DCs to create or sharpen chemotactic gradients. We further show that these self-generated gradients can sustain the long-range guidance of DCs, adapt collective migration patterns to the size and geometry of the environment, and provide a guidance cue for other comigrating cells. Such a dual role of CCR7 as a GPCR that both senses and consumes its ligand can thus provide a novel mode of cellular self-organization.}, author = {Alanko, Jonna H and Ucar, Mehmet C and Canigova, Nikola and Stopp, Julian A and Schwarz, Jan and Merrin, Jack and Hannezo, Edouard B and Sixt, Michael K}, issn = {2470-9468}, journal = {Science Immunology}, keywords = {General Medicine, Immunology}, number = {87}, publisher = {American Association for the Advancement of Science}, title = {{CCR7 acts as both a sensor and a sink for CCL19 to coordinate collective leukocyte migration}}, doi = {10.1126/sciimmunol.adc9584}, volume = {8}, year = {2023}, } @article{11182, abstract = {Immune cells are constantly on the move through multicellular organisms to explore and respond to pathogens and other harmful insults. While moving, immune cells efficiently traverse microenvironments composed of tissue cells and extracellular fibers, which together form complex environments of various porosity, stiffness, topography, and chemical composition. In this protocol we describe experimental procedures to investigate immune cell migration through microenvironments of heterogeneous porosity. In particular, we describe micro-channels, micro-pillars, and collagen networks as cell migration paths with alternative pore size choices. Employing micro-channels or micro-pillars that divide at junctions into alternative paths with initially differentially sized pores allows us to precisely (1) measure the cellular translocation time through these porous path junctions, (2) quantify the cellular preference for individual pore sizes, and (3) image cellular components like the nucleus and the cytoskeleton. This reductionistic experimental setup thus can elucidate how immune cells perform decisions in complex microenvironments of various porosity like the interstitium. The setup further allows investigation of the underlying forces of cellular squeezing and the consequences of cellular deformation on the integrity of the cell and its organelles. As a complementary approach that does not require any micro-engineering expertise, we describe the usage of three-dimensional collagen networks with different pore sizes. Whereas we here focus on dendritic cells as a model for motile immune cells, the described protocols are versatile as they are also applicable for other immune cell types like neutrophils and non-immune cell types such as mesenchymal and cancer cells. In summary, we here describe protocols to identify the mechanisms and principles of cellular probing, decision making, and squeezing during cellular movement through microenvironments of heterogeneous porosity.}, author = {Kroll, Janina and Ruiz-Fernandez, Mauricio J.A. and Braun, Malte B. and Merrin, Jack and Renkawitz, Jörg}, issn = {2691-1299}, journal = {Current Protocols}, number = {4}, publisher = {Wiley}, title = {{Quantifying the probing and selection of microenvironmental pores by motile immune cells}}, doi = {10.1002/cpz1.407}, volume = {2}, year = {2022}, } @article{10766, abstract = {Tension of the actomyosin cell cortex plays a key role in determining cell–cell contact growth and size. The level of cortical tension outside of the cell–cell contact, when pulling at the contact edge, scales with the total size to which a cell–cell contact can grow [J.-L. Maître et al., Science 338, 253–256 (2012)]. Here, we show in zebrafish primary germ-layer progenitor cells that this monotonic relationship only applies to a narrow range of cortical tension increase and that above a critical threshold, contact size inversely scales with cortical tension. This switch from cortical tension increasing to decreasing progenitor cell–cell contact size is caused by cortical tension promoting E-cadherin anchoring to the actomyosin cytoskeleton, thereby increasing clustering and stability of E-cadherin at the contact. After tension-mediated E-cadherin stabilization at the contact exceeds a critical threshold level, the rate by which the contact expands in response to pulling forces from the cortex sharply drops, leading to smaller contacts at physiologically relevant timescales of contact formation. Thus, the activity of cortical tension in expanding cell–cell contact size is limited by tension-stabilizing E-cadherin–actin complexes at the contact.