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Soifer I.,Weizmann Institute of Science | Robert L.,French National Institute for Agricultural Research | Robert L.,Agro ParisTech | Robert L.,CNRS Jean Perrin Laboratory | Amir A.,Harvard University
Current Biology | Year: 2016

To maintain a constant cell size, dividing cells have to coordinate cell-cycle events with cell growth. This coordination has long been supposed to rely on the existence of size thresholds determining cell-cycle progression [1]. In budding yeast, size is controlled at the G1/S transition [2]. In agreement with this hypothesis, the size at birth influences the time spent in G1: smaller cells have a longer G1 period [3]. Nevertheless, even though cells born smaller have a longer G1, the compensation is imperfect and they still bud at smaller cell sizes. In bacteria, several recent studies have shown that the incremental model of size control, in which size is controlled by addition of a constant volume (in contrast to a size threshold), is able to quantitatively explain the experimental data on four different bacterial species [4-7]. Here, we report on experimental results for the budding yeast Saccharomyces cerevisiae, finding, surprisingly, that cell size control in this organism is very well described by the incremental model, suggesting a common strategy for cell size control with bacteria. Additionally, we argue that for S. cerevisiae the "volume increment" is not added from birth to division, but rather between two budding events. © 2016 Elsevier Ltd.


Boubenec Y.,French National Center for Scientific Research | Boubenec Y.,Laboratoire des Systemes Perceptifs | Claverie L.N.,CNRS Jean Perrin Laboratory | Shulz D.E.,French National Center for Scientific Research | Debregeas G.,CNRS Jean Perrin Laboratory
Journal of Neuroscience | Year: 2014

Whisking rodents can discriminate finely textured objects using their vibrissae. The biomechanical and neural processes underlying such sensory tasks remain elusive. Here we combine the use of model micropatterned substrates and high-resolution videography of rats' whiskers during tactile exploration to study how texture information is mechanically encoded in the whisker motion. A biomechanical modeling of the whisker is developed, which yields quantitative predictions of the spectral and temporal characteristics of the observed whisker kinetics, for any given topography. These texture-induced whisker vibrations are then replayed via a multiwhisker stimulator while recording neuronal responses in the barrel field of the primary somatosensory cortex (S1bf). These results provide a comprehensive description of the transduction process at play during fine texture sensing in rats. They suggest that the sensory system operates through a vibratory amplitude modulation/demodulation scheme. Fine textural properties are encoded in the time-varying envelope of the whisker-resonant vibrations. This quantity is then recovered by neural demodulation, as it effectively drives the spiking-rate signal of a large fraction of S1 cortical neurons. This encoding/decoding scheme is shown to be robust against variations in exploratory conditions, such as the scanning speed or pad-to-substrate distance, thus allowing for reliable tactile discrimination in realistic conditions. © 2014 the authors.


PubMed | Research University and CNRS Jean Perrin Laboratory
Type: | Journal: Frontiers in behavioral neuroscience | Year: 2017

Rodents use their whiskers to locate nearby objects with an extreme precision. To perform such tasks, they need to detect whisker/object contacts with a high temporal accuracy. This contact detection is conveyed by classes of mechanoreceptors whose neural activity is sensitive to either slow or fast time varying mechanical stresses acting at the base of the whiskers. We developed a biomimetic approach to separate and characterize slow quasi-static and fast vibrational stress signals acting on a whisker base in realistic exploratory phases, using experiments on both real and artificial whiskers. Both slow and fast mechanical inputs are successfully captured using a mechanical model of the whisker. We present and discuss consequences of the whisking process in purely mechanical terms and hypothesize that free whisking in air sets a mechanical threshold for contact detection. The time resolution and robustness of the contact detection strategies based on either slow or fast stress signals are determined. Contact detection based on the vibrational signal is faster and more robust to exploratory conditions than the slow quasi-static component, although both slow/fast components allow localizing the object.


