Front propagation is a fundamental phenomenon in driven non-linear systems that enable transmitting information over a long distance as in fiber optics communication and neuronal signaling. Here, we report on a synthetic array of coupled microscopic DNA compartments on a chip, which support traveling gene expression fronts. The DNA compartments are programmed with an autocatalytic bi-stable gene network, and the interaction length between compartments is controlled by the array geometry. The gene expression front propagates at a constant velocity  and is composed of a recurring cycle of events: transcription factor synthesis, diffusion and expression onset in neighbor compartments. The velocity is maximal near a saddle-node bifurcation between bi-stable and mono-stable regimes where propagation fails and gene expression initiates spontaneously with a diverging onset time and a large variation between compartments.¹

Tayar AM, Karzbrun E, Noireaux V, Bar-Ziv RH. Propagating gene expression fronts in a one-dimensional coupled system of artificial cells. Nat Phys. 2015;advance on. doi:10.1038/nphys3469.