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Rap1 and Rap2 are Ras-like small G proteins. Rap1 plays major roles in embryogenesis and in hematopoietic systems, as demonstrated by gene knockout studies. On the other hand, Rap2 functions had been unclear until we identified its effectors, protein kinases upstream of c-Jun N-terminal kinase (JNK), the stress-activated mitogen-activated kinase (MAPK). Herein, we report the first gene knockout study of Rap2. Rap2b-null mutant (Rap2b–/–) mice were viable and showed no overt abnormalities in the development or homing of hematopoietic cells. Rap2b–/– CD4+ T cells exhibited MAPK activation patterns comparable to those of Rap2b+/+ counterparts upon acute T-cell receptor (TCR) stimulation. Both Rap2b–/– CD4+ T cells and Rap2b+/+ counterparts secreted similar amounts of IFN-γ upon TCR restimulation after growth under T helper 1 (Th1) polarizing condition. However, secretion of IL-4, IL-5 and IL-13 from Th2-conditioned Rap2b–/– cells was half that of Rap2b+/+ counterparts, suggesting impaired Th2 polarization. Notably, sorted Rap2b–/– CD62Lhigh CD4+ T cells, consisting mainly of naïve cells, showed normal Th2 polarization. By contrast, Rap2b–/– CD62Llow CD4+ T cells showed impaired Th2 polarization, potentially accounting for the abnormality of unsorted Rap2b–/– CD4+ T cells. Impaired Th2 polarization has not previously been reported in Rap-related genetic models and requires further investigation.

Most marine organisms have a biphasic life cycle during which a pelagic larva is transformed into a radically different juvenile. In vertebrates the role of thyroid hormones (TH) in triggering this transition is well known, but how the morphological and physiological changes are integrated in a coherent way with the ecological transition remains poorly explored. To gain insight into this question, we performed an integrative analysis of metamorphosis of a marine teleost, the clownfish Amphiprion ocellaris. We reveal how TH coordinate a change in color vision as well as a major metabolic shift in energy production, hence highlighting its central integrative role in regulating this transformation. By manipulating the activity of LXR, a major regulator of metabolism, we also reveal a tight link between metabolic changes and metamorphosis progression. Strikingly, we observed that these regulations are at play in the wild revealing how hormones coordinate energy needs with available resources during life cycle.

In this review article, we advocate for more collaborations across fields working on astrocyte function. As early-career scientists with different backgrounds and expertise, we present the major challenges faced in our fields: data acquisition, analysis and modeling of astrocyte calcium activity. We further highlight the insights gained from those different approaches, aiming at bridging the gap between them to crack the complex astrocyte "Calcium Code". Finally, we propose strategies to promote fruitful interdisciplinary collaborative projects to unravel astrocyte function in health and disease.

Massive corals of the genus Porites, common, keystone reef builders in the Indo-Pacific Ocean, are distinguished by their relative stress tolerance and longevity. In order to identify genetic bases of these attributes, we sequenced the complete genome of a massive coral, Porites australiensis. We developed a genome assembly and gene models of comparable quality to those of other coral genomes. Proteome analysis identified 60 Porites skeletal matrix protein genes, all of which show significant similarities to genes from other corals and even to those from a sea anemone, which has no skeleton. Nonetheless, 30% of its skeletal matrix proteins were unique to Porites and were not present in the skeletons of other corals. Comparative genomic analyses showed that genes widely conserved among other organisms are selectively expanded in Porites. Specifically, comparisons of transcriptomic responses of P. australiensis and Acropora digitifera, a stress-sensitive coral, reveal significant differences in regard to genes that respond to increased water temperature, and some of the genes expanded exclusively in Porites may account for the different thermal tolerances of these corals. Taken together, widely shared genes may have given rise to unique biological characteristics of Porites, massive skeletons and stress tolerance.

Molluscan shells are among the most fascinating research objects because of their diverse morphologies and textures. The formation of these delicate biomineralized structures is a matrix-mediated process. A question that arises is what are the essential components required to build these exoskeletons. In order to understand the molecular mechanisms of molluscan shell formation, it is crucial to identify organic macromolecules in different shells from diverse taxa. In the case of bivalves, however, taxon sampling in previous shell proteomics studies are focused predominantly on representatives of the class Pteriomorphia such as pearl oysters, edible oysters and mussels. In this study, we have characterized the shell organic matrix from the crocus clam, Tridacna crocea, (Heterodonta) using various biochemical techniques, including SDS-PAGE, FT-IR, monosaccharide analysis, and enzyme-linked lectin assay (ELLA). Furthermore, we have identified a number of shell matrix proteins (SMPs) using a comprehensive proteomics approach combined to RNA-seq. The biochemical studies confirmed the presence of proteins, polysaccharides, and sulfates in the T. crocea shell organic matrix. Proteomics analysis revealed that the majority of the T. crocea SMPs are novel and dissimilar to known SMPs identified from the other bivalve species. Meanwhile, the SMP repertoire of the crocus clam also includes proteins with conserved functional domains such as chitin-binding domain, VWA domain, and protease inhibitor domain. We also identified BMSP (Blue Mussel Shell Protein, originally reported from Mytilus), which is widely distributed among molluscan shell matrix proteins. Tridacna SMPs also include low-complexity regions (LCRs) that are absent in the other molluscan genomes, indicating that these genes may have evolved in specific lineage. These results highlight the diversity of the organic molecules – in particular proteins – that are essential for molluscan shell formation.

Chromosomal rearrangements can reduce fitness of heterozygotes and can thereby prevent gene flow. Therefore, such rearrangements can play a role in local adaptation and speciation. In particular, inversions are considered to be a major potential cause for chromosomal speciation. There are two closely related, partially sympatric lineages of ascidians in the genus Ciona, which we call type-A and type-B animals in the present study. Although these invertebrate chordates are largely isolated reproductively, hybrids can be found in wild populations, suggesting incomplete prezygotic barriers. Although the genome of type-A animals has been decoded and widely used, the genome for type-B animals has not been decoded at the chromosomal level. In the present study, we sequenced the genomes of two type-B individuals from different sides of the English Channel (in the zone of sympatry with type-A individuals) and compared them at the chromosomal level with the type-A genome. Although the overall structures were well conserved between type A and type B, chromosomal alignments revealed many inversions differentiating these two types of Ciona; it is probable that the frequent inversions have contributed to separation between these two lineages. In addition, comparisons of the genomes between the two type-B individuals revealed that type B had high rates of inversion polymorphisms and nucleotide polymorphisms, and thus type B might be in the process of differentiation into multiple new types or species. Our results suggest an important role of inversions in chromosomal speciation of these broadcasting spawners.

