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Liquid Crystal Coacervates Composed of Short Double-Stranded DNA and Cationic Peptides
Laboratoire Auto-Assemblage Moléculaire - Tommaso P. Fraccia and Tony Z. Jia
ACS Nano - 14, 11 15071–15082 - doi.org/10.1021/acsnano.0c05083 - 2020
Phase separation of nucleic acids and proteins is a ubiquitous phenomenon regulating subcellular compartment structure and function. While complex coacervation of flexible single-stranded nucleic acids is broadly investigated, coacervation of double-stranded DNA (dsDNA) is less studied because of its propensity to generate solid precipitates. Here, we reverse this perspective by showing that short dsDNA and poly-l-lysine coacervates can escape precipitation while displaying a surprisingly complex phase diagram, including the full set of liquid crystal (LC) mesophases observed to date in bulk dsDNA. Short dsDNA supramolecular aggregation and packing in the dense coacervate phase are the main parameters regulating the global LC-coacervate phase behavior. LC-coacervate structure was characterized upon variations in temperature and monovalent salt, DNA, and peptide concentrations, which allow continuous reversible transitions between all accessible phases. A deeper understanding of LC-coacervates can gain insights to decipher structures and phase transition mechanisms within biomolecular condensates, to design stimuli-responsive multiphase synthetic compartments with different degrees of order and to exploit self-assembly driven cooperative prebiotic evolution of nucleic acids and peptides.
Elasticity and Viscosity of DNA Liquid Crystals
Laboratoire Auto-Assemblage Moléculaire - Liana Lucchetti, Tommaso P. Fraccia, Giovanni Nava, Taras TurivTaras Turiv Advanced Materials and Liquid Crystal Institute, Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242, United States More by Taras Turiv , Fabrizio
ACS Nano - 9, 7 1034–1039 - doi.org/10.1021/acsmacrolett.0c00394 - 2020
Concentrated solutions of blunt-ended DNA oligomer duplexes self-assemble in living polymers and order into lyotropic nematic liquid crystal phase. Using the optical torque provided by three distinct illumination geometries, we induce independent splay, twist, and bend deformations of the DNA nematic and measure the corresponding elastic coefficients K1, K2, and K3, and viscosities ηsplay, ηtwist, and ηbend. We find the viscoelasticity of the system to be remarkably soft, as the viscoelastic coefficients are smaller than in other lyotropic liquid crystals. We find K1 > K3 > K2, in agreement with the elasticity of the nematic phase of flexible polymers, and ηbend > ηsplay > ηtwist a behavior that is nonconventional in the context of chromonic, polymeric, and thermotropic liquid crystals, indicating a possible role of the weakness and reversibility of the DNA aggregates.
Liquid Crystal ordering of DNA Dickerson Dodecamer duplexes with different 5’- Phosphate terminations
LABORATOIRE AUTO-ASSEMBLAGE MOLÉCULAIRE - Marco Todisco Gregory P. Smith Tommaso Pietro Fraccia
Molecular Crystals and Liquid Crystals - 683(1) 69-80 - DOI: 10.1080/15421406.2019.1581706 - 2020
The onset of liquid crystal (LC) phases in concentrated aqueous solutions of DNA oligomers crucially depends on the end-to-end interaction between the DNA duplexes, which can be provided by the aromatic stacking of the terminal base-pairs or by the pairing of complementary dangling-ends. Here we investigated the LC behavior of three blunt-end 12-base-long DNA duplexes synthesized with hydroxyl, phosphate and triphosphate 5’-termini. We experimentally characterized the concentration-temperature phase diagrams and we quantitatively estimated the end-to-end stacking free energy, by comparing the empirical data with the predictions of coarse-grained linear aggregation models. The preservation of LC ordering, even in presence of the bulky and highly charged triphosphate group, indicates that attractive stacking interactions are still present and capable of induce linear aggregation of the DNA duplexes. This finding strengthens the potential role of chromonic like self-assembly for the prebiotic formation of linear polymeric nucleic acids.
