Genome-Wide Transcriptome Analyses of Silicon Metabolism in Phaeodactylum tricornutum Reveal the Multilevel Regulation of Silicic Acid Transporters

BACKGROUND:Diatoms are largely responsible for production of biogenic silica in the global ocean. However, in surface seawater, Si(OH)(4) can be a major limiting factor for diatom productivity. Analyzing at the global scale the genes networks involved in Si transport and metabolism is critical in order to elucidate Si biomineralization, and to understand diatoms contribution to biogeochemical cycles. METHODOLOGY/PRINCIPAL FINDINGS:Using whole genome expression analyses we evaluated the transcriptional response to Si availability for the model species Phaeodactylum tricornutum. Among the differentially regulated genes we found genes involved in glutamine-nitrogen pathways, encoding putative extracellular matrix components, or involved in iron regulation. Some of these compounds may be good candidates for intracellular intermediates involved in silicic acid storage and/or intracellular transport, which are very important processes that remain mysterious in diatoms. Expression analyses and localization studies gave the first picture of the spatial distribution of a silicic acid transporter in a diatom model species, and support the existence of transcriptional and post-transcriptional regulations. CONCLUSIONS/SIGNIFICANCE:Our global analyses revealed that about one fourth of the differentially expressed genes are organized in clusters, underlying a possible evolution of P. tricornutum genome, and perhaps other pennate diatoms, toward a better optimization of its response to variable environmental stimuli. High fitness and adaptation of diatoms to various Si levels in marine environments might arise in part by global regulations from gene (expression level) to genomic (organization in clusters, dosage compensation by gene duplication), and by post-transcriptional regulation and spatial distribution of SIT proteins

Permeation and trapping in fusion-relevant materials

International audienceTritium containment and control are essential prerequisites for fusion to comply with the promise of a safe energy with low impact on the environment. In particular, the behaviour of tritium in materials, i.e its adsorption, absorption, diffusion and trapping parameters, has to be assessed. The multi-layer design of DEMO plasma-facing components as well as the foreseen breeding blankets design includes several materials and interfaces, which behaviour regarding permeation remains to be clarified. The surface processes on both sides (plasma and cooling loop) also require more investigation. In this work, hydrogen transport parameters (diffusion and trapping) are determined using gas-driven permeation experiments undertaken on Eurofer 97, 316L stainless steel, copper and CuCrZr. The purpose of the presentation is to introduce the Hydrogen PERmeation in TOkamak-relevant MATErials (Hypertomate) experiment and the subsequent results on hydrogen permeation and trapping. Eurofer97 results will be recalled first. We will show that they are in good agreement with literature in the case of a perfect material. Particular attention has been given to the effect of surface state (roughness and oxidation) that influences the permeation behaviour. The impact of roughness on permeation results will be exemplified. This permeation analysis is supplemented with thermal desorption spectroscopy performed on deuterium-loaded samples in order to investigate more thoroughly trapping in these materials. These results altogether feed our 3D finite element code which aim is to fully simulate permeation in the plasma-facing components or breeding blankets. The ongoing developments to carry out the same measurements using tritium as a driving gas will also be presented. These measurements will show whether or not tritium differs from hydrogen or deuterium, for instance because of surface effects induced by its beta emission

Permeation and trapping in fusion-relevant materials

International audienceTritium containment and control are essential prerequisites for fusion to comply with the promise of a safe energy with low impact on the environment. In particular, the behaviour of tritium in materials, i.e its adsorption, absorption, diffusion and trapping parameters, has to be assessed. The multi-layer design of DEMO plasma-facing components as well as the foreseen breeding blankets design includes several materials and interfaces, which behaviour regarding permeation remains to be clarified. The surface processes on both sides (plasma and cooling loop) also require more investigation. In this work, hydrogen transport parameters (diffusion and trapping) are determined using gas-driven permeation experiments undertaken on Eurofer 97, 316L stainless steel, copper and CuCrZr. The purpose of the presentation is to introduce the Hydrogen PERmeation in TOkamak-relevant MATErials (Hypertomate) experiment and the subsequent results on hydrogen permeation and trapping. Eurofer97 results will be recalled first. We will show that they are in good agreement with literature in the case of a perfect material. Particular attention has been given to the effect of surface state (roughness and oxidation) that influences the permeation behaviour. The impact of roughness on permeation results will be exemplified. This permeation analysis is supplemented with thermal desorption spectroscopy performed on deuterium-loaded samples in order to investigate more thoroughly trapping in these materials. These results altogether feed our 3D finite element code which aim is to fully simulate permeation in the plasma-facing components or breeding blankets. The ongoing developments to carry out the same measurements using tritium as a driving gas will also be presented. These measurements will show whether or not tritium differs from hydrogen or deuterium, for instance because of surface effects induced by its beta emission