International audience; Astrocytes regulate neuronal information processing through a variety of spatio-temporal calcium signals. Recent advances in calcium imaging have started to shine light on astrocytic activity, but the complexity and size of the recorded data strongly call for more advanced computational analysis tools. Their development is currently hindered by the lack of reliable, labeled annotations that are essential for the evaluation of algorithms and the training of learning-based methods. To solve this labeling problem, we have designed a generator of 2D/3D lattice light sheet microscopy (LLSM) sequences which realistically depict the calcium dynamics of astrocytes. By closely modeling calcium kinetics in real astrocytic ramifications, the generated datasets open the door for the deployment of convolutional neural networks in LLSM.

In turbulent rough-walled flows, the 2D friction-roughness relation differs from its 3D counterpart., The friction f is the property of wall-bounded flows that sets the pumping cost of a pipeline, the draining capacity of a river, and other variables of practical relevance. For highly turbulent rough-walled pipe flows, f depends solely on the roughness length scale r, and the f − r relation may be expressed by the Strickler empirical scaling f ∝ r1/3. Here, we show experimentally that for soap film flows that are the two-dimensional (2D) equivalent of highly turbulent rough-walled pipe flows, f ∝ r and the f − r relation is not the same in 2D as in 3D. Our findings are beyond the purview of the standard theory of friction but consistent with a competing theory in which f is linked to the turbulent spectrum via the spectral exponent α: In 3D, α = 5/3 and the theory yields f ∝ r1/3; in 2D, α = 3 and the theory yields f ∝ r.

International audience; The friction f is the property of wall-bounded flows that sets the pumping cost of a pipeline, the draining capacity of a river, and other variables of practical relevance. For highly turbulent rough-walled pipe flows, f depends solely on the roughness length scale r, and the f − r relation may be expressed by the Strickler empirical scaling f ∝ r1/3. Here, we show experimentally that for soap film flows that are the two-dimensional (2D) equivalent of highly turbulent rough-walled pipe flows, f ∝ r and the f − r relation is not the same in 2D as in 3D. Our findings are beyond the purview of the standard theory of friction but consistent with a competing theory in which f is linked to the turbulent spectrum via the spectral exponent α: In 3D, α = 5/3 and the theory yields f ∝ r1/3; in 2D, α = 3 and the theory yields f ∝ r.

14 pages, 5 figures, 2 tables, 1 appendix, supporting information https://doi.org/10.1111/1755-0998.13522.-- Data Availability Statement: All Supporting Information figures and their corresponding raw data can be accessed on Dryad (https://doi.org/10.5061/dryad.zgmsbccck), The software program STRUCTURE is one of the most cited tools for determining population structure. To infer the optimal number of clusters from STRUCTURE output, the ΔK method is often applied. However, a recent study relying on simulated microsatellite data suggested that this method has a downward bias in its estimation of K and is sensitive to uneven sampling. If this finding holds for empirical data sets, conclusions about the scale of gene flow may have to be revised for a large number of studies. To determine the impact of method choice, we applied recently described estimators of K to re-estimate genetic structure in 41 empirical microsatellite data sets; 15 from a broad range of taxa and 26 from one phylogenetic group, coral. We compared alternative estimates of K (Puechmaille statistics) with traditional (ΔK and posterior probability) estimates and found widespread disagreement of estimators across data sets. Thus, one estimator alone is insufficient for determining the optimal number of clusters; this was regardless of study organism or evenness of sampling scheme. Subsequent analysis of molecular variance (AMOVA) did not necessarily clarify which clustering solution was best. To better infer population structure, we suggest a combination of visual inspection of STRUCTURE plots and calculation of the alternative estimators at various thresholds in addition to ΔK. Disagreement between traditional and recent estimators may have important biological implications, such as previously unrecognized population structure, as was the case for many studies reanalysed here, This work was made possible by NSF grant OCE-1537959 to IBB, NIH grant T32: Computation, Bioinformatics, and Statistics (CBIOS) Training Program to KHS, a Bunton-Waller fellowship to KLVK, the strategic Funding UIDB/04423/2020 and UIDP/04423/2020 to JBL, and the Pennsylvania State University Biology Department. The project leading to this publication has received funding from European FEDER Fund under project 1166-39417 to DA. We acknowledge the funding of the Spanish government through the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928-S)

Higher-rank generalisations of electrodynamics have recently attracted considerable attention because of their ability to host "fracton" excitations, with connections to both quantum stabilizer codes and holography. However, the search for higher-rank gauge theories in experiment has been greatly hindered by the lack of materially-relevant microscopic models. Here we show how a spin liquid described by rank-2 $U(1)$ gauge theory can arise in a magnet on the breathing pyrochlore lattice. We identify Yb-based breathing pyrochlores as candidate systems, and make explicit predictions for how the rank-2 $U(1)$ spin liquid would manifest itself in experiment., Comment: 5 pages, 4 figures, with supplemental material. To appear on Phys. Rev. Lett

11 pages; International audience; To construct calcium carbonate skeletons of sophisticated architecture, scleractinian corals secrete an extracellular skeletal organic matrix (SOM) from aboral ectodermal cells. The SOM, which is composed of proteins, saccharides, and lipids, performs functions critical for skeleton formation. Even though polysaccharides constitute the major component of the SOM, its contribution to coral skeleton formation is poorly understood. To this end, we analyzed the SOM of the massive colonial coral, Porites australiensis, the skeleton of which has drawn great research interest because it records environmental conditions throughout the life of the colony. The coral skeleton was extensively cleaned, decalcified with acetic acid, and organic fractions were separated based on solubility. These fractions were analyzed using various techniques, including SDS-PAGE, FT-IR, in vitro crystallization, CHNS analysis, chromatography analysis of monosaccharide and enzyme-linked lectin assay (ELLA). We confirmed the acidic nature of SOM and the presence of sulphate, which is thought to initiate CaCO3 crystallization. In order to analyze glycan structures, we performed ELLA on the soluble SOM for the first time and found that it exhibits strong specificity to Datura stramonium lectin (DSL). Furthermore, using biotinylated DSL with anti-biotin antibody conjugated to nanogold, in situ localization of DSL-binding polysaccharides in the P. australiensis skeleton was performed. Signals were distributed on the surfaces of fiber-like crystals of the skeleton, suggesting that polysaccharides may modulate crystal shape. Our study emphasizes the importance of sugar moieties in biomineralization of scleractinian corals.

