Abstract
We report the spontaneous generation of a cell-like morphology in an environment crowded with the polymers dextran and polyethylene glycol (PEG) in the presence of DNA. DNA molecules were selectively located in the interior of dextran-rich micro-droplets, when the composition of an aqueous two-phase system (ATPS) was near the critical condition of phase-segregation. The resulting micro-droplets could be controlled by the use of optical tweezers. As an example of laser manipulation, the dynamic fusion of two droplets is reported, which resembles the process of cell division in time-reverse. A hypothetical scenario for the emergence of a primitive cell with DNA is briefly discussed.
Highlights
In living cells, DNA molecules are stored inside microcompartments, such as nuclei, where RNA and proteins exist in rather high concentrations
This indicates that aqueous solutions of the two polymers microscopically exhibit phase segregation to form microsphere-type structures, which, are not stable from an equilibrium perspective. They occur within zones that seem to be unsuitable for the separation of materials, such micrometer-sized microspheres can sharply include/exclude biological macromolecules, just like large-scale aqueous two-phase system (ATPS). We demonstrate this phenomenon through the microscopic observation of DNA molecules that were encapsulated within a dextran-rich microsphere or excluded from a polyethylene glycol (PEG)-rich microsphere
Referring to the phase diagram of segregation in a dextran/PEG ATPS that was reported by Toyama et al [13], we prepared a phase diagram (Figure 1) with our experimental scales and materials because the behavior of an ATPS near around a critical point and/or a binodal curve generally tends to fluctuate
Summary
DNA molecules are stored inside microcompartments, such as nuclei, where RNA and proteins exist in rather high concentrations. A series of pioneering studies by Keating’s group [4,11,12] showed that if a dextran/PEG solution that was homogenized above the critical temperature was encapsulated by micrometer-sized lipid vesicles, two immiscible phases could emerge in the interior as the temperature decreased According to those reports, such an encapsulated ATPS could distribute inner macromolecules and the lipid membranes of the host vesicles according to their affinities. If the dextran/PEG composition is set at or near the critical point, phase segregation proceeds slowly; if the mixture is allowed to stand, it continues to be turbid for a long time This indicates that aqueous solutions of the two polymers microscopically exhibit phase segregation to form microsphere-type structures, which, are not stable from an equilibrium perspective. This entrapment was so robust that microspheres harboring DNA aggregates could be transported through the use of optical tweezers, and, in some cases, fused to each other
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