HAL Portal ESPCI (Ecole Supérieure de Physique et de Chimie Industrielles)
Not a member yet
13939 research outputs found
Sort by
Selective band engineering of Bi/Si(111) by boron segregation
No full textAtomically thin layers of metals deposited on semiconductors display a variety of physical properties such as superconductivity, charge density waves, topological phases, strong spin-orbit (Rashba) splitting, among others. To access these exotic phases and induce new ones, it is necessary to control and tune the energies of the electronic states of those heterostructures. In this work we investigate the engineering of the band structure of the two-dimensional Bi/Si(111) -phase using a modulation doping approach based on boron segregation at the surface. We demonstrate that the Bi-induced Rashba bands can be displaced in energy by up to 200 meV without altering their strong Rashba parameter. Importantly, while the Bi states shift upward, the underlying Si valence states remain essentially fixed, which rules out a simple band-bending scenario. Our density functional theory calculations reveal that the displacement originates from changes in the hybridization of Si states near the surface, induced by the presence of B atoms. This selective mechanism halves the distance of the Rashba-split states from the Fermi level, opening the way to their exploitation in transport and spintronic devices and highlighting the broader potential of modulation doping as a band-engineering strategy for two-dimensional metals on semiconductors
Genomics of Neotropical biodiversity indicators: Two butterfly radiations with rampant chromosomal rearrangements and hybridization
No full textInternational audienceA central question in evolutionary biology is what drives the diversification of lineages. Rapid, recent radiations are ideal systems for this question because they still show key morphological and ecological adaptations associated with speciation. While most research on recent radiations focuses on those occurring in insular environments, less attention has been given to continental radiations with complex species interactions. Here, we study the drivers of continental radiations of Melinaea and Mechanitis butterflies (Nymphalidae: Ithomiini), which have rapidly radiated in the continental Neotropics. They are classical models for Amazonian biogeography and color pattern mimicry and have been proposed as biodiversity indicators. We generated reference genomes for five species of each genus and whole-genome resequencing data of most species and subspecies covering a wide geographic range to assess phylogeographic relationships, hybridization patterns, and chromosomal rearrangements. Our data help resolve the classification of these taxonomically challenging butterflies and reveal very high diversification rates. We find rampant evidence of historical hybridization and putative hybrid species in both radiations, which may have facilitated their rapid diversification by enriching the genetic diversity. Moreover, we identified dozens of chromosomal fusions and fissions between congeneric species that have likely expedited reproductive isolation. We conclude that interactions between geography, hybridization and chromosomal rearrangements have contributed to these rapid radiations in the highly diverse Neotropical region. We hypothesize that rapid radiations may be spurred if repeated periods of geographic isolation are combined with lineage-specific rapid accumulation of incompatibilities, followed by secondary contact with some gene exchange
Resource landscape shapes the composition and stability of the human vaginal microbiota
No full textAbstract The vaginal microbiota is associated with the health of women and newborns alike. Despite its comparatively simple composition relative to other human microbiota systems, the mechanisms underpinning the dynamics and stability of vaginal microbial communities remain elusive. A crucial, yet so far underexplored, aspect of vaginal microbiota ecology is the role played by nutritional resources. Glycogen and its derivatives, produced by vaginal epithelia, are accessible to all bacterial constituents of the microbiota. Concurrently, free sialic acid and fucose offer supplementary nutritional resources to bacterial strains capable of cleaving them from glycans, which are structurally integral to mucus. Notably, bacteria adept at sialic acid exploitation are often correlated with adverse clinical outcomes and are frequently implicated in bacterial vaginosis (BV). In this study, we introduce a novel mathematical model tailored to human vaginal microbiota dynamics to explore the interactions between bacteria and their respective nutritional landscape. Our resource-based model examines the impact of