Liquid Crystal Peptide/DNA Coacervates in the Context of Prebiotic Molecular Evolution
LABORATOIRE AUTO-ASSEMBLAGE MOLÉCULAIRE - Tommaso P. Fraccia and Tony Z. Jia
CRYSTALS - 10(11) 964 - https://doi.org/10.3390/cryst10110964 - 2020
Liquid–liquid phase separation (LLPS) phenomena are ubiquitous in biological systems, as various cellular LLPS structures control important biological processes. Due to their ease of in vitro assembly into membraneless compartments and their presence within modern cells, LLPS systems have been postulated to be one potential form that the first cells on Earth took on. Recently, liquid crystal (LC)-coacervate droplets assembled from aqueous solutions of short double-stranded DNA (s-dsDNA) and poly-L-lysine (PLL) have been reported. Such LC-coacervates conjugate the advantages of an associative LLPS with the relevant long-range ordering and fluidity properties typical of LC, which reflect and propagate the physico-chemical properties of their molecular constituents. Here, we investigate the structure, assembly, and function of DNA LC-coacervates in the context of prebiotic molecular evolution and the emergence of functional protocells on early Earth. We observe through polarization microscopy that LC-coacervate systems can be dynamically assembled and disassembled based on prebiotically available environmental factors including temperature, salinity, and dehydration/rehydration cycles. Based on these observations, we discuss how LC-coacervates can in principle provide selective pressures effecting and sustaining chemical evolution within partially ordered compartments. Finally, we speculate about the potential for LC-coacervates to perform various biologically relevant properties, such as segregation and concentration of biomolecules, catalysis, and scaffolding, potentially providing additional structural complexity, such as linearization of nucleic acids and peptides within the LC ordered matrix, that could have promoted more efficient polymerization. While there are still a number of remaining open questions regarding coacervates, as protocell models, including how modern biologies acquired such membraneless organelles, further elucidation of the structure and function of different LLPS systems in the context of origins of life and prebiotic chemistry could provide new insights for understanding new pathways of molecular evolution possibly leading to the emergence of the first cells on Earth
High-throughput single-cell activity-based screening and sequencing of antibodies using droplet microfluidics
Laboratoire Biochimie - Annabelle Gérard, Adam Woolfe, Guillaume Mottet, Marcel Reichen, Carlos Castrillon, Vera Menrath, Sami Ellouze, Adeline Poitou, Raphaël Doineau, Luis Briseno-Roa, Pablo Canales-Herrerias, Pascaline Mary, Gregory Rose, Charina Ortega, Matthieu Delincé, So
Nature Biotechnology - 38 715–721 - doi.org/10.1038/s41587-020-0466-7 - 2020
Mining the antibody repertoire of plasma cells and plasmablasts could enable the discovery of useful antibodies for therapeutic or research purposes1. We present a method for high-throughput, single-cell screening of IgG-secreting primary cells to characterize antibody binding to soluble and membrane-bound antigens. CelliGO is a droplet microfluidics system that combines high-throughput screening for IgG activity, using fluorescence-based in-droplet single-cell bioassays2, with sequencing of paired antibody V genes, using in-droplet single-cell barcoded reverse transcription. We analyzed IgG repertoire diversity, clonal expansion and somatic hypermutation in cells from mice immunized with a vaccine target, a multifunctional enzyme or a membrane-bound cancer target. Immunization with these antigens yielded 100–1,000 IgG sequences per mouse. We generated 77 recombinant antibodies from the identified sequences and found that 93% recognized the soluble antigen and 14% the membrane antigen. The platform also allowed recovery of ~450–900 IgG sequences from ~2,200 IgG-secreting activated human memory B cells, activated ex vivo, demonstrating its versatility.
