Annick Louis, L’invention de Troie. Les vies rêvées de Heinrich Schliemann

Le mythe vivace qui entoure la personne d’Heinrich Schliemann (1822-1890) est celui d’un transfuge de classe, un self-made-man polyglotte du XIXe siècle devenu tardivement archéologue. La puissance narrative des autobiographies de Schliemann (publiées dans Ithaque, le Péloponnèse et Troie [1869] et dans Ilios, ville et pays des Troyens [1880]) a longtemps occulté les processus narratifs qui y prenaient place. Les biographes de Schliemann ont ainsi accordé une valeur de vérité à ses récits de ..

Rôle de Caveoline-1 dans la contrôle de la capacité de stockage lipidique adipocytaire

Caveolin-1 and cavins proteins form membrane caveolae, invaginations of the plasma membrane that are particularly abundant adipocytes and endothelial cells within adipose tissue. Caveolin-1 deficiency leads to lipoatrophy in transgenic mice models suggesting a critical role in the control of lipid storage. Studies on Cav-1 deficient mice model (Cav1 (-/-) mice) also revealed important defects in the cardiovascular function, that are rescued by specific reexpression of Cav1 in endothelium (Cav1 RC mice).To address the contribution of endothelial caveolin-1 expression to the lipoatrophic phenotype, we compared metabolic phenotypes observed in Cav1 deficient with those of Cav1 RC and control mice and found a persistent lipoatrophic phenotype in Cav1 (-/-) mice. Considering the key role of caveolin-1 in the control of adipose tissue lipid storage capacity, we chose an overexpression approach of caveolin-1 and cavins 3T3-L1 adipocytes to investigate the underlying molecular mechanisms. All three cell lines contained a higher number of caveolae whereas only caveolin-1 overexpression led to lipid droplet expansion both in vitro and in vivo, suggesting that caveolin-1 control on lipid storage occurs outside of caveolae. In agreement, larger lipid droplets were found in cells expressing a caveolin-1-perilipin-GFP fusion construct, in which exogenous caveolin-1 strictly localized onto lipid droplets. Together our data demonstrate a specific role of lipid droplet caveolin-1 pool, independent of caveolae to modulate lipid droplet expansibilityLes cavéolines et les protéines cavines forment le manteau d'invaginations membranaires appelées cavéoles. Dans le tissu adipeux (TA), ces structures sont très abondantes dans les adipocytes et les cellules endothéliales. Une perte d'expression de cavéoline-1 a pour conséquence une lipoatrophie sévère chez les souris invalidées pour ce gène (Cav1(-/-)), ce qui a conduit à suggérer un rôle important de Cav1 pour le contrôle de la capacité de stockage du TA. Par ailleurs, les souris Cav1(-/-) présentent des défauts vasculaires, phénotype totalement corrigé par une réexpression spécifique de Cav1 au niveau de l'endothélium (souris Cav1 RC). Afin de déterminer les rôles respectifs de la cavéoline-1 adipocytaire et endothéliale dans l'établissement de la lipoatrophie observée chez les souris Cav1(-/-), nous avons comparé les phénotypes adipeux de souris contrôles, Cav1(-/-) et Cav1 RC et établi ainsi le rôle majeur de la cavéoline-1 adipocytaire dans l'apparition de ce phénotype. Pour caractériser les mécanismes impliqués, nous avons surexprimé Cav1 et les cavines dans la lignée adipocytaire 3T3-L1. Nous montrons que ces surexpressions augmentent le nombre de cavéoles à la membrane plasmique des adipocytes. En revanche, seule la surexpression de Cav1 induit la croissance des gouttelettes lipidiques (GL), suggérant que cet effet de Cav1 s'exerce en dehors des cavéoles. En accord, la surexpression de Cav1 exclusivement à la surface des GLs augmente la taille de ces organites dans les adipocytes. Ces résultats démontrent un rôle spécifique de la cavéoline-1 à la surface de la GL, indépendant des cavéoles, dans le contrôle de la capacité de stockage lipidique adipocytair

Serge Maury, Une secte janséniste convulsionnaire sous la Révolution française. Les Fareinistes (1783-1805)

Près d’un siècle après les grandes querelles qui déchirent l’Église catholique autour de la question du jansénisme, un mouvement figuriste émerge dans le village de Fareins, à 40 kilomètres au nord de Lyon. Le mouvement s’exporte à Paris après la Révolution et prend la forme d’une secte de plus en plus organisée. L’importance accordé au contexte de développement de la secte, l’originalité de la méthode employée par Serge Maury et la discussion permanente de l’auteur avec les spécialistes du s..

