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Functional organization of 3D plant thylakoid membranes as seen by high resolution microscopy
No full textInternational audienceIn the field of photosynthesis, only a limited number of approaches of super-resolution fluorescence microscopy can be used, as the functional architecture of the thylakoid membrane in chloroplasts is probed through the natural fluorescence of chlorophyll molecules. In this work, we have used a custom-built fluorescence microscopy method called Single Pixel Reconstruction Imaging (SPiRI) that yields a 1.4 gain in lateral and axial resolution relative to confocal fluorescence microscopy, to obtain 2D images and 3D-reconstucted volumes of isolated chloroplasts, obtained from pea (Pisum sativum), spinach (Spinacia oleracea) and Arabidopsis thaliana. In agreement with previous studies, SPiRI images exhibit larger thylakoid grana diameters when extracted from plants under low-light regimes. The three-dimensional thylakoid architecture, revealing the complete network of the thylakoid membrane in intact, non-chemically-fixed chloroplasts can be visualized from the volume reconstructions obtained at high resolution. From such reconstructions, the stromal connections between each granum can be determined and the fluorescence intensity in the stromal lamellae compared to those of neighboring grana
Mechanical Characterization of Murine Oocytes by Atomic Force Microscopy
No full textInternational audienceThe quality of murine and human oocytes correlates to their mechanical properties, which are tightly regulated to reach the blastocyst stage after fertilization. Oocytes are nonadherent spherical cells with a diameter over 80 μm. Their mechanical properties have been studied in our lab and others using the micropipette aspiration technique, particularly to obtain the oocyte cortical tension. Micropipette aspiration is affordable but has a low throughput and induces cell-scale deformation. Here we present a step-by-step protocol to characterize the mechanical properties of oocytes using atomic force microscopy (AFM), which is minimally invasive and has a much higher throughput. We used electron microscopy grids to immobilize oocytes. This allowed us to obtain local and reproducible measurements of the cortical tension of murine oocytes during their meiotic divisions. Cortical tension values obtained by AFM are in agreement with the ones previously obtained by micropipette aspiration. Our protocol could help characterize the biophysical properties of oocytes or other types of large nonadherent samples in fundamental and medical research
Non-cell autonomous OTX2 in the piriform cortex regulates parvalbumin cell maturation states and olfactory-driven behavior
No full textInternational audienceAbstract The timing of critical periods of juvenile brain plasticity is driven by the maturation of parvalbumin interneurons in the neocortex, a process regulated in part by non-cell autonomous activity of the OTX2 homeoprotein transcription factor. However, the involvement of critical periods in olfactory paleocortex maturation is unknown. Here, we find that the adult mouse piriform cortex parvalbumin interneurons display particularly low molecular maturation that increases in aged animals. Expression analysis of a large panel of genes reveals that an acute increase in piriform cortex OTX2 levels in young adult mice increases Pvalb expression as well as Adamts9 expression, resulting in increased extracellular perineuronal net levels, while reducing OTX2 transfer decreases Pvalb expression and increases Mmp9 expression, resulting in decreased perineuronal net levels. Reduction in OTX2 also stimulates odor-driven cFos activity in piriform cortex parvalbumin cells and disrupts olfactory-driven behavior. Our findings suggest plasticity in piriform cortex involves OTX2 activity on parvalbumin cells and lacks strictly defined critical periods
Generalizations of Parisi’s replica symmetry breaking and overlaps in random energy models
No full textInternational audienceThe random energy model (REM) is the simplest spin glass model which exhibits replica symmetry breaking. It is well known since the 80's that its overlaps are non-selfaveraging and that their statistics satisfy the predictions of the replica theory. All these statistical properties can be understood by considering that the low energy levels are the points generated by a Poisson process with an exponential density. Here we first show how, by replacing the exponential density by a sum of two exponentials, the overlaps statistics are modified. One way to reconcile these results with the replica theory is to allow the blocks in the Parisi matrix to fluctuate. Other examples where the sizes of these blocks should fluctuate include