Quantum spin ice materials, pyrochlore magnets with competing Ising and transverse exchange interactions, have been widely discussed as candidates for a quantum spin-liquid ground state. Here, motivated by quantum chemical calculations for Pr pyrochlores, we present the results of a study for frustrated transverse exchange. Using a combination of variational calculations, exact diagonalisation, numerical linked-cluster and series expansions, we find that the previously-studied U(1) quantum spin liquid, in its pi-flux phase, transforms into a nematic quantum spin liquid at a high-symmetry, SU(2) point., 5 pages in main text, 10 pages supplemental material

Frustration in magnetic interactions can give rise to disordered ground states with subtle and beautiful properties. The spin ices Ho2Ti2O7 and Dy2Ti2O7 exemplify this phenomenon, displaying a classical spin liquid state, with fractionalized magnetic--monopole excitations. Recently there has been great interest in closely-related "quantum spin ice" materials, following the realization that anisotropic exchange interactions could convert spin ice into a massively-entangled, quantum, spin liquid, where magnetic monopoles become the charges of an emergent quantum electrodynamics. Here we show that even the simplest model of a quantum spin ice, the XXZ model on the pyrochlore lattice, can realise a still-richer scenario. Using a combination of classical Monte Carlo simulation, semi--classical molecular--dynamics simulation, and analytic field theory, we explore the properties of this model for frustrated transverse exchange. We find not one, but three, competing forms of spin liquid, as well as a phase with hidden, spin-nematic, order. We explore the experimental signatures of each of these different states, making explicit predictions for inelastic neutron scattering. These results show an intriguing similarity to experiments on a range of pyrochlore oxides., Comment: 14 pages (8 in main text), 8 figures (5 in main text). Published in Physical Review X

International audience; The kagome lattice is a paragon of geometrical frustration, long-studied for its association with novel ground states including spin liquids. Many recently synthesized kagome materials feature rare-earth ions, which may be expected to exhibit highly anisotropic exchange interactions. The consequences of this combination of strong exchange anisotropy and extreme geometrical frustration are yet to be fully understood. Here, we establish a general picture of the interactions and resulting ground states arising from nearest-neighbor exchange anisotropy on the kagome lattice. We determine a generic anisotropic exchange Hamiltonian from symmetry arguments. In the high-symmetry case where reflection in the kagome plane is a symmetry of the system, the generic nearest-neighbor Hamiltonian can be locally defined as an XYZ model with out-of-plane Dzyaloshinskii-Moriya interactions. We proceed to study its phase diagram in the classical limit, making use of an exact reformulation of the Hamiltonian in terms of irreducible representations (irreps) of the lattice symmetry group. This reformulation in terms of irreps naturally explains the threefold mapping between three families of models supporting spin liquids, as recently studied by the present authors [Nat. Commun. 7, 10297 (2016)]. In addition, a number of unusual states are stabilized in the regions where different forms of ground-state order compete, including a stripy phase with a local Z8 symmetry and a classical analog of a chiral spin liquid. As a peculiar property of the kagome lattice, the generic model turns out to be a fruitful hunting ground for the coexistence, in the same ground-state configuration, of multiple forms of long-range magnetic orders. In exotic instances, partial long-range order may also coexist in the ground state with a finite fraction of disordered spin degrees of freedom. These results are compared and contrasted with those obtained on the pyrochlore lattice, and connection is made with recent progress in understanding quantum models with S=1/2.

Motivated by recent realizations of ${\mathrm{Dy}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ and ${\mathrm{Ho}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ spin ice thin films, and more generally by the physics of confined gauge fields, we study a model spin ice thin film with surfaces perpendicular to the [001] cubic axis. The resulting open boundaries make half of the bonds on the interfaces inequivalent. By tuning the strength of these inequivalent ``orphan'' bonds, dipolar interactions induce a surface ordering equivalent to a two-dimensional crystallization of magnetic surface charges. This surface ordering may also be expected on the surfaces of bulk crystals. For ultrathin films made of one cubic unit cell, once the surfaces have ordered, a square ice phase is stabilized over a finite temperature window. The square ice degeneracy is lifted at lower temperature and the system orders in analogy with the well-known $F$ transition of the 6-vertex model. To conclude, we consider the addition of strain effects, a possible consequence of interface mismatches at the film-substrate interface. Our simulations qualitatively confirm that strain can lead to a smooth loss of Pauling entropy upon cooling, as observed in recent experiments on ${\mathrm{Dy}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ films.

In breathing pyrochlores and kagomes, couplings between neighbouring tetrahedra and triangles are free to differ. Breathing lattices thus offer the possibility to explore a different facet of the rich physics of these systems. Here we consider nearest-neighbour classical Heisenberg interactions, both ferromagnetic and antiferromagnetic, and study how the anisotropy of breathing lattices modifies the mode spectrum of pyrochlore and kagome systems. The nature and degeneracy of the flat bands are shown to be preserved for any value of the anisotropy. These flat bands can coexist with Dirac nodes at the $\Gamma$ point when the model becomes particle-hole symmetric. We also derive the nature of the ground state for the breathing kagome lattice, which bears a spontaneous chirality when neighbouring triangles are alternatively ferromagnetic and antiferromagnetic., Comment: submitted as a proceeding for HFM 2016

The family of magnetic rare-earth pyrochlore oxides R2M2O7 plays host to a diverse array of exotic phenomena, driven by the interplay between geometrical frustration and spin-orbit interaction, which leads to anisotropy in both magnetic moments and their interactions. In this article we establish a general, symmetry--based theory of pyrochlore magnets with anisotropic exchange interactions. Starting from a very general model of nearest-neighbour exchange between Kramers ions, we find four distinct classical ordered states, all with q=0, competing with a variety of spin-liquids and unconventional forms of magnetic order. The finite-temperature phase diagram of this model is determined by Monte Carlo simulation, supported by classical spin-wave calculations. We pay particular attention to the region of parameter space relevant to the widely studied materials Er2Ti2O7, Yb2Ti2O7, and Er2Sn2O7. We find that many of the most interesting properties of these materials can be traced back to the "accidental" degeneracies where phases with different symmetries meet. These include the ordered ground state selection by fluctuations in Er2Ti2O7, the dimensional-reduction observed in Yb2Ti2O7, and the lack of reported magnetic order in Er2Sn2O7. We also discuss the application of this theory to other pyrochlore oxides., Comment: Long-paper version of "Living on the Edge", arXiv:1311.3501. 41 pages, 27 figures. Accepted for publication in Physical Review B

Single-molecule fluorescence localization microscopy has become an indispensable technique of imaging with resolution better than 10 nanometers. However, the light emission of fluorophores is not easy to control because of photobleaching. In the presence of nanoantennas, the photobleaching lifetime, blinking rate and overall photoluminescence intensity can be strongly increased due to the Purcell effect.We fabricated arrays of plasmonic nanoantennas organized as cyclic group metasurfaces coated with a fluorescent film for super-resolution imaging. Following a systematic study of fluorescence engineering using metamaterial-assisted localization microscopy (MALM), we show that improving the photostability of fluorophores and increasing the photoluminescence intensity in MALM enablesimaging resolution with a localization accuracy of 0.9 nm.