the relative availability of glycogen derivatives (accessible to all bacterial species) and sialic acid (exclusive to some BV-associated bacteria) on the composition of the vaginal microbiota. Our findings elucidate that the success of BV-associated bacteria is intricately linked to their exclusive access to specific nutritional resources. This private access fortifies communities dominated by BV-associated bacteria, rendering them resilient to compositional transitions. We empirically corroborate our model prediction with longitudinal clinical data on microbiota composition and previously unpublished metabolomic profiles obtained from a North American cohort. The insights gleaned from this study shed light on potential pathways for BV prevention and treatment. Significance statement The vaginal microbiota has a notable impact on women’s health at various stages of life, namely puberty, infection protection, sexual health, fertility, pregnancy, and menopausal changes. At present, most non-anti-microbial products developed to mitigate adverse vaginal symptoms emphasise competitive interactions through acids (boric or lactic acid) or probiotics as a means to “rebalance” microbiota communities. Despite recent advances in profiling the composition of vaginal microbiota communities, there remains a major gap in our mechanistic understanding of how to maintain or reinstate a resilient Lactobacillus -dominated microbiota that improves vaginal health and outcomes. This study explores the role of nutritional resources in the vaginal microbiota by introducing a mathematical model that analyses how access to specific nutrients like glycogen derivatives and sialic acid affects the balance of bacterial vaginosis (BV) and non-BV-associated bacteria. Our findings, supported by original cohort-derived microbiological and metabolomics data, demonstrate that exclusive access to these nutrients is linked to the dominance and resilience of BV-associated bacteria, providing new insights for BV prevention and treatment
Eliminating separase inhibition reveals absence of robust cohesin protection in oocyte metaphase II
No full textInternational audienceThe meiotic segregation pattern to generate haploid gametes is mediated by step-wise cohesion removal by separase, first from chromosome arms in meiosis I, and then from the pericentromere in meiosis II. In mammalian oocytes, separase is tightly controlled during the hours-long prometaphase and until chromosome segregation in meiosis I, activated for a short time window, and again inhibited until metaphase II arrest is lifted by fertilization. Centromeric cohesin is protected from cleavage by Sgo2-PP2A in meiosis I. It remained enigmatic how tight control of alternating separase activation and inactivation is achieved during the two divisions in oocytes, and when cohesin protection is put in place and removed. Using complementation assays in knock-out mouse models, we established the contributions of cyclin B1 and securin for separase inhibition during both divisions. When eliminating separase inhibition, we found that cohesin is not robustly protected at meiosis I resumption and during metaphase II arrest. Importantly, in meiosis II, the sole event required for cleavage of pericentromeric cohesin besides separase activation is prior kinetochore individualization in meiosis I
Evolutionary convergences and divergences in sympatric species: Morpho butterflies as a case study
No full textInternational audienceHow do closely related species interact in sympatry? And how do these interactions influence the evolution of their traits and the dynamics of species diversification? In this review, we show how recent research on the evolution of Morpho butterflies contributes to address these questions. We first show how sympatric species have colonized different vertical strata in the neotropical forest and how this divergence has produced cascading adaptive effects on behavioural (flight) but also morphological traits, including wing size, shape and coloration. We then focus on the evolution of peculiar dorsal blue coloration within the genus Morpho . During flight, the blue iridescence produces bright flashes that confuse predators and likely enhance the escape abilities of these butterflies. In turn, predators learn the association between such conspicuous coloration and escaping capacities. Such learning favours the locally abundant colour pattern and promotes the local convergence in sympatric species. However, this tight resemblance also induces sexual interference between mimetic species. Capture–Mark–Recapture data uncovered that mimetic species do not fly at the same hours: competition seems to have driven the divergence in the timing of flight activity between species. Overall, sympatry