  The ability of cells to reorganize in response to external stimuli is
important in areas ranging from morphogenesis to tissue engineering. Elongated
cells can co-align due to steric effects, forming states with local order. We
show that molecular-scale substrate anisotropy can direct cell organization,
resulting in the emergence of nematic order on tissue scales. To quantitatively
examine the disorder-order transition, we developed a high-throughput imaging
platform to analyze velocity and orientational correlations for several
thousand cells over days. The establishment of global, seemingly long-ranged
order is facilitated by enhanced cell division along the substrate's nematic
axis, and associated extensile stresses that restructure the cells' actomyosin
networks. Our work, which connects to a class of systems known as active dry
nematics, provides a new understanding of the dynamics of cellular remodeling
and organization in weakly interacting cell collectives. This enables
data-driven discovery of cell-cell interactions and points to strategies for
tissue engineering.
