Université PSL



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UNC93B1 interacts with the calcium sensor STIM1 for efficient antigen cross-presentation in dendritic cells.
Sophia Maschalidi, Paula Nunes-Hasler, Clarissa R Nascimento, Ignacio Sallent, Valérie Lannoy, Meriem Garfa-Traore, Nicolas Cagnard, Fernando E Sepulveda, Pablo Vargas, Ana-Maria Lennon-Duménil, Peter van Endert, Thierry Capiod, Nicolas Demaurex, Guillau
Nature Communications - 8 1640 - DOI : 10.1038/s41467-017-01601-5 - 2017
Dendritic cells (DC) have the unique ability to present exogenous antigens via the major histocompatibility complex class I pathway to stimulate naive CD8 T cells. In DCs with a non-functional mutation in Unc93b1 (3d mutation), endosomal acidification, phagosomal maturation, antigen degradation, antigen export to the cytosol and the function of the store-operated-Ca-entry regulator STIM1 are impaired. These defects result in compromised antigen cross-presentation and anti-tumor responses in 3d-mutated mice. Here, we show that UNC93B1 interacts with the calcium sensor STIM1 in the endoplasmic reticulum, a critical step for STIM1 oligomerization and activation. Expression of a constitutively active STIM1 mutant, which no longer binds UNC93B1, restores antigen degradation and cross-presentation in 3d-mutated DCs. Furthermore, ablation of STIM1 in mouse and human cells leads to a decrease in cross-presentation. Our data indicate that the UNC93B1 and STIM1 cooperation is important for calcium flux and antigen cross-presentation in DCs.
Lysosome signaling controls the migration of dendritic cells.
Bretou M, Sáez PJ, Sanséau D, Maurin M, Lankar D, Chabaud M, Spampanato C, Malbec O, Barbier L, Muallem S, Maiuri P, Ballabio A, Helft J, Piel , Vargas P, Lennon-Duménil AM
Sci Immunol - 2(16) 9573. - DOI: 10.1126/sciimmunol.aak9573 - 2017
Dendritic cells (DCs) patrol their environment by linking antigen acquisition by macropinocytosis to cell locomotion. DC activation upon bacterial sensing inhibits macropinocytosis and increases DC migration, thus promoting the arrival of DCs to lymph nodes for antigen presentation to T cells. The signaling events that trigger such changes are not fully understood. We show that lysosome signaling plays a critical role in this process. Upon bacterial sensing, lysosomal calcium is released by the ionic channel TRPML1 (transient receptor potential cation channel, mucolipin subfamily, member 1), which activates the actin-based motor protein myosin II at the cell rear, promoting fast and directional migration. Lysosomal calcium further induces the activation of the transcription factor EB (TFEB), which translocates to the nucleus to maintain TRPML1 expression. We found that the TRPML1-TFEB axis results from the down-regulation of macropinocytosis after bacterial sensing by DCs. Lysosomal signaling therefore emerges as a hitherto unexpected link between macropinocytosis, actomyosin cytoskeleton organization, and DC migration.
A tuneable microfluidic system for long duration chemotaxis experiments in a 3D collagen matrix.
Aizel K1, Clark AG, Simon A, Geraldo S, Funfak A, Vargas P, Bibette J, Vignjevic DM, Bremond N.
Sci Immunol - 17(22) 3851-3861 - doi: 10.1039/c7lc00649g. - 2017
In many cell types, migration can be oriented towards a chemical stimulus. In mammals, for example, embryonic cells migrate to follow developmental cues, immune cells migrate toward sites of inflammation, and cancer cells migrate away from the primary tumour and toward blood vessels during metastasis. Understanding how cells migrate in 3D environments in response to chemical cues is thus crucial to understanding directed migration in normal and disease states. To date, chemotaxis in mammalian cells has been primarily studied using 2D migration models. However, it is becoming increasingly clear that the mechanisms by which cells migrate in 2D and 3D environments dramatically differ, and cells in their native environments are confronted with a complex chemical milieu. To address these issues, we developed a microfluidic device to monitor the behaviour of cells embedded in a 3D collagen matrix in the presence of complex concentration fields of chemoattractants. This tuneable microsystem enables the generation of (1) homogeneous, stationary gradients set by a purely diffusive mechanism, or (2) spatially evolving, stationary gradients, set by a convection-diffusion mechanism. The device allows for stable gradients over several days and is large enough to study the behaviour of large cell aggregates. We observe that primary mature dendritic cells respond uniformly to homogeneous diffusion gradients, while cell behaviour is highly position-dependent in spatially variable convection-diffusion gradients. In addition, we demonstrate a directed response of cancer cells migrating away from tumour-like aggregates in the presence of soluble chemokine gradients. Together, this microfluidic device is a powerful system to observe the response of different cells and aggregates to tuneable chemical gradients.
