AMBER : a near infrared focal instrument for the VLTI

10 pagesInternational audienceAMBER is the General User near-infrared focal instrument of the Very Large Telescope interferometer. Its specifications are based on three key programs on Young Stellar Objects, Active Galactic Nuclei central regions, masses and spectra of hot Extra Solar Planets. It has an imaging capacity because it combines up to three beams and very high accuracy measurement are expected from the spatial filtering of beams by single mode fibers and the comparison of measurements made simultaneously in different spectral channels

Identification of Keratinocyte Growth Factor as a Target of microRNA-155 in Lung Fibroblasts: Implication in Epithelial-Mesenchymal Interactions

International audienceBACKGROUND: Epithelial-mesenchymal interactions are critical in regulating many aspects of vertebrate embryo development, and for the maintenance of homeostatic equilibrium in adult tissues. The interactions between epithelium and mesenchyme are believed to be mediated by paracrine signals such as cytokines and extracellular matrix components secreted from fibroblasts that affect adjacent epithelia. In this study, we sought to identify the repertoire of microRNAs (miRNAs) in normal lung human fibroblasts and their potential regulation by the cytokines TNF-alpha, IL-1beta and TGF-beta. METHODOLOGY/PRINCIPAL FINDINGS: MiR-155 was significantly induced by inflammatory cytokines TNF-alpha and IL-1beta while it was down-regulated by TGF-beta. Ectopic expression of miR-155 in human fibroblasts induced modulation of a large set of genes related to "cell to cell signalling", "cell morphology" and "cellular movement". This was consistent with an induction of caspase-3 activity and with an increase in cell migration in fibroblasts tranfected with miR-155. Using different miRNA bioinformatic target prediction tools, we found a specific enrichment for miR-155 predicted targets among the population of down-regulated transcripts. Among fibroblast-selective targets, one interesting hit was keratinocyte growth factor (KGF, FGF-7), a member of the fibroblast growth factor (FGF) family, which owns two potential binding sites for miR-155 in its 3'-UTR. Luciferase assays experimentally validated that miR-155 can efficiently target KGF 3'-UTR. Site-directed mutagenesis revealed that only one out of the 2 potential sites was truly functional. Functional in vitro assays experimentally validated that miR-155 can efficiently target KGF 3'-UTR. Furthermore, in vivo experiments using a mouse model of lung fibrosis showed that miR-155 expression level was correlated with the degree of lung fibrosis. CONCLUSIONS/SIGNIFICANCE: Our results strongly suggest a physiological function of miR-155 in lung fibroblasts. Altogether, this study implicates this miRNA in the regulation by mesenchymal cells of surrounding lung epithelium, making it a potential key player during tissue injury

The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI

The GRAVITY instrument has been revolutionary for near-infrared interferometry by pushing sensitivity and precision to previously unknown limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) in GRAVITY+, these limits will be pushed even further, with vastly improved sky coverage, as well as faint-science and high-contrast capabilities. This upgrade includes the implementation of wide-field off-axis fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser guide stars in an upgraded facility. GRAVITY+ will open up the sky to the measurement of black hole masses across cosmic time in hundreds of active galactic nuclei, use the faint stars in the Galactic centre to probe General Relativity, and enable the characterisation of dozens of young exoplanets to study their formation, bearing the promise of another scientific revolution to come at the VLTI.Comment: Published in the ESO Messenge

Le cycle d'activation de la protéine G Rac à la surface de la membrane lipidique

Les protéines Rho comme toutes les petites protéines G lient les nucléotides à guanine, GDP ou GTP. La réaction d'activation des protéines Rho, qui correspond à l'échange d'un GDP par un GTP, est intrinsèquement très lente et nécessite la catalyse par des facteurs d'échange spécifiques, les protéines à tandem DH-PH. De plus, les protéines Rho sont ancrées à la membrane via groupement prényl mais sont en majorité solubilisées dans le cytosol par une protéine régulatrice appelée GDI possédant une poche hydrophobe où se loge le prényl. Nous avons étudié le mécanisme d'activation de Rac1, une protéine de la famille Rho, et le lien entre le cycle GDP/GTP et le cycle membrane/cytosol. Pour cela, nous avons reconstitué in vitro l'activation de Rac1 sur liposomes à partir du complexe Rac/GDI purifié. Nous avons montré que l'activation de Rac par le tandem DH-PH de la protéine Tiam1 nécessite la dissociation de Rac1 de GDI qui ne peut se faire qu'en présence de lipides anioniques. Par ailleurs, l'ancrage de Rac à la membrane favorisé la réaction d'activation suggérant un changement conformationnel du tandem DH-PH sur la membrane. La dissociation de GDI et l'ancrage de Rac-GDP à la membrane rend Rac également beaucoup plus sensible à la glucosylation par la toxine létale de Clostridium Sordelli. La présence de Phosphatidyl Sérine permet un recrutement membranaire du fragment catalytique de la toxine létale et augmente très fortement son activité de glucosylation sur Rac. Cela met en évidence dans la protéine bactérienne un domaine très spécifique pour la Phosphatidyl Sérine. L'ensemble de ces résultats souligne l'importance des interfaces protéines-membrane dans le cycle d'activation de la protéine Rac.As all G proteins, Rho proteins bind guanine nucleotide, GDP or GTP. The activation reaction, which corresponds to the exchange of GDP by GTP, is intrinsically very slow and required catalysis by Rho specific exchange factors, containing a tandem of DH and PH domain. Moreover, Rho proteins are anchored at the lipidic membrane by a prenyl group, but are mostly soluble in the cytosol through the interaction of the prenyl with the hydrophobic pocket of a regulatory protein named GDI. We have studied the activation mechanism of Rac1, a Rho protein, and the link between the GDP/GTP cycle and the membrane/cytosol cycle. We have reconstituted Rac1 activation in vitro on liposomes using purified Rac/GDI complex. We showed that Rac activation by DH-PH tandem of Tiam1 required Rac dissociation from GDI, which can only occurs in the presence of anionic lipids. Moreover, the anchorage of Rac on the lipidic membrane facilitates the activation reaction suggesting a conformation change of the DH-PH tandem on the membrane surface. GDI dissociation and Rac-GDP membrane anchorage strongly facilitate the glucosylation of Rac by Clostridium Sordelli lethal toxin. The presence of Phosphatidyl Serine induces the recruitment lethal toxin to the membrane and strikingly enhances Rac glucosylation. A domain with a high specificity for Phosphatidyl Serine is present in this bacterial protein. Taken together, these results underline the importance of protein/lipid interactions in the Rac activation Cycle.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

