标题： 上皮单层中的密度-速度关系具有尺度依赖性 显示英文标题

标题： Density-Velocity Relation Is Scale-Dependent in Epithelial Monolayers

摘要： 细胞密度与速度之间的关系通常被假定为负相关，反映了拥挤引起的运动抑制。 然而，跨系统的观察揭示了一个更复杂的图景：虽然一些研究强调运动的接触抑制，但其他研究则表明，由于力的产生和应力积累，密集区域表现出增强的活动性。 在这里，我们使用实验测量结果表明，上皮单层中的密度-速度关系本质上是尺度依赖的。 通过在多个空间窗口上对细胞轨迹进行粗粒化处理，我们发现，在小尺度下，细胞速度与局部密度呈正相关，但在大尺度下则呈负相关。 利用牵引力测量，我们发现这种转变与机械压力分离的出现相吻合，定义了一个特征长度尺度，在此尺度之外，拥挤占主导地位。 一个包含活性诱导形状变化的最小模型再现了这种转变，并将活性力生成与机械限制之间的竞争确定为基本机制。 我们的结果调和了关于密度调节迁移的相互矛盾的观点，并强调了一个涌现的长度尺度作为解释集体细胞动力学的关键因素。 显示英文摘要

摘要： The relationship between cell density and velocity is often assumed to be negative, reflecting crowding-induced suppression of movement. However, observations across systems reveal a more nuanced picture: while some emphasize contact inhibition of locomotion, others suggest that dense regions exhibit enhanced activity due to force generation and stress buildup. Here, using experimental measurements we show that density-velocity relations in epithelial monolayers are inherently scale dependent. By coarse-graining cell trajectories over multiple spatial windows, we find that cell velocity correlates positively with local density at small scales, but negatively at large scales. Employing traction force measurements, we find that this crossover coincides with the emergence of mechanical pressure segregation, defining a characteristic length scale beyond which crowding dominates. A minimal model incorporating activity-induced shape changes reproduces this crossover and identifies the competition between active force generation and mechanical confinement as the underlying mechanism. Our results reconcile conflicting views of density-regulated migration and highlight an emergent length scale as a key factor in interpreting collective cell dynamics.