}, author = {Slovakova, Jana and Sikora, Mateusz K and Arslan, Feyza N and Caballero Mancebo, Silvia and Krens, Gabriel and Kaufmann, Walter and Merrin, Jack and Heisenberg, Carl-Philipp J}, issn = {10916490}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, number = {8}, publisher = {Proceedings of the National Academy of Sciences}, title = {{Tension-dependent stabilization of E-cadherin limits cell-cell contact expansion in zebrafish germ-layer progenitor cells}}, doi = {10.1073/pnas.2122030119}, volume = {119}, year = {2022}, } @article{12259, abstract = {Theoretical foundations of chaos have been predominantly laid out for finite-dimensional dynamical systems, such as the three-body problem in classical mechanics and the Lorenz model in dissipative systems. In contrast, many real-world chaotic phenomena, e.g., weather, arise in systems with many (formally infinite) degrees of freedom, which limits direct quantitative analysis of such systems using chaos theory. In the present work, we demonstrate that the hydrodynamic pilot-wave systems offer a bridge between low- and high-dimensional chaotic phenomena by allowing for a systematic study of how the former connects to the latter. Specifically, we present experimental results, which show the formation of low-dimensional chaotic attractors upon destabilization of regular dynamics and a final transition to high-dimensional chaos via the merging of distinct chaotic regions through a crisis bifurcation. Moreover, we show that the post-crisis dynamics of the system can be rationalized as consecutive scatterings from the nonattracting chaotic sets with lifetimes following exponential distributions. }, author = {Choueiri, George H and Suri, Balachandra and Merrin, Jack and Serbyn, Maksym and Hof, Björn and Budanur, Nazmi B}, issn = {1089-7682}, journal = {Chaos: An Interdisciplinary Journal of Nonlinear Science}, keywords = {Applied Mathematics, General Physics and Astronomy, Mathematical Physics, Statistical and Nonlinear Physics}, number = {9}, publisher = {AIP Publishing}, title = {{Crises and chaotic scattering in hydrodynamic pilot-wave experiments}}, doi = {10.1063/5.0102904}, volume = {32}, year = {2022}, } @article{10703, abstract = {When crawling through the body, leukocytes often traverse tissues that are densely packed with extracellular matrix and other cells, and this raises the question: How do leukocytes overcome compressive mechanical loads? Here, we show that the actin cortex of leukocytes is mechanoresponsive and that this responsiveness requires neither force sensing via the nucleus nor adhesive interactions with a substrate. Upon global compression of the cell body as well as local indentation of the plasma membrane, Wiskott-Aldrich syndrome protein (WASp) assembles into dot-like structures, providing activation platforms for Arp2/3 nucleated actin patches. These patches locally push against the external load, which can be obstructing collagen fibers or other cells, and thereby create space to facilitate forward locomotion. We show in vitro and in vivo that this WASp function is rate limiting for ameboid leukocyte migration in dense but not in loose environments and is required for trafficking through diverse tissues such as skin and lymph nodes.}, author = {Gaertner, Florian and Reis-Rodrigues, Patricia and De Vries, Ingrid and Hons, Miroslav and Aguilera, Juan and Riedl, Michael and Leithner, Alexander F and Tasciyan, Saren and Kopf, Aglaja and Merrin, Jack and Zheden, Vanessa and Kaufmann, Walter and Hauschild, Robert and Sixt, Michael K}, issn = {1878-1551}, journal = {Developmental Cell}, number = {1}, pages = {47--62.e9}, publisher = {Cell Press ; Elsevier}, title = {{WASp triggers mechanosensitive actin patches to facilitate immune cell migration in dense tissues}}, doi = {10.1016/j.devcel.2021.11.024}, volume = {57}, year = {2022}, } @article{10223, abstract = {Growth regulation tailors development in plants to their environment. A prominent example of this is the response to gravity, in which shoots bend up and roots bend down1. This paradox is based on opposite effects of the phytohormone auxin, which promotes cell expansion in shoots while inhibiting it in roots via a yet unknown cellular mechanism2. Here, by combining microfluidics, live imaging, genetic engineering and phosphoproteomics in Arabidopsis thaliana, we advance understanding of how auxin inhibits root growth. We show that auxin activates two distinct, antagonistically acting signalling pathways that converge on rapid regulation of apoplastic pH, a causative determinant of growth. Cell surface-based TRANSMEMBRANE KINASE1 (TMK1) interacts with and mediates phosphorylation and activation of plasma membrane H+-ATPases for apoplast acidification, while intracellular canonical auxin signalling promotes net cellular H+ influx, causing apoplast alkalinization. Simultaneous activation of these two counteracting mechanisms poises roots for rapid, fine-tuned growth modulation in navigating complex soil environments.