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Does DNA exert an active role in generating cell-sized spheres in an aqueous solution with a crowding binary polymer?

Tsumoto K, Arai M, Nakatani N, Watanabe SN, Yoshikawa K - Life (Basel) (2015)

Bottom Line: 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.A hypothetical scenario for the emergence of a primitive cell with DNA is briefly discussed.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Engineering, Mie University, Mie, 514-8507, Japan. tsumoto@chem.mie-u.ac.jp.

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.

No MeSH data available.


Entrapment of DNA aggregates inside dextran-rich microdroplets. (a) Schematic illustration of a dextran/PEG ATPS containing microspheres near a binodal curve. In the upper region, dextran-rich droplets are surrounded by PEG and in the lower region, vice versa. Phase contrast microscopic images show dextran-rich droplets (in the upper region) that encapsulated DNA aggregates (b) and PEG-rich droplets (in the lower region) from which DNA was excluded (c). Arrows and arrowheads indicate microdroplets and DNA aggregates, respectively. Dextran and PEG are 1.5% and 7% PEG. Bar: 10 µm.
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life-05-00459-f002: Entrapment of DNA aggregates inside dextran-rich microdroplets. (a) Schematic illustration of a dextran/PEG ATPS containing microspheres near a binodal curve. In the upper region, dextran-rich droplets are surrounded by PEG and in the lower region, vice versa. Phase contrast microscopic images show dextran-rich droplets (in the upper region) that encapsulated DNA aggregates (b) and PEG-rich droplets (in the lower region) from which DNA was excluded (c). Arrows and arrowheads indicate microdroplets and DNA aggregates, respectively. Dextran and PEG are 1.5% and 7% PEG. Bar: 10 µm.

Mentions: 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. To simply verify whether or not an ATPS at a certain point (composition) exhibits segregation, the following procedure is necessary: stock solutions of dextran and PEG are added with pure water to a micro-test tube, and the resulting solution is mixed vigorously using a vortex mixer and then either allowed to stand or briefly centrifuged. If a mixture solution remained turbid even after standing/centrifugation, the composition could be considered to be near a critical point, which means that clear separation does not occur (the compositions are indicated as “Intermediate” in Figure 1). Practically, we adopted the following criteria to determine whether or not a solution was near criticality: Under a critical condition, a turbid state might indeed last for some duration, but phase segregation could also proceed slowly. As a result, in the upper part of the tube, microdroplets containing dextran-rich solutions formed and were surrounded by PEG-rich solutions, whereas in the lower part of the tube, microdroplets containing PEG-rich solutions were observed microscopically and were surrounded by dextran-rich solutions (Figure 2a). The boundary in the diagrams, i.e., an apparent binodal curve, could be shifted sensitively due to a slight change in the environment, such as in the temperature. The reason why intermediate states might not be observed with higher dextran concentrations is because a solution containing higher-concentrated dextran is apt to be segregated into two phases relatively faster than that containing lower-concentration dextran due to difference in density between dextran and PEG. Even after mixing, solutions with high dextran concentration (that is, low PEG concentration) could not be stable in an intermediate state. In other words, the compositions indicated as Intermediate in Figure 1 seem to be in intermediate states stably only for some duration. It is noted that more rapid and/or longer centrifugation on such intermediate solutions could cause segregation into two phases.


Does DNA exert an active role in generating cell-sized spheres in an aqueous solution with a crowding binary polymer?

Tsumoto K, Arai M, Nakatani N, Watanabe SN, Yoshikawa K - Life (Basel) (2015)

Entrapment of DNA aggregates inside dextran-rich microdroplets. (a) Schematic illustration of a dextran/PEG ATPS containing microspheres near a binodal curve. In the upper region, dextran-rich droplets are surrounded by PEG and in the lower region, vice versa. Phase contrast microscopic images show dextran-rich droplets (in the upper region) that encapsulated DNA aggregates (b) and PEG-rich droplets (in the lower region) from which DNA was excluded (c). Arrows and arrowheads indicate microdroplets and DNA aggregates, respectively. Dextran and PEG are 1.5% and 7% PEG. Bar: 10 µm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390863&req=5

life-05-00459-f002: Entrapment of DNA aggregates inside dextran-rich microdroplets. (a) Schematic illustration of a dextran/PEG ATPS containing microspheres near a binodal curve. In the upper region, dextran-rich droplets are surrounded by PEG and in the lower region, vice versa. Phase contrast microscopic images show dextran-rich droplets (in the upper region) that encapsulated DNA aggregates (b) and PEG-rich droplets (in the lower region) from which DNA was excluded (c). Arrows and arrowheads indicate microdroplets and DNA aggregates, respectively. Dextran and PEG are 1.5% and 7% PEG. Bar: 10 µm.
Mentions: 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. To simply verify whether or not an ATPS at a certain point (composition) exhibits segregation, the following procedure is necessary: stock solutions of dextran and PEG are added with pure water to a micro-test tube, and the resulting solution is mixed vigorously using a vortex mixer and then either allowed to stand or briefly centrifuged. If a mixture solution remained turbid even after standing/centrifugation, the composition could be considered to be near a critical point, which means that clear separation does not occur (the compositions are indicated as “Intermediate” in Figure 1). Practically, we adopted the following criteria to determine whether or not a solution was near criticality: Under a critical condition, a turbid state might indeed last for some duration, but phase segregation could also proceed slowly. As a result, in the upper part of the tube, microdroplets containing dextran-rich solutions formed and were surrounded by PEG-rich solutions, whereas in the lower part of the tube, microdroplets containing PEG-rich solutions were observed microscopically and were surrounded by dextran-rich solutions (Figure 2a). The boundary in the diagrams, i.e., an apparent binodal curve, could be shifted sensitively due to a slight change in the environment, such as in the temperature. The reason why intermediate states might not be observed with higher dextran concentrations is because a solution containing higher-concentrated dextran is apt to be segregated into two phases relatively faster than that containing lower-concentration dextran due to difference in density between dextran and PEG. Even after mixing, solutions with high dextran concentration (that is, low PEG concentration) could not be stable in an intermediate state. In other words, the compositions indicated as Intermediate in Figure 1 seem to be in intermediate states stably only for some duration. It is noted that more rapid and/or longer centrifugation on such intermediate solutions could cause segregation into two phases.

Bottom Line: 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.A hypothetical scenario for the emergence of a primitive cell with DNA is briefly discussed.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Engineering, Mie University, Mie, 514-8507, Japan. tsumoto@chem.mie-u.ac.jp.

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.

No MeSH data available.