We study Ising antiferromagnets that have nearest-neighbour interactions on multilayer triangular lattices with frustrated ($abc$ and $abab$) stacking, and make comparisons with the unfrustrated ($aaa$) stacking. If interlayer couplings are much weaker than in-plane ones, the paramagnetic phase of models with frustrated stackings has a classical spin-liquid regime at low temperature, in which correlations are strong both within and between planes, but there is no long-range order. We investigate this regime using Monte Carlo simulations and by mapping the spin models to coupled height models, which are treated using renormalisation group methods and an analysis of the effects of vortex excitations. The classical spin-liquid regime is parametrically wide at small interlayer coupling in models with frustrated stackings. By contrast, for the unfrustrated stacking there is no extended regime in which interlayer correlations are strong without three-dimensional order., Comment: 25 pages, 21 figures; version to appear in Physical Review B, includes minor corrections

We study the interplay of topological bottlenecks and energetic barriers to equilibration in a Coulomb spin liquid where a short-range energetic coupling between defects charged under an emergent gauge field supplements their entropic long-range Coulomb interaction. This work is motivated by the prevalence of memory effects observed across a wide range of geometrically frustrated magnetic materials, possibly including the spontaneous Hall effect observed in Pr2Ir2O7. Our model is canonical spin-ice model on the pyrochlore lattice, where farther-neighbour spin couplings give rise to a nearest-neighbor interaction between topological defects which can easily be chosen to be unnatural or not, i.e. attractive or repulsive between defects of equal gauge charge. Among the novel features of this model are the following. After applying a field quench, a rich dynamical approach to equilibrium emerges, dominated by multi-scale energy barriers responsible for long-lived magnetization plateaux. These even allow for the metastability of a "fragmented" spin liquid, an elusive regime where partial order co-exists with a spin liquid. Perhaps most strikingly, the attraction produces clusters of defects whose stability is due to a combination of energetic barriers for their break-up and proximity of opposite charges along with an entropic barrier generated by the topological requirement of annihilating a defect only together with an oppositely charged counterpart. These clusters may take the form of a "jellyfish" spin texture, comprising an arrangement of same-sign gauge-charges, centered on a hexagonal ring with branches of arbitrary length. The ring carries a clockwise or counterclockwise circular flow of magnetisation. This emergent toroidal degrees of freedom provides a possibility for time reversal symmetry breaking with possible relevance to the spontaneous Hall effect observed in Pr2Ir2O7.

The mathematics of gauge theories lies behind many of the most profound advances in physics in the last 200 years, from Maxwell's theory of electromagnetism to Einstein's theory of general relativity. More recently it has become clear that gauge theories also emerge in condensed matter, a prime example being the spin ice materials which host an emergent electromagnetic gauge field. In spin ice, the underlying gauge structure is revealed by the presence of pinch-point singularities in neutron-scattering measurements. Here we report the discovery of a spin liquid where the low-temperature physics is naturally described by the fluctuations of a tensor field with a continuous gauge freedom. This gauge structure underpins an unusual form of spin correlations, giving rise to pinch-line singularities--- line-like analogues of the pinch-points observed in spin ice. Remarkably, these features may already have been observed in the pyrochlore material Tb$_2$Ti$_2$O$_7$., Comment: 4 pages of main text, 3 figures

The kagome lattice sits at the crossroad of present research efforts in quantum spin liquids, chiral phases, emergent skyrmion excitations and anomalous Hall effects to name but a few. In light of this diversity, our goal in this paper is to build a unifying picture of the underlying magnetic degrees-of-freedom on kagome. Motivated by a growing mosaic of materials, we especially consider a broad range of nearest-neighbour interactions consisting of Dzyaloshinskii-Moriya as well as anisotropic ferro$-$ and antiferromagnetic coupling. We present a three-fold mapping on the kagome lattice which transforms the celebrated Heisenberg antiferromagnet and XXZ model onto two lines of time-reversal invariant Hamiltonians. The mapping is exact for classical and quantum spins alike, i.e. it preserves the energy spectrum of the original Heisenberg and XXZ models. As a consequence, at the classical level, all phases have an extensive ground-state degeneracy. These ground states support a variety of phenomena such as ferromagnetically induced pinch points in the structure factor and the possibility for spontaneous scalar chirality. For quantum spin$-1/2$, the XXZ model has been recently shown to be a quantum spin liquid. Applying our three-fold mapping to the XXZ model gives rise to a connected network of quantum spin liquids, centered around a paragon of quantum disorder, namely the Ising antiferromagnet. We show that this quantum disorder spreads over an extended region of the phase diagram at linear order in spin wave theory, which overlaps with the parameter region of Herbertsmithite ZnCu$_3$(OH)$_6$Cl$_2$. We conclude this work by discussing the connection of our results to the chiral spin liquids found on kagome with further nearest-neighbour interactions, and to the recently synthesized ternary intermetallic materials., 8 pages, 4 figures

International audience; Much of the Ca2+ activity in astrocytes is spatially restricted to microdomains and occurs in fine processes that form a complex anatomical meshwork, the so-called spongiform domain. A growing body of literature indicates that those astrocytic Ca2+ signals can influence the activity of neuronal synapses and thus tune the flow of information through neuronal circuits. Because of technical difficulties in accessing the small spatial scale involved, the role of astrocyte morphology on Ca2+ microdomain activity remains poorly understood. Here, we use computational tools and idealized 3D geometries of fine processes based on recent super-resolution microscopy data to investigate the mechanistic link between astrocytic nanoscale morphology and local Ca2+ activity. Simulations demonstrate that the nano-morphology of astrocytic processes powerfully shapes the spatio-temporal properties of Ca2+ signals and promotes local Ca2+ activity. The model predicts that this effect is attenuated upon astrocytic swelling, hallmark of brain diseases, which we confirm experimentally in hypo-osmotic conditions. Upon repeated neurotransmitter release events, the model predicts that swelling hinders astrocytic signal propagation. Overall, this study highlights the influence of the complex morphology of astrocytes at the nanoscale and its remodeling in pathological conditions on neuron-astrocyte communication at so-called tripartite synapses, where astrocytic processes come into close contact with pre- and postsynaptic structures.

International audience; Cold Rydberg atoms are a promising platform for quantum technologies and combining them with optical waveguides has the potential to create robust quantum information devices. Here, we experimentally observe the excitation of cold rubidium atoms to a large range of Rydberg S and D states through interaction with the evanescent field of an optical nanofiber. We develop a theoretical model to account for experimental phenomena present such as the AC Stark shifts and the Casimir-Polder interaction. This work strengthens the knowledge of Rydberg atom interactions with optical nanofibers and is a critical step toward the implementation of all-fiber quantum networks and waveguide QED systems using highly excited atoms.