Mechanisms for fast cell migration in complex environments.
Vargas P, Barbier L, Sáez PJ, Piel M.
Curr Opin Cell Biol - 48 72-78 - DOI: 10.1016/j.ceb.2017.04.007 - 2017
Cell migration depends on a combination of the cell's intrinsic capacity to move and the proper interpretation of external cues. This multistep process enables leukocytes to travel long distances in organs in just a few hours. This fast migration is partly due to the leukocytes' high level of plasticity, which helps them to adapt to a changing environment. Here, we review recent progress in understanding the mechanisms used by leukocytes to move rapidly and efficiently in intricate anatomical landscapes. We shall focus on specific cytoskeletal rearrangements used by neutrophils and dendritic cells to migrate within confined environments. Lastly, we will describe the properties that facilitate the rapid migration of leukocyte in complex tissue geometries.
Fluorescence eXclusion Measurement of volume in live cells.
Cadart C, Zlotek-Zlotkiewicz E, Venkova L, Thouvenin O, Racine V, Le Berre M, Monnier S, Piel M.
Methods Cell Biol. - 139 103-120. - DOI: 10.1016/bs.mcb.2016.11.009 - 2017
Volume is a basic physical property of cells; however, it has been poorly investigated in cell biology so far, mostly because it is difficult to measure it precisely. Recently, large efforts were made to experimentally measure mammalian cell size and used mass, density, or volume as proxies for cell size. Here, we describe a method enabling cell volume measurements for single living cells. The method is based on the principle of fluorescent dye exclusion and can be easily implemented in cell biology laboratories. As this method is very versatile, it can be used for cells of different sizes, adherent or growing in suspension, over several cell cycles and is independent of cell shape changes. The method is also compatible with traditional cell biology tools such as epifluorescence imaging or drug treatments.
Fluorescence eXclusion Measurement of volume in live cells.
Lafaurie-Janvore J, Lafaurie C, Piel M.
Methods Cell Biol. - 137 137-203. - DOI: 10.1016/bs.mcb.2016.04.012 - 2017
The last step of cytokinesis, abscission, consists in the severing of the intercellular bridge connecting the two daughter cells. Because daughter cells move randomly on regular cell culture substrates, the use of adhesive micropatterns facilitates the observation of the intercellular bridge and its severing. Here we propose general rules to design micropatterns optimized to study this process. In particular, these micropatterns allow a good stabilization of the daughter cells and a predictable positioning of the intercellular bridge. We suggest a series of micropatterns controlling various cellular parameters such as distance between daughter cells or daughter cells polarization. We give recommendations for videomicroscopy acquisition during cell division and propose automated image analysis methods using kymograph analysis or bridge detection. Finally, we detail methods to artificially cut the intercellular bridge using UV-based laser ablation or using two-photons laser ablation.
Efficient laboratory evolution of computationally designed enzymes with low starting activities using fluorescence-activated droplet sorting
Obexer R, Pott M, Zeymer C, Griffiths A, Hilvert D.
Protein Eng Des Sel - 29(9) 355-66 - doi: 10.1093/protein/gzw032 - 2016
De novo biocatalysts with non-natural functionality are accessible by computational enzyme design. The catalytic activities obtained for the initial designs are usually low, but can be optimized significantly by directed evolution. Nevertheless, rate accelerations approaching the level of natural enzymes can only be achieved over many rounds of tedious and time-consuming laboratory evolution. In this work, we show that microfluidic-based screening using fluorescence-activated droplet sorting (FADS) is ideally suited for efficient optimization of designed enzymes with low starting activity, essentially straight out of the computer. We chose the designed retro-aldolase RA95.0, which had been previously evolved by conventional microtiter plate screening, as an example and reoptimized it using the microfluidic-based assay. Our results show that FADS is sufficiently sensitive to detect enzyme activities as low as kcat/Km = 0.5 M(-1)s(-1) The ultra-high throughput of this system makes screening of large mutant libraries possible in which clusters of up to five residues are randomized simultaneously. Thus, combinations of beneficial mutations can be identified directly, leading to large jumps in catalytic activity of up to 80-fold within a single round of evolution. By exploring several evolutionary trajectories in parallel, we identify alternative active site arrangements that exhibit comparably enhanced efficiency but opposite enantioselectivity
Hierarchy and extremes in selections from pools of randomized proteins
Boyer S, Biswas D, Kumar Soshee A, Scaramozzino N, Nizak C2, Rivoire O.
