Toward Experimental Evolution with Giant Vesicles

Abstract

Experimental evolution in chemical models of cells could reveal the fundamental mechanisms of cells today. Various chemical cell models, water-in-oil emulsions, oil-on-water droplets, and vesicles have been constructed in order to conduct research on experimental evolution. In this review, firstly, recent studies with these candidate models are introduced and discussed with regards to the two hierarchical directions of experimental evolution (chemical evolution and evolution of a molecular self-assembly). Secondly, we suggest giant vesicles (GVs), which have diameters larger than 1 µm, as promising chemical cell models for studying experimental evolution. Thirdly, since technical difficulties still exist in conventional GV experiments, recent developments of microfluidic devices to deal with GVs are reviewed with regards to the realization of open-ended evolution in GVs. Finally, as a future perspective, we link the concept of messy chemistry to the promising, unexplored direction of experimental evolution in GVs.

Keywords: experimental evolution; giant vesicle; machine assisted experiment; microfluidic device; oil-on-water droplet; water-in-oil emulsion.

Figure 1

Hypothetical representation of an experimental evolution with giant vesicles (GVs) as a modular association evolutionary body. The inner components are modularly associated across generations, and these inner reactions are linked to their fitness or growth rate (left). The growth rate or “fitness” is dependent on deformation process in self-reproduction with diverse pathways partly because of the difference of the initial state, intake kinetics of membrane molecules and inner substances, and stochastic fluctuations (right).

Figure 2

Schematic illustration of chemical evolution implemented in the water-in-oil emulsion. Well-reproduced sequences are prone to occupy the gene pool of the next generation. Strongly colored emulsions at the bottom part have a higher concentration of ribonucleic acid (RNA). Compartmentalization prevents the spreading of parasitic RNA species to the whole system, and the catalytic cycle can be maintained through the course of evolution. For visual readability, the color of Qβ replicase at the top was homologized to that of the emulsions at the bottom.

Figure 3

Schematic illustration of the evolutionary cycle of water-on-oil droplets. Oil droplets are ranked based on the observation, and the “gene” pools of the next generation are computationally constructed based on the high-ranked compositions. Oil droplet movements become sophisticated with the passing of generations, according to their compositions.

Figure 4

Schematic illustration of updating the manipulation techniques of GVs by microfluidic technology. The gentle hydration method and water-in-oil emulsion transfer method are illustrated as examples of traditional GV preparation methods, and batch observation and flow cytometer are depicted as examples of traditional observation methods.