Publications by authors named "Masatoshi Ichikawa"

43 Publications

Straight-to-Curvilinear Motion Transition of a Swimming Droplet Caused by the Susceptibility to Fluctuations.

Phys Rev Lett 2021 Aug;127(8):088005

Department of Physics, Kyoto University, Kyoto 606-8502, Japan.

In this Letter, a water-in-oil swimming droplet's transition from straight to curvilinear motion is investigated experimentally and theoretically. An analysis of the experimental results and the model reveal that the motion transition depends on the susceptibility of the droplet's direction of movement to external stimuli as a function of environmental parameters such as droplet size. The simplicity of the present experimental system and the model suggests implications for a general class of transitions in self-propelled swimmers.
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http://dx.doi.org/10.1103/PhysRevLett.127.088005DOI Listing
August 2021

Swimming droplets in 1D geometries: an active Bretherton problem.

Soft Matter 2021 Jul;17(27):6646-6660

UMR CNRS Gulliver 7083, ESPCI Paris, PSL Research University, 75005 Paris, France.

We investigate experimentally the behavior of self-propelled water-in-oil droplets, confined in capillaries of different square and circular cross-sections. The droplet's activity comes from the formation of swollen micelles at its interface. In straight capillaries the velocity of the droplet decreases with increasing confinement. However, at very high confinement, the velocity converges toward a non-zero value, so that even very long droplets swim. Stretched circular capillaries are used to explore even higher confinement. The lubrication layer around the droplet then takes a non-uniform thickness which constitutes a significant difference to usual flow-driven passive droplets. A neck forms at the rear of the droplet, deepens with increasing confinement, and eventually undergoes successive spontaneous splitting events for large enough confinement. Such observations stress the critical role of the activity of the droplet interface in the droplet's behavior under confinement. We then propose an analytical formulation by integrating the interface activity and the swollen micelle transport problem into the classical Bretherton approach. The model accounts for the convergence of the droplet's velocity to a finite value for large confinement, and for the non-classical shape of the lubrication layer. We further discuss on the saturation of the micelle concentration along the interface, which would explain the divergence of the lubrication layer thickness for long enough droplets, eventually leading to spontaneous droplet division.
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http://dx.doi.org/10.1039/d1sm00387aDOI Listing
July 2021

Force generation by a propagating wave of supramolecular nanofibers.

Nat Commun 2020 07 15;11(1):3541. Epub 2020 Jul 15.

Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto, 615-8510, Japan.

Dynamic spatiotemporal patterns that arise from out-of-equilibrium biochemical reactions generate forces in living cells. Despite considerable recent efforts, rational design of spatiotemporal patterns in artificial molecular systems remains at an early stage of development. Here, we describe force generation by a propagating wave of supramolecular nanofibers. Inspired by actin dynamics, a reaction network is designed to control the formation and degradation of nanofibers by two chemically orthogonal stimuli. Real-time fluorescent imaging successfully visualizes the propagating wave based on spatiotemporally coupled generation and collapse of nanofibers. Numerical simulation indicates that the concentration gradient of degradation stimulus and the smaller diffusion coefficient of the nanofiber are critical for wave emergence. Moreover, the force (0.005 pN) generated by chemophoresis and/or depletion force of this propagating wave can move nanobeads along the wave direction.
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http://dx.doi.org/10.1038/s41467-020-17394-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7363860PMC
July 2020

Influence of cellular shape on sliding behavior of ciliates.

Commun Integr Biol 2018 15;11(4):e1506666. Epub 2018 Aug 15.

Department of Physics, Kyoto University, Sakyo, Kyoto, Japan.

Some types of ciliates accumulate on solid/fluid interfaces. This behavior is advantageous to survival in nature due to the presence of sufficient nutrition and stable environments. Recently, the accumulating mechanisms of at the interface were investigated. The synergy of the ellipsoidal shape of the cell body and the mechanosensing feature of the cilia allow for cells to slide on interfaces, and the sliding behavior leads to cell accumulation on the interfaces. Here, to examine the generality of the sliding behavior of ciliates, we characterized the behavior of , which is a commonly studied ciliate. Our experimental and numerical results confirmed that also slid on the solid/fluid interface by using the same mechanism as . In addition, we evaluated the effects of cellular ellipticity on their behaviors near the wall with a phase diagram produced via numerical simulation.
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http://dx.doi.org/10.1080/19420889.2018.1506666DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6284593PMC
August 2018

DSH5, a dihydrosphingosine C4 hydroxylase gene family member, shows spatially restricted expression in rice and is lethal when expressed ectopically.

