Temperature-Promoted Giant Unilamellar Vesicle (GUV) Aggregation: A Way of Multicellular Formation

Abstract

The evolution of unicellular to multicellular life is considered to be an important step in the origin of life, and it is crucial to study the influence of environmental factors on this process through cell models in the laboratory. In this paper, we used giant unilamellar vesicles (GUVs) as a cell model to investigate the relationship between environmental temperature changes and the evolution of unicellular to multicellular life. The zeta potential of GUVs and the conformation of the headgroup of phospholipid molecules at different temperatures were examined using phase analysis light scattering (PALS) and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), respectively. In addition, the effect of increasing temperature on the aggregation of GUVs was further investigated in ionic solutions, and the possible mechanisms involved were explored. The results showed that increasing temperature reduced the repulsive forces between cells models and promoted their aggregation. This study could effectively contribute to our understanding of the evolution of primitive unicellular to multicellular life.

Keywords: aggregation; giant unilamellar vesicles; headgroup reorientation; phospholipid; zeta potential.

Figure 1

Basic properties of giant unilamellar vesicles(GUVs). (a) Light microscope observation of DPPC-GUVs (labeled by DiO) at RT. (b) Particle diameter distribution of GUVs; scale bar 100 μm.

Figure 2

The degree of GUVs aggregation changed at different temperatures and incubation times. (a) Changes in the number of GUVs and aggregates from zero to seven days of incubation at 4 °C, 25 °C, 37 °C, and 45 °C; (b–e) Proportional variation of GUVs and different categories of aggregates (contained different number of GUV) at 4 °C, 25 °C, 37 °C, 45 °C from zero to seven days. Gray: GUV, blue: aggregates formed by two GUVs, Yellow: aggregates formed by three GUVs, Green: aggregates formed by four GUVs, Orange: aggregates formed by more than four GUVs.

Figure 3

Incubation of DPPC-GUVs mixed solution (red GUV: labeled by DiI; green GUV: labeled by DiO). (a) Fresh GUVs; (b–e) dfGUVs were incubated at various temperatures for seven days (b: 4 °C; c: 25 °C; d: 37 °C; e: 45 °C); (f) The proportion of aggregates of different colors; scale bars 100 μm (a–e figures) and 20 μm (a–e: top right figures), respectively.

Figure 4

Zeta potential of DPPC-GUVs in water and 1 mM NaCl solution at different temperatures.

Figure 5

ATR-FTIR spectra of the choline groups of DPPC molecules at different temperatures. The inset indicates the directional change in the choline group after the temperature increase.

Figure 6

Zeta potential and degree of aggregation of GUVs prepared from DMPC, DPPC, and DSPC in water. (a) Differences in zeta potential in GUVs at 25 °C. (b) Differences in the degree of GUVs aggregation after seven days incubation at 25 °C; “***” indicate p < 0.001.

Figure 7

Differences in the percentage of aggregates between DPPC-GUVs incubated in 1 mM NaCl and water. (a) 4 °C; (b) 25 °C; (c) 37 °C; (d) 45 °C.