Cell-free protein synthesis in microcompartments towards cell–cell communication

Recent efforts in bottom-up synthetic biology focus on fabricating programmable biological units that can be viewed as synthetic cells. Combining microfluidic techniques with cell-free protein expression systems defines the geometrical limits of the synthetic cell (e.g. microfluidic compartments, droplets, vesicles) and facilitates communication pathways to distribute functions over an assembly of synthetic cells. In this review, we describe and compare the different strategies implemented to reconstitute cell-cell communication among synthetic cells. We focus especially on various experimental setups of microcompartmentalization containing a cell-free expression system and genetic material. We highlight efforts to develop and engineer different modes of communication among the synthetic cells in different forms, varying by the degree of permeability, resource renewal, stability, and scalability, and how these influence the trade-off between programmability and biomimicry. We then summarize recent progress in the realization of different stages of communication (signaling, processing, and output generation) by genetic circuits, holding great promise for applications in synthetic biology and biotechnology.