Callan-Jones A.C.,University Paris Diderot | Ruprecht V.,Institute of Science and Technology Austria | Wieser S.,Innsbruck Medical University | Heisenberg C.P.,Institute of Science and Technology Austria | And 2 more authors.
Physical Review Letters | Year: 2016

Nonadherent polarized cells have been observed to have a pearlike, elongated shape. Using a minimal model that describes the cell cortex as a thin layer of contractile active gel, we show that the anisotropy of active stresses, controlled by cortical viscosity and filament ordering, can account for this morphology. The predicted shapes can be determined from the flow pattern only; they prove to be independent of the mechanism at the origin of the cortical flow, and are only weakly sensitive to the cytoplasmic rheology. In the case of actin flows resulting from a contractile instability, we propose a phase diagram of three-dimensional cell shapes that encompasses nonpolarized spherical, elongated, as well as oblate shapes, all of which have been observed in experiment. © 2016 American Physical Society.


Maiuri P.,University Pierre and Marie Curie | Rupprecht J.-F.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Wieser S.,AM Technology | Ruprecht V.,AM Technology | And 16 more authors.
Cell | Year: 2015

Cell movement has essential functions in development, immunity, and cancer. Various cell migration patterns have been reported, but no general rule has emerged so far. Here, we show on the basis of experimental data in vitro and in vivo that cell persistence, which quantifies the straightness of trajectories, is robustly coupled to cell migration speed. We suggest that this universal coupling constitutes a generic law of cell migration, which originates in the advection of polarity cues by an actin cytoskeleton undergoing flows at the cellular scale. Our analysis relies on a theoretical model that we validate by measuring the persistence of cells upon modulation of actin flow speeds and upon optogenetic manipulation of the binding of an actin regulator to actin filaments. Beyond the quantitative prediction of the coupling, the model yields a generic phase diagram of cellular trajectories, which recapitulates the full range of observed migration patterns. © 2015 Elsevier Inc.


Ke R.,University of California at Los Angeles | Ke R.,Los Alamos National Laboratory | Loverdo C.,University of California at Los Angeles | Loverdo C.,CNRS Jean Perrin Laboratory | And 6 more authors.
PLoS Computational Biology | Year: 2015

Recent discoveries of direct acting antivirals against Hepatitis C virus (HCV) have raised hopes of effective treatment via combination therapies. Yet rapid evolution and high diversity of HCV populations, combined with the reality of suboptimal treatment adherence, make drug resistance a clinical and public health concern. We develop a general model incorporating viral dynamics and pharmacokinetics/ pharmacodynamics to assess how suboptimal adherence affects resistance development and clinical outcomes. We derive design principles and adaptive treatment strategies, identifying a high-risk period when missing doses is particularly risky for de novo resistance, and quantifying the number of additional doses needed to compensate when doses are missed. Using data from large-scale resistance assays, we demonstrate that the risk of resistance can be reduced substantially by applying these principles to a combination therapy of daclatasvir and asunaprevir. By providing a mechanistic framework to link patient characteristics to the risk of resistance, these findings show the potential of rational treatment design. © 2015 Ke et al.


Romero V.,Paris-Sorbonne University | Romero V.,CNRS Jean Perrin Laboratory | Wandersman E.,Paris-Sorbonne University | Wandersman E.,CNRS Jean Perrin Laboratory | And 4 more authors.
Physical Review Letters | Year: 2014

We report on the multicontact frictional dynamics of model elastomer surfaces rubbed against bare glass slides. The surfaces consist of layers patterned with thousands of spherical caps distributed both spatially and in height, regularly or randomly. Use of spherical asperities yields circular microcontacts whose radii are a direct measure of the contact pressure distribution. Optical tracking of individual contacts provides the in-plane deformations of the tangentially loaded interface, yielding the shear force distribution. We then investigate the stick-slip frictional dynamics of a regular hexagonal array. For all stick phases, slip precursors are evidenced and found to propagate quasistatically, normally to the isopressure contours. A simple quasistatic model relying on the existence of interfacial stress gradients is derived and predicts qualitatively the position of slip precursors. © 2014 American Physical Society.


