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Sato K.,RIKEN | Kuramoto Y.,International Institute for Advanced Studies | Ohtaki M.,Waseda University | Shimamoto Y.,Rockefeller University | And 2 more authors.
Physical Review Letters | Year: 2013

At an intermediate activation level, striated muscle exhibits autonomous oscillations called SPOC, in which the basic contractile units, sarcomeres, oscillate in length, and various oscillatory patterns such as traveling waves and their disrupted forms appear in a myofibril. Here we show that these patterns are reproduced by mechanically connecting in series the unit model that explains characteristics of SPOC at the single-sarcomere level. We further reduce the connected model to phase equations, revealing that the combination of local and global couplings is crucial to the emergence of these patterns. © 2013 American Physical Society. Source

Arai S.,National University of Singapore | Arai S.,Waseda University | Lee S.-C.,Agency for Science, Technology and Research Singapore | Zhai D.,National University of Singapore | And 4 more authors.
Scientific Reports | Year: 2014

The dynamics of cellular heat production and propagation remains elusive at a subcellular level. Here we report the first small molecule fluorescent thermometer selectively targeting the endoplasmic reticulum (ER thermo yellow), with the highest sensitivity reported so far (3.9%/°C). Unlike nanoparticle thermometers, ER thermo yellow stains the target organelle evenly without the commonly encountered problem of aggregation, and successfully demonstrates the ability to monitor intracellular temperature gradients generated by external heat sources in various cell types. We further confirm the ability of ER thermo yellow to monitor heat production by intracellular Ca2+ changes in HeLa cells. Our thermometer anchored at nearly-zero distance from the ER, i.e. the heat source, allowed the detection of the heat as it readily dissipated, and revealed the dynamics of heat production in real time at a subcellular level. Source

Ishiwata S.,Waseda University | Ishiwata S.,Waseda Bioscience Research Institute in Singapore WABIOS | Shimamoto Y.,Rockefeller University | Fukuda N.,Jikei University School of Medicine
Progress in Biophysics and Molecular Biology | Year: 2011

It is widely known that the contractile system of muscle takes on either the state of contraction (force-generating) or the state of relaxation (non-force-generating), which is known as the " all-or-nothing" principle. However, it is important to note that under intermediate activation conditions there exists a third state, which demonstrates auto-oscillatory properties and is termed SPOC (SPontaneous Oscillatory Contraction) state. We present a phase diagram, in which the states of the contractile system of muscle are divided into three regions consisting of contraction, relaxation and SPOC states. In the present review, experimental data related to the characteristics of SPOC are summarized and the mechanism of SPOC is described. We propose that the bio-motile system itself is an auto-oscillator, even in a membrane-less supra-molecular structure composed of an assembly of molecular motors and cytoskeletons (actin filaments and microtubules). Finally, the physiological significance of SPOC is discussed. © 2010 Elsevier Ltd. Source

Chiba M.,Waseda University | Miyazaki M.,Waseda University | Ishiwata S.,Waseda University | Ishiwata S.,Waseda Bioscience Research Institute in Singapore WABIOS
Biophysical Journal | Year: 2014

The inverted emulsion method is used to prepare giant liposomes by pushing water-in-oil droplets through the oil/water interface into an aqueous medium. Due to the high encapsulation efficiency of proteins under physiological conditions and the simplicity of the protocol, it has been widely used to prepare various cell models. However, the lamellarity of liposomes prepared by this method has not been evaluated quantitatively. Here, we prepared liposomes that were partially stained with a fluorescent dye, and analyzed their fluorescence intensity under an epifluorescence microscope. The fluorescence intensities of the membranes of individual liposomes were plotted against their diameter. The plots showed discrete distributions, which were classified into several groups. The group with the lowest fluorescence intensity was determined to be unilamellar by monitoring the exchangeability of the inner and the outer solutions of the liposomes in the presence of the pore-forming toxin α-hemolysin. Increasing the lipid concentration dissolved in oil increased the number of liposomes ∼100 times. However, almost all the liposomes were unilamellar even at saturating lipid concentrations. We also investigated the effects of lipid composition and liposome content, such as highly concentrated actin filaments and Xenopus egg extracts, on the lamellarity of the liposomes. Remarkably, over 90% of the liposomes were unilamellar under all conditions examined. We conclude that the inverted emulsion method can be used to efficiently prepare giant unilamellar liposomes and is useful for designing cell models. © 2014 Biophysical Society. Source

Oguchi Y.,Waseda University | Uchimura S.,RIKEN | Ohki T.,Waseda University | Mikhailenko S.V.,Waseda University | And 2 more authors.
Nature Cell Biology | Year: 2011

During cell division the replicated chromosomes are segregated precisely towards the spindle poles. Although many cellular processes involving motility require ATP-fuelled force generation by motor proteins, most models of the chromosome movement invoke the release of energy stored at strained (owing to GTP hydrolysis) plus ends of microtubules. This energy is converted into chromosome movement through passive couplers, whereas the role of molecular motors is limited to the regulation of microtubule dynamics. Here we report, that the microtubule-depolymerizing activity of MCAK (mitotic centromere-associated kinesin), the founding member of the kinesin-13 family, is accompanied by the generation of significant tensiongremarkably, at both microtubule ends. An MCAK-decorated bead strongly attaches to the microtubule side, but readily slides along it in either direction under weak external loads and tightly captures and disassembles both microtubule ends. We show that the depolymerization force increases with the number of interacting MCAK molecules and is ∼1-pN per motor. These results provide a simple model for the generation of driving force and the regulation of chromosome segregation by the activity of MCAK at both kinetochores and spindle poles through aside-sliding, end-catchinmechanism. © 2011 Macmillan Publishers Limited. All rights reserved. Source

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