Effects of biotic and abiotic factors on the DNA methylation status in Gammarus fossarum

International audienceThe interest of epigenetic regulation is becoming increasingly important in ecotoxicology. Among epigenetic marks, DNA methylation could be a biomarker of interest. The aim of this study is to investigate the measurement of genomic DNA methylation level as a possible stress biomarker in the ecologically relevant freshwater species Gammarus fossarum

Niveau de méthylation de l'ADN génomique : marqueur moléculaire de stress chez l'espèce Gammarus fossarum ?

International audienceGenotoxic evaluation has been developing for a couple decade among ecotoxicological assessment approaches in the aquatic field. It offers some prospect for understanding delayed effects on the offspring and the population dynamics (provided genetic mutations affect gametic genome). However, the modification of the DNA sequence by genetic mutation (as a result of primary DNA damage) is not the only impact of toxic substances on the genome. For example, epigenetic effects, defined as hereditary effects on the DNA function, may add up to mediated effects by genetics way. Among these marks, DNA methylation is very studied by scientists. As such, it is important to examine epigenetic changes in the context of population level perspective. This provides a complementary approach to effects on the primary structure of the genome for taking into account the time interval between the exposure to environmental contaminants and their effects. This issue is a real challenge in ecotoxicology. Moreover, the epigenetic allows improving the understanding of changes of life history traits (reproduction, growth and development). These parameters are suitable for assessing the toxicity and are known to be regulated by epigenetic. Finally, epigenic could also help better understand the variability of effects related to experimental conditions between the studies. Therefore, epigenetic marks have an innovative nature for the evaluation of environmental risks. In this regard, we have investigated the measurement of genomic DNA methylation level as a possible stress biomarker in the ecologically relevant species Gammarus fossarum. First, the basal level was explored by studying the difference of overall DNA methylation between male, female and juvenile. Then, we evaluated the effects of natural factors on genomic DNA methylation level as starvation and exposed to different temperatures (8, 12 and 18°C) for 7 days and 1 month. To know the variability of DNA methylation in populations of Gammarus fossarum, three French populations from the same genetic strain, were studied. Lastly, the epigenetic biomarker response to a chemical stress was evaluated in a field experience. We encaged gammarids stemming from a reference unpolluted station in sited impacted by various human activities

Photooxidation reactions of nucleic acids

SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : RM 1443 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Light-Induced Acclimation of the Arabidopsis chlorina1 Mutant to Singlet Oxygen.

International audienceSinglet oxygen (O-1(2)) is a reactive oxygen species that can function as a stress signal in plant leaves leading to programmed cell death. In microalgae, O-1(2)-induced transcriptomic changes result in acclimation to O-1(2). Here, using a chlorophyll b-less Arabidopsis thaliana mutant (chlorina1 [ch1]), we show that this phenomenon can also occur in vascular plants. The ch1 mutant is highly photosensitive due to a selective increase in the release of O-1(2) by photosystem II. Under photooxidative stress conditions, the gene expression profile of ch1 mutant leaves very much resembled the gene responses to O-1(2) reported in the Arabidopsis mutant flu. Preexposure of ch1 plants to moderately elevated light intensities eliminated photooxidative damage without suppressing O-1(2) formation, indicating acclimation to O-1(2). Substantial differences in gene expression were observed between acclimation and high-light stress: A number of transcription factors were selectively induced by acclimation, and contrasting effects were observed for the jasmonate pathway. Jasmonate biosynthesis was strongly induced in ch1 mutant plants under high-light stress and was noticeably repressed under acclimation conditions, suggesting the involvement of this hormone in O-1(2)-induced cell death. This was confirmed by the decreased tolerance to photooxidative damage of jasmonate-treated ch1 plants and by the increased tolerance of the jasmonate-deficient mutant delayed-dehiscence2

High-frequency monitoring of debris flows in the French Alps: preliminary results of a starting program