The generality of transient compartmentalization and its associated error thresholds
Laboratoire Biochimie - Alex Blokhuis, Philippe Nghe , Luca Peliti , David Lacoste
J Theor Biol . - 487 110110 - doi: 10.1016/j.jtbi.2019.110110 - 2020
Can prelife proceed without cell division? A recently proposed mechanism suggests that transient compartmentalization could have preceded cell division in prebiotic scenarios. Here, we study transient compartmentalization dynamics in the presence of mutations and noise in replication, as both can be detrimental the survival of compartments. Our study comprises situations where compartments contain uncoupled autocatalytic reactions feeding on a common resource, and systems based on RNA molecules copied by replicases, following a recent experimental study. Using the theory of branching processes, we show analytically that two regimes are possible. In the diffusion-limited regime, replication is asynchronous which leads to a large variability in the composition of compartments. In contrast, in a replication-limited regime, the growth is synchronous and thus the compositional variability is low. Typically, simple autocatalysts are in the former regime, while polymeric replicators can access the latter. For deterministic growth dynamics, we introduce mutations that turn functional replicators into parasites. We derive the phase boundary separating coexistence or parasite dominance as a function of relative growth, inoculation size and mutation rate. We show that transient compartmentalization allows coexistence beyond the classical error threshold, above which the parasite dominates. Our findings invite to revisit major prebiotic transitions, notably the transitions towards cooperation, complex polymers and cell division.
Predicting Evolution Using Regulatory Architecture
Laboratoire Biochimie - Philippe Nghe , Marjon G J de Vos , Enzo Kingma , Manjunatha Kogenaru , Frank J Poelwijk , Liedewij Laan , Sander J Tans
Annu Rev Biophys - 6(49) 181-197 - doi: 10.1146/annurev-biophys-070317-032939 - 2020
The limits of evolution have long fascinated biologists. However, the causes of evolutionary constraint have remained elusive due to a poor mechanistic understanding of studied phenotypes. Recently, a range of innovative approaches have leveraged mechanistic information on regulatory networks and cellular biology. These methods combine systems biology models with population and single-cell quantification and with new genetic tools, and they have been applied to a range of complex cellular functions and engineered networks. In this article, we review these developments, which are revealing the mechanistic causes of epistasis at different levels of biological organization-in molecular recognition, within a single regulatory network, and between different networks-providing first indications of predictable features of evolutionary constraint.

Metabolic cost of rapid adaptation of single yeast cells
Laboratoire Biochimie - Gabrielle Woronoff, Philippe Nghe, Jean Baudry, Laurent Boitard, Erez Bra
PNAS - 117 (20) 10660-10666 - doi.org/10.1073/pnas.1913767117 - 2020
We establish, using single-cell analysis of metabolism and division in a droplet microfluidic system, that yeast can adapt, resuming division, extremely rapidly to an unforeseen environmental challenge, and that adaptation is an active process, requiring the consumption of a characteristic amount energy. The adapted state is stable over at least several days, showing that this is a genuine adaptation process. The adaptation rate (10−3 cells per hour) is orders of magnitude higher than expected based on known mutation rates, suggesting an epigenetic origin, and the tight energetic coupling implies that there is active exploration of different states, and fixation of the solution(s) that allow adaptation.


Flux, toxicity and protein expression costs shape genetic interaction in a metabolic pathways
Laboratoire Biochimie - Gabrielle Woronoff, Philippe Nghe, Jean Baudry, Laurent Boitard, Erez Bra
Science Advances - 6 23 - DOI: 10.1126/sciadv.abb2236 - 2020
Our ability to predict the impact of mutations on traits relevant for disease and evolution remains severely limited by the dependence of their effects on the genetic background and environment. Even when molecular interactions between genes are known, it is unclear how these translate to organism-level interactions between alleles. We therefore characterized the interplay of genetic and environmental dependencies in determining fitness by quantifying ~4000 fitness interactions between expression variants of two metabolic genes, starting from various environmentally modulated expression levels. We detect a remarkable variety of interactions dependent on initial expression levels and demonstrate that they can be quantitatively explained by a mechanistic model accounting for catabolic flux, metabolite toxicity, and expression costs. Complex fitness interactions between mutations can therefore be predicted simply from their simultaneous impact on a few connected molecular phenotypes.



