Mutations in the Polycomb Group Gene polyhomeotic Lead to Epithelial Instability in both the Ovary and Wing Imaginal Disc in Drosophila

Most human cancers originate from epithelial tissues and cell polarity and adhesion defects can lead to metastasis. The Polycomb-Group of chromatin factors were first characterized in Drosophila as repressors of homeotic genes during development, while studies in mammals indicate a conserved role in body plan organization, as well as an implication in other processes such as stem cell maintenance, cell proliferation, and tumorigenesis. We have analyzed the function of the Drosophila Polycomb-Group gene polyhomeotic in epithelial cells of two different organs, the ovary and the wing imaginal disc.Clonal analysis of loss and gain of function of polyhomeotic resulted in segregation between mutant and wild-type cells in both the follicular and wing imaginal disc epithelia, without excessive cell proliferation. Both basal and apical expulsion of mutant cells was observed, the former characterized by specific reorganization of cell adhesion and polarity proteins, the latter by complete cytoplasmic diffusion of these proteins. Among several candidate target genes tested, only the homeotic gene Abdominal-B was a target of PH in both ovarian and wing disc cells. Although overexpression of Abdominal-B was sufficient to cause cell segregation in the wing disc, epistatic analysis indicated that the presence of Abdominal-B is not necessary for expulsion of polyhomeotic mutant epithelial cells suggesting that additional polyhomeotic targets are implicated in this phenomenon.Our results indicate that polyhomeotic mutations have a direct effect on epithelial integrity that can be uncoupled from overproliferation. We show that cells in an epithelium expressing different levels of polyhomeotic sort out indicating differential adhesive properties between the cell populations. Interestingly, we found distinct modalities between apical and basal expulsion of ph mutant cells and further studies of this phenomenon should allow parallels to be made with the modified adhesive and polarity properties of different types of epithelial tumors

Imaging a pore network in a clay-rock at the sub-nanometer scale

International audienceMini-Symposium Description (2.22) Clayey rocks properties are the focus of an ever-increasing interest from the geoscience community. These fine-grained sedimentary rocks (mudstone, argillite, shalesetc.) are recognized as key-components for energy-related technologies, for which they could serve as isolation material (in radioactive waste disposal), caprocks (in CO 2 capture and storage systems), or as reservoir rocks for hydrocarbons (gas and oil shales) (Bourg, 2015; Tournassat et al., 2015b). For all of these applications, accurate predictions of mechanical, flow, and reactive properties at the field scale are necessary. However, macroscale properties of clayey rocks arise for a large part from the surface properties of their nano-sized clay minerals constituents and from the characteristics of associated microstructure and pore network. Pore networks in clayey rocks are highly heterogeneous with pore widths/diameters ranging in the categories of micropores ( 2 nm and 50 nm). The fact that the pore size distribution in clayey rocks encompasses all of these pore size categories evinces the multiplicity of coupled physical processes that must be taken into account to explain observations at the core and field scales. Even if, FIB-SEM has enabled to improve the nanoscale characterization up to 5 nm (Gaboreau et al.,2016) must of the smallest pores, ensuring the connectivity, are not probed at this scale. One of the biggest challenges in the present downscaling approaches is a lack of understanding of the pore structure down to the (sub)nanometer pore sizes, which can contain up to 30 % of the total porosity, and which is also hypothesized to ensure most of the connectivity between bigger pores (Ma et al., 2016). In this study, we imaged in three dimensions the structure of a clayey rock down to the sub-nanometer scale using electron tomography. Pore network connectivity was extracted at the nanometer scale, providing key information for the building of future pore scale models. References Bourg, I.C., 2015.Sealing shales versus brittle shales: A sharp threshold in the material properties and energy technology uses of fine-grained sedimentary rocks.Environmental Science &TechnologyLetters 2, 255–259. Gaboreau, S., Robinet, J.-C., Prêt, D., 2016. Optimization of pore network characterization of compacted clay materials by TEM and FIB/SEM imaging.Microporous and Mesoporous Materials 224, 116–128., Courtois, L., 2016. Novel 3D centimetre-to nano-scale quantification of an organic-rich mudstone: The Carboniferous Bowland Shale, Northern England. Marine and Petroleum Geology 72, 193–205

Effect of the local clay distribution on the effective electrical conductivity of clay rocks

