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Invited Talks

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These talks are given by invited speakers at LIPhy. The intended audience is the whole LIPhy. A large general introduction intended for non-specialist is usually provided.

Typical talk duration is around one hour and includes about 15 mn of questions. The talks are scheduled usually every monday at 2PM. The place is at the conference room, second floor. Access to the lab can be obtained through the secretaries.

Agenda

  • Monday 27 March 14:00-15:30 - Céline LABOUESSE - Chalut lab, Stem Cell Institute, University of Cambridge, UK

    Mechanical Signals in Embryonic Stem Cells’ Differentiation

    Résumé : Embryonic stem cells (ESCs) cultured in vitro are functionally equivalent to the pluripotent stem cells of the early pre-implantation embryo. These cells have the potential to differentiate into all embryonic germ layers. The differentiation of ESCs is triggered by the removal of specific kinase inhibitors, which leads to the destabilization of the naïve pluripotency gene network, and the priming of lineage specification genes. The transition from naïve to primed state is characterized by striking morphological changes as cells go from tight round colonies to being flatter and spread out. They also appear to be increasingly sensitive to mechanical forces, as evidenced by the compliance and auxeticity of transition ESC nuclei (Pagliara et al., Nat. Mat., 2014). The actin cytoskeleton is known to have a significant role in determining cell morphology, adhesion strength and mechanosensitivity, yet how these properties are connected to ESC fate determination is unknown. We have developed several systems to test how external mechanical constraints impact cytoskeleton organization in ESCs, nuclear structure and ultimately regulate the exit of pluripotency. We first use compliant substrates with controlled adhesive density to study the crosstalk between mechanical signals and biochemical signaling pathways in naïve ESCs. Preliminary results show that compliant substrates enhance self-renewal of ESCs, through regulation of MAPK pathway. We also are developing a colony compression system to investigate how anisotropic stresses may drive different cell fates in colonies exiting pluripotency.



    contact: Pierre Recho

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères


  • Monday 3 April 14:00-15:30 - Marcel A. LAUTERBACH - Max Planck Institute for Brain Research, Dpt of Neural Systems, Frankfurt am Main, Germany

    STED Microscopy and its Applications in Neuroscience

    Résumé : Stimulated Emission Depletion (STED) microscopy overcomes the diffraction barrier of conventional light microscopy, which limits resolution and thus useful magnification. STED microscopy allows using an increased magnification under physiological conditions.
    I will demonstrate how simultaneous holographic photo-stimulation and super-resolution STED imaging can be achieved by incorporating Computer Generated Holography into a STED microscope. This system is applied to study the morphological changes of dendritic spines in neurons after stimulation.
    Furthermore, Fast STED microscopy with 28 frames per second enabling the detailed analysis of the motion of synaptic vesicles in living neurons is shown. Dynamic imaging with up to 200 frames per second is exemplified by the observation of colloidal-crystal formation.
    Whereas STED microscopy resolves nanostructures even in vivo, it is often difficult to relate super-resolved structures to other non-labeled features. Integrating phase contrast into a STED microscope provides a second, label-free contrast channel. This allows for easy correlation of morphological structures with high-resolution fluorescence images. It is demonstrated that Spiral Phase Contrast in scanning confocal configuration yields improved optical contrast and allows quantitative phase measurements. Scanning phase contrast allows for registration with the fluorescence images and for simultaneous recording of phase contrast and STED images. It enables therefore dual imaging and overlay in two contrast modes in fixed and in living specimen.



    contact: Aurélie Dupont

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères


  • Monday 10 April 14:00-15:30 - Ludovic PAUCHARD - Laboratoire FAST, Orsay

    Crack Patterns in Drying Colloidal Films: Application to Art Paintings Study

    Résumé : Most coatings are made by depositing a volatile liquid that contains dispersed colloidal particles or dissolved macromolecules.
    The liquid is then evaporated until a dry film is obtained. When the wet film dries, non-uniform shrinkage occurs; this generates tensile stresses that can eventually lead to mechanical instabilities. In particular cracks can form leading to a large variety of morphologies.
    Such structures affect the quality of the final product ; however the presence of cracks can be of great interest in the domain of conservation/restoration of paintings.
    Indeed, the crack patterns can reveal the mechanical properties of the pictorial matter that exhibit a complex system, both from a geometrical and a physicochemical point of views.
    These processes will be presented, and highlighted studying a model system.



    contact: Thomas Podgorski

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères


  • Thursday 11 May 11:00-12:30 - Silvio FRANZ

    LIPHY Seminar

    Résumé :



    contact: Giacomo Gradenigo

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères


  • Monday 15 May 14:00-15:30 - Marc Barthelemy - CEA, Paris

    LIPHY Seminar

    Résumé :



    contact: Chaouqi Misbah

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères


  • Monday 22 May 14:00-15:30 - Loïc Tadrist

    LIPHY Seminar

    Résumé :



    contact: Jean-François Louf

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères


  • Monday 29 May 14:00-15:30 - Maria Consiglia Merola - Stanford University, USA

    Viscoelastic properties of corneal epithelial cells using the “Linear Cell Monolayer Rheometer”

    Résumé : Mechanical properties of cells are determined by complex intracellular structures. In other words, there is a strong connection between biological processes and cellular mechanical response to external stimuli. In fact, cells’ interactions with their living environment are affected by their own mechanical behavior during biological deformations. These interactions, notably adhesion, are crucial to understand the cells adaptation in presence of artificial material such as contact lenses or medical devices.
    During the last decades, different experimental techniques have been used to investigate cell mechanics. Among them, we can mention atomic force microscopy (AFM) and microrheology. While they present a great interest, these techniques are however limited since they can only probe a single cell. In order to overcome the challenges with the biological variation between individual cells, new technologies are thus necessary.
    In this work, we present measurements using a purpose made Linear Cell Monolayer Rheometer (LCMR) that can characterize averaged cell mechanics or averaged cell adhesion. The LCMR enables the investigation of biologically active layers: controlled amounts of live cells with or without artificial materials (e.g., contact lenses). It is used in this study to measure the mechanics of corneal epithelial cells in order to characterize how these cells mechanically deform to external stimuli.
    To simulate physiological conditions, cell mechanics is quantified in experiments in which cells are strained tangential to the cell monolayer. Time-dependent step-strain tests are used to determine the mechanical relaxation of the cell layers.
    The quantification of cell mechanics using the LCMR has the potential for multiple biomedical applications, including disease diagnosis and drug-efficacy screening.



    contact: Claude Verdier

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères


  • Thursday 8 June 11:00-12:30 - Stefanos Papanikolaou

    LIPHY Seminar

    Résumé :



    contact: Kirsten Martens

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères


  • Monday 12 June 14:00-15:30 - Kaare Jensen

    LIPHY Seminar

    Résumé :



    contact: Jean-François Louf

    Lieu : LIPhy, conference room - 140 Avenue de la Physique 38402 Saint Martin d’Hères


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