Dynamic single-cell phenotyping of immune cells using the microfluidic platform DropMap
Laboratoire Biochimie - Yacine Bounab, Klaus Eyer, Sophie Dixneuf, Magda Rybczynska, Cécile Chauvel, Maxime Mistretta, Trang Tran, Nathan Aymerich, Guilhem Chenon, Jean-François Llitjos, Fabienne Venet, Guillaume Monneret, Iain A. Gillespie, Pierre Cortez, Virginie Moucadel, Al
Protocol - 15 2920–2955 - doi.org/10.1073/pnas.1913767117 - 2020
Characterization of immune responses is currently hampered by the lack of systems enabling quantitative and dynamic phenotypic characterization of individual cells and, in particular, analysis of secreted proteins such as cytokines and antibodies. We recently developed a simple and robust microfluidic platform, DropMap, to measure simultaneously the kinetics of secretion and other cellular characteristics, including endocytosis activity, viability and expression of cell-surface markers, from tens of thousands of single immune cells. Single cells are compartmentalized in 50-pL droplets and analyzed using fluorescence microscopy combined with an immunoassay based on fluorescence relocation to paramagnetic nanoparticles aligned to form beadlines in a magnetic field. The protocol typically takes 8–10 h after preparation of microfluidic chips and chambers, which can be done in advance. By contrast, enzyme-linked immunospot (ELISPOT), flow cytometry, time-of-flight mass cytometry (CyTOF), and single-cell sequencing enable only end-point measurements and do not enable direct, quantitative measurement of secreted proteins. We illustrate how this system can be used to profile downregulation of tumor necrosis factor-α (TNF-α) secretion by single monocytes in septic shock patients, to study immune responses by measuring rates of cytokine secretion from single T cells, and to measure affinity of antibodies secreted by single B cells.



The Quantitative Assessment of the Secreted IgG Repertoire after Recall to Evaluate the Quality of Immunizations
Laboratoire Biochimie - Klaus Eyer, Carlos Castrillon, Guilhem Chenon, Jérôme Bibette, Pierre Bruhns, Andrew D. Griffiths and Jean Baudry
J Immunol July - 206 10 - DOI: https://doi.org/10.4049/jimmunol.2000112 - 2020
One of the major goals of vaccination is to prepare the body to rapidly secrete specific Abs during an infection. Assessment of the vaccine quality is often difficult to perform, as simple measurements like Ab titer only partly correlate with protection. Similarly, these simple measurements are not always sensitive to changes in the preceding immunization scheme. Therefore, we introduce in this paper a new, to our knowledge, method to assay the quality of immunization schemes for mice: shortly after a recall with pure Ag, we analyze the frequencies of IgG-secreting cells (IgG-SCs) in the spleen, as well as for each cells, the Ag affinity of the secreted Abs. We observed that after recall, appearance of the IgG-SCs within the spleen of immunized mice was fast (<24 h) and this early response was free of naive IgG-SCs. We further confirmed that our phenotypic analysis of IgG-SCs after recall strongly correlated with the different employed immunization schemes. Additionally, a phenotypic comparison of IgG-SCs presented in the spleen during immunization or after recall revealed similarities but also significant differences. The developed approach introduced a novel (to our knowledge), quantitative, and functional highly resolved alternative to study the quality of immunizations.




Polarization of Myosin II Refines Tissue Material Properties to Buffer Mechanical Stress
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Maria Duda, Natalie J Kirkland, Nargess Khalilgharibi, Melda Tozluoglu , Alice C Yuen , Nicolas Carpi , Anna Bove , Matthieu Piel , Guillaume Charras , Buzz Baum , Yanlan Mao
Dev Cell - 48(2) 245-260.e7 - DOI: 10.1016/j.devcel.2018.12.020 - 2020
mTOR activation is essential and sufficient to cause polycystic kidneys in Tuberous Sclerosis Complex (TSC) and other genetic disorders. In disease models, a sharp increase of proliferation and cyst formation correlates with a dramatic loss of oriented cell division (OCD). We find that OCD distortion is intrinsically due to S6 kinase 1 (S6K1) activation. The concomitant loss of S6K1 in Tsc1-mutant mice restores OCD but does not decrease hyperproliferation, leading to non-cystic harmonious hyper growth of kidneys. Mass spectrometry-based phosphoproteomics for S6K1 substrates revealed Afadin, a known component of cell-cell junctions required to couple intercellular adhesions and cortical cues to spindle orientation. Afadin is directly phosphorylated by S6K1 and abnormally decorates the apical surface of Tsc1-mutant cells with E-cadherin and α-catenin. Our data reveal that S6K1 hyperactivity alters centrosome positioning in mitotic cells, affecting oriented cell division and promoting kidney cysts in conditions of mTOR hyperactivity.
