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Collective Cell Motion in an Epithelial Sheet Can Be Quantitatively Described by a Stochastic Interacting
Particle Model, Nestor Sepu lveda, Laurence Petit-jean, Olivier Cochet, Erwan Grasland-Mongrain, Pascal Silberzan and Vincent Hakim
PLoS Comp. Biol. - 10(6) e1003717 - DOI:10.1371/journal.pcbi.1003717 - 2013
Modelling the displacement of thousands of cells that move in a collective way is required for the simulation and the theoretical analysis of various biological processes. Here, we tackle this question in the controlled setting where the motion of Madin-Darby Canine Kidney (MDCK) cells in a confluent epithelium is triggered by the unmasking of free surface. We develop a simple model in which cells are described as point particles with a dynamic based on the two premises that, first, cells move in a stochastic manner and, second, tend to adapt their motion to that of their neighbors. Detailed comparison to experimental data show that the model provides a quantitatively accurate description of cell motion in the epithelium bulk at early times. In addition, inclusion of model “leader” cells with modified characteristics, accounts for the digitated shape of the interface which develops over the subsequent hours, providing that leader cells invade free surface more easily than other cells and coordinate their motion with their followers. The previously-described progression of the epithelium border is reproduced by the model and quantitatively explained.
Cellular capsules as a tool for multicellular spheroid production and for investigating the mechanics of tumor progression in vitro
K. Alessandri, Bibhu Ranjan Sarangi, V. Valérïévitch Gurchenkov, B. Sinha, T. Kissling, L. Fetler, F. Rico, Simon Scheuring, Christophe Lamaze, S. Geraldo, D. Vignjević, H. Doméjean, L. Rolland, A. Funfak, Jérôme Bibette, Nicolas Bremond, Pierre Nas
Proc. Nat. Acad. Sci. USA - vol.110(n°37) 14843–48 - DOI: 10.1073/pnas.1309482110 - 2013
Deciphering the multifactorial determinants of tumor progression requires standardized high-throughput preparation of 3D in vitro cellular assays. We present a simple microfluidic method based on the encapsulation and growth of cells inside permeable, elastic, hollow microspheres. We show that this approach enables mass production of size-controlled multicellular spheroids. Due to their geometry and elasticity, these microcapsules can uniquely serve as quantitative mechanical sensors to measure the pressure exerted by the expanding spheroid. By monitoring the growth of individual encapsulated spheroids after confluence, we dissect the dynamics of pressure buildup toward a steady-state value, consistent with the concept of homeostatic pressure. In turn, these confining conditions are observed to increase the cellular density and affect the cellular organization of the spheroid. Postconfluent spheroids exhibit a necrotic core cemented by a blend of extracellular material and surrounded by a rim of proliferating hypermotile cells. By performing invasion assays in a collagen matrix, we report that peripheral cells readily escape preconfined spheroids and cell–cell cohesivity is maintained for freely growing spheroids, suggesting that mechanical cues from the surrounding microenvironment may trigger cell invasion from a growing tumor. Overall, our technology offers a unique avenue to produce in vitro cell-based assays useful for developing new anticancer therapies and to investigate the interplay between mechanics and growth in tumor evolution.
Influence of Size, Surface Coating and Fine Chemical Composition on the In Vitro Reactivity and In Vivo Biodistribution of Lipid Nanocapsules Versus Lipid Nanoemulsions in Cancer Models
Samuli Hirsjärvi, Sandrine Dufort, Julien Gravier, Isabelle Texier, Qiao Yan, Jérome Bibette, Lucie Sancey, Véronique Josserand, Catherine Passirani, Jean-Pierre Benoit and Jean-Luc Coll
Nanomed. Nanotech. Biol. and Med. - 9(3) 375-87 - DOI: 10.1016/j.nano.2012.08.005 - 2013
Lipid nanocapsules (LNCs) and lipid nanoemulsions (LNEs) are biomimetic synthetic nanocarriers. Their in vitro and in vivo performance was evaluated as a function of their size (25, 50 and 100 nm) and the surface PEG chain length. Analysis methods included complement activation test, particle uptake in macrophage and HEK293(β3) cells and biodistribution studies with tumor-grafted mice by fluorescence imaging. A particular attention was paid to keep the concentration of each nanocarrier and to the amount of fluorescent dye in comparable conditions between the in vitro and in vivo studies. Under these conditions, no significant differences were found among the three tested particle sizes and the two nanocarrier types. Longer PEG chains on the LNE surface provided better stealth properties, whereas PEG modification on the LNC formulations inhibited the production of stable nanocarriers. Passive accumulation of LNCs and LNEs in different tumor types depended on the degree of tumor vascularization.