Genes Genet Syst 2018 Nov 4;93(4):135-142. Epub 2018 Sep 4.

Department of Biological Science and Technology, Tokyo University of Science.

Dihydrosphingosine C4 hydroxylase (DSH), a diiron-binding membrane enzyme, catalyzes the hydration of dihydrosphingosine and acyl-sphinganine to produce phytosphingosine and phytoceramide, respectively. Rice has two types of DSH homologs: general DSHs, namely DSH1, DSH2 and DSH4, and others that show spatial expression profiles, namely DSH3 and DSH5. The general DSHs exist in many plant species. These DSHs showed similarity in their functions and complemented the yeast sur2D mutation. In contrast, homologs of DSH3 and DSH5 were found only in monocot plants. Phylogenetic analysis placed these DSHs in different clades that are evolutionarily divergent from those of the general DSHs. DSH3 and DSH5 showed low-level expression. DSH5 expression was specifically in vascular bundle tissues. Ectopic expression of DSH5 induced a dwarf phenotype characterized by severe growth inhibition and an increase in the thickness of the leaf body caused by enlargement of bulliform cells in the leaves. However, no significant difference was observed in the amount of sphingolipid species. DSH5 did not complement the yeast sur2D mutation, implying that DSH5 has little effect on sphingolipid metabolism. These findings suggested that DSH3 and DSH5 originated and diverged in monocot plants.
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http://dx.doi.org/10.1266/ggs.17-00054DOI Listing
November 2018

Self-propelled motion switching in nematic liquid crystal droplets in aqueous surfactant solutions.

Phys Rev E 2018 Jun;97(6-1):062703

Department of Physics, School of Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.

The self-propelled motions of micron-sized nematic liquid crystal droplets in an aqueous surfactant solution have been studied by tracking individual droplets over long time periods. Switching between self-propelled modes is observed as the droplet size decreases at a nearly constant dissolution rate: from random to helical and then straight motion. The velocity of the droplet decreases with its size for straight and helical motions but is independent of size for random motion. The switching between helical and straight motions is found to be governed by the self-propelled velocity, and is confirmed by experiments at various surfactant concentrations. The helical motion appears along with a shifting of a point defect from the self-propelled direction of the droplet. The critical velocity for this shift of the defect position is found to be related with the Ericksen number, which is defined by the ratio of the viscous and elastic stresses. In a thin cell whose thickness is smaller than that of the initial droplet size, the droplets show more complex trajectories, including "figure-8s" and zigzags. The appearance of those characteristic motions is attributed to autochemotaxis of the droplet.
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http://dx.doi.org/10.1103/PhysRevE.97.062703DOI Listing
June 2018

Simple mechanosense and response of cilia motion reveal the intrinsic habits of ciliates.

Proc Natl Acad Sci U S A 2018 03 12;115(13):3231-3236. Epub 2018 Mar 12.

Department of Physics, Kyoto University, Sakyo, Kyoto 606-8502, Japan;

An important habit of ciliates, namely, their behavioral preference for walls, is revealed through experiments and hydrodynamic simulations. A simple mechanical response of individual ciliary beating (i.e., the beating is stalled by the cilium contacting a wall) can solely determine the sliding motion of the ciliate along the wall and result in a wall-preferring behavior. Considering ciliate ethology, this mechanosensing system is likely an advantage in the single cell's ability to locate nutrition. In other words, ciliates can skillfully use both the sliding motion to feed on a surface and the traveling motion in bulk water to locate new surfaces according to the single "swimming" mission.
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http://dx.doi.org/10.1073/pnas.1718294115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5879680PMC
March 2018

Geometry-driven collective ordering of bacterial vortices.

Soft Matter 2017 Jul;13(29):5038-5043

Department of Physics, Kyushu University, Motooka 744, Fukuoka 812-0395, Japan.