mTOR and S6K1 drive polycystic kidney by the control of Afadin-dependent oriented cell division
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Martina Bonucci, Nicolas Kuperwasser, Serena Barbe, Vonda Koka, Delphine de Villeneuve, Chi Zhang, Nishit Srivastava, Xiaoying Jia, Matthew P Stokes, Frank Bienaimé, Virginie Verkarre, Jean Baptiste Lopez, Fanny Jaulin, Marco Pontoglio, Fabiola Terzi, Be
Nature Communications - - DOI : 10.1038/s41467-020-16978-z - 2020
mTOR activation is essential and sufficient to cause polycystic kidneys in Tuberous Sclerosis Complex (TSC) and other genetic disorders. In disease models, a sharp increase of proliferation and cyst formation correlates with a dramatic loss of oriented cell division (OCD). We find that OCD distortion is intrinsically due to S6 kinase 1 (S6K1) activation. The concomitant loss of S6K1 in Tsc1-mutant mice restores OCD but does not decrease hyperproliferation, leading to non-cystic harmonious hyper growth of kidneys. Mass spectrometry-based phosphoproteomics for S6K1 substrates revealed Afadin, a known component of cell-cell junctions required to couple intercellular adhesions and cortical cues to spindle orientation. Afadin is directly phosphorylated by S6K1 and abnormally decorates the apical surface of Tsc1-mutant cells with E-cadherin and α-catenin. Our data reveal that S6K1 hyperactivity alters centrosome positioning in mitotic cells, affecting oriented cell division and promoting kidney cysts in conditions of mTOR hyperactivity.
Mechanochemical Crosstalk Produces Cell-Intrinsic Patterning of the Cortex to Orient the Mitotic Spindle.
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Andrea Dimitracopoulos, Pragya Srivastava, Agathe Chaigne, Zaw Win, Roie Shlomovitz, Oscar M Lancaster, Maël Le Berre, Matthieu Piel, Kristian Franze, Guillaume Salbreux, Buzz Baum
Current biology - - DOI : S0960-9822(20)30984-2 - 2020
Proliferating animal cells are able to orient their mitotic spindles along their interphase cell axis, setting up the axis of cell division, despite rounding up as they enter mitosis. This has previously been attributed to molecular memory and, more specifically, to the maintenance of adhesions and retraction fibers in mitosis [1-6], which are thought to act as local cues that pattern cortical Gαi, LGN, and nuclear mitotic apparatus protein (NuMA) [3, 7-18]. This cortical machinery then recruits and activates Dynein motors, which pull on astral microtubules to position the mitotic spindle. Here, we reveal a dynamic two-way crosstalk between the spindle and cortical motor complexes that depends on a Ran-guanosine triphosphate (GTP) signal [12], which is sufficient to drive continuous monopolar spindle motion independently of adhesive cues in flattened human cells in culture. Building on previous work [1, 12, 19-23], we implemented a physical model of the system that recapitulates the observed spindle-cortex interactions. Strikingly, when this model was used to study spindle dynamics in cells entering mitosis, the chromatin-based signal was found to preferentially clear force generators from the short cell axis, so that cortical motors pulling on astral microtubules align bipolar spindles with the interphase long cell axis, without requiring a fixed cue or a physical memory of interphase shape. Thus, our analysis shows that the ability of chromatin to pattern the cortex during the process of mitotic rounding is sufficient to translate interphase shape into a cortical pattern that can be read by the spindle, which then guides the axis of cell division.