RiboProfiling: a Bioconductor package for standard Ribo-seq pipeline processing [version 1; referees: 2 approved]

The ribosome profiling technique (Ribo-seq) allows the selective sequencing of translated RNA regions. Recently, the analysis of genomic sequences associated to Ribo-seq reads has been widely employed to assess their coding potential. These analyses led to the identification of differentially translated transcripts under different experimental conditions, and/or ribosome pausing on codon motifs. In the context of the ever-growing need for tools analyzing Ribo-seq reads, we have developed ‘RiboProfiling’, a new Bioconductor open-source package. ‘RiboProfiling’ provides a full pipeline to cover all key steps for the analysis of ribosome footprints. This pipeline has been implemented in a single R workflow. The package takes an alignment (BAM) file as input and performs ribosome footprint quantification at a transcript level. It also identifies footprint accumulation on particular amino acids or multi amino-acids motifs. Report summary graphs and data quantification are generated automatically. The package facilitates quality assessment and quantification of Ribo-seq experiments. Its implementation in Bioconductor enables the modeling and statistical analysis of its output through the vast choice of packages available in R. This article illustrates how to identify codon-motifs accumulating ribosome footprints, based on data from Escherichia coli

First results from VLTI near-infrared interferometry on high-mass young stellar objects

11 pages, 4 figures, to appear in Proceedings of SPIE Astronomical Telescopes and Instrumentation 2010Due to the recent dramatic technological advances, infrared interferometry can now be applied to new classes of objects, resulting in exciting new science prospects, for instance, in the area of high-mass star formation. Although extensively studied at various wavelengths, the process through which massive stars form is still only poorly understood. For instance, it has been proposed that massive stars might form like low-mass stars by mass accretion through a circumstellar disk/envelope, or otherwise by coalescence in a dense stellar cluster. After discussing the technological challenges which result from the special properties of these objects, we present first near-infrared interferometric observations, which we obtained on the massive YSO IRAS 13481-6124 using VLTI/AMBER infrared long-baseline interferometry and NTT speckle interferometry. From our extensive data set, we reconstruct a model-independent aperture synthesis image which shows an elongated structure with a size of 13x19 AU, consistent with a disk seen under an inclination of 45 degree. The measured wavelength-dependent visibilities and closure phases allow us to derive the radial disk temperature gradient and to detect a dust-free region inside of 9.5 AU from the star, revealing qualitative and quantitative similarities with the disks observed in low-mass star formation. In complementary mid-infrared Spitzer and sub-millimeter APEX imaging observations we detect two bow shocks and a molecular out ow which are oriented perpendicular to the disk plane and indicate the presence of a bipolar outflow emanating from the inner regions of the system

Unzipped genome assemblies of polyploid root-knot nematodes reveal unusual and clade-specific telomeric repeats

International audienceUsing long-read sequencing, we assembled and unzipped the polyploid genomes of Meloidogyne incognita , M. javanica and M. arenaria , three of the most devastating plant-parasitic nematodes. We found the canonical nematode telomeric repeat to be missing in these and other Meloidogyne genomes. In addition, we find no evidence for the enzyme telomerase or for orthologs of C. elegans telomere-associated proteins, suggesting alternative lengthening of telomeres. Instead, analyzing our assembled genomes, we identify species-specific composite repeats enriched mostly at one extremity of contigs. These repeats are G-rich, oriented, and transcribed, similarly to canonical telomeric repeats. We confirm them as telomeric using fluorescent in situ hybridization. These repeats are mostly found at one single end of chromosomes in these species. The discovery of unusual and specific complex telomeric repeats opens a plethora of perspectives and highlights the evolutionary diversity of telomeres despite their central roles in senescence, aging, and chromosome integrity