Permeation and trapping in Eurofer97: a wide-angle approach

International audienc

Development of fibered LIBS device for tokamak Plasma Facing Components characterization

International audienceThe LIBS technique enables to measure the deposits composition in fusion machines, particularly the tritium concentration on tokamak Plasma Facing Components (PFC), thus allowing the estimation of the deposited tritium quantity for safety control and the composition of the PFC surface in light impurities (oxides) which can pollute the plasma when evaporated. This paper presents the development of a fibered LIBS device, mounted on an articulated arm and able to operate in nanosecond and picosecond laser regimes for PFC characterizations. The different components of the LIBS device are presented as well as the first LIBS spectra on tungsten targets

Hydrogen permeation and trapping through Eurofer97

International audienc

APOBEC3G is a single-stranded DNA cytidine deaminase and functions independently of HIV reverse transcriptase

In the absence of the viral vif gene, human immunodeficiency virus (HIV) may be restricted by the APOBEC3G gene on chromosome 22. The role of the HIV Vif protein is to exclude host cell APOBEC3G from the budding virion. As APOBEC3G shows sequence homology to cytidine deaminases, it is presumed that in the absence of Vif, cytidine residues in the cDNA are deaminated yielding uracil. It is not known if additional proteins mediate APOBEC3G function or if deamination occurs in concert with reverse transcription. This report describes an in vitro assay showing that Baculovirus derived APOBEC3G alone extensively deaminates cDNA independently of reverse transcriptase. It reproduces the dinucleotide context typical of G → A hypermutants derived from a Δvif virus. By using an RNaseH(–) form of reverse transcriptase, it was shown that the cDNA has to be free of its RNA template to allow deamination. APOBEC3G deamination of dC or dCTP was not detected. In short, APOBEC3G is a single-stranded DNA cytidine deaminase capable of restricting retroviral replication

Herpes Simplex Virus Type 1 Infection Disturbs the Mitochondrial Network, Leading to Type I Interferon Production through the RNA Polymerase III/RIG-I Pathway

International audienceViruses have evolved a plethora of mechanisms to impair host innate immune responses. Herpes simplex virus type 1 (HSV-1), a double-stranded linear DNA virus, impairs the mitochondrial network and dynamics predominantly through the UL12.5 gene. We demonstrated that HSV-1 infection induced a remodeling of mitochondrial shape, resulting in a fragmentation of the mitochondria associated with a decrease in their volume and an increase in their sphericity. This damage leads to the release of mitochondrial DNA (mtDNA) to the cytosol. By generating a stable THP-1 cell line expressing the DNase I-mCherry fusion protein and a THP-1 cell line specifically depleted of mtDNA upon ethidium bromide treatment, we showed that cytosolic mtDNA contributes to type I interferon and APOBEC3A upregulation. This was confirmed by using an HSV-1 strain (KOS37 UL98-SPA) with a deletion of the UL12.5 gene that impaired its ability to induce mtDNA stress. Furthermore, by using an inhibitor of RNA polymerase III, we demonstrated that upon HSV-1 infection, cytosolic mtDNA enhanced type I interferon induction through the RNA polymerase III/RIG-I pathway. APOBEC3A was in turn induced by interferon. Deep sequencing analyses of cytosolic mtDNA mutations revealed an APOBEC3A signature predominantly in the 5'TpCpG context. These data demonstrate that upon HSV-1 infection, the mitochondrial network is disrupted, leading to the release of mtDNA and ultimately to its catabolism through APOBEC3-induced mutations. IMPORTANCE Herpes simplex virus 1 (HSV-1) impairs the mitochondrial network through the viral protein UL12.5. This leads to the fusion of mitochondria and simultaneous release of mitochondrial DNA (mtDNA) in a mouse model. We have shown that released mtDNA is recognized as a danger signal, capable of stimulating signaling pathways and inducing the production of proinflammatory cytokines. The expression of the human cytidine deaminase APOBEC3A is highly upregulated by interferon responses. This enzyme catalyzes the deamination of cytidine to uridine in single-stranded DNA substrates, resulting in the catabolism of edited DNA. Using human cell lines deprived of mtDNA and viral strains deficient in UL12, we demonstrated the implication of mtDNA in the production of interferon and APOBEC3A expression during viral infection. We have shown that HSV-1 induces mitochondrial network fragmentation in a human model and confirmed the implication of RNA polymerase III/RIG-I signaling in the capture of cytosolic mtDNA

Numerical modeling of the impact of leakage under divertor baffle in WEST

International audienc