ATR is essential for preservation of cell mechanics and nuclear integrity during interstitial migration
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Gururaj Rao Kidiyoor, Qingsen Li, Giulia Bastianello, Christopher Bruhn, Irene Giovannetti, Adhil Mohamood, Galina V. Beznoussenko, Alexandre Mironov, Matthew Raab, Matthieu Piel, Umberto Restuccia, Vittoria Matafora, Angela Bachi, Sara
Nature Communications - 11 4828 - https://doi.org/10.1038/s41467-020-18580-9 - 2020
ATR responds to mechanical stress at the nuclear envelope and mediates envelope-associated repair of aberrant topological DNA states. By combining microscopy, electron microscopic analysis, biophysical and in vivo models, we report that ATR-defective cells exhibit altered nuclear plasticity and YAP delocalization. When subjected to mechanical stress or undergoing interstitial migration, ATR-defective nuclei collapse accumulating nuclear envelope ruptures and perinuclear cGAS, which indicate loss of nuclear envelope integrity, and aberrant perinuclear chromatin status. ATR-defective cells also are defective in neuronal migration during development and in metastatic dissemination from circulating tumor cells. Our findings indicate that ATR ensures mechanical coupling of the cytoskeleton to the nuclear envelope and accompanying regulation of envelope-chromosome association. Thus the repertoire of ATR-regulated biological processes extends well beyond its canonical role in triggering biochemical implementation of the DNA damage response.

The nucleus acts as a ruler tailoring cell responses to spatial constraints
Laboratoire Biologie cellulaire systémique de la polarité et de la division - A. J. Lomakin, C. J. Cattin, D. Cuvelier, Z. Alraies, M. Molina. Nader, N. Sri
Science - 6514 370 - DOI: 10.1126/science.aba2894 - 2020
Single cells continuously experience and react to mechanical challenges in three-dimensional tissues. Spatial constraints in dense tissues, physical activity, and injury all impose changes in cell shape. How cells can measure shape deformations to ensure correct tissue development and homeostasis remains largely unknown (see the Perspective by Shen and Niethammer). Working independently, Venturini et al. and Lomakin et al. now show that the nucleus can act as an intracellular ruler to measure cellular shape variations. The nuclear envelope provides a gauge of cell deformation and activates a mechanotransduction pathway that controls actomyosin contractility and migration plasticity. The cell nucleus thereby allows cells to adapt their behavior to the local tissue microenvironment.
Sliding walls: a new paradigm for fluidic actuation and protocol implementation in microfluidics
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Venzac, Bastien; Liu, Yang; Ferrante, Ivan; Vargas, Pablo; Yamada, Ayako; Courson, Rémi; Verhulsel, Marine; Malaquin, Laurent; Viovy, Jean-Louis; Descroix, Stéphanie
Microsystems & Nanoengineering - 6(1) 18 - DOI: 10.1038/s41378-019-0125-7 - 2020
Currently, fluidic control in microdevices is mainly achieved either by external pumps and valves, which are expensive and bulky, or by valves integrated in the chip. Numerous types of internal valves or actuation methods have been proposed, but they generally impose difficult compromises between performance and fabrication complexity. We propose here a new paradigm for actuation in microfluidic devices based on rigid or semi-rigid walls with transversal dimensions of hundreds of micrometres that are able to slide within a microfluidic chip and to intersect microchannels with hand-driven or translation stage-based actuation. With this new concept for reconfigurable microfluidics, the implementation of a wide range of functionalities was facilitated and allowed for no or limited dead volume, low cost and low footprint. We demonstrate here several fluidic operations, including on/off or switch valving, where channels are blocked or reconfigured depending on the sliding wall geometry. The valves sustain pressures up to 30 kPa. Pumping and reversible compartmentalisation of large microfluidic chambers were also demonstrated. This last possibility was applied to a "4D" migration assay of dendritic cells in a collagen gel. Finally, sliding walls containing a hydrogel-based membrane were developed and used to concentrate, purify and transport biomolecules from one channel to another, such functionality involving complex fluidic transport patterns not possible in earlier microfluidic devices. Overall, this toolbox is compatible with "soft lithography" technology, allowing easy implementation within usual fabrication workflows for polydimethylsiloxane chips. This new technology opens the route to a variety of microfluidic applications, with a focus on simple, hand-driven devices for point-of-care or biological laboratories with low or limited equipment and resources.