Controlling the phases of matter is a challenge that spans from condensed materials to biological systems. Here, by imposing a geometric boundary condition, we study the controlled collective motion of Escherichia coli bacteria. A circular microwell isolates a rectified vortex from disordered vortices masked in the bulk. For a doublet of microwells, two vortices emerge but their spinning directions show transition from parallel to anti-parallel. A Vicsek-like model for confined self-propelled particles gives the point where the two spinning patterns occur in equal probability and one geometric quantity governs the transition as seen in experiments. This mechanism shapes rich patterns including chiral configurations in a quadruplet of microwells, thus revealing a design principle of active vortices.
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http://dx.doi.org/10.1039/c7sm00999bDOI Listing
July 2017

Wrinkling of a spherical lipid interface induced by actomyosin cortex.

Phys Rev E Stat Nonlin Soft Matter Phys 2015 Dec 21;92(6):062711. Epub 2015 Dec 21.

Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.

Actomyosin actively generates contractile forces that provide the plasma membrane with the deformation stresses essential to carry out biological processes. Although the contractile property of purified actomyosin has been extensively studied, to understand the physical contribution of the actomyosin contractile force on a deformable membrane is still a challenging problem and of great interest in the field of biophysics. Here, we reconstitute a model system with a cell-sized deformable interface that exhibits anomalous curvature-dependent wrinkling caused by the actomyosin cortex underneath the spherical closed interface. Through a shape analysis of the wrinkling deformation, we find that the dominant contributor to the wrinkled shape changes from bending elasticity to stretching elasticity of the reconstituted cortex upon increasing the droplet curvature radius of the order of the cell size, i.e., tens of micrometers. The observed curvature dependence is explained by the theoretical description of the cortex elasticity and contractility. Our present results provide a fundamental insight into the deformation of a curved membrane induced by the actomyosin cortex.
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http://dx.doi.org/10.1103/PhysRevE.92.062711DOI Listing
December 2015

Non-periodic oscillatory deformation of an actomyosin microdroplet encapsulated within a lipid interface.

Sci Rep 2016 Jan 12;6:18964. Epub 2016 Jan 12.

Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.

Active force generation in living organisms, which is mainly involved in actin cytoskeleton and myosin molecular motors, plays a crucial role in various biological processes. Although the contractile properties of actomyosin have been extensively investigated, their dynamic contribution to a deformable membrane remains unclear because of the cellular complexities and the difficulties associated with in vitro reconstitution. Here, by overcoming these experimental difficulties, we demonstrate the dynamic deformation of a reconstituted lipid interface coupled with self-organized structure of contractile actomyosin. Therein, the lipid interface repeatedly oscillates without any remarkable periods. The oscillatory deformation of the interface is caused by the aster-like three-dimensional hierarchical structure of actomyosin inside the droplet, which is revealed that the oscillation occurs stochastically as a Poisson process.
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http://dx.doi.org/10.1038/srep18964DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4709586PMC
January 2016

Dynamic clustering of driven colloidal particles on a circular path.

Phys Rev E Stat Nonlin Soft Matter Phys 2015 Sep 8;92(3):032303. Epub 2015 Sep 8.

Department of Physics, School of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.

We studied the collective motion of particles forced to move along a circular path in water by utilizing an optical vortex. Their collective motion, including the spontaneous formation of clusters and their dissociation, was observed. The observed temporal patterns depend on the number of particles on the path and the variation of their sizes. The addition of particles with different sizes suppresses the dynamic formation and dissociation of clusters and promotes the formation of specific stationary clusters. These experimental findings are reproduced by numerical simulations that take into account the hydrodynamic interaction between the particles and the radial trapping force confining the particles to the circular path. A transition between stationary and nonstationary clustering of the particles was observed by varying their size ratio in the binary-size systems. Our simulation reveals that the transition can be either continuous or discontinuous depending on the number of different-size particles. This result suggests that the size distribution of particles has a significant effect on the collective behavior of self-propelled particles in viscous fluids.
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http://dx.doi.org/10.1103/PhysRevE.92.032303DOI Listing
September 2015

Droplet-Shooting and Size-Filtration (DSSF) Method for Synthesis of Cell-Sized Liposomes with Controlled Lipid Compositions.

Chembiochem 2015 Sep 17;16(14):2029-35. Epub 2015 Aug 17.

Department of Computational Intelligence and Systems Science, Tokyo Institute of Technology, Kanagawa, 226-8502, Japan.

