Soft jamming of viral particles in nanopores.

Viruses have remarkable physical properties and complex interactions with their environment. However, their aggregation in confined spaces remains unexplored, although this phenomenon is of paramount importance for understanding viral infectivity. Using hydrodynamical driving and optical detection, we developed a method to detect the transport of single virus in real time through synthetic nanopores.

Optical single molecule characterisation of natural and synthetic polymers through nanopores.

Nanopore techniques are now widely used to sequence DNA, RNA and even oligopeptide molecules at the base pair level by measuring the ionic current. In order to build a more versatile characterisation system, optical methods for the detection of a single molecule translocating through a nanopore have been developed, achieving very promising results. In this work, we developed a series of tools to interpret the optical signals in terms of the physical behaviour of various types of natural and synthetic polymers, with high throughput.

[Structural and mechanical plasticity of the nuclear pore].

The nuclear pore, which can be seen as the gateway to the cell nucleus, is central to many processes including gene regulation. It is a complex and dynamic structure composed of more than 30 proteins present in multiple copies that allows the selective and directional transport of RNA and proteins. As shown by recent studies, it is able to adapt its overall structure to the state of the cell.

Thermally Switchable Nanogate Based on Polymer Phase Transition.

Mimicking and extending the gating properties of biological pores is of paramount interest for the fabrication of membranes that could be used in filtration or drug processing. Here, we build a selective and switchable nanopore for macromolecular cargo transport. Our approach exploits polymer graftings within artificial nanopores to control the translocation of biomolecules.

Experimental study of a nanoscale translocation ratchet.

Despite an extensive theoretical and numerical background, the translocation ratchet mechanism, which is fundamental for the transmembrane transport of biomolecules, has never been experimentally reproduced at the nanoscale. Only the Sec61 and bacterial type IV pilus pores were experimentally shown to exhibit a translocation ratchet mechanism. Here we designed a synthetic translocation ratchet and quantified its efficiency as a nanopump.

Optical Quantification by Nanopores of Viruses, Extracellular Vesicles, and Nanoparticles.

Nanopores combined with optical approaches can be used to detect viral particles. In this work, we demonstrate the ability of hydrodynamical driving and optical sensing to identify and quantify viral particles in a biological sample. We have developed a simple and rapid method which requires only fluorescent labeling of the particles and can therefore be applied to a wide range of virus type.

Polynucleotide transport through lipid membrane in the presence of starburst cyclodextrin-based poly(ethylene glycol)s.

Symmetrical cyclodextrin-based 14-arm star polymers with poly(ethylene glycol) PEG branches were synthesized and characterized. Interactions of the star polymers with lipid bilayers were studied by the "black lipid membrane" technique in order to demonstrate the formation of monomolecular artificial channels. The conditions for the insertion are mainly based on dimensions and amphiphilic properties of the star polymers, in particular the molar mass of the water-soluble polymer branches.

Uncooked spaghetti in a colander: Injection of semiflexible polymers in a nanopore.

We study the flow injection of semiflexible polymers in a nanopore with a diameter smaller than the persistence length of the macromolecules. The suction model from de Gennes and Brochard is modified to take into account the effect of the rigidity of the polymer in the Odijk regime. We show that in this case of extreme confinement the flow threshold vanishes slowly and that in the limit of infinitely small nanopore the free energy barrier eventually disappears.

[DNA sequencing by nanopores: achievements and prospects].

After years of development, the use of nanopore as a sensor to sequence DNA molecules is now a viable and promising possibility. Single base pair detection during DNA transport enables to record ultra-long threads with high parallelization and rates. I will present in this review the current methodologies based on electrical detection and biological nanopores and the new methods based on solid state nanopores and optical detection.

Nuclear pore complex plasticity during developmental process as revealed by super-resolution microscopy.

Nuclear Pore Complex (NPC) is of paramount importance for cellular processes since it is the unique gateway for molecular exchange through the nucleus. Unraveling the modifications of the NPC structure in response to physiological cues, also called nuclear pore plasticity, is key to the understanding of the selectivity of this molecular machinery. As a step towards this goal, we use the optical super-resolution microscopy method called direct Stochastic Optical Reconstruction Microscopy (dSTORM), to analyze oocyte development impact on the internal structure and large-scale organization of the NPC.

Extensive characterization of magnetic microrods observed using optical microscopy.

The usage of micro or nanorods is steadily increasing in various applications from fundamental research to industry. Therefore their geometrical, mechanical and eventually magnetic properties need to be well determined. Here, using an optical microscope equipped with magnetic tweezers, we report an experimental procedure to obtain all those information on a single magnetic rod.

Compressive stress inhibits proliferation in tumor spheroids through a volume limitation.

In most instances, the growth of solid tumors occurs in constrained environments and requires a competition for space. A mechanical crosstalk can arise from this competition. In this article, we dissect the biomechanical sequence caused by a controlled compressive stress on multicellular spheroids (MCSs) used as a tumor model system.

Zero-mode waveguide detection of flow-driven DNA translocation through nanopores.