International audienceDebris-flows mobilize high sediment loads and are often responsible for most of the sediment yield from upland headwaters and may endanger the safety of life and infrastructure in the vicinity of torrent channels. Two very active debris-flow torrents with different physiographic settings have been equipped in the French Alps, the Manival Torrent (3.6 km²) and the Réal Torrent (2.3 km²). At these two sites, debris-flow monitoring systems are based on a combination of different techniques involving rain gauges, soil vibrations and flow elevation measurements and high-resolution/frequency imagery acquisition. Only flash floods with bed load transport have been observed on the Manival Torrent. Conversely, in spring/summer 2011 four meteorological events triggered debris flows on the Réal Torrent. Most of the debris fronts deposited immediately in the upstream part of the channel. Only one debris-flow propagated from the sediment source area to the basin’s outlet. A 1.8 m high debris front propagated with a mean velocity of about 3 m s-1. Its volume was 4,400 m3 upstream and it increased because of bed erosion. The debris flow reached 6,100 m3 in the middle part of the basin and then decreased slightly further downstream (8,600 m3). These measurements highlight the interaction between the debris flow and the torrent channel in the first part of the basin. These results are in accordance with previous sediment budgets estimated for the debris flows which occurred in 2009 and 2010

The Arg-4 mutant factor IX Strasbourg 2 shows a delayed activation by factor XIa

We have characterized at the DNA and protein levels a mutant factor IX, factor IX Strasbourg 2, which is responsible for a severe form (<0.01 U/ml) of haemophilia B. Factor IX Strasbourg 2 has a higher molecular weight than normal factor IX. A mutation G-->A at position 6365 of the gene was demonstrated by DNA sequencing and confirmed by restriction mapping which showed absence of a Hae III site. This leads to the substitution of glutamine for arginine at position -4 of the propeptide. Factor IX Strasbourg 2 was purified from plasma by DEAE Sepharose chromatography and immunoaffinity and relative to normal factor IX, binding of calcium to the mutant protein was clearly reduced in calcium lactate agarose gel. Quantification of gamma-carboxyglutamic acid residues gave about 50% carboxylation as compared to normal factor IX. Microsequencing of the NH2-terminal part of factor IX Strasbourg 2 confirmed the attachment of the propeptide and the mutation Arg-->Gln. Activation of factor IX Strasbourg 2 by purified factor XIa was found to be retarded as compared to normal factor IX, but after activation the mutant factor IXa was able to activate factor X. In conclusion, factor IX Strasbourg 2 circulates with the attached propeptide and shows reduced gamma-carboxylation and delayed activation by factor XIa but a normal capacity to activate factor X after total cleavage by factor XI

Gadolinium nanoparticles and contrast agent as radiation sensitizers

International audienceThe goal of the present study was to evaluate and compare the radiosensitizing properties of gadolinium nanoparticles (NPs) with the gadolinium contrast agent (GdCA) Magnevist® in order to better understand the mechanisms by which they act as radiation sensitizers. This was determined following either low energy synchrotron irradiation or high energy gamma irradiation of F98 rat glioma cells exposed to ultrasmall gadolinium NPs (GdNPs, hydrodynamic diameter of 3 nm) or GdCA. Clonogenic assays were used to quantify cell survival after irradiation in the presence of Gd using monochromatic x-rays with energies in the 25 keV–80 keV range from a synchrotron and 1.25 MeV gamma photons from a cobalt-60 source. Radiosensitization was demonstrated with both agents in combination with X-irradiation. At the same concentration (2.1 mg mL−1), GdNPS had a greater effect than GdCA. The maximum sensitization-enhancement ratio at 4 Gy (SER4Gy) was observed at an energy of 65 keV for both the nanoparticles and the contrast agent (2.44   ±   0.33 and 1.50   ±   0.20, for GdNPs and GdCA, respectively). At a higher energy (1.25 MeV), radiosensitization only was observed with GdNPs (1.66   ±   0.17 and 1.01   ±   0.11, for GdNPs and GdCA, respectively). The radiation dose enhancements were highly 'energy dependent' for both agents. Secondary-electron-emission generated after photoelectric events appeared to be the primary mechanism by which Gd contrast agents functioned as radiosensitizers. On the other hand, other biological mechanisms, such as alterations in the cell cycle may explain the enhanced radiosensitizing properties of GdNPs