Lamina-associated domains: peripheral matters and internal affairs

At the nuclear periphery, associations of chromatin with the nuclear lamina through lamina-associated domains (LADs) aid functional organization of the genome. We review the organization of LADs and provide evidence of LAD heterogeneity from cell ensemble and single-cell data. LADs are typically repressive environments in the genome; nonetheless, we discuss findings of lamin interactions with regulatory elements of active genes, and the role lamins may play in genome regulation. We address the relationship between LADs and other genome organizers, and the involvement of LADs in laminopathies. The current data lay the basis for future studies on the significance of lamin-chromatin interactions in health and disease

Laminopathy-causing lamin A mutations reconfigure lamina-associated domains and local spatial chromatin conformation

The nuclear lamina contributes to the regulation of gene expression and to chromatin organization. Mutations in A-type nuclear lamins cause laminopathies, some of which are associated with a loss of heterochromatin at the nuclear periphery. Until recently however, little if any information has been provided on where and how lamin A interacts with the genome and on how disease-causing lamin A mutations may rearrange genome conformation. Here, we review aspects of nuclear lamin association with the genome. We highlight recent evidence of reorganization of lamin A-chromatin interactions in cellular models of laminopathies, and implications on the 3-dimensional rearrangement of chromatin in these models, including patient cells. We discuss how a hot-spot lipodystrophic lamin A mutation alters chromatin conformation and epigenetic patterns at an anti-adipogenic locus, and conclude with remarks on links between lamin A, Polycomb and the pathophysiology of laminopathies. The recent findings presented here collectively argue towards a deregulation of large-scale and local spatial genome organization by a subset of lamin A mutations causing laminopathies

Lamin A, Chromatin and FPLD2: Not Just a Peripheral Ménage-à-Trois

At the nuclear periphery, the genome is anchored to A- and B-type nuclear lamins in the form of heterochromatic lamina-associated domains. A-type lamins also associate with chromatin in the nuclear interior, away from the peripheral nuclear lamina. This nucleoplasmic lamin A environment tends to be euchromatic, suggesting distinct roles of lamin A in the regulation of gene expression in peripheral and more central regions of the nucleus. The hot-spot lamin A R482W mutation causing familial partial lipodystrophy of Dunnigan-type (FPLD2), affects lamin A association with chromatin at the nuclear periphery and in the nuclear interior, and is associated with 3-dimensional (3D) rearrangements of chromatin. Here, we highlight features of nuclear lamin association with the genome at the nuclear periphery and in the nuclear interior. We address recent data showing a rewiring of such interactions in cells from FPLD2 patients, and in adipose progenitor and induced pluripotent stem cell models of FPLD2. We discuss associated epigenetic and genome conformation changes elicited by the lamin A R482W mutation at the gene level. The findings argue that the mutation adversely impacts both global and local genome architecture throughout the nucleus space. The results, together with emerging new computational modeling tools, mark the start of a new era in our understanding of the 3D genomics of laminopathies

Characterization of marine eukaryotic biofilms at offshore wind farm sites: assessment of DNA extraction methods and marker gene used for metabarcoding approaches

Among marine lifestyles, biofilms are considered as diversified communities embedded in complex exopolymers whose development depends on several factors, related to both environmental conditions and physical-chemical characteristics of substrates (Antunes et al. 2019, Bellou et al. 2012). For the maritime industry, bio-colonization and its impact on human activities were well-described (Schultz et al. 2011). However, this phenomenon represents a new challenge in Renewable Marine Energies (RME) due to their specificities (materials, structures, localization…). In particular, macro-organism assemblages appeared to include a wide variety of eukaryotic groups but the literature is sparse considering the sequencing of eukaryotic diversity in comparison to those of bacterial communities (Briand et al. 2018, Dang and Lovell 2000, Salta et al. 2013). As a matter of fact, the very small size of some of the eukaryotes and/or their insufficient morphological discernible features appear to considerably limit their detection and identification, leading to underestimate their diversity (Carugati et al. 2015). When talking about molecular approaches, analysis of eukaryotes also represents a challenge because such organisms possess resilient cellular structures which can give poor DNA extraction yield (Hermans et al., 2018Hermans et al. 2018). In addition, SSU rRNA in eukaryotes fails to be as universal as for prokaryotes (Bik et al. 2012, Medinger et al. 2010). However, the use of marker genes from environmental DNA, when focused on the targeted eukaryotic community, remains critical to decoding the complexity of marine biofilms diversity.In this study, four extraction methods, including a preliminary mechanic cell lysis, both soil and biofilm kits, and global approaches, have been compared. We also examined the coverage and the identification capability of several primers to characterize eukaryotic communities colonizing three plastic surface types (polyvinyl chloride, HD polyethylene, and polyamide) which have been immersed in several locations along the French Mediterranean and Atlantic coasts. Sequence quality and number remain the same whatever the extraction method. However, the richness and community structure were clearly affected regardless of the sample type (Figure 1). Finally, two kits (PowerMaxSoil, and PowerBiofilm kits) evaluated in this study were considered as the most powerful overall.Secondly, we amplified and sequenced short fragments of two genes: one region of the mitochondrial Cytochrome Oxidase subunit I (COI) and five variable regions of the 18S small subunit ribosomal DNA (rDNA) gene (V1V2, V4TAR, V4UNI, V7, and V9). The Chao1 index was considerably lower for the CO1 gene compared to those of the 18S rDNA regions. The V4TAR and V7 regions showed a significant highest richness, followed closely by the V1V2 and V9 regions. The 18S rDNA gene sequences were dominated by microeukaryotes whereas the COI sequences were dominated by macro-organisms. Each of the 18rDNA primer pairs also exhibited dissimilar community structures although the dominant taxa seemed to be common.To conclude, our results provided a global assessment of tools dedicated to the description of the diversity of marine eukaryotes biofilms from three surfaces used in the design of RME. Among the four extraction methods described here, PowerMaxSoil and PowerBiofilm kits allowed recovering the highest diversity. COI and 18S rDNA gene sequencing covered different groups including at high taxonomic levels. Despite limitations, metabarcoding will help in the characterization of marine biofilms diversity on RME. Especially, it may be relevant to use primers targeting these two genes to better cover the eukaryotic diversity