Single-cell analysis and sorting using droplet-based microfluidics
Linas Mazutis, John Gilbert, W Lloyd Ung, David A Weitz, Andrew D Griffiths and John A Heyman
Nature Protocols - -8 870–891 - DOI: 10.1038/nprot.2013.046 - 2013
We present a droplet-based microfluidics protocol for high-throughput analysis and sorting of single cells. Compartmentalization of single cells in droplets enables the analysis of proteins released from or secreted by cells, thereby overcoming one of the major limitations of traditional flow cytometry and fluorescence-activated cell sorting. As an example of this approach, we detail a binding assay for detecting antibodies secreted from single mouse hybridoma cells. Secreted antibodies are detected after only 15 min by co-compartmentalizing single mouse hybridoma cells, a fluorescent probe and single beads coated with anti-mouse IgG antibodies in 50-pl droplets. The beads capture the secreted antibodies and, when the captured antibodies bind to the probe, the fluorescence becomes localized on the beads, generating a clearly distinguishable fluorescence signal that enables droplet sorting at ∼200 Hz as well as cell enrichment. The microfluidic system described is easily adapted for screening other intracellular, cell-surface or secreted proteins and for quantifying catalytic or regulatory activities. In order to screen ∼1 million cells, the microfluidic operations require 2–6 h; the entire process, including preparation of microfluidic devices and mammalian cells, requires 5–7 d.
Multiplex Picodroplet Digital PCR to Detect KRAS Mutations in Circulating DNA from the Plasma of Colorectal Cancer Patients
Valerie Taly, Deniz Pekin, Leonor Benhaim, Steve K. Kotsopoulos, Delphine Le Corre, Xinyu Li, Ivan Atochin, Darren R. Link, Andrew D. Griffiths, Karine Pallier, Hélène Blons, Olivier Bouche, Bruno Landi, J. Brian Hutchison, and Pierre Laurent-Puig
Clin. Chem. - 59(12) 1722-31 - DOI: 10.1373/clinchem.2013.206359 - 2013
BACKGROUND: Multiplex digital PCR (dPCR) enables noninvasive and sensitive detection of circulating tumor DNA with performance unachievable by current molecular-detection approaches. Furthermore, picodroplet dPCR facilitates simultaneous screening for multiple mutations from the same sample.

METHODS: We investigated the utility of multiplex dPCR to screen for the 7 most common mutations in codons 12 and 13 of the KRAS (Kirsten rat sarcoma viral oncogene homolog) oncogene from plasma samples of patients with metastatic colorectal cancer. Fifty plasma samples were tested from patients for whom the primary tumor biopsy tissue DNA had been characterized by quantitative PCR.

RESULTS: Tumor characterization revealed that 19 patient tumors had KRAS mutations. Multiplex dPCR analysis of the plasma DNA prepared from these samples identified 14 samples that matched the mutation identified in the tumor, 1 sample contained a different KRAS mutation, and 4 samples had no detectable mutation. Among the tumor samples that were wild type for KRAS, 2 KRAS mutations were identified in the corresponding plasma samples. Duplex dPCR (i.e., wild-type and single-mutation assay) was also used to analyze plasma samples from patients with KRAS-mutated tumors and 5 samples expected to contain the BRAF (v-raf murine sarcoma viral oncogene homolog B) V600E mutation. The results for the duplex analysis matched those for the multiplex analysis for KRAS-mutated samples and, owing to its higher sensitivity, enabled detection of 2 additional samples with low levels of KRAS-mutated DNA. All 5 samples with BRAF mutations were detected.

CONCLUSIONS: This work demonstrates the clinical utility of multiplex dPCR to screen for multiple mutations simultaneously with a sensitivity sufficient to detect mutations in circulating DNA obtained by noninvasive blood collection.
Enhanced imine synthesis in water: from surfactantmediated catalysis to host–guest mechanisms
Kamel Meguellati, Ali Fallah-Araghi, Jean-Christophe Baret, Abdeslam El Harrak, Thomas Mangeat, Carlos M. Marques, Andrew D. Griffiths and Sylvain Ladame
Chem. Comm. - 49 11332-34 - DOI: 10.1039/C3CC46461J - 2013
An environment-responsive and fluorogenic reaction is reported and used as a model system to demonstrate experimentally three mechanisms of enhanced imine synthesis in water using either surfactants (below and above their CMC) or double-stranded DNA (acting as a reaction host).
Enhanced chemical synthesis at soft interfaces: a universal reaction-adsorption mechanism in microcompartments
A. Fallah-Araghi, K. Meguellati, J.-C. Baret, A. El Harrak, T. Mangeat, M. Karplus, S. Ladame, C. M. Marques and A.D. Griffiths
Phys. Rev. Lett. - 112 28301 - DOI: 10.1103/PhysRevLett.112.028301 - 2013
A bimolecular synthetic reaction (imine synthesis) was performed compartmentalized in micrometer-diameter emulsion droplets. The apparent equilibrium constant (Keq) and apparent forward rate constant (k1) were both inversely proportional to the droplet radius. The results are explained by a noncatalytic reaction-adsorption model in which reactants adsorb to the droplet interface with relatively low binding energies of a few kBT, react and diffuse back to the bulk. Reaction thermodynamics is therefore modified by compartmentalization at the mesoscale—without confinement on the molecular scale—leading to a universal mechanism for improving unfavorable reactions.
