Cell-in-the-loop pattern formation with optogenetically emulated cell-to-cell signaling

1Designing and implementing synthetic biological pattern formation remains a challenge due to underlying theoretical complexity as well as the difficulty of engineering multicellular networks bio-chemically. Here, we introduce a \"cell-in-the-loop\" approach where living cells interact through in silico signaling, establishing a new testbed to interrogate theoretical principles when internal cell dynamics are incorporated rather than modeled. We present a theory that offers an easy-to-use test to predict the emergence of contrasting patterns in gene expression among laterally inhibiting cells. Guided by the theory, we experimentally demonstrated spontaneous checkerboard patterning in an optogenetic setup where cell-to-cell signaling was emulated with light inputs calculated in silico from real-time gene expression measurements. The scheme successfully produced spontaneous, persistent checkerboard patterns for systems of sixteen patches, in quantitative agreement with theoretical predictions. Our research highlights how tools from dynamical systems theory may inform our understanding of patterning, and illustrates the potential of cell-in-the-loop for engineering synthetic multicellular systems.