Hui-Bon-Hoa G.,French Institute of Health and Medical Research | Kaddour H.,CNRS Systematics, Biodiversity and Evolution Institute | Vergne J.,CNRS Systematics, Biodiversity and Evolution Institute | Kruglik S.G.,CNRS Jean Perrin Laboratory | Maurel M.-C.,CNRS Systematics, Biodiversity and Evolution Institute
BMC Biophysics | Year: 2014

Background: Viroids are the smallest pathogens of plants. To date the structural and conformational details of the cleavage of Avocado sunblotch viroid (ASBVd) and the catalytic role of Mg2+ ions in efficient self-cleavage are of crucial interest. Results: We report the first Raman characterization of the structure and activity of ASBVd, for plus and minus viroid strands. Both strands exhibit a typical A-type RNA conformation with an ordered double-helical content and a C3′-endo/anti sugar pucker configuration, although small but specific differences are found in the sugar puckering and base-stacking regions. The ASBVd(-) is shown to self-cleave 3.5 times more actively than ASBVd(+). Deuteration and temperature increase perturb differently the double-helical content and the phosphodiester conformation, as revealed by corresponding characteristic Raman spectral changes. Our data suggest that the structure rigidity and stability are higher and the D2O accessibility to H-bonding network is lower for ASBVd(+) than for ASBVd(-). Remarkably, the Mg2+-activated self-cleavage of the viroid does not induce any significant alterations of the secondary viroid structure, as evidenced from the absence of intensity changes of Raman marker bands that, however exhibit small but noticeable frequency downshifts suggesting several minor changes in phosphodioxy, internal loops and hairpins of the cleaved viroids. Conclusions: Our results demonstrate the sensitivity of Raman spectroscopy in monitoring structural and conformational changes of the viroid and constitute the basis for further studies of its interactions with therapeutic agents and cell membranes. © 2014 Hui-Bon-Hoa et al.


Chupeau M.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Benichou O.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Voituriez R.,CNRS Laboratory of Theoretical Physics and Condensed Matter | Voituriez R.,CNRS Jean Perrin Laboratory
Nature Physics | Year: 2015

How long must one undertake a random search to visit all sites of a given domain? This time, known as the cover time, is a key observable to quantify the efficiency of exhaustive searches, which require a complete exploration of an area and not only the discovery of a single target. Examples range from immune-system cells chasing pathogens to animals harvesting resources, from robotic exploration for cleaning or demining to the task of improving search algorithms. Despite its broad relevance, the cover time has remained elusive and so far explicit results have been scarce and mostly limited to regular random walks. Here we determine the full distribution of the cover time for a broad range of random search processes, including Lévy strategies, intermittent strategies, persistent random walks and random walks on complex networks, and reveal its universal features. We show that for all these examples the mean cover time can be minimized, and that the corresponding optimal strategies also minimize the mean search time for a single target, unambiguously pointing towards their robustness. © 2015 Macmillan Publishers Limited. All rights reserved.


Callan-Jones A.C.,University Paris Diderot | Voituriez R.,CNRS Jean Perrin Laboratory
Current Opinion in Cell Biology | Year: 2016

Eukaryotic cell movement is characterized by very diverse migration modes. Recent studies show that cells can adapt to environmental cues, such as adhesion and geometric confinement, thereby readily switching their mode of migration. Among this diversity of motile behavior, actin flows have emerged as a highly conserved feature of both mesenchymal and amoeboid migration, and have also been identified as key regulators of cell polarity. This suggests that the various observed migration modes are continuous variations of elementary locomotion mechanisms, based on a very robust physical property of the actin/myosin system - its ability to sustain flows at the cell scale. This central role of actin/myosin flows is shown to affect the large scale properties of cell trajectories. © 2016 Elsevier Ltd.

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