Live Imaging of Bicoid-Dependent Transcription in Drosophila Embryos
Tanguy Lucas, Teresa Ferraro, Baptiste Roelens, Jose De Las Heras Chanes, Aleksandra M. Walczak, Mathieu Coppey, and Nathalie Dostatni
Curr Biol. - Vol. 23(21) 2135–39 - DOI: 10.1016/j.cub.2013.08.053 - 2013
The early Drosophila embryo is an ideal model to understand the transcriptional regulation of well-defined patterns of gene expression in a developing organism [ 1 ]. In this system, snapshots of transcription measurements obtained by RNA FISH on fixed samples [ 2, 3 ] cannot provide the temporal resolution needed to distinguish spatial heterogeneity [ 3 ] from inherent noise [ 4, 5 ]. Here, we used the MS2-MCP system [ 6, 7 ] to visualize in living embryos nascent transcripts expressed from the canonical hunchback (hb) promoter [ 8, 9 ] under the control of Bicoid (Bcd) [ 10 ]. The hb-MS2 reporter is expressed as synchronously as endogenous hb in the anterior half of the embryo, but unlike hb it is also active in the posterior, though more heterogeneously and more transiently than in the anterior. The length and intensity of active transcription periods in the anterior are strongly reduced in absence of Bcd, whereas posterior ones are mostly Bcd independent. This posterior noisy signal decreases progressively through nuclear divisions, so that the MS2 reporter expression mimics the known anterior hb pattern at cellularization. We propose that the establishment of the hb pattern relies on Bcd-dependent lengthening of transcriptional activity periods in the anterior and may require two distinct repression mechanisms in the posterior.
Foam Drainage Control Using Thermocapillary Stress in a Two-Dimensional Microchamber
V. Miralles, B. Selva, I. Cantat, and M.-C. Jullien
Phys. Rev. Lett. - Vol.112(23) 238302 - DOI: 10.1103/PhysRevLett.112.238302 - 2013
We investigate the drainage of a 2D microfoam in a vertical Hele-Shaw cell, and show that the Marangoni stress at the air-water interface generated by a constant temperature gradient applied in situ can be tuned to control the drainage. The temperature gradient is applied in such a way that thermocapillarity and gravity have an antagonistic effect. We characterize the drainage over time by measuring the liquid volume fraction in the cell and find that thermocapillarity can overcome the effect of gravity, effectively draining the foam towards the top of the cell, or exactly compensate it, maintaining the liquid fraction at its initial value over at least 60 s. We quantify these results by solving the mass balance in the cell, and provide insight into the interplay between gravity, thermocapillarity, and capillary pressure governing the drainage dynamics.
A low cost and high throughput magnetic bead-based immuno-agglutination assay in confined droplets
Teste B, Ali-Cherif A, Viovy JL and Malaquin L
Lab. Chip - 13(12) 2344-9 - DOI: 10.1039/c3lc50353d - 2013
Although passive immuno-agglutination assays consist of one step and simple procedures, they are usually not adapted for high throughput analyses and they require expensive and bulky equipment for quantitation steps. Here we demonstrate a low cost, multimodal and high throughput immuno-agglutination assay that relies on a combination of magnetic beads (MBs), droplets microfluidics and magnetic tweezers. Antibody coated MBs were used as a capture support in the homogeneous phase. Following the immune interaction, water in oil droplets containing MBs and analytes were generated and transported in Teflon tubing. When passing in between magnetic tweezers, the MBs contained in the droplets were magnetically confined in order to enhance the agglutination rate and kinetics. When releasing the magnetic field, the internal recirculation flows in the droplet induce shear forces that favor MBs redispersion. In the presence of the analyte, the system preserves specific interactions and MBs stay in the aggregated state while in the case of a non-specific analyte, redispersion of particles occurs. The analyte quantitation procedure relies on the MBs redispersion rate within the droplet. The influence of different parameters such as magnetic field intensity, flow rate and MBs concentration on the agglutination performances have been investigated and optimized. Although the immuno-agglutination assay described in this work may not compete with enzyme linked immunosorbent assay (ELISA) in terms of sensitivity, it offers major advantages regarding the reagents consumption (analysis is performed in sub microliter droplet) and the platform cost that yields to very cheap analyses. Moreover the fully automated analysis procedure provides reproducible analyses with throughput well above those of existing technologies. We demonstrated the detection of biotinylated phosphatase alkaline in 100 nL sample volumes with an analysis rate of 300 assays per hour and a limit of detection of 100 pM.

346 publications.