Université PSL



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Anthrax receptors position the spindle
Minc N, Piel M
Nat. Cell Biol. - 15(1) :11-3 - DOI:10.1038/ncb2664 - 2012
Oriented mitosis is essential during tissue morphogenesis. The Wnt/planar cell polarity (Wnt/PCP) pathway orients mitosis in a number of developmental systems, including dorsal epiblast cell divisions along the animal-vegetal (A-V) axis during zebrafish gastrulation. How Wnt signalling orients the mitotic plane is, however, unknown. Here we show that, in dorsal epiblast cells, anthrax toxin receptor 2a (Antxr2a) accumulates in a polarized cortical cap, which is aligned with the embryonic A-V axis and forecasts the division plane. Filamentous actin (F-actin) also forms an A-V polarized cap, which depends on Wnt/PCP and its effectors RhoA and Rock2. Antxr2a is recruited to the cap by interacting with actin. Antxr2a also interacts with RhoA and together they activate the diaphanous-related formin zDia2. Mechanistically, Antxr2a functions as a Wnt-dependent polarized determinant, which, through the action of RhoA and zDia2, exerts torque on the spindle to align it with the A-V axis.
Microfabricated devices for cell biology: all for one and one for all
Lautenschläger F, Piel M
Curr Opin Cell Biol - 25(1) :116-24 - DOI:10.1016/j.ceb.2012.10.017 - 2012
Individual cells in their native physiological states face a dynamic multi-factorial environment. This is true of both single-celled and multi-cellular organisms. A key challenge in cell biology is the design of experimental methods and specific assays to disentangle the contribution of each of the parameters governing cell behavior. After decades of studying cells cultured in Petri dishes or on glass coverslips, researchers can now benefit from a range of recent technological developments that allow them to study cells in a variety of contexts, with different levels of complexity and control over a range of environmental parameters. These technologies include new types of microscopy for detailed imaging of large cell aggregates or even whole tissues, and the development of cell culture substrates, such as 3D matrices. Here we will review the contribution of a third type of tool, collectively known as microfabricated tools. Derived from techniques originally developed for microelectronics, these tools range in size from hundreds of microns to hundreds of nanometers.
Monitoring Single Cell Bioenergetics via the Coarsening of Emulsion Droplets
L. Boitard, D. Cottinet, C. Kleinschmitt, N. Bremond, J. Baudry, G. Yvert, J. Bibette
Proc. Nat. Acad. Sci. USA - 109(19) :7181-6 - DOI:10.1073/pnas.1200894109 - 2012
Microorganisms are widely used to generate valuable products, and their efficiency is a major industrial focus. Bioreactors are typically composed of billions of cells, and available measurements only reflect the overall performance of the population. However, cells do not equally contribute, and process optimization would therefore benefit from monitoring this intrapopulation diversity. Such monitoring has so far remained difficult because of the inability to probe concentration changes at the single-cell level. Here, we unlock this limitation by taking advantage of the osmotically driven water flux between a droplet containing a living cell toward surrounding empty droplets, within a concentrated inverse emulsion. With proper formulation, excreted products are far more soluble within the continuous hydrophobic phase compared to initial nutrients (carbohydrates and salts). Fast diffusion of products induces an osmotic mismatch, which further relaxes due to slower diffusion of water through hydrophobic interfaces. By measuring droplet volume variations, we can deduce the metabolic activity down to isolated single cells. As a proof of concept, we present the first direct measurement of the maintenance energy of individual yeast cells. This method does not require any added probes and can in principle apply to any osmotically sensitive bioactivity, opening new routes for screening, and sorting large libraries of microorganisms and biomolecules.
Fast multi-color 3D imaging using aberration corrected multi-focus microscopy
F. Etoc, D. Lisse, Y. Bellaiche, J. Piehler, M. Coppey and M. Dahan
Nat. Methods - 10(1) :60-3 - DOI:10.1038/nmeth.2277 - 2012
Conventional acquisition of three-dimensional (3D) microscopy data requires sequential z scanning and is often too slow to capture biological events. We report an aberration-corrected multifocus microscopy method capable of producing an instant focal stack of nine 2D images. Appended to an epifluorescence microscope, the multifocus system enables high-resolution 3D imaging in multiple colors with single-molecule sensitivity, at speeds limited by the camera readout time of a single image.
Compressive Fluorescence Microscopy for Biological and hyperspectral imaging
Ibrahim Cisse, Ignacio Izeddin, Sebastien Causse, Lydia Boudarene, Adrien Senecal, Leila Muresan, Claire Dugast-Darzacq, Bassam Hajj, Maxime Dahan and Xavier Darzacq
Proc. Nat. Acad. Sci. USA - 109(26) :E1679-87 - DOI:10.1073/pnas.1119511109 - 2012
The mathematical theory of compressed sensing (CS) asserts that one can acquire signals from measurements whose rate is much lower than the total bandwidth. Whereas the CS theory is now well developed, challenges concerning hardware implementations of CS-based acquisition devices---especially in optics---have only started being addressed. This paper presents an implementation of compressive sensing in fluorescence microscopy and its applications to biomedical imaging. Our CS microscope combines a dynamic structured wide-field illumination and a fast and sensitive single-point fluorescence detection to enable reconstructions of images of fluorescent beads, cells and tissues with undersampling ratios (between the number of pixels and number of measurements) up to 32. We further demonstrate a hyperspectral mode and record images with 128 spectral channels and undersampling ratios up to 64, illustrating the potential benefits of CS acquisition for higher dimensional signals which typically exhibits extreme redundancy. Altogether, our results emphasize the interest of CS schemes for acquisition at a significantly reduced rate and point out to some remaining challenges for CS fluorescence microscopy.