}, author = {Li, Lanxin and Verstraeten, Inge and Roosjen, Mark and Takahashi, Koji and Rodriguez Solovey, Lesia and Merrin, Jack and Chen, Jian and Shabala, Lana and Smet, Wouter and Ren, Hong and Vanneste, Steffen and Shabala, Sergey and De Rybel, Bert and Weijers, Dolf and Kinoshita, Toshinori and Gray, William M. and Friml, Jiří}, issn = {14764687}, journal = {Nature}, keywords = {Multidisciplinary}, number = {7884}, pages = {273--277}, publisher = {Springer Nature}, title = {{Cell surface and intracellular auxin signalling for H+ fluxes in root growth}}, doi = {10.1038/s41586-021-04037-6}, volume = {599}, year = {2021}, } @unpublished{10095, abstract = {Growth regulation tailors plant development to its environment. A showcase is response to gravity, where shoots bend up and roots down1. This paradox is based on opposite effects of the phytohormone auxin, which promotes cell expansion in shoots, while inhibiting it in roots via a yet unknown cellular mechanism2. Here, by combining microfluidics, live imaging, genetic engineering and phospho-proteomics in Arabidopsis thaliana, we advance our understanding how auxin inhibits root growth. We show that auxin activates two distinct, antagonistically acting signalling pathways that converge on the rapid regulation of the apoplastic pH, a causative growth determinant. Cell surface-based TRANSMEMBRANE KINASE1 (TMK1) interacts with and mediates phosphorylation and activation of plasma membrane H+-ATPases for apoplast acidification, while intracellular canonical auxin signalling promotes net cellular H+-influx, causing apoplast alkalinisation. The simultaneous activation of these two counteracting mechanisms poises the root for a rapid, fine-tuned growth modulation while navigating complex soil environment.}, author = {Li, Lanxin and Verstraeten, Inge and Roosjen, Mark and Takahashi, Koji and Rodriguez Solovey, Lesia and Merrin, Jack and Chen, Jian and Shabala, Lana and Smet, Wouter and Ren, Hong and Vanneste, Steffen and Shabala, Sergey and De Rybel, Bert and Weijers, Dolf and Kinoshita, Toshinori and Gray, William M. and Friml, Jiří}, booktitle = {Research Square}, issn = {2693-5015}, title = {{Cell surface and intracellular auxin signalling for H+-fluxes in root growth}}, doi = {10.21203/rs.3.rs-266395/v3}, year = {2021}, } @article{7875, abstract = {Cells navigating through complex tissues face a fundamental challenge: while multiple protrusions explore different paths, the cell needs to avoid entanglement. How a cell surveys and then corrects its own shape is poorly understood. Here, we demonstrate that spatially distinct microtubule dynamics regulate amoeboid cell migration by locally promoting the retraction of protrusions. In migrating dendritic cells, local microtubule depolymerization within protrusions remote from the microtubule organizing center triggers actomyosin contractility controlled by RhoA and its exchange factor Lfc. Depletion of Lfc leads to aberrant myosin localization, thereby causing two effects that rate-limit locomotion: (1) impaired cell edge coordination during path finding and (2) defective adhesion resolution. Compromised shape control is particularly hindering in geometrically complex microenvironments, where it leads to entanglement and ultimately fragmentation of the cell body. We thus demonstrate that microtubules can act as a proprioceptive device: they sense cell shape and control actomyosin retraction to sustain cellular coherence.}, author = {Kopf, Aglaja and Renkawitz, Jörg and Hauschild, Robert and Girkontaite, Irute and Tedford, Kerry and Merrin, Jack and Thorn-Seshold, Oliver and Trauner, Dirk and Häcker, Hans and Fischer, Klaus Dieter and Kiermaier, Eva and Sixt, Michael K}, issn = {1540-8140}, journal = {The Journal of Cell Biology}, number = {6}, publisher = {Rockefeller University Press}, title = {{Microtubules control cellular shape and coherence in amoeboid migrating cells}}, doi = {10.1083/jcb.201907154}, volume = {219}, year = {2020}, } @article{8597, abstract = {Error analysis and data visualization of positive COVID-19 cases in 27 countries have been performed up to August 8, 2020. This survey generally observes a progression from early exponential growth transitioning to an intermediate power-law growth phase, as recently suggested by Ziff and Ziff. The occurrence of logistic growth after the power-law phase with lockdowns or social distancing may be described as an effect of avoidance. A visualization of the power-law growth exponent over short time windows is qualitatively similar to the Bhatia visualization for pandemic progression. Visualizations like these can indicate the onset of second waves and may influence social policy.