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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CELL PRESS  

The spatial gradient of signaling molecules is pivotal for establishing developmental patterns of multicellular organisms. It has long been proposed that these gradients could arise from the pure diffusion process of signaling molecules between cells, but whether this simplest mechanism establishes the formation of the tissue-scale gradient remains unclear. Plasmodesmata are unique channel structures in plants that connect neighboring cells for molecular transport. In this study, we measured cellular- and tissue-scale kinetics of molecular transport through plasmodesmata in Arabidopsis thaliana developing leaf primordia by fluorescence recovery assays. These trans-scale measurements revealed biophysical properties of diffusive molecular transport through plasmodesmata and revealed that the tissue-scale diffusivity, but not the cellular-scale diffusivity, is spatially different along the leaf proximal-to-distal axis. We found that the gradient in cell size along the developmental axis underlies this spatially different tissue-scale diffusivity. We then asked how this diffusion-based framework functions in establishing a signaling gradient of endogenous molecules. ANGUSTIFOLIA3 (AN3) is a transcriptional co-activator, and as we have shown here, it forms a long-range signaling gradient along the leaf proximal-to-distal axis to determine a cell-proliferation domain. By genetically engineering AN3 mobility, we assessed each contribution of cell-to-cell movement and tissue growth to the distribution of the AN3 gradient. We constructed a diffusion-based theoretical model using these quantitative data to analyze the AN3 gradient formation and demonstrated that it could be achieved solely by the diffusive molecular transport in a growing tissue. Our results indicate that the spatially different tissue-scale diffusivity is a core mechanism for AN3 gradient formation. This provides evidence that the pure diffusion process establishes the formation of the long-range signaling gradient in leaf development.

DOI： 10.1016/j.bpj.2017.06.072

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROCKEFELLER UNIV PRESS  

Although mechanisms that contribute to microtubule (MT) aster positioning have been extensively studied, still little is known on how asters move inside cells to faithfully target a cellular location. Here, we study sperm aster centration in sea urchin eggs, as a stereotypical large-scale aster movement with extreme constraints on centering speed and precision. By tracking three-dimensional aster centration dynamics in eggs with manipulated shapes, we show that aster geometry resulting from MT growth and interaction with cell boundaries dictates aster instantaneous directionality, yielding cell shape-dependent centering trajectories. Aster laser surgery and modeling suggest that dynein-dependent MT cytoplasmic pulling forces that scale to MT length function to convert aster geometry into directionality. In contrast, aster speed remains largely independent of aster size, shape, or absolute dynein activity, which suggests it may be predominantly determined by aster growth rate rather than MT force amplitude. These studies begin to define the geometrical principles that control aster movements.

DOI： 10.1083/jcb.201510064

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Language：Japanese   Publisher：The Biophysical Society of Japan General Incorporated Association  

<p>The various molecules and organelles in a eukaryotic cell are suitably positioned within the cell to carry out their functions at the appropriate time. This intracellular positioning is accomplished through interplay among the active transport mechanisms, intracellular fluctuations, and physical properties of the components inside the cell. Here, we review the recent advances in research on how the nucleus moves toward, and maintains its position at, the geometrical center of the cell. This question has attracted researchers from various fields, and is a good subject for interdisciplinary collaboration.</p>

DOI： 10.2142/biophys.56.271

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Other Link： http://search.jamas.or.jp/link/ui/2017077753

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CELL PRESS  

Intracellular structures and organelles such as the nucleus, the centrosome, or the mitotic spindle typically scale their size to cell size [1]. Similarly, cortical polarity domains built around the active form of conserved Rho-GTPases, such as Cdc42p, exhibit widths that may range over two orders of magnitudes in cells with different sizes and shapes [2-6]. The establishment of such domains typically involves positive feedback loops based on reaction-diffusion and/or actin-mediated vesicle transport [3, 7, 8]. How these elements may adapt polarity domain size to cellular geometry is not known. Here, by tracking the width of successive oscillating Cdc42-GTP domains in fission yeast spores [9], we find that domain width scales with local cell-surface radii of curvature over an 8-fold range, independently of absolute cell volume, surface, or Cdc42-GTP concentration. This local scaling requires formin-nucleated cortical actin cables and the fusion of secretory vesicles transported along these cables with the membrane. These data suggest that reaction-diffusion may set a minimal domain size and that secretory vesicle transport along actin cables may dilute and extend polarity domains to adapt their size to local cell-surface curvature. This work reveals that actin networks may act as micrometric curvature sensors and uncovers a generic morphogenetic principle for how polarity domains define their size according to cell morphologies.

DOI： 10.1016/j.cub.2015.08.046

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Language：English   Publisher：SPRINGER JAPAN KK  

Signaling molecules move between cells to form a characteristic distribution pattern within a developing organ; thereafter, they spatiotemporally regulate organ development. A key question in this process is how the signaling molecules robustly form the precise distribution on a tissue scale in a reproducible manner. Despite of an increasing number of quantitative studies regarding the mobility of signaling molecules, the detail mechanism of organogenesis via intercellular signaling is still unclear. We here review the potential advantages of plant development to address this question, focusing on the cytoplasmic continuity of plant cells through the plasmodesmata. The plant system would provide a unique opportunity to define the simple transportation mode of diffusion process, and, hence, the mechanism of organogenesis via intercellular signaling. Based on the advances in the understanding of intercellular signaling at the molecular level and in the quantitative imaging techniques, we discuss our current challenges in measuring the mobility of signaling molecules for deciphering plant organogenesis.

DOI： 10.1007/s10265-014-0692-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CELL PRESS  

For biophysical understanding of cell motility, the relationship between mechanical force and cell migration must be uncovered, but it remains elusive. Since cells migrate at small scale in dissipative circumstances, the inertia force is negligible and all forces should cancel out. This implies that one must quantify the spatial pattern of the force instead of just the summation to elucidate the force-motion relation. Here, we introduced multipole analysis to quantify the traction stress dynamics of migrating cells. We measured the traction stress of Dictyostelium discoideum cells and investigated the lowest two moments, the force dipole and quadrupole moments, which reflect rotational and front-rear asymmetries of the stress field. We derived a simple force-motion relation in which cells migrate along the force dipole axis with a direction determined by the force quadrupole. Furthermore, as a complementary approach, we also investigated fine structures in the stress field that show front-rear asymmetric kinetics consistent with the multipole analysis. The tight force-motion relation enables us to predict cell migration only from the traction stress patterns.

DOI： 10.1016/j.bpj.2013.10.041

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY  

We consider random walks of active deformable particles (ADP) that can move by actively deforming their shape from a sphere. A theory is developed by assuming that the equation of velocity includes a coupling with active random deformation. It is shown that the model exhibits a truncated power-law distribution of velocity, whose exponent is determined by the intensity of the random deformation and the strength of the dissipation. Two characteristic variants of the ADP model that have different preferences in the direction of the deformation are investigated in detail. Copyright (C) EPLA, 2013

DOI： 10.1209/0295-5075/102/40012

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report a quantitative measurement of traction stress exerted by dividing eukaryotic cells. The stress field was highly dynamic and sequentially changed as follows: (1) strong and localized as two spots, (2) weak and broadly distributed, and (3) strong and localized as four spots. At the final stage of cytokinesis, the dividing cells exerted strong tensile force on the intercellular bridge. The asymmetry of the traction stress and the orientation of the division axis matched throughout the division process, suggesting the possible role of the mechanical force as a "store" of the orientational information. DOI: 10.1103/PhysRevLett.109.248110

DOI： 10.1103/PhysRevLett.109.248110

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