The Effect of In-Plane Shear on Pattern Formation in Cell Populations

Abstract

Dictyostelium discoideum is a free-living amoeba and a striking example of biological pattern formation. Upon starvation, individual cells aggregate via chemotaxis into mul- ticellular structures through the propagation of spiral waves of cyclic AMP, making it an excellent system for studying excitable media and reaction–diffusion processes in bi- ology. While decades of work have shown how chemical signalling and collective motion generate robust spatiotemporal patterns, most studies have focused on quiescent environ- ments dominated by biochemical and diffusive dynamics. In natural and physiological settings, however, cells are exposed to many different environmental perturbations to their signalling and motility. Despite this, little is known about how such mechanical forces influence chemotactic wave dynamics and pattern formation. Here, D. discoideum populations were studied in real time under controlled in-plane shear using a custom-built shearing device. Time-lapse brightfield and dark-field mi- croscopy, combined with a dedicated image-analysis pipeline, were used to quantify wave morphology and cellular dynamics. We find that applied shear induces strong anisotropy in chemotactic waves, altering their direction, wavelength, and morphology relative to qui- escent conditions. Remarkably, these effects closely resemble those produced by external flow, despite the absence of net medium transport. This framework enables controlled studies of active matter and excitable systems under shear and provides new insight into collective cell behaviour.