Phys. Rev. Lett. 114, 068301 (2015)

Zebra stripes and leopard spots are but two examples of natural patterns that are the result of nonlinear biochemical processes. To explain this biological morphogenesis various models have been proposed, but designing networks of chemical reactions that can recreate such patterns in the laboratory remains a challenge. André Estevez-Torres and colleagues — at the CNRS in Marcoussis and the University of Tokyo — have now developed a simple experimental toolbox that allows them to create propagating chemical wavefronts that behave in accordance with the reaction–diffusion model that is normally used to describe biological morphogenesis.

The system is composed of a DNA strand that hybridizes to a twice-as-long template made of two repeating units. Once the DNA hybridizes to either one of the units, an enzyme promotes the replication to the other template unit, thus forming a 2:1 complex. Finally, another enzyme disassembles the complex. The net outcome is the self-replication of the initial DNA strand.

To test the approach, Estevez-Torres and colleagues built a linear reactor and filled it with all the reactants except for the DNA strand. On addition of the strand on one side of the reactor, a concentration wave propagates through the reactor to the other side. The researchers can control the reaction and diffusion rates independently, allowing them to design a more sophisticated version of the experiment in which two fronts propagating from each side of the reactor meet in the middle without perturbing each other.