Oncogenic Signaling Alters Cell Shape and Mechanics to Facilitate Cell Division under Confinement
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Helen K.Matthews, Sushila Ganguli, KatarzynaPlak, Anna V.Taubenberger, Zaw Win, Max Williamson, Matthieu Piel, Jochen Guck, Buzz Baum
Dev Cell - 52(5) 563-573.e3 - doi.org/10.1016/j.devcel.2020.01.004 - 2020
To divide in a tissue, both normal and cancer cells become spherical and mechanically stiffen as they enter mitosis. We investigated the effect of oncogene activation on this process in normal epithelial cells. We found that short-term induction of oncogenic RasV12 activates downstream mitogen-activated protein kinase (MEK-ERK) signaling to alter cell mechanics and enhance mitotic rounding, so that RasV12-expressing cells are softer in interphase but stiffen more upon entry into mitosis. These RasV12-dependent changes allow cells to round up and divide faithfully when confined underneath a stiff hydrogel, conditions in which normal cells and cells with reduced levels of Ras-ERK signaling suffer multiple spindle assembly and chromosome segregation errors. Thus, by promoting cell rounding and stiffening in mitosis, oncogenic RasV12 enables cells to proliferate under conditions of mechanical confinement like those experienced by cells in crowded tumors.
The nucleus acts as a ruler tailoring cell responses to spatial constraints
Laboratoire Biologie cellulaire systémique de la polarité et de la division - A. J. Lomakin, C. J. Cattin, D. Cuvelier, Z. Alraies, M. Molina, G. P. F. Nader, N. Srivastava, P. J. Saez, J. M. Garcia-Arcos, I. Y. Zhitnyak, A. Bhargava, M. K. Driscoll, E. S. Welf, R. Fiolka, R. J. Petrie, N. S. De Silva, J. M. González-Grana
Science - 370 6514 - DOI: 10.1126/science.aba2894 - 2020
The human body is a crowded place. This crowding is even more acute when the regulation of cell growth and proliferation fails during the formation of a tumor. Dealing with the lack of space in crowded environments presents cells with a challenge. This is especially true for immune cells, whose task is to patrol tissues, causing them to experience both acute and sustained deformation as they move. Although changes in tissue crowding and associated cell shape alterations have been known by pathologists to be key diagnostic traits of late-stage tumors since the 19th century, the impact of these changes on the biology of cancer and immune cells remains unclear. Moreover, it is not known whether cells can detect and adaptively respond to deformations in densely packed spaces.
A statistical inference approach to reconstruct intercellular interactions in cell migration experiments
Laboratoire Biologie cellulaire systémique de la polarité et de la division - Elena Agliari1, Pablo J. Sáez, Adriano Barra, Matthieu Piel, Pablo Vargas
Science Advances - 6 11 - DOI: 10.1126/sciadv.aay2103 - 2020
Migration of cells can be characterized by two prototypical types of motion: individual and collective migration. We propose a statistical inference approach designed to detect the presence of cell-cell interactions that give rise to collective behaviors in cell motility experiments. This inference method has been first successfully tested on synthetic motional data and then applied to two experiments. In the first experiment, cells migrate in a wound-healing model: When applied to this experiment, the inference method predicts the existence of cell-cell interactions, correctly mirroring the strong intercellular contacts that are present in the experiment. In the second experiment, dendritic cells migrate in a chemokine gradient. Our inference analysis does not provide evidence for interactions, indicating that cells migrate by sensing independently the chemokine source. According to this prediction, we speculate that mature dendritic cells disregard intercellular signals that could otherwise delay their arrival to lymph vessels.

638 publications.