Marc Delluc (1957-2017)

Marc Delluc nous a quittés le 3 décembre 2017, foudroyé par une crise cardiaque. Membre de la Compagnie des Beunes, du Spéléo Club des Eyzies et du Spéléo Club de Périgueux, aucune cavité de la région n’avait plus de secret pour lui. La vie de Marc Delluc c’était les grottes. Certes, ceux qui l’ont connu savent ce que sa famille et ses amis représentaient pour cet homme rare, serviable, discret et d’une totale modestie. Mais sa passion, c’était le monde souterrain, la recherche et la découv..

Strigolactones Stimulate Arbuscular Mycorrhizal Fungi by Activating Mitochondria

The association of arbuscular mycorrhizal (AM) fungi with plant roots is the oldest and ecologically most important symbiotic relationship between higher plants and microorganisms, yet the mechanism by which these fungi detect the presence of a plant host is poorly understood. Previous studies have shown that roots secrete a branching factor (BF) that strongly stimulates branching of hyphae during germination of the spores of AM fungi. In the BF of Lotus, a strigolactone was found to be the active molecule. Strigolactones are known as germination stimulants of the parasitic plants Striga and Orobanche. In this paper, we show that the BF of a monocotyledonous plant, Sorghum, also contains a strigolactone. Strigolactones strongly and rapidly stimulated cell proliferation of the AM fungus Gigaspora rosea at concentrations as low as 10 (−13) M. This effect was not found with other sesquiterperne lactones known as germination stimulants of parasitic weeds. Within 1 h of treatment, the density of mitochondria in the fungal cells increased, and their shape and movement changed dramatically. Strigolactones stimulated spore germination of two other phylogenetically distant AM fungi, Glomus intraradices and Gl. claroideum. This was also associated with a rapid increase of mitochondrial density and respiration as shown with Gl. intraradices. We conclude that strigolactones are important rhizospheric plant signals involved in stimulating both the pre-symbiotic growth of AM fungi and the germination of parasitic plants

Mass spectrometry studies of metabolic systems: using the Pascal’s triangle to probe the isotopologue space.

International audienceMass spectrometry (MS) is increasingly used for isotopic studies of metabolism with a broad range of applications going from system biology to biotechnology. The analytical information is derived from the exploitation of the isotopic cluster, from which the contribution of each isotopologue (i.e. molecular entities differing only in the number of isotopic substitutions) of metabolites can be quantified. The correctness of biological interpretations depends on the quality of the isotopic measurements (isotopologue distributions). Despite an increasing number of stable isotope labeling studies, there has been so far very limited investigations of the accuracy and precision of the measurement of isotopologue distributions by MS. The main reason is the lack of relevant standards to evaluate the MS equipments and the entire experimental workflow. Here, we present a strategy to probe the accuracy and the precision of 13C-isotopologue measurements by MS, which is based upon the production of a biological sample containing a mixture of metabolites with controlled and predictable proportions of the isotopic species. This can be achieved by feeding a micro-organism with a mixture of labelled substrate in which 13C atoms are statistically distributed. As proof of concept, two model microorganisms, the eukaryotic cell Pichia augusta and the prokaryotic cell Escherichia coli, have been cultivated respectively on methanol or acetate as sole carbon source and at appropriate proportions of all existing isotopic species. These proportions have been chosen to produce metabolites in which the isotopologue distribution should remarkably give the binomial coefficients of the Pascal’s triangle. After preparation of the cellular extracts using state-of-art procedures, the entire isotopologue distributions of intracellular metabolites with carbon skeletons ranging from 3 to 10 carbon elements were quantified by LC-MS/MS and compared to predicted values. For both P. augusta or E. coli metabolites, the experimental MIDs were in close agreement with predictions, i.e. within 0.7% accuracy and of ±1% precision. This strategy can be used for i) evaluating instruments, ii) determining the occurrence of isotopic effects, iii) evaluating the quality of isotopic data for metabolic flux analysis

Detection of undercover karst features by geophysics (ERT) Lascaux cave hill

The study of karst features under a detrital cover is difficult to obtain using punctual traditional tools. This paper presents a 3D geostatistical modeling of ERT (Electrical Resistivity Tomography) data to describe undercover karst features. A case study was carried out on the karstic site of the prehistoric decorated Lascaux cave (France). Geophysical measurements were used to define the limit between outcropping Coniacian or Santonian limestones (southwest) and clayey sands (northeast), with a main orientation of N140°. A geometrical description of the scarp was also constructed; pinnacles and notches were found under the clayey sand detrital formation. By combining 3D ERT with geomorphological and geological observations, the geometry of the stratigraphic limit between the Coniacian and Santonian limestone could be determined. This stratigraphic limit separates two domains, one is a potential aquifer, and acts as a feeder for the intermittent spring at the cave entrance, while the other is less permeable, resulting in a permeability contrast with the later rock type. All these observations help define the geological cave environment and ensure better protection for the paintings