We combine two aspects of magnetic frustration, multiferroicity and emergent quasi-particles in spin liquids, by studying magneto-electric monopoles. Spin ice offers to couple these emergent topological defects to external fields, and to each other, in unusual ways, making possible to lift the degeneracy underpinning the spin liquid and to potentially stabilize novel forms of charge crystals, opening the path to a "magnetic crystallography". In developing the general phase diagram including nearest-neighbour coupling, Zeeman energy, electric and magnetic dipolar interactions, we uncover the emergence of a bi-layered crystal of singly-charged monopoles, whose stability, remarkably, is strengthened by an external [110] magnetic field. Our theory is able to account for the ordering process of Tb2Ti2O7 in large field for reasonably small electric energy scales., 10 pages, 10 figures

If spin liquids have been famously defined by what they are not, i.e. ordered, the past years have seen the frontier between order and spin liquid starting to fade, with a growing number of materials whose low-temperature physics cannot be explained without co-existence of (partial) magnetic order and spin fluctuations. Here we study an example of such co-existence in the presence of magnetic dipolar interactions, related to spin ice, where the order is long range and the fluctuations support a Coulomb gauge field. Topological defects are effectively coupled via energetic and entropic Coulomb interactions, the latter one being stronger than for the spin-ice ground state. Depending on whether these defects break the divergence-free condition of the Coulomb gauge field or the long-range order, they are respectively categorized as monopoles - as in spin ice - or monopole holes, in analogy with electron holes in semiconductors. The long-range order plays the role of a fully-occupied valence band, while the Coulomb spin liquid can be seen as an empty conducting band. These results are discussed in the context of other lattices and models which support a similar co-existence of Coulomb gauge field and long-range order. We conclude this work by explaining how dipolar interactions lift the spin liquid degeneracy at very low energy scale by maximizing the number of flippable plaquettes, in light of the equivalent quantum dimer model., Comment: invited paper for the special issue on "Quantum Spin Ice and Liquid in Geometrically Frustrated Magnets" edited by Y.-J. Kao, S. Onoda and S. Nakatsuji

If magnetic frustration is most commonly known for undermining long-range order, as famously illustrated by spin liquids, the ability of matter to develop new collective mechanisms in order to fight frustration is no less fascinating, providing an avenue for the exploration and discovery of unconventional properties of matter. Here we study an ideal minimal model of such mechanisms which, incidentally, pertains to the perplexing quantum spin ice candidate Yb2Ti2O7. Specifically, we explain how thermal and quantum fluctuations, optimized by order-by-disorder selection, conspire to expand the stability region of an accidentally degenerate continuous symmetry U(1) manifold against the classical splayed ferromagnetic ground state that is displayed by the sister compound Yb2Sn2O7. The resulting competition gives rise to multiple phase transitions, in striking similitude with recent experiments on Yb2Ti2O7 [Lhotel et al., Phys. Rev. B 89 224419 (2014)]. Considering the effective Hamiltonian determined for Yb2Ti2O7, we provide, by combining a gamut of numerical techniques, compelling evidence that such multiphase competition is the long-sought missing key to understanding the intrinsic properties of this material. As a corollary, our work offers a pertinent illustration of the influence of chemical pressure in rare-earth pyrochlores., Comment: 9 pages

Single-molecule localization microscopies have gained much attention for their efficient realization of a sub-diffraction-limit imaging with the resolution down to the 10-nm range. In contrast to conventional localization microscopes, which rely on particular fluorescent probes in specific conditions, metamaterial-assisted super-resolution microscopies can be implemented with any fluorescent dye under general conditions. Here, we present a systematic study of fluorescence engineering in metamaterial assisted localization microscopy by using cyclic group metasurfaces coated with a fluorescent film. Tailored variations are clearly demonstrated in both the photoluminescence intensity and the photobleaching lifetime of fluorophores based on the spatially varied Purcell effect near the metasurfaces. The enhanced emissions and blinking dynamics of the fluorophores on these metasurfaces lead to an increased signal-to-noise ratio, and therefore give rise to a super-resolution localization image with 0.9-nm localization accuracy. Our results are not only beneficial for super-resolution localization imaging but also push the control of light–matter interactions beyond the diffraction limit.

The mutualistic ectomycorrhizal (ECM) fungal genus Pisolithus comprises 19 species defined to date which colonize the roots of >50 hosts worldwide suggesting that substantial genomic and functional evolution occurred during speciation. To better understand this intra-genus variation, we undertook a comparative multi-omic study of nine Pisolithus species sampled from North America, South America, Asia, and Australasia. We found that there was a small core set of genes common to all species (13%), and that these genes were more likely to be significantly regulated during symbiosis with a host than accessory or species-specific genes. Thus, the genetic “toolbox” foundational to the symbiotic lifestyle in this genus is small. Transposable elements were located significantly closer to gene classes including effector-like small secreted proteins (SSPs). Poorly conserved SSPs were more likely to be induced by symbiosis, suggesting that they may be a class of protein that tune host specificity. The Pisolithus gene repertoire is characterized by divergent CAZyme profiles when compared with other fungi, both symbiotic and saprotrophic. This was driven by differences in enzymes associated with symbiotic sugar processing, although metabolomic analysis suggest that neither copy number nor expression of these genes is sufficient to predict sugar capture from a host plant or its metabolism in fungal hyphae. Our results demonstrate that intra-genus genomic and functional diversity within ECM fungi is greater than previously thought, underlining the importance of continued comparative studies within the fungal tree of life to refine our focus on pathways and evolutionary processes foundational to this symbiotic lifestyle.

International audience; Fish development and acclimation to environmental conditions are strongly mediated by the hormonal endocrine system. In environments contaminated by anthropogenic stressors, hormonal pathway alterations can be detrimental for growth, survival, fitness, and at a larger scale for population maintenance. In the context of increasingly contaminated marine environments worldwide, numerous laboratory studies have confirmed the effect of one or a combination of pollutants on fish hormonal systems. However, this has not been confirmed in situ. In this review, we explore the body of knowledge related to the influence of anthropogenic stressors disrupting fish endocrine systems, recent advances (focusing on thyroid hormones and stress hormones such as cortisol), and potential research perspectives. Through this review, we highlight how harbours can be used as "in situ laboratories" given the variety of anthropogenic stressors (such as plastic, chemical, sound, light pollution, and invasive species) that can be simultaneously investigated in harbours over long periods of time.

