Cell jamming transitions shape regulatory protein gradients and prime evolutionary divergence

A long-standing goal of evolutionary developmental biology is to identify the mechanisms underlying criticality of developmental transitions that allow processes governing individual cells scale up to the organism-level patterning. The viscoelastic properties of embryonic tissues imply collective cell behaviors, leading to the expectation that signaling networks should capitalize on the material properties of tissues, structuring morphogenesis around the spatial and temporal transitions that they induce. Here, we show that this interaction is evident even prior to tissue differentiation and is traceable to behavior of individual cells. In avian beak primordia, we find that fields of mesenchymal cells undergo cycles of local jamming dynamically modulating coordination of cell shape and movement. These cycles progressively alter the spatial reach of regulatory proteins, strongly expanding or restricting their gradients based on tissue mechanical state. Tissue-level gradients of proteins most sensitive to local cell jamming transitions also diverge the most across populations, priming tissue compartmentalization. These findings suggest that the material state transition is an effective interface for integration of stochastic physical processes and genetic regulation and is well placed to underlie criticality of developmental systems allowing local rules governing cell-state transitions scale up to tissue-level patterning. More broadly, our findings reveal how transient material transitions reset developmental trajectories and promote diversification while preserving robustness.