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Abstract Collective migration of epithelial cells drives diverse tissue remodeling processes. In many cases, a free tissue edge polarizes the cells to promote directed motion, but how edge-free or closed epithelia initiate migration remains unclear. Here, we show that the rotational migration of follicular epithelial cells in theDrosophilaegg chamber is a self-organizing process. Combining experiments and theoretical modeling, we identify a positive feedback loop in which the mechanosensitive behavior of the atypical cadherin Fat2 synergizes with the rigid-body dynamics of the egg chamber to both initiate and sustain rotation. Mechanical constraints arising from cell–cell interactions and tissue geometry further align this motion around the egg chamber’s anterior–posterior axis. Our findings reveal a biophysical mechanism — combining Fat2-mediated velocity–polarity alignment, rigid-body dynamics, and tissue geometry — by which a closed epithelial tissue self-organizes into persistent, large-scale rotational migrationin vivo, expanding current flocking theories. 

Abstract Coherent structures—flow features that organize material transport and deformation—are central to analyzing complex flows in fluids, plasmas, and active matter. Yet, identifying such structures on dynamic surfaces remains an open challenge, limiting their application to many living and synthetic systems. Here, we introduce a geometric framework to extract Lagrangian and Eulerian coherent structures from velocity data on arbitrarily shaped, time-evolving surfaces. Our method operates directly on triangulated meshes, avoiding global parametrizations while preserving objectivity and robustness to noise. Applying this framework to active nematic vesicles, collectively migrating epithelial spheroids, and beating zebrafish hearts, we uncover hidden transport barriers and Lagrangian deformation patterns—such as dynamic attractors, repellers, isotropic and anisotropic strain—missed by conventional Eulerian analyses. This approach offers a new perspective on soft and living matter, revealing how geometry and activity can be harnessed to program synthetic materials, and how Lagrangian strain and principal deformation directions can help uncover mechanosensitive processes and directional cues in morphogenesis. 

Embryogenesis integrates morphogenesis—coordinated cell movements—with morphogen patterning and cell differentiation. While largely studied independently, morphogenesis and patterning often unfold simultaneously in early embryos. Yet how cell movements affect morphogen transport and cells' exposure over time remains unclear, as most pattern formation models assume static tissues. Here we develop a theoretical framework for morphogen patterning in dynamic tissues, recasting advection-reaction-diffusion equations in the cells' moving reference frames. This framework (i) elucidates how morphogenesis mediates morphogen transport and compartmentalization: cell-cell diffusive transport is enhanced at multicellular flow attractors, while repellers act as barriers, affecting cell fate induction and bifurcations. (ii) It formalizes cell-cell signaling ranges in dynamic tissues, deconfounding morphogenetic movements to identify which cells could communicate via morphogens. (iii) It provides two new nondimensional numbers to assess when and where morphogenesis affects morphogen transport. We demonstrate this framework by analyzing classical patterning models with common morphogenetic motifs as well as experimental tissue flows. Our work rationalizes dynamic tissue patterning in development, constraining candidate patterning mechanisms and parameters using accessible cell motion data. 

Gastrulation is an essential process in the early embryonic development of all higher animals. During gastrulation, the three embryonic germ layers, the ectoderm, mesoderm and endoderm, form and move to their correct positions in the developing embryo. This process requires the integration of cell division, differentiation and movement of thousands of cells. These cell behaviours are coordinated through shortand long-range signalling and must involve feedback to execute gastrulation in a reproducible and robust manner. Mechanosensitive signalling pathways and processes are being uncovered, revealing that shortand long-range mechanical stresses integrate cell behaviours at the tissue and organism scale. Because the interactions between cell behaviours, signalling and feedback are complex, combining experimental and modelling approaches is necessary to elucidate the regulatory mechanisms that drive development. We highlight how recent experimental and theoretical studies provided key insights into mechanical feedback that coordinates relevant cell behaviours at the organism scale during gastrulation. We outline advances in modelling the mechanochemical processes controlling primitive streak formation in the early avian embryo and discuss future developments.