Recent years have shown an increasing number of studies dedicated to new light emitters for diverse applications such as optoelectronics, bio-imaging, and quantum technologies. In this context, graphene quantum dots (GQD) have important assets since bottom-up chemistry allows complete control of the structure, opening the way to wide customization of their electronic, optical, and spin properties [1-3]. The full benefit from these opportunities requires addressing GQD’s intrinsic photophysical properties.To do so, single molecule photoluminescence experiment is a powerfull tool [4]. Here, we highlight the influence of vibrations on GQDs’ optical properties, by comparing optical studies to extensive DFT/TDDFT calculations combined with molecular dynamics simulations. Specifically, we discussed their role in the transitions' oscillator strengths [5]. In order to get deeper in the photophysics of GQD, we investigate the spectroscopy of single GQDs at cryogenic temperatures. In particular, we show a narrowing of the emission lines at low temperature, that allows us to characterize and identify vibrational replicas that are characteristic to GQDs [6]. [1] M. G. Debije, J. Am. Chem. Soc. 2004, 126, 4641 [2] X. Yan, X. Cui, and L.-s. Li, J. Am. Chem. Soc. 2010 132, 5944 [3] A. Konishi et al, J. Am. Chem. Soc. 2010, 132, 11021 [4] S. Zhao et al, Nature Communications, 2018, 9, 3470 [5] T. Liu et al, under review [6] T. Liu et al, in preparation

Background Amphiprion ocellaris is one of the rare reef fish species that can be reared in aquaria. It is increasingly used as a model species for Eco‐Evo‐Devo. Therefore, it is important to have an embryonic development table based on high quality images that will allow for standardized sampling by the scientific community. Results Here we provide high‐resolution time‐lapse videos to accompany a detailed description of embryonic development in A ocellaris. We describe a series of developmental stages and we define six broad periods of embryogenesis: zygote, cleavage, blastula, gastrula, segmentation, and organogenesis that we further subdivide into 32 stages. These periods highlight the changing spectrum of major developmental processes that occur during embryonic development. Conclusions We provide an easy system for the determination of embryonic stages, enabling the development of A ocellaris as a coral reef fish model species. This work will facilitate evolutionary development studies, in particular studies of the relationship between climate change and developmental trajectories in the context of coral reefs. Thanks to its lifestyle, complex behavior, and ecology, A ocellaris will undoubtedly become a very attractive model in a wide range of biological fields., Key Findings Six periods have been identified to describe the embryonic development of the false clown‐fish Amphiprion ocellaris.We provide a staging series organized similarly to other models allowing comparative stud‐ies of embryonic development.We provide high‐resolution time‐lapse videos to accompany a detailed description of embry‐onic development in Amphiprion ocellaris.These data provide a general framework that can be used as a tool to standardize studies and experimental procedures throughout false clownfish development.

In this review article, we present the major insights from and challenges faced in the acquisition, analysis and modeling of astrocyte calcium activity, aiming at bridging the gap between those fields to crack the complex astrocyte “Calcium Code”. We then propose strategies to reinforce interdisciplinary collaborative projects to unravel astrocyte function in health and disease.

Environmental variation within a species’ range can create contrasting selective pressures, leading to divergent selection and novel adaptations. The conservation value of populations inhabiting environmentally marginal areas remains in debate and is closely related to the adaptive potential in changing environments. Strong selection caused by stressful conditions may generate novel adaptations, conferring these populations distinct evolutionary potential and high conservation value under climate change. On the other hand, environmentally marginal populations may be genetically depauperate, with little potential for new adaptations to emerge. Here, we explored the use of ecological niche models (ENMs) linked with common garden experiments to predict and test for genetically determined phenotypic differentiation related to contrasting environmental conditions. To do so, we built an ENM for the alpine plant Silene ciliata in central Spain and conducted common garden experiments, assessing flowering phenology changes and differences in leaf cell resistance to extreme temperatures. The suitability patterns and response curves of the ENM led to the predictions that: (1) the environmentally marginal populations experiencing less snowpack and higher minimum temperatures would have delayed flowering to avoid risks of late-spring frosts and (2) those with higher minimum temperatures and greater potential evapotranspiration would show enhanced cell resistance to high temperatures to deal with physiological stress related to desiccation and heat. The common garden experiments revealed the expected genetically based phenotypic differentiation in flowering phenology. In contrast, they did not show the expected differentiation for cell resistance, but these latter experiments had high variance and hence lower statistical power. The results highlight ENMs as useful tools to identify contrasting putative selective pressures across species ranges. Linking ENMs with common garden experiments provides a theoretically justified and practical way to study adaptive processes, including insights regarding the conservation value of populations inhabiting environmentally marginal areas under ongoing climate change., This work was funded by the projects AdAptA (CGL2012-33528) and EVA (CGL2016-77377-R) of the Spanish Ministry of Science and Innovation. JML was supported by a predoctoral fellowship (BES-2013-064951) and by a short research stay fellowship at the City College of New York (EEBB-I-16-11347) from the Spanish Ministry of Science and Innovation. JML was also supported by the REMEDINAL TE-CM project postdoctoral fellowship (S2018/EMT-4338). CLR was supported by a Juan de la Cierva post-doctoral fellowship (MINECO: FJCI-2015-24712). JMK received support from the City College of New York, the Graduate Center of the City University of New York, a Japan Society for the Promotion of Science Postdoctoral Fellowship for Foreign Researchers, and the Okinawa Institute of Science and Technology Graduate University. The Consejo Superior de Investigaciones Científicas covered open access charges of the publication.

Combining strong light absorption and outstanding electrical conductivity, hybrid nanographene–graphene (NG–Gr) van der Waals heterostructures (vdWHs) represent an emerging material platform for versatile optoelectronic devices. Interfacial charge transfer (CT), a fundamental process whose full control remains limited, plays a paramount role in determining the final device performance. Here, we demonstrate that the interlayer vdW interactions can be engineered by tuning the sizes of bottom-up synthesized NGs to control the interfacial electronic coupling strength and, thus, the CT process in NG–Gr vdWHs. By increasing the dimensions of NGs from 42 to 96 sp2 carbon atoms in the polyaromatic core to enhance the interfacial coupling strength, we find that the CT efficiency and rate in NG–Gr vdWHs display a drastic increase of one order of magnitude, despite the fact that the interfacial energy driving the CT process is unfavorably reduced. Our results shed light on the CT mechanism and provide an effective knob to tune the electronic coupling at NG–Gr interfaces by controlling the size-dependent vdW interactions.

International audience; Photosynthesis in cyanobacteria, green algae, and basal land plants is protected against excess reducing pressure on the photosynthetic chain by flavodiiron proteins (FLV) that dissipate photosynthetic electrons by reducing O$_2$. In these organisms, the genes encoding FLV are always conserved in the form of a pair of two-type isozymes (FLVA and FLVB) that are believed to function in O$_2$ photo-reduction as a heterodimer. While coral symbionts (dinoflagellates of the family Symbiodiniaceae) are the only algae to harbor FLV in photosynthetic red plastid lineage, only one gene is found in transcriptomes and its role and activity remain unknown. Here, we characterized the FLV genes in Symbiodiniaceae and found that its coding region is composed of tandemly repeated FLV sequences. By measuring the O$_2$-dependent electron flow and P700 oxidation, we suggest that this atypical FLV is active in vivo. Based on the amino-acid sequence alignment and the phylogenetic analysis, we conclude that in coral symbionts, the gene pair for FLVA and FLVB have been fused to construct one coding region for a hybrid enzyme, which presumably occurred when or after both genes were inherited from basal green algae to the dinoflagellate. Immunodetection suggested the FLV polypeptide to be cleaved by a post-translational mechanism, adding it to the rare cases of polycistronic genes in eukaryotes. Our results demonstrate that FLV are active in coral symbionts with genomic arrangement that is unique to these species. The implication of these unique features on their symbiotic living environment is discussed.

