A Genome-Wide Collection of Mos1 Transposon Insertion Mutants for the C. elegans Research Community

Methods that use homologous recombination to engineer the genome of C. elegans commonly use strains carrying specific insertions of the heterologous transposon Mos1. A large collection of known Mos1 insertion alleles would therefore be of general interest to the C. elegans research community. We describe here the optimization of a semi-automated methodology for the construction of a substantial collection of Mos1 insertion mutant strains. At peak production, more than 5,000 strains were generated per month. These strains were then subject to molecular analysis, and more than 13,300 Mos1 insertions characterized. In addition to targeting directly more than 4,700 genes, these alleles represent the potential starting point for the engineered deletion of essentially all C. elegans genes and the modification of more than 40% of them. This collection of mutants, generated under the auspices of the European NEMAGENETAG consortium, is publicly available and represents an important research resource

Mos as a tool for genome-wide insertional mutagenesis in Caenorhabditis elegans: results of a pilot study

The sequence of the Caenorhabditis elegans genome contains approximately 19 000 genes. Available mutants currently exist for <20% of these genes. The existence of a Mos-based inducible transposon system in C.elegans could theoretically serve as a tool to saturate the genome with insertions. We report here the results of a pilot study aimed at assaying this strategy. We generated 914 independent random Mos insertions and determined their location by inverse PCR. The distribution of the insertions throughout the genome does not reveal any gross distortion, with the exception of a major hotspot on chromosome I (rDNA locus). Transposons are evenly distributed between the genic and intergenic regions. Within genes, transposons insert preferentially into the introns. We derived the consensus target site for Mos in C.elegans (ATATAT), which is common to Tc1, another mariner element. Finally, we assayed the mutagenic properties of insertions located in exons by comparing the phenotype of homozygous strains to that of known mutations or RNAi of the same gene. This pilot experiment shows that a Mos-based approach is a viable strategy that can contribute to the constitution of genome-wide collections of identified C.elegans mutants

Sintering behaviour of MOX SFR nuclear fuel obtained by freeze-granulation and co-milling route

International audiencePlutonium can be reprocessed from spent nuclear fuels to be integrated in MOX (mixed oxide) fuels that can be used in current reactors or future SFR (sodium-cooled fast neutron reactors). The present work focuses on the fabrication of MOX fuel pellets dedicated to SFR. These fuels are (U,Pu)O2-x pellets with a plutonium content Pu/(U+Pu) between 15 and 35 %mol and oxygen-to-metal ratio comprised between 2.00 and 1.94. In this study, the starting powders were prepared by two manufacturing routes: one by a conventional dry co-milling route (grinding, mixing and sieving) and a second by freeze granulation, which yields smooth spherical agglomerates with great flowability and a good pelletizing behaviour. The sintering behaviours of these powders were investigated and compared through the sintering map approach. Dilatometric measurements were performed to follow the densification during different heat treatments and were combined with microstructural characterizations of the sintered pellets, notably to measure their grain size. Due to the wide range of densities achieved, these two approaches allow plotting the sintering map of each powder, i.e., the grain size versus relative density trajectory. To investigate the sintering mechanisms, the relation between density and grain size during sintering was fitted with theoretical expressions to identify the main mechanisms responsible for densification and grain growth for both powders. Furthermore, dilatometric data were used to calculate sintering activation energies by the CRH (constant rates of heating) and MSC (master sintering curve) methods. Diffusion coefficients were also calculated and compared to those from the literature. In order to complete this study, other characterisations were made on the sintered samples notably regarding their porosities distribution (by optical microscopy and SEM), to investigate porosity size and shape evolutions during sintering. The uranium plutonium distributions were also investigated by EPMA and XRD, both to observe the chemical homogenisation occurring during sintering and to compare the final distributions obtained for the two processes.Finally, the MSC approach was expanded to isothermal sintering conditions to build up predictive sintering models to optimize the sintering heat cycle for each powder. Such predictive models are notably very useful tools to lower the maximum temperature and duration required during sintering without affecting the fuel compliance with SFR specifications