We report a centrifugal microfluidic method, droplet-shooting and size-filtration (DSSF), for the production of cell-sized liposomes with controlled lipid compositions. This involves the generation of large and small droplets from the tip of a glass capillary and the selective transfer of small droplets through an oil-water interface, thus resulting in the generation of cell-sized liposomes. We demonstrate control of the microdomain formation as well as the formation of asymmetric lipid bilayer liposomes of uniform size by the control of lipid composition. The DSSF method involves simple microfluidics and is easy to use. In addition, only a small volume (0.5-2 μL) of sample solution is required for the formation of hundreds of cell-sized liposomes. We believe that this method can be applied to generate cell-sized liposomes for a wide variety of uses, such as the construction of artificial cell-like systems.
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http://dx.doi.org/10.1002/cbic.201500354DOI Listing
September 2015

Molecular behavior of DNA in a cell-sized compartment coated by lipids.

Phys Rev E Stat Nonlin Soft Matter Phys 2015 Jun 29;91(6):062717. Epub 2015 Jun 29.

School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.

The behavior of long DNA molecules in a cell-sized confined space was investigated. We prepared water-in-oil droplets covered by phospholipids, which mimic the inner space of a cell, following the encapsulation of DNA molecules with unfolded coil and folded globule conformations. Microscopic observation revealed that the adsorption of coiled DNA onto the membrane surface depended on the size of the vesicular space. Globular DNA showed a cell-size-dependent unfolding transition after adsorption on the membrane. Furthermore, when DNA interacted with a two-phase membrane surface, DNA selectively adsorbed on the membrane phase, such as an ordered or disordered phase, depending on its conformation. We discuss the mechanism of these trends by considering the free energy of DNA together with a polyamine in the solution. The free energy of our model was consistent with the present experimental data. The cooperative interaction of DNA and polyamines with a membrane surface leads to the size-dependent behavior of molecular systems in a small space. These findings may contribute to a better understanding of the physical mechanism of molecular events and reactions inside a cell.
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http://dx.doi.org/10.1103/PhysRevE.91.062717DOI Listing
June 2015

Mode bifurcation of a bouncing dumbbell with chirality.

Phys Rev E Stat Nonlin Soft Matter Phys 2015 May 8;91(5):052905. Epub 2015 May 8.

Faculty of Life and Medical Sciences, Doshisha University, Kyotanabe, 610-0394, Japan.

We studied the behavior of a dumbbell bouncing upon a sinusoidally vibrating plate. By introducing chiral asymmetry to the geometry of the dumbbell, we observed a cascade of bifurcations with an increase in the vibration amplitude: spinning, orbital, and rolling. In contrast, for an achiral dumbbell, bifurcation is generated by a change from random motion to vectorial inchworm motion. A simple model particle was considered in a numerical simulation that reproduced the essential aspects of the experimental observation. The mode bifurcation from directional motion to random motion is interpreted analytically by a simple mechanical discussion.
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http://dx.doi.org/10.1103/PhysRevE.91.052905DOI Listing
May 2015

Quantification of the Influence of Endotoxins on the Mechanics of Adult and Neonatal Red Blood Cells.

J Phys Chem B 2015 Jun 11;119(25):7837-45. Epub 2015 Jun 11.

‡Institute of Physical Chemistry, University of Heidelberg, D69120 Heidelberg, Germany.

In this study, we physically modeled the influence of endotoxin-induced sepsis symptoms on human red blood cells (RBCs) by quantifying the impact of endotoxins on the cell mechanics by the analysis of Fourier-transformed mean square amplitude of shape fluctuation, called flicker spectroscopy. With the aid of a microfluidic diffusion chamber, we noninvasively determined principal mechanical parameters of human RBCs in the absence and presence of endotoxins for individual RBCs for the first time. Because of the elongation of saccharide chain length of endotoxins, we found an increase in the morphological transition from discocytes to echinocytes, and monotonic changes in the mechanical parameters. Since septic shocks often cause lethal risks of neonates, we measured the mechanical parameters of neonatal RBCs, and compared them to those of adult RBCs. The quantitative comparison reveals that neonatal RBCs are more susceptible to the effect of endotoxins than adult RBCs. Furthermore, coincubation with the antiseptic peptide P19-2.5 (Aspidasept) with endotoxin results in a slight suppression of the impact of the endotoxin. The strategy proposed in our study can potentially be applied for the quantitative diagnosis of RBCs based on mechanical readouts.
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http://dx.doi.org/10.1021/acs.jpcb.5b01544DOI Listing
June 2015

Dynamics of microdroplets over the surface of hot water.