International audienceThe local porosity theory proposed by Hilfer was revisited to develop a local clay theory (LCT) that establishes a quantitative relationship between the effective electrical conductivity and clay distribution in clay rocks. This theory is primarily based on a local simplicity assumption; under this assumption, the complexity of spatial clay distribution can be captured by two local functions, namely, the local clay distribution and the local percolation probability, which are calculated from a partitioning of a mineral map. The local clay distribution provides information about spatial clay fluctuations, and the local percolation probability describes the spatial fluctuations in the clay connectivity. This LCT was applied to (a) a mineral map made from a Callovo-Oxfordian mudstone sample and (b) (macroscopic) electrical conductivity measurements performed on the same sample. The direct and inverse modeling shows two results. First, the textural and classical model assuming that the electrical anisotropy of clay rock is mainly controlled by the anisotropy of the sole clay matrix provides inconsistent inverted values. Another textural effect, the anisotropy induced by elongated and oriented nonclayey grains, should be considered. Second, the effective conductivity values depend primarily on the choice of the inclusion-based models used in the LCT. The impact of local fluctuations of clay content and connectivity on the calculated effective conductivity is lower

Effect of the local clay distribution on the effective elastic properties of shales

International audienceThis paper revisits the ``Local Porosity Theory'' developed by Hilfer to propose a ``local clay theory'' (LCT) that establishes a quantitative relationship between the effective elastic properties and clay distribution of shales. This approach is primarily based on a ``local simplicity'' assumption; under this assumption, the complexity of spatial clay distribution can be captured by two local functions, namely, the local clay fraction distribution mu and the local percolation probability lambda which are calculated by partitioning a mineral map. The local clay fraction distribution provides information about spatial fluctuations of clay fraction and the local percolation probability describes the spatial fluctuations in the clay connectivity. This LCT was applied to a mineral map made from a Callovo-Oxfordian mudstone sample for which petrophysical data were available. This application demonstrated that the local functions mu and lambda can be reasonably approximated by a Gaussian and simple sigmoid function, respectively. LCT was also used in a sensitivity analysis to evaluate the impact of the spatial fluctuations of the clay phase and clay connectivity on the effective elastic properties of shales. This impact has been investigated by comparing the effective properties obtained from LCT with those provided by a percolating inclusion-based model (a non-clay spherical grain embedded in a transverse isotropic clay matrix with neither spatial clay fluctuations nor spatial fluctuations in the clay connectivity). This inclusion-based model was built from a differential effective medium scheme. The results of this sensitivity analysis indicated that spatial clay fluctuations have only, a slight impact on the calculated effective properties. However, when the spatial fluctuations of clay connectivity were considered, the quantitative deviations between the effective properties inferred from LCT and those from the percolating inclusion-based model were large exceeding 50% in some cases

Influence of the ionic strength and solid/solution ratio on Ca(II)-for-Na+ exchange on montmorillonite. Part 2: Understanding the effect of the m/V ratio. Implications for pore water composition and element transport in natural media

International audienceThe aim of the present paper is to clarify previous results [1] showing that selectivity coefficients determined for the exchange of Na+ for Ca2+ in montmorillonite were dependent on the solid/solution ratio. The organization of montmorillonite suspensions upon Na+/Ca(II) exchange was analyzed by combining optical microscopy, small-angle X-ray scattering and X-ray diffraction. All samples displayed flocculated characteristics, eliminating the possibility of contrasting accessibility of sorption sites with the solid/ solution ratio. Modeling of experimental X-ray diffraction patterns was used to quantify the relative proportions of interlayer Ca2+ and Na+ cations along the exchange isotherm. The results further confirmed the influence of the solid/solution ratio on the degree of interlayer Ca(II)-for-Na+ exchange, and specific selectivity coefficients for interlayer sites were determined. The effect of the solid/solution ratio was finally interpreted by the resulting local changes in the solution chemistry. We demonstrated that by accounting for the Donnan effect, the different data can be interpreted using a single selectivity coefficient. The obtained Kc constant was successfully applied to interpret existing hydrogeochemical data on a natural aquitard. This most likely represents a more constrained and valid approach for the modeling of reactive element transport in natural media than does the poorly defined Kd parameter

Splicing of the Alternative Exons of the Chicken, Rat, and Xenopus Beta-Tropomyosin Transcripts Requires Class-Specific Elements

The diversity of protein isoforms is often generated from single genes by alternative splicing of the primary transcript. Using transfection of beta tropomyosin minigene constructs into homologous and heterologous cell systems, we show that there are differences, among higher vertebrates, in the components of the splicing machinery which control the conserved regulated splicing pattern of two mutually exclusive exons (6A and 6B) present in this gene. These experiments demonstrate that genes which give rise to alternative transcripts may require an appropriate combination of splicing factors which are species-specific, or at least restricted to the same taxonomic subgroup (class). An important practical implication is that the splicing of these genes may be deregulated in heterologous systems in vitro and in vivo, i.e. in transgenic animals

Ion-exchange reactions on clay minerals coupled with advection/dispersion processes. Application to Na+/Ca2+ exchange on vermiculite: Reactive-transport modeling, batch and stirred flow-through reactor experiments