Preparation and co-dispersion of TiO2-Y2O3 suspensions through the study of their rheological and electrokinetic properties

International audienceThe development of Generation IV sodium-cooled fast reactors (SFR) is currently studied by several countries, France in particular. To manufacture the UO2-PuO2 fuels for these new types of reactors, new innovative wet colloidal processing routes are investigated. Among these wet colloidal processes, some involve at first the preparation of high solid content water-based suspensions. This key step needs to be investigated in order to obtain highly and easily processable suspensions, featuring optimal viscosity and dispersion state. The structures and properties for all intermediate and final products involved in such ceramic manufacturing processes are heavily affected by these suspension characteristics. Therefore, they are critical to ensure a compliant final product (i.e. fuel pellets) with the required density, homogeneity, mechanical strength and absence of defects. In this scope, preparation process of such suspensions was developed by the use of UO2 and PuO2 surrogating (i.e. mimicking) powders, TiO2 and Y2O3 respectively

Influence of the PuO2 content on the sintering behaviour of UO2-PuO2 freeze-granulated powders under reducing conditions

International audienceThe sintering behaviour of freeze-granulated UO2-PuO2 powders containing 33 and 15 mol% Pu/(U+Pu) was investigated under reducing conditions up to 1700 °C. For both compositions, the grain size versus relative density trajectory was constructed. All the experimental points form a single trajectory meaning that a relative density/grain size pair obtained after sintering is independent of the thermal path (heating rate, soak time, soak temperature) and of the Pu content. Exploiting the grain size versus relative density trajectory enabled also to propose that densification was controlled by grain boundary diffusion and grain growth by the grain boundaries. An activation energy around 510 kJ/mol was obtained for densification, which was close to the value reported for the grain boundary diffusion of plutonium cations in U1-xPuxO2 polycrystals. Whatever the Pu content, the sintered microstructure of 98% dense samples appeared homogeneous regarding the distribution of the plutonium and uranium cations

Use of nonsteroidal anti-inflammatory drugs in early axial spondyloarthritis in daily practice: Data from the DESIR cohort

International audienc

Patient-physician discordance in global assessment in early spondyloarthritis and its change over time: the DESIR cohort

International audienc

Sintering investigations of a UO2-PuO2 powder synthesized using the freeze-granulation route

International audienceSintering investigations of a UO2-PuO2 powder, integrating 11 wt% of PuO2 and synthesized by freeze-granulation, were completed at temperatures up to 1700°C, in an atmosphere of Ar/4 vol% H2 and 1200 vpm H2O. Analyzing the “grain size versus relative density” trajectory enabled to propose that densification was controlled by volume diffusion and grain growth by the grain boundaries. An activation energy around 630 kJ/mol was obtained for densification, which was close to the value reported for volume diffusion of plutonium cations in U1-xPuxO2 polycrystals. The sintered microstructure appeared homogeneous regarding the plutonium and uranium cations distribution

Sintering of a UO2 - PuO2 freeze-granulated powder under reducing conditions

International audienceA freeze-granulated powder made of UO 2 and PuO 2 , containing 15 mol% of Pu/(U+Pu), was sintered under reducing conditions (oxygen potential of-468 kJ/mol at 1700 °C). Constructing trajectory, using the constant rates of heating and the master sintering curves approaches and calculating the diffusion coefficients by exploiting the results of the sintering runs enabled to propose that densification was probably controlled by grain boundary diffusion and grain growth by the grain boundaries. An activation energy around 525 kJ/mol was obtained for densification, which was close to what was reported for grain boundary diffusion of plutonium cations in U 0.55 Pu 0. 45 O 2-x polycrystalline materials. The sintered microstructure appeared homogeneous regarding the plutonium and uranium cations spatial distribution. By combining the master sintering curve approach for anisothermal and isothermal conditions, it was possible to predict the evolution of the relative density over time for any type of thermal path

Characterization by electron probe microanalysis, Raman spectroscopy and transmission electron microscopy of a MOX fuel sintered from a freeze-granulated powder

International audienc