the finite size corrections of the REM, the case of discrete energies and the overlaps between two temperatures. In all these cases, the block sizes not only fluctuate but need to take complex values if one wishes to reproduce the results of our replica-free calculations.Le modèle d'énergies aléatoires (REM) est le modèle de verre de spin le plus simple qui présente une brisure de symétrie des répliques. Il est bien connu depuis les années 80 que ses overlaps ne sont pas automoyennants et que leurs statistiques sont celles prédites par la méthode des répliques. Ces propriétés statistiques peuvent être comprises en considérant que les niveaux d'énergie les plus bas sont les points générés par un processus de Poisson de densité exponentielle. Nous montrons ici dans un premier temps comment ces statistiques d'overlaps sont modifiées lorsqu'on remplace la densité exponentielle par une somme de deux exponentielles. Une façon de concilier ces résultats avec la théorie des répliques est de permettre aux blocs de la matrice de Parisi de fluctuer. D'autres exemples où la taille de ces blocs doit fluctuer incluent les corrections de taille finie du REM, le cas des énergies discrètes et les overlaps entre deux températures. Dans tous ces cas, non seulement la taille des blocs fluctue mais elle doit prendre des valeurs complexes si l'on souhaite reproduire nos résultats obtenus directement, c'est à dire sans utiliser la méthode des répliques
MALS discovery of a rare H I 21 cm absorber at z ∼ 1.35: Origin of the absorbing gas in powerful active galactic nuclei
No full textInternational audienceWe report a new, rare detection of H I 21 cm absorption associated with a quasar (only six quasars are known at 1 < z < 2) toward J2339−5523 at zem = 1.3531, discovered through the MeerKAT Absorption Line Survey (MALS). The absorption profile is broad (∼400 km s-1), and the peak is redshifted by ∼200 km s-1 from z em . Interestingly, optical/far-UV spectra of the quasar from the Magellan-MIKE/HST-COS spectrographs do not show any absorption features associated with the 21 cm absorption, despite the coincident presence of the optical quasar and the radio core inferred from a flat-spectrum component with a flux density of ∼65 mJy at high frequencies (> 5 GHz). The simplest explanation would be that no large H I column ( N (H I ) > 1017cm-2) is present toward the radio core and the optical active galactic nucleus. Based on the joint optical and radio analysis of a heterogeneous sample of 16 quasars (zmedian = 0.7) and 19 radio galaxies (zmedian= 0.4) with H I 21 cm absorption detection and matched in 1.4 GHz luminosity (L1.4 GHz), a consistent picture emerges according to which quasars primarily trace the gas in the inner circumnuclear disk and cocoon created by the interaction of the jet with interstellar medium. They (i.e., quasars) exhibit a L1.4 GHz – ΔVnull correlation and a frequent mismatch of the radio and optical spectral lines. The radio galaxies show no such correlation and likely trace the gas from the cocoon and the galaxy-wide interstellar medium outside the photoionization cone. The analysis presented here demonstrates the potential of radio spectroscopic observations to reveal the origin of the absorbing gas associated with active galactic nuclei that may be missed in optical observations
De la « fausse réputation » d’Edogawa Ranpo : quand un écrivain s’inquiète de l’influence de son style
No full textInternational audienceEdogawa Ranpo (1894-1965) is regarded as the creator of the modern Japanese detective novel. From his first works in 1923, he established himself as a writer and a specialist of the genre. However, he soon realised that the style he supported, close to the Western classics, was often far removed from his own work. How did Ranpo and his fellow writers at the time analyse this discrepancy, which paradoxically distracted from the style of the classical detective novel a growing number of Japanese readers who saw Ranpo’s style as representative of the genre?Edogawa Ranpo (1894-1965) est considéré comme le créateur du roman policier japonais moderne. Dès ses premières œuvres en 1923 il s’impose en tant qu’écrivain mais aussi en tant que spécialiste du genre. Cependant, il prend très rapidement conscience que le style qu’il soutient, proche des classiques occidentaux, est souvent très éloigné de ses propres productions. Comment Ranpo et ses compagnons de l’époque vont-ils analyser cet écart qui détourne paradoxalement du roman policier classique les lecteurs japonais toujours plus nombreux à voir dans le style de Ranpo le format représentatif du genre
Lost in Transition: Financial Barriers to Green Growth
