Morphological changes in liposomes caused by polymerization of encapsulated actin and spontaneous formation of actin bundles.

Miyata, Hidetake; Hotani, Hirokazu

doi:10.1073/pnas.89.23.11547

Cited by 99 publications

(70 citation statements)

References 25 publications

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“…For example, quantitative experiments on the deformation of vesicles upon the polymerization of cytoskeleton proteins have been performed (Fig. 5 A-C) (79)(80)(81)(82)(83). These experiments, however, do not incorporate the information flow.…”

Section: Bottom-up Development Of An Artificial Cell: Broad Consideramentioning

confidence: 99%

Development of an artificial cell, from self-organization to computation and self-reproduction

Noireaux¹,

Maeda

Libchaber

2011

Proc. Natl. Acad. Sci. U.S.A.

297

267

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This article describes the state and the development of an artificial cell project. We discuss the experimental constraints to synthesize the most elementary cell-sized compartment that can self-reproduce using synthetic genetic information. The original idea was to program a phospholipid vesicle with DNA. Based on this idea, it was shown that in vitro gene expression could be carried out inside cell-sized synthetic vesicles. It was also shown that a couple of genes could be expressed for a few days inside the vesicles once the exchanges of nutrients with the outside environment were adequately introduced. The development of a cell-free transcription/translation toolbox allows the expression of a large number of genes with multiple transcription factors. As a result, the development of a synthetic DNA program is becoming one of the main hurdles. We discuss the various possibilities to enrich and to replicate this program. Defining a program for self-reproduction remains a difficult question as nongenetic processes, such as molecular self-organization, play an essential and complementary role. The synthesis of a stable compartment with an active interface, one of the critical bottlenecks in the synthesis of artificial cell, depends on the properties of phospholipid membranes. The problem of a self-replicating artificial cell is a long-lasting goal that might imply evolution experiments.Defining Life Since Schrödinger's classic book What Is Life? (1), the definition of life has always been a puzzle with a variety of partial answers, none really satisfying. One answer is that life is a coded system with mutation and error correction (2). The information is encoded into DNA (the genotype) and the genetic code allows translating this information into proteins (the phenotype). The genetic code is universal, and the genome can support mutations, recombination, duplication, and partial transfer from organisms to organisms. Error correction limits the risk of melting the information into random sequences. This is fine, but life is also metabolism with a permanent absorption and transformation of nutrients from the environment (3). A constant flux of energy is needed to sustain the operation of this living dynamical system out of equilibrium. But life is also self-reproduction (4). Cells originate from preexisting cells by cell division. The DNA genome is replicated, the cell self-reproduces as well as the complete organism. Is self-reproduction a constraint of evolution present at each step and imposing severe design constraints or a possible definition of life? Or is life an emerging phenomenon resulting from complex chemical reactions, developing networks and cycles until, at a certain critical size of this network, life starts as an emerging property (5)? Within this approach, life is a dynamical system where signal to noise is just marginal; a living system positions itself at the edge of chaos. Finally the only generally accepted theme is that life is the result of evolution, natural selection, and adaptation (6), a...

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Section: Bottom-up Development Of An Artificial Cell: Broad Consideramentioning

confidence: 99%

Development of an artificial cell, from self-organization to computation and self-reproduction

Noireaux¹,

Maeda

Libchaber

2011

Proc. Natl. Acad. Sci. U.S.A.

297

267

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“…Liposomes with bovine serum albumin are fragile, and their shapes fluctuate continually via Brownian motion. When actin (Miyata and Hotani, 1992) is added instead, it polymerizes, and filaments bundling at the periphery of the liposome can cause disk-shaped liposomes to transform into dumbbells. Both dumbbell and disk liposomes are rigid and keep their shapes until actin filaments are destabilized by cytochalasin.…”

Section: Liposomes With Filamentsmentioning

confidence: 99%

How did cells get their size?

Morris

2002

Anat. Rec.

