This system coupled the communication to a timed phenotype: the maturation of blood cells by growth factors. Engineering networks inspired by embryonic developmental patterning is also a growing field within

mammalian synthetic biology. Tetracycline gradient band-pass receiver systems [47] have been followed by fully genetically-encoded S–R systems [48]. In the latter study, diffusing activators and inhibitors, based on growth factors, were used to communicate and control gene expression over fields of cells, in 3D collagen cell culture. In principle, these components can be rewired to build many different pattern-forming network motifs [49 and 50]. Connecting sender–receiver systems in parallel yields combinatorial mTOR inhibitor increases in complexity, and current efforts are exploring the possibility of building computational functions from communicating cells. An elegant trick to reduce the number of ‘wiring’ components for sending, receiving and processing signals, is to distribute tasks in consortia of different genetically-modified cells [51]. In this way, single cells perform

simple robust functions, using a Akt inhibitor review few well-characterised components, such as bacterial repressor proteins. The components can be reused in different logical gates or circuits — one per cell — so that the cell mixtures coordinate to process the information flow. Perhaps it is no accident that such work has come from researchers who were among the first to develop information theory in the context of genetic networks [52]. Cellular

consortia have proved to be an efficient way of engineering complex tasks that are not easily solvable using single cells [42 and 53], including a 1-bit adder with carry function [ 51]. There has also been significant progress in the amount of complexity that can be engineered within the single cells, with logic gates such as NOR being achieved in bacteria [ 53]. Importantly, NOR gates are ‘functionally complete’ and can be layered to achieve any computational operation; this opens P-type ATPase up many engineering possibilities. For practical reasons, robustness in output can be increased at a population level by coupling the cell consortia using S–R systems with AHL signalling molecules. The frontier of synthetic S–R systems is getting more and more diverse with the latest systems combining cell-cell communication and doped amyloid fibre formation [54]. Hence, communication systems are being coupled to self-assembling electrically conducting nanosystems, resulting in a convergence of biology, electronics and computation. Synthetic biology builds systems in order to understand them. Synthetic S–R systems are no exception, potentially giving insights into processes as diverse as spatiotemporal patterning, cellular computing through signalling, and neurological calculations. Moreover, the application of information theory puts biological communication on a quantitative footing, providing objective insights into how cell systems process signals.