We directly measure the flow-driven injection of DNA through nanopores at the level of single molecule and single pore using a modified zero-mode waveguide method. We observe a flow threshold independent of the pore radius, the DNA concentration, and length. We demonstrate that the flow injection of DNA in nanopores is controlled by an energy barrier as proposed in the de Gennes-Brochard suction model.

Mechanical control of cell flow in multicellular spheroids.

Collective cell motion is observed in a wide range of biological processes. In tumors, physiological gradients of nutrients, growth factors, or even oxygen give rise to gradients of proliferation. We show using fluorescently labeled particles that these gradients drive a velocity field resulting in a cellular flow in multicellular spheroids.

The N-terminal domains of TRF1 and TRF2 regulate their ability to condense telomeric DNA.

TRF1 and TRF2 are key proteins in human telomeres, which, despite their similarities, have different behaviors upon DNA binding. Previous work has shown that unlike TRF1, TRF2 condenses telomeric, thus creating consequential negative torsion on the adjacent DNA, a property that is thought to lead to the stimulation of single-strand invasion and was proposed to favor telomeric DNA looping. In this report, we show that these activities, originating from the central TRFH domain of TRF2, are also displayed by the TRFH domain of TRF1 but are repressed in the full-length protein by the presence of an acidic domain at the N-terminus.

Stress clamp experiments on multicellular tumor spheroids.

The precise role of the microenvironment on tumor growth is poorly understood. Whereas the tumor is in constant competition with the surrounding tissue, little is known about the mechanics of this interaction. Using a novel experimental procedure, we study quantitatively the effect of an applied mechanical stress on the long-term growth of a spheroid cell aggregate.

RSC remodeling of oligo-nucleosomes: an atomic force microscopy study.

The 'remodels structure of chromatin' (RSC) complex is an essential chromatin remodeling factor that is required for the control of several processes including transcription, repair and replication. The ability of RSC to relocate centrally positioned mononucleosomes at the end of nucleosomal DNA is firmly established, but the data on RSC action on oligo-nucleosomal templates remains still scarce. By using atomic force microscopy (AFM) imaging, we have quantitatively studied the RSC-induced mobilization of positioned di- and trinucleosomes as well as the directionality of mobilization on mononucleosomal template labeled at one end with streptavidin.

The docking domain of histone H2A is required for H1 binding and RSC-mediated nucleosome remodeling.

Histone variants within the H2A family show high divergences in their C-terminal regions. In this work, we have studied how these divergences and in particular, how a part of the H2A COOH-terminus, the docking domain, is implicated in both structural and functional properties of the nucleosome. Using biochemical methods in combination with Atomic Force Microscopy and Electron Cryo-Microscopy, we show that the H2A-docking domain is a key structural feature within the nucleosome.

Remosomes: RSC generated non-mobilized particles with approximately 180 bp DNA loosely associated with the histone octamer.

Chromatin remodelers are sophisticated nano-machines that are able to alter histone-DNA interactions and to mobilize nucleosomes. Neither the mechanism of their action nor the conformation of the remodeled nucleosomes are, however, yet well understood. We have studied the mechanism of Remodels Structure of Chromatin (RSC)-nucleosome mobilization by using high-resolution microscopy and biochemical techniques.

The dynamics of individual nucleosomes controls the chromatin condensation pathway: direct atomic force microscopy visualization of variant chromatin.

Chromatin organization and dynamics is studied at scales ranging from single nucleosome to nucleosomal array by using a unique combination of biochemical assays, single molecule imaging technique, and numerical modeling. We show that a subtle modification in the nucleosome structure induced by the histone variant H2A.Bbd drastically modifies the higher order organization of the nucleosomal arrays.

TRF2 promotes, remodels and protects telomeric Holliday junctions.

The ability of the telomeric DNA-binding protein, TRF2, to stimulate t-loop formation while preventing t-loop deletion is believed to be crucial to maintain telomere integrity in mammals. However, little is known on the molecular mechanisms behind these properties of TRF2. In this report, we show that TRF2 greatly increases the rate of Holliday junction (HJ) formation and blocks the cleavage by various types of HJ resolving activities, including the newly identified human GEN1 protein.

Dynamic kinesin-1 clustering on microtubules due to mutually attractive interactions.

Molecular motors often work collectively inside the cell. While the properties of individual motors have been extensively studied over the last decade, much less is known on how motors coordinate their action when working in ensembles. The motor collective behaviour in conditions where they contact each other, as in intracellular transport, may strongly depend on their mutual interactions.

Atomic force microscopy imaging of SWI/SNF action: mapping the nucleosome remodeling and sliding.

We propose a combined experimental (atomic force microscopy) and theoretical study of the structural and dynamical properties of nucleosomes. In contrast to biochemical approaches, this method allows us to determine simultaneously the DNA-complexed length distribution and nucleosome position in various contexts. First, we show that differences in the nucleoproteic structure observed between conventional H2A and H2A.

Dissection of the unusual structural and functional properties of the variant H2A.Bbd nucleosome.

The histone variant H2A.Bbd appeared to be associated with active chromatin, but how it functions is unknown. We have dissected the properties of nucleosome containing H2A.