We consider two rubidium atoms, prepared in the same S or P Rydberg states near an optical nanofibre. We determine the van der Waals interaction between them and identify novel features, including the reshaping of the interaction anisotropy and the formation of an interaction potential well near the nanofibre for P states. We attribute these phenomena to the breaking of the rotation symmetry around the interatomic axis due to the presence of the fibre. Our work constitutes an important step in the assessment of Rydberg atom-nanofibre quantum interfaces and devices., Comment: 28 pages, 18 figures

The European flat oyster (Ostrea edulis L.) is a native bivalve of the European coasts. Harvest of this species has declined during the last decades because of the appearance of two parasites that have led to the collapse of the stocks and the loss of the natural oyster beds. O. edulis has been the subject of numerous studies in population genetics and on the detection of the parasites Bonamia ostreae and Marteilia refringens. These studies investigated immune responses to these parasites at the molecular and cellular levels. Several genetic improvement programs have been initiated especially for parasite resistance. Within the framework of a European project (PERLE 2) that aims to produce genetic lines of O. edulis with hardiness traits (growth, survival, resistance) for the purpose of repopulating natural oyster beds in Brittany and reviving the culture of this species in the foreshore, obtaining a reference genome becomes essential as done recently in many bivalve species of aquaculture interest. Here, we present a chromosome-level genome assembly and annotation for the European flat oyster, generated by combining PacBio, Illumina, 10X linked, and Hi-C sequencing. The finished assembly is 887.2 Mb with a scaffold-N50 of 97.1 Mb scaffolded on the expected 10 pseudochromosomes. Annotation of the genome revealed the presence of 35,962 protein-coding genes. We analyzed in detail the transposable element (TE) diversity in the flat oyster genome, highlighted some specificities in tRNA and miRNA composition, and provided the first insight into the molecular response of O. edulis to M. refringens. This genome provides a reference for genomic studies on O. edulis to better understand its basic physiology and as a useful resource for genetic breeding in support of aquaculture and natural reef restoration.

International audience; The precise bottom-up synthesis of graphene nanoribbons (GNRs) with controlled width and edge structures may compensate for graphene's limitations, such as the absence of an electronic bandgap. At the same time, GNRs maintain graphene's unique lattice structure in one dimension and provide more open-edge structures compared to graphene, thus allowing faster ion diffusion, which makes GNRs highly promising for energy storage systems. However, the current solution-synthesized GNRs suffer from severe aggregation due to the strong π–π interactions, which limits their potential applications. Thus, it is indispensable to develop a facile and scalable approach to exfoliate the GNRs from the postsynthetic aggregates, yielding individual nanoribbons. Here, a high-shear-mixing approach is demonstrated to untie the GNR bundles into practically individual GNRs, by introducing suitable molecular interactions. The micro-supercapacitor (MSC) electrode based on solution-processed GNR film exhibits an excellent volumetric capacitance of 355 F cm−3 and a high power density of 550 W cm−3, reaching the state-of-the-art performance of graphene and related carbon materials, and thus demonstrating the great potential of GNRs as electrode materials for future energy storage.

Made available in DSpace on 2022-05-01T11:07:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-01-01 These recommendations are specifically for polymers and polymer systems showing a significant response to an electromagnetic field or one of its components (electric field or magnetic field), i.e., for electromagnetic-field-responsive polymer materials. The structures, processes, phenomena and quantities relating to this interdisciplinary field of materials science and technology are herein defined. Definitions are unambiguously explained and harmonized for wide acceptance by the chemistry, physics, polymer and materials science communities. A survey of typical electromagnetic-field-responsive polymers is included. Department of Physical and Macromolecular Chemistry Faculty of Sciences Charles University, Albertov 2030 DF-FC UNESP - Universidade Estadual Paulista, Av. Eng. Luiz Edmundo Carrijo Coube 14-01 Institut des Science Analytiques et Physico-Chimie Pour l'Environnement et les Materiaux CNRS Univ Pau and Pays Adour University of Kent Pi-Conjugated Polymer Unit Okinawa Institute of Science and Technology, Onna-son Organisation Moléculaire Evolution et Matériaux Fluores UMR CNRS 5073 Laboratoire de Chimie Macromoléculaire Université Montpellier II Science et Techniques du Languedoc, Place Eugène Bataillon, Cedex 5 Department of Materials Centre of Plastic Electronics (CPE) Imperial College, Exhibition Road Department of Chemistry University of North Carolina at Charlotte DF-FC UNESP - Universidade Estadual Paulista, Av. Eng. Luiz Edmundo Carrijo Coube 14-01

Live (Rose Bengal stained) shelf foraminiferal faunas have been studied at seven stations located along a shore-open ocean transect between 39 and 69-m depth in the West-Gironde Mud Patch (WGMP) (Bay of Biscay, NE Atlantic) to understand how complex environmental conditions (e.g., organic matter, oxygenation, sedimentary facies) control their ecological patterns (i.e., diversity, faunal composition, standing stock, and microhabitats). To do so, the WGMP was sampled in August 2017, at the end of the succession of phytoplankton blooms occurring in spring and summer. This morpho-sedimentary unit is bathed by well-oxygenated bottom waters and characterized by clay-silt facies containing variably degraded phytodetritus and traces of terrestrial organic matter. Oxygen penetration depth within the sediment is less than 7 ± 3 mm, indicating efficient organic matter in-sediment mineralization by aerobic respiration. Foraminiferal richness (S) presents relatively moderate values ranging between 15 and 35 taxa. According to Shannon Index H’, foraminiferal diversity tends to increase with water depth. Accordingly, the relative contribution of Eggerelloides scaber, the dominant foraminiferal species at all stations, decreases with increased depth and decreased proximity to the coast. The shallowest station (Station 1, 39 m), closest to the shore, is characterised by E. scaber, Quinqueloculina laevigata and Ammonia beccarii, species typical of inner-shelf environments constrained by high-energy hydrodynamics and river discharge. Surficial sediments at Station 1 constitute of winnowed sands depleted in organic carbon. Towards the centre of the WGMP, where clay-silt facies contain variably degraded marine phytodetritus and terrestrial organic compounds, foraminiferal faunas are characterized by Bulimina aculeata, Ammonia falsobeccarrii, Nouria polymorphinoides and Nonionoides turgidus. Yet E. scaber remains the most dominant taxon. Deeper stations (>55 m depth) located at the distal part of the mud patch are dominated by B. aculeata, A. falsobeccarrii, N. polymorphinoides and E. scaber. Accompanying these taxa are Bulimina marginata, Rectuvigerina phlegeri, Nonion faba and Paracassidulina neocarinata, which are typical of mid- and outer-shelf ecosystems enriched in sedimentary organic matter.