therefore promotes the intricated evolution of convergent and divergent traits among tightly related species, that jointly facilitate their coexistence. Whether ecological speciation was involved in this evolution is an intriguing open question. At the genomic level, analyses revealed a faster evolution of the sexual chromosome Z as compared to the autosomes, with extensive rearrangements and molecular signals of positive selection: these data thus suggest an important role for the Z chromosome in adaptive evolution in Morpho and possibly in speciation. Paving the way for future research, these various, multilevel studies show that Morpho are not just those showy butterflies in the box: they can also teach us much about evolutionary processes
Continuous self-repair protects vimentin intermediate filaments from fragmentation
No full textInternational audienceIntermediate filaments are key regulators of cell mechanics. Vimentin, a type of intermediate filament expressed in mesenchymal cells and involved in migration, forms a dense network in the cytoplasm that is constantly remodeling through filament transport, elongation/shortening, and subunit exchange. While it is known that filament elongation involves end-to-end annealing, the reverse process of filament shortening by fragmentation remains unclear. Here, we use a combination of in vitro reconstitution, probed by fluorescence imaging and atomic force microscopy, with theoretical modeling to uncover the molecular mechanism involved in filament breakage. We first show that vimentin filaments are composed of two populations of subunits, half of which are exchangeable and half immobile. We also show that the exchangeable subunits are tetramers. Furthermore, we reveal a mechanism of continuous filament self-repair, where a soluble pool of vimentin tetramers in equilibrium with the filaments is essential to maintain filament integrity. Filaments break due to local fluctuations in the number of tetramers per cross-section, induced by the constant subunit exchange. We determine that a filament tends to break if approximately four tetramers are removed from the same filament cross-section. Finally, we analyze the dynamics of association/dissociation and fragmentation to estimate the binding energy of a tetramer to a complete versus a partially disassembled filament. Our results provide a comprehensive description of vimentin turnover and reveal the link between subunit exchange and fragmentation
Wave induced fracture of a sea ice analog
No full textWe study at the laboratory scale the rupture of thin floating sheets made of a brittle material under wave induced mechanical forcing. We show that the rupture occurs where the curvature is maximum, and the break up threshold strongly depends on the wave properties. We observe that the corresponding critical stress for fracture depends on the forcing wavelength: our observations are thus incompatible with a critical stress criteria for fracture. Our measurements can rather be rationalized using a energy criteria: a fracture propagates when the material surface energy is lower than the released elastic energy, which depends on the forcing geometry. Our results suggest that current models of sea ice fracture by ocean waves could be refined
Local translation controls early reactive changes in perisynaptic astrocyte processes at pre-symptomatic stages of Alzheimer’s disease
No full textUnderstanding the progression of cellular dysfunction in preclinical Alzheimer’s disease (AD) is essential for developing new therapeutic strategies. Early alterations in astrocyte perisynaptic functions have been observed in AD [1], yet the molecular underpinnings remain poorly characterized. Here, we hypothesized that local protein synthesis—a critical mechanism for maintaining astrocyte polarity and subcellular compartmentalization [2, 3]—could be impaired at early AD stages. METHODS We studied the effect of oligomeric Aß on mRNA translation by imaging puromycylated-nascent protein chains in primary astrocytes alone or in coculture with neurons. To further characterize effects on astrocyte translation, we extracted by translating ribosome affinity purification (TRAP) [4], ribosome-bound mRNAs from hippocampal astrocytes and perisynaptic astrocyte processes (PAP) in wild type (WT) and APPswe/PS1dE9 (APP) mice at 5.5 months, a pre-symptomatic stage corresponding to the initiation of Aß plaque formation. mRNAs were analyzed by high throughput RNA sequencing and compared between genotypes and astrocyte compartments. Results were further verified by RT-qPCR in purified hippocampal synaptogliosomes as well as gliovascular units, and by fluorescent in situ hybridization (FISH). We addressed the role of the Janus Kinase (JAK)-Signal Transducer and Activator of Transcription 3 (STAT3) pathway - a master regulator of reactive astrocytes [5] - on the early mRNA expression and distribution in astrocytes by astrocyte-specific viral gene transfer of the pathway inhibitor Suppressor Of Cytokine Signaling 3 (SOCS3) in hippocampal astrocytes in WT and APP mice. RESULTS Aß induced global and local translational perturbations in primary astrocytes. 