Sci Rep 2015 Jan 27;5:8046. Epub 2015 Jan 27.

Department of Physics, Kyoto University, Kyoto 606-8502, Japan.

When drinking a cup of coffee under the morning sunshine, you may notice white membranes of steam floating on the surface of the hot water. They stay notably close to the surface and appear to almost stick to it. Although the membranes whiffle because of the air flow of rising steam, peculiarly fast splitting events occasionally occur. They resemble cracking to open slits approximately 1 mm wide in the membranes, and leave curious patterns. We studied this phenomenon using a microscope with a high-speed video camera and found intriguing details: i) the white membranes consist of fairly monodispersed small droplets of the order of 10 μm; ii) they levitate above the water surface by 10 ~ 100 μm; iii) the splitting events are a collective disappearance of the droplets, which propagates as a wave front of the surface wave with a speed of 1 ~ 2 m/s; and iv) these events are triggered by a surface disturbance, which results from the disappearance of a single droplet.
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http://dx.doi.org/10.1038/srep08046DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4306967PMC
January 2015

Emergence of DNA-encapsulating liposomes from a DNA-lipid blend film.

J Phys Chem B 2014 Sep 28;118(36):10688-94. Epub 2014 Aug 28.

Department of Physics, Graduate School of Science, Kyoto University , Kyoto 606-8502, Japan.

Spontaneous generation of DNA-enclosing liposomes from a DNA-lipid blend film is investigated. The special properties of the lipid vesicles, namely, micrometer size, unilamellarity, and dense polymer encapsulation acquired by the dehydration-rehydration process, are physicochemically revealed. We found that the formation of giant unilamellar vesicles encapsulating DNAs are governed by micropatterns of the films, such as dots and network patterns. From the results, we proposed a plausible physical mechanism for the dehydration-rehydration process, making it possible to optimize the encapsulation of any agent.
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http://dx.doi.org/10.1021/jp506096hDOI Listing
September 2014

Communication: Mode bifurcation of droplet motion under stationary laser irradiation.

J Chem Phys 2014 Aug;141(5):051103

Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.

The self-propelled motion of a mm-sized oil droplet floating on water, induced by a local temperature gradient generated by CW laser irradiation is reported. The circular droplet exhibits two types of regular periodic motion, reciprocal and circular, around the laser spot under suitable laser power. With an increase in laser power, a mode bifurcation from rectilinear reciprocal motion to circular motion is caused. The essential aspects of this mode bifurcation are discussed in terms of spontaneous symmetry-breaking under temperature-induced interfacial instability, and are theoretically reproduced with simple coupled differential equations.
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http://dx.doi.org/10.1063/1.4892085DOI Listing
August 2014

[Creation and manipulation of an artificial cellular system].

Seikagaku 2014 Apr;86(2):209-13

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April 2014

Back-and-forth micromotion of aqueous droplets in a dc electric field.

Phys Rev E Stat Nonlin Soft Matter Phys 2013 Oct 21;88(4):042918. Epub 2013 Oct 21.

Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.

Recently, it was reported that an aqueous droplet in an oil phase exhibited rhythmic back-and-forth motion under stationary dc voltage on the order of 100 V. Here, we demonstrate that the threshold voltage for inducing such oscillation is successfully decreased to the order of 10 V through downsizing of the experimental system. Notably, the threshold electric field tends to decrease with a nonlinear scaling relationship accompanied by the downsizing. We derive a simple theoretical model to interpret the system size dependence of the threshold voltage. This model equation suggests the unique effect of additional noise, which is qualitatively characterized as a coherent resonance by an actual experiment as a kind of coherent resonance. Our result would provide insight into the construction of micrometer-sized self-commutating motors and actuators in microfluidic and micromechanical devices.
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http://dx.doi.org/10.1103/PhysRevE.88.042918DOI Listing
October 2013

Dynamical formation of lipid bilayer vesicles from lipid-coated droplets across a planar monolayer at an oil/water interface.

Soft Matter 2013 Oct;9(40):9539-47

Department of Physics, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan.

