Collective Motion of Cells Mediates Segregation and Pattern Formation in Co-Cultures

Pattern formation by segregation of cell types is an important process during embryonic development. We show that an experimentally yet unexplored mechanism based on collective motility of segregating cells enhances the effects of known pattern formation mechanisms such as differential adhesion, mechanochemical interactions or cell migration directed by morphogens. To study in vitro cell segregation we use time-lapse videomicroscopy and quantitative analysis of the main features of the motion of individual cells or groups. Our observations have been extensive, typically involving the investigation of the development of patterns containing up to 200,000 cells. By either comparing keratocyte types with different collective motility characteristics or increasing cells' directional persistence by the inhibition of Rac1 GTP-ase we demonstrate that enhanced collective cell motility results in faster cell segregation leading to the formation of more extensive patterns. The growth of the characteristic scale of patterns generally follows an algebraic scaling law with exponent values up to 0.74 in the presence of collective motion, compared to significantly smaller exponents in case of diffusive motion.

细胞类型分离介导的图案形成是胚胎发育过程中的重要生物学进程。我们发现，一种尚未经实验探究的、基于分离细胞集体运动（collective motility）的机制，可强化已知图案形成机制的作用效果——包括差异黏附、机械化学相互作用，或是由形态发生原（morphogen）引导的细胞迁移。为研究体外（in vitro）细胞分离现象，我们采用延时视频显微镜技术（time-lapse videomicroscopy），并对单个细胞或细胞群体运动的核心特征开展定量分析；本研究的观测覆盖范围广泛，通常涉及对包含至多20万个细胞的图案发育过程的研究。我们通过两类实验验证了上述结论：一是比较具有不同集体运动特征的角质细胞（keratocyte）类型，二是通过抑制Rac1 GTP酶（Rac1 GTP-ase）以增强细胞的定向持久性；结果证实，增强的细胞集体运动可加速细胞分离过程，进而促成更大范围的图案形成。与扩散运动场景下指数值显著更小的情况相比，存在集体运动时，图案特征尺度的增长通常遵循代数标度律（algebraic scaling law），其指数最高可达0.74。