Pierre-François Lenne

Bio: Pierre-François Lenne is an academic researcher from Aix-Marseille University. The author has contributed to research in topics: Fluorescence correlation spectroscopy & Microscope. The author has an hindex of 35, co-authored 112 publications receiving 7392 citations. Previous affiliations of Pierre-François Lenne include Université Paul Cézanne Aix-Marseille III & Centre national de la recherche scientifique.

Cell surface mechanics and the control of cell shape, tissue patterns and morphogenesis.

Abstract: Many signalling pathways have been shown to control cell shape and cell surface mechanics. Recent insights from diverse disciplines point to adhesion and cortical tension as regulators of cell shape and provide insights into how cell shape controls tissue geometry. Embryonic morphogenesis requires the execution of complex mechanisms that regulate the local behaviour of groups of cells. The orchestration of such mechanisms has been mainly deciphered through the identification of conserved families of signalling pathways that spatially and temporally control cell behaviour. However, how this information is processed to control cell shape and cell dynamics is an open area of investigation. The framework that emerges from diverse disciplines such as cell biology, physics and developmental biology points to adhesion and cortical actin networks as regulators of cell surface mechanics. In this context, a range of developmental phenomena can be explained by the regulation of cell surface tension.

Planar polarized actomyosin contractile flows control epithelial junction remodelling

Abstract: Myosin-II has a central role in generating the forces that drive cell shape changes during embryo development. Thomas Lecuit and colleagues study germ-band extension in Drosophila, in which epithelial cells undergo an ordered process of intercalation resulting in tissue extension through remodelling of cell junctions. They find that cell-junction shrinkage is driven by polarized flow of medial myosin-II pulses towards junctions, which organizes the whole process of intercalation. In addition, the flow of myosin-II is driven by the polarized distribution of E-cadherin/β-catenin/ α-catenin complexes at adherens junctions. Thus, epithelial morphogenesis is driven by polarized contractile actomyosin flows emerging from interactions between E-cadherin and actomyosin networks. Here, germ-band extension in Drosophila is studied in which epithelial cells undergo an ordered process of intercalation resulting in tissue extension through remodelling of cell junctions. Cell junction shrinkage is driven by polarized flow of medial Myosin-II pulses towards junctions which organizes the whole process of intercalation. The flow of Myosin II is driven by the polarized distribution of E-cadherin complexes at adherens junctions. Thus, epithelial morphogenesis is driven by polarized contractile actomyosin flows emerging from interactions between E-cadherin and actomyosin networks. Force generation by Myosin-II motors on actin filaments drives cell and tissue morphogenesis1,2,3,4,5,6,7,8,9,10,11,12,13,14,15. In epithelia, contractile forces are resisted at apical junctions by adhesive forces dependent on E-cadherin16, which also transmits tension6,17,18,19. During Drosophila embryonic germband extension, tissue elongation is driven by cell intercalation20, which requires an irreversible and planar polarized remodelling of epithelial cell junctions4,5. We investigate how cell deformations emerge from the interplay between force generation and cortical force transmission during this remodelling in Drosophila melanogaster. The shrinkage of dorsal–ventral-oriented (‘vertical’) junctions during this process is known to require planar polarized junctional contractility by Myosin II (refs 4, 5, 7, 12). Here we show that this shrinkage is not produced by junctional Myosin II itself, but by the polarized flow of medial actomyosin pulses towards ‘vertical’ junctions. This anisotropic flow is oriented by the planar polarized distribution of E-cadherin complexes, in that medial Myosin II flows towards ‘vertical’ junctions, which have relatively less E-cadherin than transverse junctions. Our evidence suggests that the medial flow pattern reflects equilibrium properties of force transmission and coupling to E-cadherin by α-Catenin. Thus, epithelial morphogenesis is not properly reflected by Myosin II steady state distribution but by polarized contractile actomyosin flows that emerge from interactions between E-cadherin and actomyosin networks.

Nature and anisotropy of cortical forces orienting Drosophila tissue morphogenesis.

Abstract: The morphogenesis of developing embryos and organs relies on the ability of cells to remodel their contacts with neighbouring cells. Using quantitative modelling and laser nano-dissection, we probed the mechanics of a morphogenetic process, the elongation of Drosophila melanogaster embryos, which results from polarized cell neighbour exchanges. We show that anisotropy of cortical tension at apical cell junctions is sufficient to drive tissue elongation. We estimated its value through comparisons between in silico and in vivo data using various tissue descriptors. Nano-dissection of the actomyosin network indicates that tension is anisotropically distributed and depends on myosin II accumulation. Junction relaxation after nano-dissection also suggests that cortical elastic forces are dominant in this process. Interestingly, fluctuations in vertex position (points where three or more cells meet) facilitate neighbour exchanges. We delineate the contribution of subcellular tensile activity polarizing junction remodelling, and the permissive role of vertex fluctuations during tissue elongation.