Proc. Nat. Acad. Sci. USA - 113(13) 3482-7 - doi: 10.1073/pnas. - 2016
Variation and selection are the core principles of Darwinian evolution, but quantitatively relating the diversity of a population to its capacity to respond to selection is challenging. Here, we examine this problem at a molecular level in the context of populations of partially randomized proteins selected for binding to well-defined targets. We built several minimal protein libraries, screened them in vitro by phage display, and analyzed their response to selection by high-throughput sequencing. A statistical analysis of the results reveals two main findings. First, libraries with the same sequence diversity but built around different "frameworks" typically have vastly different responses; second, the distribution of responses of the best binders in a library follows a simple scaling law. We show how an elementary probabilistic model based on extreme value theory rationalizes the latter finding. Our results have implications for designing synthetic protein libraries, estimating the density of functional biomolecules in sequence space, characterizing diversity in natural populations, and experimentally investigating evolvability (i.e., the potential for future evolution).
Lineage Tracking for Probing Heritable Phenotypes at Single-Cell Resolution
Denis Cottinet , Florence Condamine, Nicolas Bremond, Andrew D. Griffiths, Paul B. Rainey, J. Arjan G. M. de Visser, Jean Baudry, Jérôme Bibette
Nature Biotechnology - 11(4) e0152395 - doi.org/10.1371/journal.pone.0152395 - 2016
Determining the phenotype and genotype of single cells is central to understand microbial evolution. DNA sequencing technologies allow the detection of mutants at high resolution, but similar approaches for phenotypic analyses are still lacking. We show that a drop-based millifluidic system enables the detection of heritable phenotypic changes in evolving bacterial populations. At time intervals, cells were sampled and individually compartmentalized in 100 nL drops. Growth through 15 generations was monitored using a fluorescent protein reporter. Amplification of heritable changes–via growth–over multiple generations yields phenotypically distinct clusters reflecting variation relevant for evolution. To demonstrate the utility of this approach, we follow the evolution of Escherichia coli populations during 30 days of starvation. Phenotypic diversity was observed to rapidly increase upon starvation with the emergence of heritable phenotypes. Mutations corresponding to each phenotypic class were identified by DNA sequencing. This scalable lineage-tracking technology opens the door to large-scale phenotyping methods with special utility for microbiology and microbial population biology.
Transient microfluidic compartmentalization using actionable microfilaments for biochemical assays, cell culture and organs-on-chip.
Yamada A, Renault R, Chikina A, Venzac B, Pereiro I, Coscoy S, Verhulsel M, Parrini MC, Villard C, Viovy JL, Descroix S.
Lab. Chip - 16(24) 16(24) - DOI: 10.1039/c6lc01143h - 2016
We report here a simple yet robust transient compartmentalization system for microfluidic platforms. Cylindrical microfilaments made of commercially available fishing lines are embedded in a microfluidic chamber and employed as removable walls, dividing the chamber into several compartments. These partitions allow tight sealing for hours, and can be removed at any time by longitudinal sliding with minimal hydrodynamic perturbation. This allows the easy implementation of various functions, previously impossible or requiring more complex instrumentation. In this study, we demonstrate the applications of our strategy, firstly to trigger chemical diffusion, then to make surface co-coating or cell co-culture on a two-dimensional substrate, and finally to form multiple cell-laden hydrogel compartments for three-dimensional cell co-culture in a microfluidic device. This technology provides easy and low-cost solutions, without the use of pneumatic valves or external equipment, for constructing well-controlled microenvironments for biochemical and cellular assays.

396 publications.