Growth of vesicles

Vesicles are commonly considered models for biological cells. This is due to the bilayer spherical structure which is also present in most biological cells, and to the fact that vesicles can incorporate biopolymers and host biological reactions. Self-reproduction, an autocatalytic reaction already illustrated in the chapters on self-reproduction and autopoiesis, also belongs to the field of reactivity of vesicles. Some additional aspects of this process will be considered here, together with some particular properties of the growth of vesicles - the so-called matrix effect. 

Figure 10.11 The use of ferritin as a label for the mechanism of growth of vesicles (adapted from Berclaz et al, 2001a b). Schematic representation of the possible vesicle formation and transformation processes when oleate, and oleic acid, are added to pre-formed vesicles which have been labelled, (a) The situation if only de novo vesicle formation occurs, (b) Growth in size of the pre-formed and labeled vesicles which may lead to division, either yielding vesicles that all contain marker molecules (case i, a statistical redistribution of the ferritin molecules) or also yielding vesicles that do not contain markers (case ii). Compare all this with Figure 10.9.

We have seen experiments of growth of vesicles, whereby fresh surfactant binds to the surface of pre-formed vesicles. How would you devise an experiment, so that the growth rate is determined - or affected - by the vesicle content ... 

Robinson, B.H. Bucak. S. Fontana, A. On the concept of driving force applied to micelle and vesicle self-assembly. Langmuir 2000, 16. 8231-8237, and references therein. Shioi. A. Hatton, T.A. Model for formation and growth of vesicles in mixed anionic/cationic surfactant systems. Langmuir 2002. 18, 7341-7348. 

YatciUa et al. investigated the conversion of a mixtime of cationic and anionic surfactants to form vesicles. In this case, the reaction was veiy slow and a kinetic phase was associated with the evolution and growth of vesicles over a period of weeks (see Figure 6.12) to a final vesicular system, which, as already mentioned, was thought by the authors to be thermodynamically stable. A subsequent study explored the system CTAB mixed with sodium perfiuorooctanoate. Cylinders, disks, and spherical uni-lamellar vesicles were found to coexist at equilibrium by cryo-TEM. This observation confirms the importance of structural confirmation by cryo-TEM when this technique can be applied. Erom their analysis of the data, the mean curvature modulus, the Gaussian curvature modulus, and the spontaneous curvature could all be evaluated. 

In the first step, lipid model membranes have been generated (Fig. 15) on the air/liquid interface, on a glass micropipette (see Section VIII.A.1), and on an aperture that separates two cells filled with subphase (see Section VIII.A.2). Further, amphiphilic lipid molecules have been self-assembled in an aqueous medium surrounding unilamellar vesicles (see Section VIII.A.3). Subsequently, the S-layer protein of B. coagulans E38/vl, B. stearother-mophilus PV72/p2, or B. sphaericus CCM 2177 have been injected into the aqueous subphase (Fig. 15). As on solid supports, crystal growth of S-layer lattices on planar or vesicular lipid films is initiated simultaneously at many randomly distributed nucleation... 

Hubert DHW, Jung M, Frederick PM, Bomans PHH, Meuldijk J, German AL (2000) Vesicle-directed growth of silica. Adv Mater 12(17) 1286-1290... 

Fig. 13 Phase diagram of PS310-PAA52 in dioxane/water mixtures (A). Shaded regions between sphere and rod phases and between rod and vesicle phases correspond to coexistence regions. Reversibility of vesicle formation and growth process for PS300-PAA44 as function of THF/dioxane composition of nonselective solvent (B). Reprinted with permission from [239]. Copyright (2002) American Association for the Advancement of Science...

Exposing young male prairie deer mice, Peromyscus maniculatus, to soiled bedding from adult male conspecifics retards the growth of their testes and seminal vesicles. Male, but not female, urine applied to the nose has the same effect. Removal of the olfactory lobes at the age of 3 weeks blocks this effect (Lawton, 1979). The reproductive development of male California voles, M. californicus, is suppressed hy chemical cues from the mother (Rissman etah, 1984). 

Wu SX, Zeng HX, Schelly ZA (2005) Growth of uncapped, subnanometer size gold clusters prepared via electroporation of vesicles. J Phys Chem B 109 18715-18718... 

It is clear, as shown in Figure 10.9, that the choice between the two pathways is the result of a competition between the velocities of the two processes, regulated hy the relative rate of binding, and assembly formation, respectively. If the rate of vesicle formation is per se very high, there is no possibility for binding and for the eventual growth and reproduction of the old vesicles. 

These considerations have given rise to an intensive TEM investigation (Berclaz et al., 2001a, b). As an example. Figure 10.12 shows the size distribution of empty (no ferritin) and filled vesicles at the start it also shows the size distribution of empty and filled vesicles after oleate addition and finally the comparison between filled vesicles before and after addition. It is clear that there is a significant growth of... 

The growth of fatty acid vesicles has been re-investigated by Chen and Szostack (2004) who, by the use of stopped-flow and fluorescence resonance energy transfer (FRET) techniques, provided interesting insights into the kinetics of this process. 

The uptake of oleate by pre-added vesicles, and in particular the matrix effect, permits regulation of the growth of the size and the number of particles, and in this way it is possible to tackle a series of novel questions. One such question is is there a difference in the rate of uptake of fresh surfactant between two vesicle populations of different sizes ... 

In the meantime, the intense study of the simpler vesicle systems has unravelled novel, unsuspected physicochemical aspects - for example growth, fusion and fission, the matrix effect, self-reproduction, the effect of osmotic pressure, competition, encapsulation of enzymes, and complex biochemical reactions, as will be seen in the next chapter. Of course the fact that vesicles are viewed under the perspective of biological cell models renders these findings of great interest. In particular, one tends immediately to ask the question, whether and to what extent they might be relevant for the origin of life and the development of the early cells. In fact, the basic studies outlined in this chapter can be seen as the prelude to the use of vesicles as cell models, an aspect that we will considered in more detail in the next chapter. 

Berclaz, N., Muller, M., Walde, R, and Luisi, P. L. (2001b). Growth and transformation of vesicles studied by ferritin labeling and cryotransmission electron microscopy. J. Phys. Chem. B, 105, 1056-64. 

These steroids control the development of male characteristics sperm production and growth of the sex organs (penis, testes), prostate, and seminal vesicles (their androgenic... 

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