Fluid flows controlling morphology: How flows coordinate the collective behaviour of protrusions for directed migration

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Living systems are often challenged to coordinate collective behaviour of individual entities across large spatial scales. The morphology of amoeboid cells, for example, arises due to the coordination of randomly forming protrusions that facilitates the cell's directed migration. To propagate information across large scales, fluid flows can be instrumental as they may transport signalling molecules or rapidly propagate changes in pressure. Yet, the dynamic nature of flows and the associated challenges in imaging them has so far limited our understanding on their role in coordinating collective behaviour and morphology.The slime mould Physarum polycephalum grows as a single giant cell of network-like shape spanning orders of magnitude in size from 500 µm to tens of cm in size. Due to the large extent, chemotaxis and morphogenesis of the entire cell require a mechanism for coordination among competing protrusions. P. polycephalum is renowned for its organism-wide cytoplasmic fluid flows spanning the fluid-filled tubular network in a peristaltic wave. These strong and large-scale flows make this organism an ideal model to investigate the role of fluid flows in coordinating the collective behaviour of competing protrusions during the morphological changes in chemotaxis.We will perform experiments of chemotacting P. polycephalum specimen of varying sizes and quantify the dynamics of individual protrusions in addition to the chemotactic performance of the entire specimen. Correlations between growing and retracting protrusions over time will lead us to identify the mechanism of communication which could be either diffusive or flow-based transport of an inhibitory signal or simply hydrodynamic coupling within the closed system of a single cell. Theoretical simulations of the identified mechanism will confirm our findings and broaden our analysis to understand the mechanisms' robustness. The project will teach us how fluid flows control collective behaviour of protrusions during directed migration. The theoretical framework being devised allows us to readily adapt cell morphology and boundary conditions to test for the identified principles in other systems.