No full textGreen innovation offers a solution to climate change without compromising living standards. Yet the share of climate-enhancing innovations in total patents, after booming for two decades, has seized to grow since the Global Financial Crisis. We develop a quantitative framework in which firms direct innovation towards green or polluting technologies, and become better at innovating in technologies that they have previously succeeded in. This causes mature, incumbent firms to predominantly innovate in polluting technologies. When green technologies become more attractive, e.g. due to a carbon tax, young firms are responsible for a large share of the transition to green innovation. As young firms are financially constrained, a credit shock harms their innovation, bringing the green transition to a halt. We validate the theory with two empirical exercises. First, we use micro data to provide causal evidence that tight credit disproportionately affects green innovation, through its effect on young firms. Second, we show that contractionary monetary policy shocks have a significantly larger effect on green patenting than non-green patenting, in line with the model. Quantifying the model, we find that tight credit can explain around 60% of the recent slowdown in the rise of green patenting. This translates to a cumulative increase in emissions by half a year of the initial (high pollution) steady state
Evolution of divergent daily temporal niches shaped by male-male competition can generate sympatric speciation
No full textAbstract Specialisation into different ecological niches can participate to species divergence and co-existence in sympatry. Here, we focus on the partitioning into different timings of reproductive activities during the day, as observed in many insect species living in sympatry. We thus investigate the evolution of the reproductive activity timing of individuals within populations, using a comprehensive stochastic model, employing a Doob-Gillespie-like simulation process. We model the evolution of (1) the timing of reproductive activity as a quantitative trait and (2) neutral loci that may generate genetic incompatibilities among divergent individuals. We specifically explore how male-male competition for female access can generate negative frequency-dependence on the timing of reproductive activities and fuel population divergence. Our simulations in finite populations highlight the strong effect of male-male competition and operational sex-ratio on the evolution of divergent temporal niches. It also shows how genetic incompatibilities fuel the differentiation among populations with divergent temporal niches, but may impair their coexistence. We then compare our results on the evolution of daily temporal niches to a previous model investigating the evolution of seasonal phenology and show the significant effect of overlapping vs. non-overlapping generations on the evolution of daily vs. seasonal niches. Our model therefore highlights male-male competition as an important factor shaping the evolution of diel niches, that may fuel sympatric speciation
C-CEDILLE : Changements Climatiques et Déglaciation dans les Alpes méditerranéennes
No full textInternational audienceDans les vallées glaciaires d'altitude des Alpes françaises, les moraines marquant les étapes de la déglaciation sont nombreuses mais elles n'ont que rarement été datées de manière directe. Cette lacune touche en particulier la région de la Haute Provence, où la chronologie de la déglaciation n'a été construite que de manière relative en utilisant les datations 14 C et la chronostratigraphie pollinique des remplissages lacustres d'altitude. Dans le cadre du projet C_Cedille, nous associons les compétences complémentaires des équipes du CEREGE et de l'IMBE, pour caler chronologiquement de manière précise les phases clés de la déglaciation à deux sites en Haute Provence, au Lac d'Allos et au Col Bas. Nos résultats montrent une cohérence remarquable entre les datations des héritages glaciaires aux nucléides cosmogéniques (béryllium-10) et les analyses effectuées dans des carottes à Allos et au Col-Bas. Les analyses polliniques, qui permettent de retracer la végétation passée, les analyses sédimentologiques, qui renseignent sur la dynamique des versants, et les datations au 14C qui ont pu être effectuées, sont en excellent accord avec les extensions glaciaires au cours du Tardi-glaciaire (il y a ~18 – 13 ka) et de la transition entre le Dryas Récent et l'Holocène (il y a ~13 – 11 ka). Les moraines datées dans les Alpes méditerranéennes semblent indiquer que les glaciers y ont connu des dynamiques similaires à celles du reste des Alpes à la fin du Tardiglaciaire. Les datations des moraines autour du lac d'Allos confirment notamment que l'extension glaciaire lors du refroidissement maximal du Dryas récent (YD) a été relativement faible, comme dans l'ensemble de la chaine alpine