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ABout our activities on physico-mathematical modelling of intracellularmolecular transport

Activities around modelling DNA segregation and positioning in the bacterial genome

Synthesis temperatures of composite materials are usually far less than the ones of their use, thus carbon nanotubes (CNTs) embedded into a polymer matrix undergo significant axial stress. We develop a continuous theory, which describes the dynamics of stressed single-walled (SW-) CNTs and predicts their low-frequency phonon spectra. The changes in dispersion laws of SWCNT low-frequency phonon modes due to the axial stress of different signs are discussed. Then, the results obtained are used to analyze low-temperature (T<70 K) heat capacity and thermal conductivity of individual nanotubes. We demonstrate that compressive stress leads to increase in heat capacity CV of an individual SWCNT, while tensile stress causes CV to decrease. In the latter case at T→0 heat capacity diminishes according to a linear law ~T instead of a power one ~T1/2.Nevertheless, according to our results, axial stress hardly affects low-temperature thermal conductance of SWCNTs.Influence of investigated effects on the corresponding macroscopic properties of CNT-based composite materials are discussed as well.

In vitro, depending on extracellular matrix (ECM) architecture, macrophages migrate either in amoeboid or mesenchymal mode; while the first is a general trait of leukocytes, the latter is associated with tissue remodelling via Matrix Metalloproteinases (MMPs). To assess whether these stereotyped migrations could be also observed in a physiological context, we used the zebrafish embryo and monitored macrophage morphology, behaviour and capacity to mobilisation haematopoietic stem/progenitor cells (HSPCs), as a final functional readout. Morphometric analysis identified 4 different cell shapes. Live imaging revealed that macrophages successively adopt all four shapes as they migrate through ECM. Treatment with inhibitors of MMPs or Rac GTPase to abolish mesenchymal migration, suppresses both ECM degradation and HSPC mobilisation while differently affecting macrophage behaviour. This study depicts real time macrophage behaviour in a physiological context and reveals extreme reactivity of these cells constantly adapting and switching migratory shapes to achieve HSPCs proper mobilisation.

Efficient bacterial chromosome segregation typically requires the coordinated action of a three-component, fueled by adenosine triphosphate machinery called the partition complex. We present a phenomenological model accounting for the dynamic activity of this system that is also relevant for the physics of catalytic particles in active environments. The model is obtained by coupling simple linear reaction-diffusion equations with a proteophoresis, or “volumetric” chemophoresis, force field that arises from protein-protein interactions and provides a physically viable mechanism for complex translocation. This minimal description captures most known experimental observations: dynamic oscillations of complex components, complex separation and subsequent symmetrical positioning. The predictions of our model are in phenomenological agreement with and provide substantial insight into recent experiments. From a non-linear physics view point, this system explores the active separation of matter at micrometric scales with a dynamical instability between static positioning and travelling wave regimes triggered by the dynamical spontaneous breaking of rotational symmetry.Walter J.-C. et al (2017) Phys. Rev. Lett. 119, 028101.*ANR IBM (ANR-14-CE09-0025-01), ANR-10-LABX-0020 and Labex NUMEV

During embryogenesis of all vertebrates, haematopoietic stem/progenitor cells 16 (HSPCs) extrude from the aorta by a complex process named Endothelial-to-17 Haematopoietic Transition (EHT). HSPCs will then colonize haematopoietic organs 18 allowing haematopoiesis throughout adult life. The mechanism underlying EHT 19 including the role of each aortic endothelial cell within the global aorta dynamics 20 remains unknown. In the present study, we show for the first time that EHT involves the 21 remodelling of individual cells within a collective migration of endothelial cells which is 22 tightly orchestrated, resulting in HSPCs extrusion in the sub-aortic space without 23 compromising aorta integrity. By performing a cross-disciplinary study which combines 24 high resolution 4D imaging and theoretical analysis based on the concepts of classical 25 mechanics, we propose that this complex developmental process is dependent on 26 mechanical instabilities of the aorta preparing and facilitating the extrusion of HSPCs. 27 28 29 We dedicate this work to the memory of our friend and colleague, V. Lorman. 30 31 All rights reserved. No reuse allowed without permission. (which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.