A survey of denitrifying communities in a wetland

1 p.A hydrological and geochemical survey of a wetland (Normandy, France) highlighted the presence of a major spatiotemporal variability of sulphates and nitrates concentrations related to a distinct hydrologic regime represented by the stream proximity. An experimental approach was carried out to determine the factors influencing the dynamic of nitrate and sulphate concentrations observed in field; and the denitrifiers' community structuration related to different environmental stresses. We investigated the effects of stream proximity and associated nutrients fluxes, on microbial activity. Experiments were performed with peat sampled from different plots along a hydrologic flow gradient to characterize the biogeochemical processes and estimate the potential reactivity. We used bioreactors containing the peat-soils and a synthetic solution (similar to the field stream composition) to understand biogeochemical fluxes related to different nitrate availability and redox conditions. The evolution of nitrates and sulphates concentrations was analysed over time. The results demonstrated a spatial variability of the potential reactivity and a biological activity reacting unevenly to experimental conditions. We highlighted the control of the temporal evolution of nitrate and sulphate concentration by redox conditions and nitrate availability (nitrates, P<0.001; sulphates, P<0.001) and by distinct hydrologic regime (nitrates, P <0,001; sulphates, P<0,001). We established the reduction of nitrate is a heterotrophic denitrification and the sulphate production is related to bio-geochemical processes. The fate of microbial activity seems to be regulated by hydrogeological fluxes especially at the stream-soil, soil-water interface. Spatial and temporal dynamic of denitrifying community composition is currently investigated by a narG gene analysis and t-RFLP

Eukaryotic diversity of marine biofouling from coastal to offshore areas

International audienceMarine biofouling communities, including biofilms, are composed of many eukaryotes with high taxonomic and functional diversities. However, molecular characterization of eukaryotic diversity of marine biofouling has been barely developed due to the only recent interest in research areas such as marine renewable energies, antifouling technologies, or plastic pollution. The aim of this study was to compare the diversity and taxonomic composition of biofouling through different metabarcoding approaches used to detect the widest range of taxa from samples collected in several contrasted marine environments (French Atlantic and Mediterranean coasts). Thus, we assessed four DNA extraction methods and six primers pairs targeting the 18S rDNA gene (including the V1-V2, V4TAR, V4UNI, V7 and V9 regions) and the COI gene, the latter with two databases (BOLD and MIDORI). In addition the influence of primers selection was analyzed at three sites to compare geographic variations in eukaryotic diversity. Although none of the extraction methods greatly altered the community diversity or composition. we have observed that eukaryotic biofouling community diversity and structure varied depending on primers pairs, reference databases and sites. 18S rDNA regions allowed the detection of more taxa at the species level, including microeukaryotes, while the COI recovered more ASVs, but with a large proportion that remained taxonomically unassigned probably because BOLD and MIDORI specifically targeted metazoans. Interestingly, the spatial pattern obtained with both COI and 18S rDNA markers were similar showing that spatial selection occurred throughout a wide diversity of eukaryotic taxa. These results encouraged the use of these two complementary markers for future metabarcoding investigations but also highlighted the relevance of completing databases to enhance the identification of biofouling eukaryotes

Influence of hydrological fluxes on the structure of nitrate-reducing bacteria communities in a peatland

International audienceFactors influencing nitrate dynamics and nitrate-reducing bacteria in peat soil in the field, were investigated in laboratory experiments. A previous study had indicated that the on-site effects of redox conditions and nutrient fluxes on microbial activity were influenced by hydrological conditions. However, the laboratory experiments indicated that peat samples from sites under different hydrological regimes exhibited different microbial activities independently of oxygenation conditions. The effects of redox conditions and nutrient fluxes (i.e. influence of NO3 and O2 concentration) on the nitrate reducer community were therefore assessed. Microbial community structures in peat samples from sites under different hydrologic regimes were compared using Terminal-Restriction Fragment Length Polymorphism diversity signatures of the narG gene. This gene encodes the catalytic subunit of the nitrate reductase. Unexpectedly, the nitrate reducer communities were very similar at the beginning of the experiment whatever the peatland soil analysed. However, a strong structuration and divergence within the nitrate reducer communities, that was site-dependent, was evident after 76 h of incubation. These modifications within the microbial communities seemed to be due to differences in peat saturation at the sampling sites resulting from the different hydrological regimes. Of the forcing variables tested, oxygenation had a slight effect on the composition of the nitrate-reducers' community whereas nitrate addition had no effect. This study shows that a physical constraint such as hydrological regime might be considered important in microbial community composition