Background Nuclear receptors are transcription factors of central importance in human biology and associated diseases. Much of the knowledge related to their major functions, such as ligand and DNA binding or dimerization, derives from functional studies undertaken in classical model animals. It has become evident, however, that a deeper understanding of these molecular functions requires uncovering how these characteristics originated and diversified during evolution, by looking at more species. In particular, the comprehension of how dimerization evolved from ancestral homodimers to a more sophisticated state of heterodimers has been missing, due to a too narrow phylogenetic sampling. Here, we experimentally and phylogenetically define the evolutionary trajectory of nuclear receptor dimerization by analyzing a novel NR7 subgroup, present in various metazoan groups, including cnidarians, annelids, mollusks, sea urchins, and amphioxus, but lost in vertebrates, arthropods, and nematodes. Results We focused on NR7 of the cephalochordate amphioxus B. lanceolatum. We present a complementary set of functional, structural, and evolutionary analyses that establish that NR7 lies at a pivotal point in the evolutionary trajectory from homodimerizing to heterodimerizing nuclear receptors. The crystal structure of the NR7 ligand-binding domain suggests that the isolated domain is not capable of dimerizing with the ubiquitous dimerization partner RXR. In contrast, the full-length NR7 dimerizes with RXR in a DNA-dependent manner and acts as a constitutively active receptor. The phylogenetic and sequence analyses position NR7 at a pivotal point, just between the basal class I nuclear receptors that form monomers or homodimers on DNA and the derived class II nuclear receptors that exhibit the classical DNA-independent RXR heterodimers. Conclusions Our data suggest that NR7 represents the “missing link” in the transition between class I and class II nuclear receptors and that the DNA independency of heterodimer formation is a feature that was acquired during evolution. Our studies define a novel paradigm of nuclear receptor dimerization that evolved from DNA-dependent to DNA-independent requirements. This new concept emphasizes the importance of DNA in the dimerization of nuclear receptors, such as the glucocorticoid receptor and other members of this pharmacologically important oxosteroid receptor subfamily. Our studies further underline the importance of studying emerging model organisms for supporting cutting-edge research.

Direct numerical simulations are carried out to study the effect of finite Weissenberg number up to $Wi=16$ on laminar and turbulent channel flows of an elastoviscoplastic (EVP) fluid, at a fixed bulk Reynolds number of $2800$ . The incompressible flow equations are coupled with the evolution equation for the EVP stress tensor by a modified Saramito model that extends both the Bingham viscoplastic and the finite extensible nonlinear elastic-Peterlin (FENE-P) viscoelastic models. In turbulent flow, we find that drag decreases with both the Bingham and Weissenberg numbers, until the flow laminarises at high enough elastic and yield stresses. Hence, a higher drag reduction is achieved than in the viscoelastic flow at the same Weissenberg number. The drag reduction persists at Bingham numbers up to 20, in contrast to viscoplastic flow, where the drag increases in the laminar regime compared with a Newtonian flow. Moreover, elasticity affects the laminarisation of an EVP flow in a non-monotonic fashion, delaying it at lower and promoting it at higher Weissenberg numbers. A hibernation phenomenon is observed in the EVP flow, leading to large changes in the unyielded regions. Finally, plasticity is observed to affect both low- and high-speed streaks equally, attenuating the turbulent dissipation and the fragmentation of turbulent structures.

International audience; Astrocytes are cells of the central nervous system that can regulate neuronal activity. Most astrocyte-neuron communication occurs at so-called tripartite synapses, where calcium signals are triggered in astrocytes by neuronal activity, resulting in the release of neuroactive molecules by the astrocyte. Most astrocytic Ca 2+ signals occur in very thin astrocytic branchlets, containing low copy number of molecules, so that reactions are highly stochastic. As those sub-cellular compartments cannot be resolved by diffraction-limited microscopy techniques, stochastic reaction-diffusion computational approaches can give crucial insights on astrocyte activity. Here, we use our stochastic voxel-based model of IP 3 R-mediated Ca 2+ signals to investigate the effect of the distance between the synapse and the closest astrocytic endoplasmic reticulum (ER) on neuronal activityinduced Ca 2+ signals. Simulations are performed in three dimensional meshes characterized by various ER-synapse distances. Our results suggest that Ca 2+ peak amplitude, duration and frequency decrease rapidly as ER-synapse distance increases. We propose that this effect mostly results from the increased cytosolic volume of branchlets that are characterized by larger ER-synapse distances. In particular, varying ER-synapse distance with constant cytosolic volume does not affect local Ca 2+ activity. This study illustrates the insights that can be provided by three-dimensional stochastic reaction-diffusion simulations on the biophysical constraints that shape the spatio-temporal characteristics of astrocyte activity at the nanoscale.

International audience; Foraminifera are unicellular eukaryotes that are an integral part of benthic fauna in many marine ecosystems, including the deep sea, with direct impacts on benthic biogeochemical cycles. In these systems, different foraminiferal species are known to have a distinct vertical distribution, i.e., microhabitat preference, which is tightly linked to the physico-chemical zonation of the sediment. Hence, foraminifera are well-adapted to thrive in various conditions, even under anoxia. However, despite the ecological and biogeochemical significance of foraminifera, their ecology remains poorly understood. This is especially true in terms of the composition and diversity of their microbiome, although foraminifera are known to harbor diverse endobionts, which may have a significant meaning to each species’ survival strategy. In this study, we used 16S rRNA gene metabarcoding to investigate the microbiomes of five different deep-sea benthic foraminiferal species representing differing microhabitat preferences. The microbiomes of these species were compared intra- and inter-specifically, as well as with the surrounding sediment bacterial community. Our analysis indicated that each species was characterized with a distinct, statistically different microbiome that also differed from the surrounding sediment community in terms of diversity and dominant bacterial groups. We were also able to distinguish specific bacterial groups that seemed to be strongly associated with particular foraminiferal species, such as the family Marinilabiliaceae for Chilostomella ovoidea and the family Hyphomicrobiaceae for Bulimina subornata and Bulimina striata . The presence of bacterial groups that are tightly associated to a certain foraminiferal species implies that there may exist unique, potentially symbiotic relationships between foraminifera and bacteria that have been previously overlooked. Furthermore, the foraminifera contained chloroplast reads originating from different sources, likely reflecting trophic preferences and ecological characteristics of the different species. This study demonstrates the potential of 16S rRNA gene metabarcoding in resolving the microbiome composition and diversity of eukaryotic unicellular organisms, providing unique in situ insights into enigmatic deep-sea ecosystems.