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Cells exercise size homeostasis, and the origins of their ability to do so is the topic of this essay. Before there were cells, there were protocells. The most basic questions about protocells as objects are: What were they made of, and how big were they? Asking how big they were implies that the answer to the first part includes a boundary. The best candidate for that boundary is a self-assembling lipid bilayer. Therefore, protocells are defined here as Darwinian liposomes-bilayer vesicles with mutable on-board replicases linked to phenotypes. Because liposomes undergo spontaneous fission and fusion, and are subject to osmotic forces, size regulation in the earliest protocells would essentially have been liposome physics. For successful protocells, averting osmotic lysis would have been the first order of business. However, from the outset size mattered too, because of sex and reproduction (i.e., genome mixing and genome copying in entities with phenotypes). Protocell fission and fusion would have blended seamlessly into protocell sex and reproduction, making any gene product that furnished control over protocell size changes doubly adaptive. A recurrent theme is the feedback role of bilayer tension in protocell size control. Ways in which primitive peptides and their aggregates (e.g., channels) might have allowed liposomes to gain improved volume and surface area homeostasis are suggested. Domain-swapped proteins that polymerize as filaments are discussed as the origin of cytoskeleton structures that diversify and stabilize liposome shapes and sizes. Throughout, attention is paid to the question of set points for cell size.

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“…he polymerization of soluble actin monomers between filament ''barbed ends'' and the plasma membrane (PM) generates the force of protrusion in cell motility (1,2). Other proteins required for lamellipodial motility (3) are arp2/3, which nucleates (branches) free barbed ends at Ϸ70 degrees from existing ones (4); a PMbound activator of arp2/3 (5); ADF/cofilin, which promotes the depolymerization of pointed ends (6) and perhaps debranching reactions (7); and capping protein, a terminator of barbed end growth (8).…”

mentioning

confidence: 99%

Self-organization of actin filament orientation in the dendritic-nucleation/array-treadmilling model

Schaus

Taylor

Borisy

2007

Proc. Natl. Acad. Sci. U.S.A.

115

112

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The dendritic-nucleation/array-treadmilling model provides a conceptual framework for the generation of the actin network driving motile cells. We have incorporated it into a 2D, stochastic computer model to study lamellipodia via the self-organization of filament orientation patterns. Essential dendritic-nucleation submodels were incorporated, including discretized actin monomer diffusion, Monte-Carlo filament kinetics, and flexible filament and plasma membrane mechanics. Model parameters were estimated from the literature and simulation, providing values for the extent of the leading edge-branching/capping-protective zone (5.4 nm) and the autocatalytic branch rate (0.43/sec). For a given set of parameters, the system evolved to a steady-state filament count and velocity, at which total branching and capping rates were equal only for specific orientations; net capping eliminated others. The standard parameter set evoked a sharp preference for the ؎35 degree filaments seen in lamellipodial electron micrographs, requiring Ϸ12 generations of successive branching to adapt to a 15 degree change in protrusion direction. This pattern was robust with respect to membrane surface and bending energies and to actin concentrations but required protection from capping at the leading edge and branching angles >60 degrees. A ؉70/0/؊70 degree pattern was formed with flexible filaments Ϸ100 nm or longer and with velocities <Ϸ20% of free polymerization rates.lamellipodium ͉ cytoskeleton ͉ plasma membrane T he polymerization of soluble actin monomers between filament ''barbed ends'' and the plasma membrane (PM) generates the force of protrusion in cell motility (1, 2). Other proteins required for lamellipodial motility (3) are arp2/3, which nucleates (branches) free barbed ends at Ϸ70 degrees from existing ones (4); a PMbound activator of arp2/3 (5); ADF/cofilin, which promotes the depolymerization of pointed ends (6) and perhaps debranching reactions (7); and capping protein, a terminator of barbed end growth (8). The generation and persistence of lamellipodia from these elements is described in the ''dendritic-nucleation/arraytreadmilling'' conceptual model (2,4,9). This model can be subdivided into three main processes: the kinetics of filament (de)polymerization, branching, and capping; filament-PM interactions, which limit polymerization rates; and the diffusion of actin monomers and other soluble components. Such a system is ''complex'' in the sense that many copies of each component type interact to exhibit ''emergent'' system properties not expected from the individual rules of interaction (10). In contrast to ''complicated'' systems of many dissimilar components with precisely defined interactions, complex systems can self-organize and adapt to environmental change.An important emergent property is the self-organization of lamellipodial actin filaments into orientations at Ϯ35 degrees with respect to the direction of protrusion (11,12). Maly and Borisy (11) predicted Ϯ35 or ϩ70/0/Ϫ70 degree patterns with a 2D mathematical...

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Morphological changes in liposomes caused by polymerization of encapsulated actin and spontaneous formation of actin bundles.

Cited by 99 publications

References 25 publications

Development of an artificial cell, from self-organization to computation and self-reproduction

Development of an artificial cell, from self-organization to computation and self-reproduction

How did cells get their size?

Self-organization of actin filament orientation in the dendritic-nucleation/array-treadmilling model

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