A low-cost, label-free DNA detection method in lab-on-chip format based on electrohydrodynamic instabilities, with application to long-range PCR
M. Lemine Youba Diakité, J. Champ, S. Descroix, L. Malaquin, F. Amblard and J.-L. Viovy
Lab. Chip - 12(22) :4738-47 - DOI:10.1039/C2LC40372B - 2012
In order to evolve from a "chip in the lab" to a "lab on a chip" paradigm, there is still a strong demand for low-cost, portable detection technologies, notably for analytes at low concentrations. Here we report a new label-free DNA detection method with direct electronic read, and apply it to long-range PCR. This method uses a nonlinear electrohydrodynamic phenomenon: when subjected to high electric fields (typically above 100 V cm(-1)), suspensions of large polyelectrolytes, such as long DNA molecules, create "giant" dynamic concentration fluctuations. These fluctuations are associated with large conductivity inhomogeneities, and we use here a contact-mode local conductivity detector to detect these fluctuations. In order to decouple the detection electronics from the high voltage excitation one, an original "doubly symmetric" floating mode battery-operated detection scheme was developed. A wavelet analysis was then applied, to unravel from the chaotic character of the electohydrodynamic instabilities a scalar signal robustly reflecting the amplification of DNA. As a first proof of concept, we measured the products of the off-chip amplification of 10 kbp DNA from lambda phage DNA, achieving a sensitivity better than 100 fg DNA in the original 50 µl sample. This corresponds to the amplification products of less than 100 initial copies of target DNA. The companion enabling technologies developed to implement this new concept, i.e. the doubly symmetric contact conductivity detection and wavelet analysis, may also find various other applications in lab-on-chips.
A programmable magnetic tweezers and droplet microfluidic platform for high throughput nanoliter multi-steps assays
Ali-Cherif, S. Begolo, S. Descroix, J.L. Viovy, L.Malaquin
Angew Chem Int Ed Engl. - 51(43) :10765-9 - DOI:10.1002/anie.201203862 - 2012
Tweezing out the answer: A microfluidic device combining droplets (less than 100 nL) and magnetic particles was implemented for fast heterogeneous multiplexed assays. Magnetic tweezers can perform the manipulations required in an immunoassay (capture, extraction, mixing, and rinsing). This method was applied to the diagnosis of congenital hypothyroidism with 14 pM sensitivity. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Obstructed breakup of slender drops in a microfluidic T-junction
A.M. Leshansky, S. Afkhami, M.C Jullien, P. Tabeling
Phys. Rev. Lett. - 108(26) :4502 - DOI:10.1103/PhysRevLett.108.264502 - 2012
In this Letter we present a theoretical analysis of the droplet breakup with “permanent obstruction” in a microfluidic T junction [M.-C. Jullien et al., Phys. Fluids 21 072001 (2009)]. The proposed theory is based on a simple geometric construction for the interface shape combined with Tanner’s law for the local contact angle. The resulting scaling of the droplet deformation with time and capillary number is in excellent agreement with the results of direct numerical simulations and prior experiments. More rigorous analysis based on the lubrication approximation reveals a self-similar behavior analogous to the classical problem of a droplet spreading over a preexisting liquid film.
Automated Velocity Mapping of Migrating Cell Populations (AVeMap)
Deforet M., Parrini M. C., Petitjean L., Biondini M., Buguin A., Camonis J., Silberzan P.
Nat. Methods - 9(11) :1081-3 - DOI:10.1038/nmeth.2209 - 2012
Characterizing the migration of a population of cells as required for wound-healing experiments, remains laborious and somewhat subjective. Advances in genetics and robotics allow performing many experiments in parallel but analyzing the large sets of data remains a bottleneck. Here, we propose a rapid, fully automated correlation-based method, compatible with standard video-microscopy. This method allows the computation of quantitative migration parameters via an extensive dynamical mapping of the displacements.
Modeling E. coli tumbles by rotational diffusion
Saragosti J., Silberzan P., Buguin A.
PLoS One - 7(4) :e35412 - DOI:10.1371/journal.pone.0035412 - 2012
The bacterium Escherichia coli in suspension in a liquid medium swims by a succession of runs and tumbles, effectively describing a random walk. The tumbles randomize incompletely, i.e. with a directional persistence, the orientation taken by the bacterium. Here, we model these tumbles by an active rotational diffusion process characterized by a diffusion coefficient and a diffusion time. In homogeneous media, this description accounts well for the experimental reorientations. In shallow gradients of nutrients, tumbles are still described by a unique rotational diffusion coefficient. Together with an increase in the run length, these tumbles significantly contribute to the net chemotactic drift via a modulation of their duration as a function of the direction of the preceding run. Finally, we discuss the limits of this model in propagating concentration waves characterized by steep gradients. In that case, the effective rotational diffusion coefficient itself varies with the direction of the preceding run. We propose that this effect is related to the number of flagella involved in the reorientation process.

405 publications.