Fig. 1

Design of the synthetic network to compute population borders. a Mechanistic background. The sender/receiver cell population (light grey) produces a signal (green spheres) that diffuses across the population border into the processing cell population (dark grey). The processing cell population responds by the production of a second signal (red stars) that diffuses back into the sender/receiver population, where it elicits a response from cells at the edge of the two cell populations that are exposed to high enough concentrations of the signaling molecule. b Molecular configuration of the synthetic network. The sender/receiver cells produce L-tryptophan from indole via constitutively expressed tryptophan synthase (TrpB). L-tryptophan diffuses into the processing population and is sensed by the chimeric TrpR-VP16 transcription factor that in turn triggers production of interleukin-4 (IL-4). Interleukin-4 diffuses back into the sender/receiver cell population, where it is perceived by the endogenous interleukin-4 receptor (IL4R). The signal is relayed onwards via exogenously expressed STAT6 that finally triggers production of a yellow fluorescent reporter protein