Combining Metabolomics and Gene Expression Analysis Reveals that Propionyl- and Butyryl-Carnitines Are Involved in Late Stages of Arbuscular Mycorrhizal Symbiosis

International audienceThe arbuscular mycorrhizal (AM) symbiosis is a widespread mutualistic association between soil fungi (Glomeromycota) and the roots of most plant species. AM fungi are obligate biotrophs whose development is partially under the control of their plant host. We explored the possibility to combine metabolomic and transcriptomic approaches to find putative mycorrhiza-associated metabolites regulating AM fungal development. Methanol extracts of Medicago truncatula roots colonized or not with the AM fungus Rhizophagus irregularis were analyzed and compared by ultra-high-performance liquid chromatography (UHPLC), high-resolution mass spectrometry (Q-TOF), and multivariate statistical discrimination. We detected 71 mycorrhiza-associated analytes exclusively present or at least 10-fold more abundant in mycorrhizal roots. To identify among these analytes those that could regulate AM fungal development, we fractionated by preparative and semi-preparative HPLC the mycorrhizal and non-mycorrhizal root extracts and established how the 71 analytes were distributed among the fractions. Then we tested the activity of the fractions on germinating spores of R. irregularis by quantifying the expression of 96 genes known for their diverse in planta expression patterns. These investigations reveal that propionyl- and butyryl-carnitines accumulated in mycorrhizal roots. The results suggest that these two molecules regulate fungal gene expression in planta and represent interesting candidates for further biological characterization

Climate of a cave laboratory representative for rock art caves in the Vézère area (south-west France)

Leye Cave (Dordogne, France) is a laboratory cave in the Vézère area, a region that contains some of the most famous rock art caves in the world such as Lascaux, Font-de-Gaume and Combarelles, and is listed as Human World Heritage by UNESCO. Leye Cave was selected because it is representative of painted caves, with respect to parameters such as its geological stage, the presence of water and carbon dioxide, the geological state of its walls, and the size of the cave. These wall states are studied to better understand the conditions of conservation of rock art caves without damaging them. The choice of an equivalent medium, i.e., a non-painted cave, was made to be able to conduct experiments or take measurements that would not have been possible in a rock art cave. The climatic conditions (temperature, hygrometry, etc.) monitored since 2011 are central to our understanding of the genesis and evolution of wall states. Leye Cave is sub-horizontal then descendant, forming a cold air trap. The phenomenon of condensation is thought to be important in the genesis of these wall states. Our article presents a model which describes the competition that exists between the conduction of the rock heating the air and the convection cooling the rock, in the area named the “Throne Chamber”, located in the deepest parts of the cave

Approche taphonomique des loci à restes humains de la grotte de Cussac

International audienc

The metabolic signaling of the nucleoredoxin-like 2 gene supports brain function

International audienceThe nucleoredoxin gene NXNL2 encodes for two products through alternative splicing, rod-derived cone viability factor-2 (RdCVF2) that mediates neuronal survival and the thioredoxin-related protein (RdCVF2L), an enzyme that regulates the phosphorylation of TAU. To investigate the link between NXNL2 and tauopathies, we studied the Nxnl2 knockout mouse (Nxnl2−/−). We established the expression pattern of the Nxnl2 gene in the brain using a Nxnl2 reporter mouse line, and characterized the behavior of the Nxnl2−/− mouse at 2 months of age. Additionally, long term potentiation and metabolomic from hippocampal specimens were collected at 2 months of age. We studied TAU oligomerization, phosphorylation and aggregation in Nxnl2−/− brain at 18 months of age. Finally, newborn Nxnl2−/− mice were treated with adeno-associated viral vectors encoding for RdCVF2, RdCVF2L or both and measured the effect of this therapy on long-term potential, glucose metabolism and late-onset tauopathy. Nxnl2−/− mice at 2 months of age showed severe behavioral deficiency in fear, pain sensitivity, coordination, learning and memory. The Nxnl2−/− also showed deficits in long-term potentiation, demonstrating that the Nxnl2 gene is involved in regulating brain functions. Dual delivery of RdCVF2 and RdCVF2L in newborn Nxnl2−/− mice fully correct long-term potentiation through their synergistic action. The expression pattern of the Nxnl2 gene in the brain shows a predominant expression in circumventricular organs, such as the area postrema. Glucose metabolism of the hippocampus of Nxnl2−/− mice at 2 months of age was reduced, and was not corrected by gene therapy. At 18-month-old Nxnl2−/− mice showed brain stigmas of tauopathy, such as oligomerization, phosphorylation and aggregation of TAU. This late-onset tauopathy can be prevented, albeit with modest efficacy, by recombinant AAVs administrated to newborn mice. The Nxnl2−/− mice have memory dysfunction at 2-months that resembles mild-cognitive impairment and at 18-months exhibit tauopathy, resembling to the progression of Alzheimer's disease. We propose the Nxnl2−/− mouse is a model to study multistage aged related neurodegenerative diseases. The NXNL2 metabolic and redox signaling is a new area of therapeutic research in neurodegenerative diseases