Coupling Mechanical Regulation with Biochemical Reaction-Diffusion Circuits Yields Robust Self-Organized Pattern Formation.

Cell-cell signaling circuits that combine local self-activation with long-range inhibition have long been proposed as a theoretical mechanism sufficient to generate cellular patterns, such as spots and stripes. Here we construct synthetic pattern-forming circuits, implementing local self-activation (positive feedback) using juxtacrine synNotch receptor interactions, and implementing long-range inhibition using diffusible competitor molecules. While combining local positive feedback with long-range inhibition leads to more spatially heterogeneous cell states, these synthetic circuits do not robustly lead to well defined patterns. We find, however, that if we couple these reaction-diffusion circuits with induction of genes that regulate cell mechanics - such Cadherin molecules that promote local cell adhesion and sorting - we observed the emergence of much more well-defined cellular patterns. Theoretical analysis indicates while reaction-diffusion circuits can be sufficient to generate patterns under precisely balanced parameter conditions, the close coupling of cell mechanical/sorting significantly increases the robustness of pattern formation (the parameter space yielding patterns). Thus, circuits that closely integrate signaling and mechanical changes may underlie many evolved morphogenic pattern formation systems.