5.5 months APP PAPs showed prominent translational changes compared to whole APP astrocytes and WT. They were related mainly to axon development, neurotransmitter transport, inflammation and endoplasmic reticulum (ER) stress. Some upregulated mRNAs accumulated in APP PAPs from 3 months, but not in astrocyte perivascular processes (PvAP). From this stage, Serpina3n total mRNAs encoding the serine protease inhibitor A3 accumulated in astrocyte soma and PAPs, and this effect was rescued in PAPs upon JAK-STAT3 inhibition. DISCUSSION Our findings show that in APP mice, significant translational changes predominantly occur in PAPs at pre-symptomatic stages of AD. They are sustained, as observed for Serpina3n, by the upregulation and distribution of total mRNAs specifically in PAPs from 3 months. The JAK-STAT3 pathway contribute to the distribution of Serpina3n mRNAs in APP PAPs as early as 3 months. These early local events could be related to soluble Aβ as well as early synaptic dysregulations sensed by PAPs, which may trigger local astrocyte reactivity. Thus, targeting local translation in astrocytes may represent a promising therapeutic strategy to counteract early synaptic alterations in AD. HIGHLIGHTS Soluble Aβ influences the global and local translation in primary astrocytes At 5.5 months, when Aβ plaques start to form, translation is severely and predominantly altered in APP PAPs. Local translation changes in APP PAPs impact mRNAs encoding proteins involved in astrocyte reactivity, synaptic development and functions and ER stress. Upregulation of Serpina3n mRNAs in APP astrocyte soma and processes occurs as early as 3 months. JAK-STAT3 pathway contributes to Serpina3n mRNA upregulation in PAPs as early as 3 months
Resonance of an object floating within a surface wavefield
No full textWe examine the interaction between floating cylindrical objects and surface waves in the gravity regime. Since the impact of resonance phenomena associated with floating bodies, particularly at laboratory scales, remains underexplored, we focus on the influence of the floats' resonance frequency on wave emission. First, we study the response of floating rigid cylinders to external mechanical perturbations. Using an optical reconstruction technique to measure surface wave fields in both space and time, we study the natural resonance frequency of floats with different sizes. The results indicate that the resonance frequency is influenced by the interplay between the cylinder geometry and the solid-to-fluid density ratio. Second, these floating objects are placed in an incoming wave field. These experiments demonstrate that floats diffract incoming waves, while radiating secondary waves that interfere with the incident wavefield. Minimal wave generation is observed at resonance frequencies. These findings can provide insights for elucidating the behavior of larger structures, such as sea ice floes, in natural wave fields
High Resolution and High-Speed Live Optical Flow Velocimetry
No full textParticle Image Velocimetry (PIV) is the most widely used optical technique for measuring two-dimensional velocity fields in fluids. However, with the standard cross-correlation (CC) algorithm, improving the spatial resolution of instantaneous velocity fields and obtaining dense velocity fields in real time remains challenging. Optical Flow Velocimetry (OFV) offers a way to overcome these limitations. In this study, we demonstrate that dense velocity fields (one vector per pixel) with high spatial resolution can be obtained in real time at frequencies up to thousands of Hertz using an optical flow approach. We show that high resolution is achievable with optimized seeding, and that computational speed can be increased by choosing appropriate parameters and running on a single GPU. Using this method, 21 Mp velocity fields can be computed in real-time at 90 Hz, while 4 Mp velocity fields can be computed up to 460 Hz. These measurements enable the computation of various flow quantities in real time, during the experiment. It makes this technique perfectly suitable for many new type of experiments, from closed-loop flow control experiments based on OFV measurements, to very low frequency measurements or monitoring of the flow to find rare events. They also greatly accelerate post-processing leading to potential large time and energy gain for post-processing