The Physical Basis of Coordinated Tissue Spreading

This study demonstrates that tissue fluidization, rather than changes in cell proliferation or migration speed, drives elongation of the zebrafish body axis during development. Using mechanical measurements of embryonic tissue explants, the authors show that posterior tissues transition from solid-like to fluid-like behavior through reductions in yield stress and relaxation time. This fluidization enables tissue flow and deformation required for axis elongation. Genetic and pharmacological perturbations revealed that cell–cell adhesion and actomyosin contractility regulate this mechanical state transition. The work establishes tissue material properties as key regulators of morphogenesis.