Gastruloid patterning reflects division of labor among biased stem cell clones.

Embryonic development typically requires precise coordination among cells to achieve reproducible outcomes, leading to the assumption that cellular heterogeneity must be minimized or buffered against. Using fluorescence-based lineage tracing in combination with spatial transcriptomics, we show that, in the gastruloid model of early development, pre-existing heterogeneity promotes proper axial organization through division of labor among stem cell clones. Individual clones isolated from a common population exhibit consistent spatial propensities for anterior or posterior fates. While pure clones generate elongated structures less frequently than a polyclonal population, mixing clones restores proper axial elongation. Spatial transcriptomics reveals that pure clones show disrupted gene expression with inappropriate coexpression of anterior and posterior markers, while clone combinations restore proper spatial organization. Using RNA-seq, ATAC-seq, and perturbations to key developmental signaling pathways, we further profile differences among clones and suggest a model whereby developmental precision emerges from the coordinated action of intrinsically biased clonal populations.