The limits of scaling in aggregation-driven patterning of cell collectives

Robust development requires maintaining correct proportions as overall size varies. What controls and limits this scaling remains poorly understood due to the complex interplay of mechanical and biochemical embryonic factors. Combining confinement of dissociated embryonic presomitic mesoderm cells with imaging and chemical perturbations, we identified cell aggregation as the initial event in de novo posterior pole formation. Using a continuum model based solely on cell-cell attraction, we quantitatively map how the time available for aggregation-driven patterning limits the maximum scalable system size. Small systems allow rapid, robust pattern scaling, whereas coarsening dynamics substantially delay scaled patterns in large systems. Our experiments quantitatively confirm these predicted scaling regimes. Together, our results reveal a developmental time-size tradeoff governing the scaling of aggregation-driven patterns.