Diverse mechanisms have been proposed to explain natural pattern formation processes, such as slime mold aggregation, feather branching, and tissue stratification. Regardless of the specific molecular interactions, the vast majority of these mechanisms invoke morphogen gradients, which are either predefined or generated as part of the patterning processes. However, using E. coli programmed by a simple synthetic gene circuit, I demonstrate here the generation of robust, self-organized ring patterns of gene expression in the absence of an apparent morphogen gradient. Interestingly, modeling and experimental tests show that the temporal dynamics of the global morphogen concentration serve as a timing mechanism to trigger formation and maintenance of these ring patterns, which are readily tunable by experimentally controllable environmental factors. This mechanism represents a novel mode of pattern formation that has implications for understanding natural developmental processes. In addition, the system can be coupled with inkjet printing technology and metabolic engineering approaches to develop future complex patterned biomaterials.