Recently, the transfer method has been shown to be useful for preparing cell-sized phospholipid bilayer vesicles, within which desired substances at desired concentrations can be encapsulated, with a desired asymmetric lipid composition. Here, we investigated the transfer process of water-in-oil (W/O) droplets coated by phospholipid monolayers across an oil/water interface by both experimental observation and theoretical modeling. Real-time experimental observation of the transfer revealed that the transfer process is characterized by three kinetic regimes: a precontact process (approaching regime), an early fast process (entering regime), and a late slow process (relaxation regime). In addition, bigger droplets require much more time to transfer than smaller droplets. We propose a theoretical model to interpret this kinetic process. Our theoretical model reproduces the essential aspects of the transfer kinetics, including its size-dependence.
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http://dx.doi.org/10.1039/c3sm51766gDOI Listing
October 2013

Structural change of DNA induced by nucleoid proteins: growth phase-specific Fis and stationary phase-specific Dps.

Biophys J 2013 Aug;105(4):1037-44

Department of Physics, Kyoto University, Kyoto, Japan.

The effects of nucleoid proteins Fis and Dps of Escherichia coli on the higher order structure of a giant DNA were studied, in which Fis and Dps are known to be expressed mainly in the exponential growth phase and stationary phase, respectively. Fis causes loose shrinking of the higher order structure of a genome-sized DNA, T4 DNA (166 kbp), in a cooperative manner, that is, the DNA conformational transition proceeds through the appearance of a bimodal size distribution or the coexistence of elongated coil and shrunken globular states. The effective volume of the loosely shrunken state induced by Fis is 30-60 times larger than that of the compact state induced by spermidine, suggesting that cellular enzymes can access for DNA with the shrunken state but cannot for the compact state. Interestingly, Dps tends to inhibit the Fis-induced shrinkage of DNA, but promotes DNA compaction in the presence of spermidine. These characteristic effects of nucleotide proteins on a giant DNA are discussed by adopting a simple theoretical model with a mean-field approximation.
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http://dx.doi.org/10.1016/j.bpj.2013.07.025DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3752111PMC
August 2013

Controlling negative and positive photothermal migration of centimeter-sized droplets.

Phys Rev E Stat Nonlin Soft Matter Phys 2013 Jul 18;88(1):012403. Epub 2013 Jul 18.

Department of Physics, Kyoto University, Kyoto 606-8502, Japan.

The photoinduced motion of an oil droplet on an aqueous solution under local irradiation by a green laser is reported. The results showed that a repulsive force is generated on pure water, while an attractive force is observed with an aqueous solution containing a surfactant. The driving force is discussed in terms of a thermal Marangoni effect. The switching on the photothermal effect is interpreted by taking into account the advection caused by the spatial gradient of the surface tension under local heating by a laser. A numerical model revealed that the geometrical profile of the surface tension around the droplet determines the mode of advection around the droplet and causes switching in the direction of migrations.
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http://dx.doi.org/10.1103/PhysRevE.88.012403DOI Listing
July 2013

Reconstruction of active regular motion in amoeba extract: dynamic cooperation between sol and gel states.

PLoS One 2013 5;8(8):e70317. Epub 2013 Aug 5.

Department of Life Science, Graduate School of Life Science, University of Hyogo, Harima Science Park City, Hyogo, Japan.

Amoeboid locomotion is one of the typical modes of biological cell migration. Cytoplasmic sol-gel conversion of an actomyosin system is thought to play an important role in locomotion. However, the mechanisms underlying sol-gel conversion, including trigger, signal, and regulating factors, remain unclear. We developed a novel model system in which an actomyosin fraction moves like an amoeba in a cytoplasmic extract. Rheological study of this model system revealed that the actomyosin fraction exhibits shear banding: the sol-gel state of actomyosin can be regulated by shear rate or mechanical force. Furthermore, study of the living cell indicated that the shear-banding property also causes sol-gel conversion with the same order of magnitude as that of shear rate. Our results suggest that the inherent sol-gel transition property plays an essential role in the self-regulation of autonomous translational motion in amoeba.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0070317PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3734023PMC
March 2014

Plasmonic imaging of brownian motion of single DNA molecules spontaneously binding to Ag nanoparticles.

Nano Lett 2013 May 5;13(5):1877-82. Epub 2013 Apr 5.

Health Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Takamatsu, Kagawa 761-0395, Japan.