International audienceThe present study aims at testing the validity of using an Na+/Ca2+ ion-exchange model, derived from batch data to interpret experimental Ca2+-for-Na+ exchange breakthrough curves obtained on vermiculite (a common swelling clay mineral in surface environments). The ion-exchange model was constructed considering the multi-site nature of the vermiculite surface as well as the exchange of all aqueous species (Mg2+ derived from the dissolution of the solid and H+). The proposed ion-exchange model was then coupled with a transport model, and the predicted breakthrough curves were compared with the experimental ones obtained using a well stirred flow-through reactor. For a given solute residence time in the reactor (typically 50 min), our thermodynamic model based on instantaneous equilibrium was found to accurately reproduce several of the experimental breakthrough curves, depending on the Na+ and Ca2+ concentrations of the influents pumped through the reactor. However the model failed to reproduce experimental breakthrough curves obtained at high flow rates and low chemical gradient between the exchanger phase and the solution. An alternative model based on a hybrid equilibrium/kinetic approach was thus used and allowed predicting experimental data. Based on these results, we show that a simple parameter can be used to differentiate between thermodynamic and kinetic control of the exchange reaction with water flow. The results of this study are relevant for natural systems where two aquatic environments having contrasted chemistries interact. Indeed, the question regarding the attainment of a full equilibrium in such a system during the contact time of the aqueous phase with the particle/colloid remains most often open. In this context, we show that when a river (a flow of fresh water) encounters marine colloids, a systematic full equilibrium can be assumed (i.e., the absence of kinetic effects) when the residence time of the solute in 1 m3 of the system is ⩾6200 h

Upscaling the porosity of the Callovo-Oxfordian mudstone from the pore scale to the formation scale; insights from the 3H-PMMA autoradiography technique and SEM BSE imaging

International audienceThe Callovo-Oxfordian mudstone (Meuse/Haute-Marne, France) is currently considered as the host rock barrier for a deep geological repository. The intimate relationships between the porosity and mineralogy of this host rock were investigated at the small scale (mu m-mm) and large scale (m-hm). At the small scale, we have adapted the H-3-PMMA autoradiographic method to inap the porosity of the Callovo-Oxfordian mudstone. The H-3-PMMA autoradiographic method was improved in terms of its spatial resolution. H-3-PMMA porosity maps were then compared to-homologous mineral maps (clay minerals, carbonates and tectosilicates) built from scanning electron microscopy images (using back-scattered electron imaging). Based on an inversion procedure, the specific porosity of each mineral group was estimated from the mineral and porosity maps. We found that the spatial distribution of porosity at the small scale is mainly controlled by the spatial distribution of the clay matrix (the average porosity of the clay matrix is 40-45%), whereas quartz and carbonate mineral grains have low porosities (0-4%). At the geological formation scale, the porosity and mineralogy distributions were determined by logging tool techniques (nuclear magnetic resonance and spectral gamma-ray). The coupled evolution of clay content and porosity with depth was analyzed according to the porosity/mineralogy relationship defined at the small scale. Finally, we modeled the evolution of the porosity of the Callovo-Oxfordian mudstone with depth by considering the clay content and the effect of physical compaction during burial

Effects of mineral distribution at mesoscopic scale on solute diffusion in a clay-rich rock: Example of the Callovo-Oxfordian mudstone (Bure, France)

International audienceThe mesostructure (millimeter to micrometer scale) of clay-rich sedimentary rocks is generally characterized by a connected fine-grained clay matrix embedding coarser nonclay minerals. We use the Callovo-Oxfordian clay-rich rock formation (France) to illustrate how mesostructure influences solute transfer in clay-rich rocks at larger scales. Using micrometer resolution imaging techniques (SEM and micro-CT) major mineral phases (clay matrix, carbonates, tectosilicates, and heavy minerals) were mapped both in two dimensional (2-D) and three dimensional (3-D) at the mesoscale. Orientation and elongation distributions of carbonate and tectosilicate grains measured on mineral maps reveal an anisotropic mesostructure relative to the bedding plane, in agreement with the geological history of the sedimentary rock. Diffusion simulations were performed based on the 3-D mineral maps using a random walk method thus allowing direct computation of mesoscopic scale-related diffusion anisotropy and tortuosity. Considering an isotropic clay matrix, simulated diffusion anisotropy (1.11-1.26) was found lower than the one experimentally measured on macroscopic samples (1.5 to 2), due to the anisotropy feature of pores within the clay matrix. The effects of the mineral content variations on diffusion properties were then investigated by numerical modifications of a mineral map combined with diffusion simulations. Evolution of the tortuosity and diffusion anisotropy with the clay matrix content were successfully interpreted by the Koponen percolation/diffusion model, whereas the Archie approach fails to reproduce diffusion properties at low clay contents. A comparison of fitting parameters with those obtained experimentally indicates that diffusion coefficient variations observed at a large scale could be mainly controlled by the mesostructure