}, author = {Merrin, Jack}, issn = {14783975}, journal = {Physical Biology}, number = {6}, publisher = {IOP Publishing}, title = {{Differences in power law growth over time and indicators of COVID-19 pandemic progression worldwide}}, doi = {10.1088/1478-3975/abb2db}, volume = {17}, year = {2020}, } @article{7885, abstract = {Eukaryotic cells migrate by coupling the intracellular force of the actin cytoskeleton to the environment. While force coupling is usually mediated by transmembrane adhesion receptors, especially those of the integrin family, amoeboid cells such as leukocytes can migrate extremely fast despite very low adhesive forces1. Here we show that leukocytes cannot only migrate under low adhesion but can also transmit forces in the complete absence of transmembrane force coupling. When confined within three-dimensional environments, they use the topographical features of the substrate to propel themselves. Here the retrograde flow of the actin cytoskeleton follows the texture of the substrate, creating retrograde shear forces that are sufficient to drive the cell body forwards. Notably, adhesion-dependent and adhesion-independent migration are not mutually exclusive, but rather are variants of the same principle of coupling retrograde actin flow to the environment and thus can potentially operate interchangeably and simultaneously. As adhesion-free migration is independent of the chemical composition of the environment, it renders cells completely autonomous in their locomotive behaviour.}, author = {Reversat, Anne and Gärtner, Florian R and Merrin, Jack and Stopp, Julian A and Tasciyan, Saren and Aguilera Servin, Juan L and De Vries, Ingrid and Hauschild, Robert and Hons, Miroslav and Piel, Matthieu and Callan-Jones, Andrew and Voituriez, Raphael and Sixt, Michael K}, issn = {14764687}, journal = {Nature}, pages = {582–585}, publisher = {Springer Nature}, title = {{Cellular locomotion using environmental topography}}, doi = {10.1038/s41586-020-2283-z}, volume = {582}, year = {2020}, } @article{7225, abstract = {This is a literature teaching resource review for biologically inspired microfluidics courses or exploring the diverse applications of microfluidics. The structure is around key papers and model organisms. While courses gradually change over time, a focus remains on understanding how microfluidics has developed as well as what it can and cannot do for researchers. As a primary starting point, we cover micro-fluid mechanics principles and microfabrication of devices. A variety of applications are discussed using model prokaryotic and eukaryotic organisms from the set of bacteria (Escherichia coli), trypanosomes (Trypanosoma brucei), yeast (Saccharomyces cerevisiae), slime molds (Physarum polycephalum), worms (Caenorhabditis elegans), flies (Drosophila melangoster), plants (Arabidopsis thaliana), and mouse immune cells (Mus musculus). Other engineering and biochemical methods discussed include biomimetics, organ on a chip, inkjet, droplet microfluidics, biotic games, and diagnostics. While we have not yet reached the end-all lab on a chip, microfluidics can still be used effectively for specific applications.}, author = {Merrin, Jack}, issn = {23065354}, journal = {Bioengineering}, number = {4}, publisher = {MDPI}, title = {{Frontiers in microfluidics, a teaching resource review}}, doi = {10.3390/bioengineering6040109}, volume = {6}, year = {2019}, } @article{6328, abstract = {During metazoan development, immune surveillance and cancer dissemination, cells migrate in complex three-dimensional microenvironments1,2,3. These spaces are crowded by cells and extracellular matrix, generating mazes with differently sized gaps that are typically smaller than the diameter of the migrating cell4,5. Most mesenchymal and epithelial cells and some—but not all—cancer cells actively generate their migratory path using pericellular tissue proteolysis6. By contrast, amoeboid cells such as leukocytes use non-destructive strategies of locomotion7, raising the question how these extremely fast cells navigate through dense tissues. Here we reveal that leukocytes sample their immediate vicinity for large pore sizes, and are thereby able to choose the path of least resistance. This allows them to circumnavigate local obstacles while effectively following global directional cues such as chemotactic gradients. Pore-size discrimination is facilitated by frontward positioning of the nucleus, which enables the cells to use their bulkiest compartment as a mechanical gauge. Once the nucleus and the closely associated microtubule organizing centre pass the largest pore, cytoplasmic protrusions still lingering in smaller pores are retracted. These retractions are coordinated by dynamic microtubules; when microtubules are disrupted, migrating cells lose coherence and frequently fragment into migratory cytoplasmic pieces. As nuclear positioning in front of the microtubule organizing centre is a typical feature of amoeboid migration, our findings link the fundamental organization of cellular polarity to the strategy of locomotion.}, author = {Renkawitz, Jörg and Kopf, Aglaja and Stopp, Julian A and de Vries, Ingrid and Driscoll, Meghan K. and Merrin, Jack and Hauschild, Robert and Welf, Erik S. and Danuser, Gaudenz and Fiolka, Reto and Sixt, Michael K}, journal = {Nature}, pages = {546--550}, publisher = {Springer Nature}, title = {{Nuclear positioning facilitates amoeboid migration along the path of least resistance}}, doi = {10.1038/s41586-019-1087-5}, volume = {568}, year = {2019}, } @inbook{153, abstract = {Cells migrating in multicellular organisms steadily traverse complex three-dimensional (3D) environments. To decipher the underlying cell biology, current experimental setups either use simplified 2D, tissue-mimetic 3D (e.g., collagen matrices) or in vivo environments. While only in vivo experiments are truly physiological, they do not allow for precise manipulation of environmental parameters. 