We find the spontaneous binding of single DNA molecules to uncoated silver nanoparticles (AgNPs) in aqueous solution with Mn(2+) (3 mM). From dark-field optical microscopic imaging of AgNPs bound to DNA molecules, we demonstrate analysis of the Brownian motion of single DNA molecules via plasmon resonance elastic light scattering. Our results provide that the plasmonic imaging technique is free from photobleaching and blinking and thus is useful in long-time observations of single-molecule DNA dynamics.
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http://dx.doi.org/10.1021/nl304247nDOI Listing
May 2013

Rotational motion of a droplet induced by interfacial tension.

Phys Rev E Stat Nonlin Soft Matter Phys 2013 Jan 9;87(1):013009. Epub 2013 Jan 9.

Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan.

Spontaneous rotation of a droplet induced by the Marangoni flow is analyzed in a two-dimensional system. The droplet with the small particle which supplies a surfactant at the interface is considered. We calculated flow field around the droplet using the Stokes equation and found that advective nonlinearity breaks symmetry for rotation. Theoretical calculation indicates that the droplet spontaneously rotates when the radius of the droplet is an appropriate size. The theoretical results were validated through comparison with the experiments.
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http://dx.doi.org/10.1103/PhysRevE.87.013009DOI Listing
January 2013

Direct measurement of single soft lipid nanotubes: nanoscale information extracted in a noninvasive manner.

Phys Rev E Stat Nonlin Soft Matter Phys 2012 Dec 14;86(6 Pt 1):061905. Epub 2012 Dec 14.

Department of Physics, Kyoto University, Sakyo, Kyoto 606-8502, Japan.

We investigated the dynamics of single soft nanotubes of phospholipids to extract nanoscale information such as the size of the tube, which were several tens to hundreds of nanometers thick. The dynamic properties of the tubes obtained from direct observation by fluorescent microscopy, such as their persistence length, enable us to access the nanoscale characteristics through a simple elastic model of the membrane. The present methodology should be applicable to the nanosized membrane structure in living cells.
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http://dx.doi.org/10.1103/PhysRevE.86.061905DOI Listing
December 2012

Physicochemical analysis from real-time imaging of liposome tubulation reveals the characteristics of individual F-BAR domain proteins.

Langmuir 2013 Jan 13;29(1):328-36. Epub 2012 Dec 13.

Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan.

The Fer-CIP4 homology-BAR (F-BAR) domain, which was identified as a biological membrane-deforming module, has been reported to transform lipid bilayer membranes into tubules. However, details of the tubulation process, the mechanism, and the properties of the generated tubules remain unknown. Here, we successfully monitored the entire process of tubulation and the behavior of elongated tubules caused by four different F-BAR domain family proteins (FBP17, CIP4, PSTPIP1, and Pacsin2) using direct real-time imaging of giant unilamellar liposomes with dark-field optical microscopy. FBP17 and CIP4 develop many protrusions simultaneously over the entire surface of individual liposomes, whereas PSTPIP1 and Pacsin2 develop only a few protrusions from a narrow restricted part of the surface of individual liposomes. Tubules formed by FBP17 or CIP4 have higher bending rigidities than those formed by PSTPIP1 or Pacsin2. The results provide striking evidence that these four F-BAR domain family proteins should be classified into two groups: one group of FBP17 and CIP4 and another group of PSTPIP1 and Pacsin2. This classification is consistent with the phylogenetic proximity among these proteins and suggests that the nature of the respective tubulation is associated with biological function. These findings aid in the quantitative assessment with respect to manipulating the morphology of lipid bilayers using membrane-deforming proteins.
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January 2013

Emergence of a thread-like pattern with charged phospholipids on an oil/water interface.

J Chem Phys 2012 May;136(20):204903

Department of Physics, Graduate School of Science, Kyoto University, 606-8501 Kyoto, Japan.

The spontaneous formation of a thread-like pattern with negatively charged lipids on an oil/water interface is reported. An analysis of the time-dependent change at the interface observed by fluorescence microscopy revealed that the thread-like pattern is generated through a two-step mechanism. First, inverted lipid micelles in the bulk-oil phase gradually diffuse onto the oil/water interface. Next, the micelles are adsorbed on the interface and self-assemble to form the thread-like pattern. The essential characteristics of this pattern formation are theoretically reproduced by a simple Monte Carlo simulation that takes into account the kinetics in the coalescence of charged micelles on a 2D interface.
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http://dx.doi.org/10.1063/1.4722079DOI Listing
May 2012
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