Force Generation, Transmission, and Integration during Cell and Tissue Morphogenesis

Abstract: Cell shape changes underlie a large set of biological processes ranging from cell division to cell motility. Stereotyped patterns of cell shape changes also determine tissue remodeling events such as extension or invagination. In vitro and cell culture systems have been essential to understanding the fundamental physical principles of subcellular mechanics. These are now complemented by studies in developing organisms that emphasize how cell and tissue morphogenesis emerge from the interplay between force-generating machines, such as actomyosin networks, and adhesive clusters that transmit tensile forces at the cell cortex and stabilize cell-cell and cell-substrate interfaces. Both force production and transmission are self-organizing phenomena whose adaptive features are essential during tissue morphogenesis. A new era is opening that emphasizes the similarities of and allows comparisons between distant dynamic biological phenomena because they rely on core machineries that control universal features of cytomechanics.

Dynamic molecular confinement in the plasma membrane by microdomains and the cytoskeleton meshwork

Abstract: It is by now widely recognized that cell membranes show complex patterns of lateral organization. Two mechanisms involving either a lipid-dependent (microdomain model) or cytoskeleton-based (meshwork model) process are thought to be responsible for these plasma membrane organizations. In the present study, fluorescence correlation spectroscopy measurements on various spatial scales were performed in order to directly identify and characterize these two processes in live cells with a high temporal resolution, without any loss of spatial information. Putative raft markers were found to be dynamically compartmented within tens of milliseconds into small microdomains (∅<120 nm) that are sensitive to the cholesterol and sphingomyelin levels, whereas actin-based cytoskeleton barriers are responsible for the confinement of the transferrin receptor protein. A free-like diffusion was observed when both the lipid-dependent and cytoskeleton-based organizations were disrupted, which suggests that these are two main compartmentalizing forces at work in the plasma membrane.

Plasmonics: Fundamentals and Applications

Abstract: Fundamentals of Plasmonics.- Electromagnetics of Metals.- Surface Plasmon Polaritons at Metal / Insulator Interfaces.- Excitation of Surface Plasmon Polaritons at Planar Interfaces.- Imaging Surface Plasmon Polariton Propagation.- Localized Surface Plasmons.- Electromagnetic Surface Modes at Low Frequencies.- Applications.- Plasmon Waveguides.- Transmission of Radiation Through Apertures and Films.- Enhancement of Emissive Processes and Nonlinearities.- Spectroscopy and Sensing.- Metamaterials and Imaging with Surface Plasmon Polaritons.- Concluding Remarks.

Lipid Rafts As a Membrane-Organizing Principle

Abstract: Cell membranes display a tremendous complexity of lipids and proteins designed to perform the functions cells require. To coordinate these functions, the membrane is able to laterally segregate its constituents. This capability is based on dynamic liquid-liquid immiscibility and underlies the raft concept of membrane subcompartmentalization. Lipid rafts are fluctuating nanoscale assemblies of sphingolipid, cholesterol, and proteins that can be stabilized to coalesce, forming platforms that function in membrane signaling and trafficking. Here we review the evidence for how this principle combines the potential for sphingolipid-cholesterol self-assembly with protein specificity to selectively focus membrane bioactivity.

Real-Time DNA Sequencing from Single Polymerase Molecules

Abstract: We present single-molecule, real-time sequencing data obtained from a DNA polymerase performing uninterrupted template-directed synthesis using four distinguishable fluorescently labeled deoxyribonucleoside triphosphates (dNTPs). We detected the temporal order of their enzymatic incorporation into a growing DNA strand with zero-mode waveguide nanostructure arrays, which provide optical observation volume confinement and enable parallel, simultaneous detection of thousands of single-molecule sequencing reactions. Conjugation of fluorophores to the terminal phosphate moiety of the dNTPs allows continuous observation of DNA synthesis over thousands of bases without steric hindrance. The data report directly on polymerase dynamics, revealing distinct polymerization states and pause sites corresponding to DNA secondary structure. Sequence data were aligned with the known reference sequence to assay biophysical parameters of polymerization for each template position. Consensus sequences were generated from the single-molecule reads at 15-fold coverage, showing a median accuracy of 99.3%, with no systematic error beyond fluorophore-dependent error rates.

Light in tiny holes

Abstract: The presence of tiny holes in an opaque metal film, with sizes smaller than the wavelength of incident light, leads to a wide variety of unexpected optical properties such as strongly enhanced transmission of light through the holes and wavelength filtering. These intriguing effects are now known to be due to the interaction of the light with electronic resonances in the surface of the metal film, and they can be controlled by adjusting the size and geometry of the holes. This knowledge is opening up exciting new opportunities in applications ranging from subwavelength optics and optoelectronics to chemical sensing and biophysics.