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Biomembranes can transmit forces over cellular length scales. Now, however, their active role in generating stress is demonstrated. The adhesion and spreading of a liposome that has no active cytoskeletal machinery are shown to contract the substrate, exerting traction stresses that are comparable with those of living cells.

Adherent cells actively probe the rigidity of their substrates. Guptaet al. show that actin cytoskeleton rheology transitions from fluid to solid with increased substrate stiffness along with an isotropic to nematic ordering, implicating the remodelling of the whole actin network in rigidity sensing.

Cell clusters mechanically reorganize viscoelastic collagen networks, resulting in transient gradients in collagen density, alignment and stiffness that promote spontaneous persistent migration.

How the mitotic spindle is positioned in the centre of the cell during the first mitotic division is not clear. Here Chaigne et al.show that the pronucleus coarsely centres using F-actin/Myosin-Vb dynamics, and the metaphase plate is finely centred by an F-actin cage influenced by high cortical tension.

Verlhac, Terret and colleagues report that softening of the mouse oocyte cortex during meiosis I is needed for spindle migration and positioning. They show that Mos/mAPK signalling triggers myosin II exclusion from the cortex and an Arp2/3-dependent cortical F-actin thickening that contributes to cortical softening.

The first-passage time relates the efficiency of a search process, but fails to do so for searches in which several targets are sought. Now, the distribution of times required for a random search to visit all sites has been determined analytically.

Friction forces at the interface between tissues play a key role in tissue morphogenesis. Now friction at the cellular scale is shown to influence cell shape and cell rearrangements.

Actin filaments generate force in diverse contexts, although how they can produce nanonewtons of force is unclear. Here, the authors apply cryo-electron tomography, quantitative analysis, and modelling to reveal the podosome core is a dense, spring-loaded, actin network storing elastic energy.

Cells can modify their environment by depositing biochemical signals or mechanically remodelling the extracellular matrix; the impact of such self-induced environmental perturbations on cell trajectories at various scales remains unexplored. Here authors show that motile cells leave long-lived physicochemical footprints along their way, which determine their future path.

Within three-dimensional environments, leukocytes can migrate even in the complete absence of adhesive forces using the topographical features of the substrate to propel themselves.

The immune synapse promotes cellular information exchange but the role of biophysical forces in synapse function is unclear. Here, the authors show that B cells exert two types of forces, a centripetal myosin II-driven force and a central actin protrusive force at the site of antigen extraction.

Dendritic cells alternate between fast and slow migratory behaviours, however in the absence of a component of the antigen processing machinery, migration is uniform and fast. Chabaudet al. now show that slow migration results from the relocalisation of myosin II to the cell front where it promotes antigen capture.

The mechanism of force production by invadopodia is unclear. Here, the authors show that cell surface MT1-MMP when in contact with collagen, induces Arp2/3 branched actin polymerisation on the concave side of invadopodia, which generates a pushing force along with collagen cleavage by MT1-MMP to invade.

Ependymal ciliary beating contributes to the flow of cerebrospinal fluid in the brain ventricles and these cilia resist the flow forces. Here the authors show that the assembly of a dense actin network around the centrioles is induced by cilia beating to protect centrioles against the shear stress generated by ciliary motility.

Changes in membrane curvature influence how migrating cells navigate their environment. Experiments and modelling reveal that dynamic reorganization of the actin cytoskeleton in response to these changes provides cells with a sensing mechanism.

Podosomes are actin-rich adhesion structures that show periodic oscillations in stiffness. Here, Labernadie et al.develop a method to measure the protrusion force and mechanosensing activity of individual podosomes, using an atomic force microscope and a flexible substrate membrane.

Cell motility is typically described as a random walk due to the presence of noise. But a dynamical model suggests that dendritic cells move deterministically, alternating between fast and slow motility, and exhibiting periodic polarity reversals.

During transcription, replication and repair, DNA-binding proteins must find specific interaction sites hidden within a vast excess of genomic DNA. Here the authors use single-molecule tracking to quantitatively determine the contributions of the different processes that underlie target search in human cells.

Cytoskeletal activity generates mechanical forces known to agitate and displace membrane-bound organelles in the cytoplasm. In oocytes, Al Jord et al. discover that these cytoplasmic forces functionally remodel nuclear RNA-processing condensates across scales for developmental success.

By live imaging of mouse oocytes, Verlhac and colleagues demonstrate that actin-coated vesicles together with myosin Vb participate in centring of the nucleus by creating a gradient of cytoplasmic forces.

Vargas et al. report that innate immune signalling activation controls dendritic cell migration mode and function by regulating distinct F-actin networks at the cell front and rear.

Roman et al. demonstrate that crosslinking and contraction of myofibrils mediate the movement of nuclei to the periphery of myofibres, and describe a role for Arp2/3 in organizing desmin.

Massou et al. combine cell stretching, super-resolution imaging and single-protein tracking to investigate integrin-based mechanosensing in live cells.

Chemical reactions often require multiple random encounters between reactants, but a general, analytical treatment such imperfect transport-limited/influenced reactions in confined spaces has not yet been proposed. Here, the authors predict the full kinetics of these reactions for Markovian processes in large confining volumes.