2D in vitro experiments do allow mechanical and chemical manipulations, but increasing evidence demonstrates substantial differences of migratory mechanisms in 2D and 3D. Here, we describe simple, robust, and versatile “pillar forests” to investigate cell migration in complex but fully controllable 3D environments. Pillar forests are polydimethylsiloxane-based setups, in which two closely adjacent surfaces are interconnected by arrays of micrometer-sized pillars. Changing the pillar shape, size, height and the inter-pillar distance precisely manipulates microenvironmental parameters (e.g., pore sizes, micro-geometry, micro-topology), while being easily combined with chemotactic cues, surface coatings, diverse cell types and advanced imaging techniques. Thus, pillar forests combine the advantages of 2D cell migration assays with the precise definition of 3D environmental parameters.}, author = {Renkawitz, Jörg and Reversat, Anne and Leithner, Alexander F and Merrin, Jack and Sixt, Michael K}, booktitle = {Methods in Cell Biology}, issn = {0091679X}, pages = {79 -- 91}, publisher = {Academic Press}, title = {{Micro-engineered “pillar forests” to study cell migration in complex but controlled 3D environments}}, doi = {10.1016/bs.mcb.2018.07.004}, volume = {147}, year = {2018}, } @article{192, abstract = {The phytohormone auxin is the information carrier in a plethora of developmental and physiological processes in plants(1). It has been firmly established that canonical, nuclear auxin signalling acts through regulation of gene transcription(2). Here, we combined microfluidics, live imaging, genetic engineering and computational modelling to reanalyse the classical case of root growth inhibition(3) by auxin. We show that Arabidopsis roots react to addition and removal of auxin by extremely rapid adaptation of growth rate. This process requires intracellular auxin perception but not transcriptional reprogramming. The formation of the canonical TIR1/AFB-Aux/IAA co-receptor complex is required for the growth regulation, hinting to a novel, non-transcriptional branch of this signalling pathway. Our results challenge the current understanding of root growth regulation by auxin and suggest another, presumably non-transcriptional, signalling output of the canonical auxin pathway.}, author = {Fendrych, Matyas and Akhmanova, Maria and Merrin, Jack and Glanc, Matous and Hagihara, Shinya and Takahashi, Koji and Uchida, Naoyuki and Torii, Keiko U and Friml, Jirí}, journal = {Nature Plants}, number = {7}, pages = {453 -- 459}, publisher = {Springer Nature}, title = {{Rapid and reversible root growth inhibition by TIR1 auxin signalling}}, doi = {10.1038/s41477-018-0190-1}, volume = {4}, year = {2018}, } @article{674, abstract = {Navigation of cells along gradients of guidance cues is a determining step in many developmental and immunological processes. Gradients can either be soluble or immobilized to tissues as demonstrated for the haptotactic migration of dendritic cells (DCs) toward higher concentrations of immobilized chemokine CCL21. To elucidate how gradient characteristics govern cellular response patterns, we here introduce an in vitro system allowing to track migratory responses of DCs to precisely controlled immobilized gradients of CCL21. We find that haptotactic sensing depends on the absolute CCL21 concentration and local steepness of the gradient, consistent with a scenario where DC directionality is governed by the signal-to-noise ratio of CCL21 binding to the receptor CCR7. We find that the conditions for optimal DC guidance are perfectly provided by the CCL21 gradients we measure in vivo. Furthermore, we find that CCR7 signal termination by the G-protein-coupled receptor kinase 6 (GRK6) is crucial for haptotactic but dispensable for chemotactic CCL21 gradient sensing in vitro and confirm those observations in vivo. These findings suggest that stable, tissue-bound CCL21 gradients as sustainable “roads” ensure optimal guidance in vivo.}, author = {Schwarz, Jan and Bierbaum, Veronika and Vaahtomeri, Kari and Hauschild, Robert and Brown, Markus and De Vries, Ingrid and Leithner, Alexander F and Reversat, Anne and Merrin, Jack and Tarrant, Teresa and Bollenbach, Tobias and Sixt, Michael K}, issn = {09609822}, journal = {Current Biology}, number = {9}, pages = {1314 -- 1325}, publisher = {Cell Press}, title = {{Dendritic cells interpret haptotactic chemokine gradients in a manner governed by signal to noise ratio and dependent on GRK6}}, doi = {10.1016/j.cub.2017.04.004}, volume = {27}, year = {2017}, }