Plasmas and Controlled Nuclear Fusion

Contains report on one research project.U.S. Atomic Energy Commission (Contract AT(30-1)-3980

Detecting short spatial scale local adaptation and epistatic selection in climate-related candidate genes in European beech (Fagus sylvatica) populations

Detecting signatures of selection in tree populations threatened by climate change is currently a major research priority. Here, we investigated the signature of local adaptation over a short spatial scale using 96 European beech (Fagus sylvatica L.) individuals originating from two pairs of populations on the northern and southern slopes of Mont Ventoux (south-eastern France). We performed both single and multi-locus analysis of selection based on 53 climate-related candidate genes containing 546 SNPs. FST outlier methods at the SNP level revealed a weak signal of selection, with three marginally significant outliers in the northern populations. At the gene-level, considering haplotypes as alleles, two additional marginally significant outliers were detected, one on each slope. To account for the uncertainty of haplotype inference, we averaged the Bayes Factors over many possible phase reconstructions. Epistatic selection offers a realistic multi-locus model of selection in natural populations. Here, we used a test suggested by Ohta based on the decomposition of the variance of linkage disequilibrium. Over all populations, 0.23% of the SNP pairs (haplotypes) showed evidence of epistatic selection, with nearly 80% of them being within genes. One of the between gene epistatic selection signals arose between an FST outlier and a non-synonymous mutation in a drought response gene. Additionally, we identified haplotypes containing selectively advantageous allele combinations which were unique to high or low-elevations and northern or southern populations. Several haplotypes contained non-synonymous mutations situated in genes with known functional importance for adaptation to climatic factor

QuanTI-FRET: a framework for quantitative FRET measurements in living cells

Forster Resonance Energy Transfer (FRET) allows for the visualization of nanometer-scale distances and distance changes. This sensitivity is regularly achieved in single-molecule experiments in vitro but is still challenging in biological materials. Despite many efforts, quantitative FRET in living samples is either restricted to specific instruments or limited by the complexity of the required analysis. With the recent development and expanding utilization of FRET-based biosensors, it becomes essential to allow biologists to produce quantitative results that can directly be compared. Here, we present a new calibration and analysis method allowing for quantitative FRET imaging in living cells with a simple fluorescence microscope. Aside from the spectral crosstalk corrections, two additional correction factors were defined from photophysical equations, describing the relative differences in excitation and detection efficiencies. The calibration is achieved in a single step, which renders the Quantitative Three-Image FRET (QuanTI-FRET) method extremely robust. The only requirement is a sample of known stoichiometry donor:acceptor, which is naturally the case for intramolecular FRET constructs. We show that QuanTI-FRET gives absolute FRET values, independent of the instrument or the expression level. Through the calculation of the stoichiometry, we assess the quality of the data thus making QuanTI-FRET usable confidently by non-specialists

Inférer les capacités de dispersion et de migration : de l'échelle locale à l'échelle globale -

Dans le contexte actuel de changements climatiques, il est important de pouvoir connaître au mieux les capacités de migration et de déplacement des espèces. Jusqu'à présent, on utilisait des approches empiriques pour évaluer cette dynamique. Aujourd'hui, la science devient plus prédictive, utilisant des approches basées sur des modèles intégrateurs, comme celui présenté ici, le noyau de dispersion, qui décrit la répartition spatiale des graines dispersées à partir d'une source

β1A Integrin Is a Master Regulator of Invadosome Organization and Function

Use of patterned surfaces, reverse genetics, and time-controlled photoinactivation showed that β1 but not β3 integrins are required for invadosome formation, self-assembly, and stabilization into a ring structure. The activation state of β1 as well as its phosphorylation by protein kinase C on Ser785 control these process and link to the degradative function

Anisotropic diffusion of water molecules in hydroxyapatite nanopores

Funded by EPSRC Grant EP/K000128/1

Paternity analysis of pollen-mediated gene flow for Fraxinus excelsior L. in a chronically fragmented landscape

Paternity analysis based on microsatellite marker genotyping was used to infer contemporary genetic connectivity by pollen of three population remnants of the wind-pollinated, wind-dispersed tree Fraxinus excelsior, in a deforested Scottish landscape. By deterministically accounting for genotyping error and comparing a range of assignment methods, individual-based paternity assignments were used to derive population-level estimates of gene flow. Pollen immigration into a 300ha landscape represents between 43% and 68% of effective pollination, mostly depending on assignment method. Individual male reproductive success is unequal, with 31 of 48 trees fertilising one seed or more, but only three trees fertilising more than ten seeds. Spatial analysis suggests a fat-tailed pollen dispersal curve with 85% of detected pollination occurring within 100m, and 15% spreading between 300m and 1900m from the source. Identification of immigrating pollen sourced from two neighbouring remnants indicates further effective dispersal at 2900m. Pollen exchange among remnants is driven by population size rather than geographic distance, with larger remnants acting predominantly as pollen donors, and smaller remnants as pollen recipients. Enhanced wind dispersal of pollen in a barren landscape ensures that the seed produced within the catchment includes genetic material from a wide geographic area. However, gene flow estimates based on analysis of non-dispersed seeds were shown to underestimate realised gene immigration into the remnants by a factor of two suggesting that predictive landscape conservation requires integrated estimates of post-recruitment gene flow occurring via both pollen and seed

Instabilité cyclotronique collisionnelle dans les gaz ionisés à effet Ramsauer

Anomalous cyclotron radiation due to a collisionnal instability in an ionized Ramsauer gas has been studied experimentally in different rare gases discharges. Under specific conditions strong low frequency oscillations in the plasma potential are related to synchronous high frequency radiation pulses. The emission spectrum shows a sharp and intense peak in the vicinity of the electron cyclotron frequency. Calculations based on the theory of fluctuations for dense plasma are in agreement with experimental data. A model is presented where a required bumped velocity distribution function is created by the electric field of an ionisation wave. Under such conditions it is shown that the medium has an absolute instability and behaves like an oscillator.Le rayonnement cyclotronique anormal, dû à l'instabilité cyclotronique collisionnelle d'un gaz ionisé à effet Ramsauer a été étudié dans différentes décharges de gaz rares. Sous certaines conditions, de forte oscillations de basse fréquence du potentiel du plasma sont accompagnées d'impulsions synchrones de rayonnement hyperfréquence dont le spectre présente une raie intense et étroite au voisinage de la fréquence cyclotronique électronique. Les résultats de la théorie utilisée, basée sur l'étude des fluctuations du mode extraordinaire dans un plasma dense, sont en bon accord avec les observations expérimentales. Il est présenté un modèle où l'édification d'une fonction de distribution à population inversée, nécessaire à l'instabilité, résulte de la présence du champ électrique d'une onde d'ionisation. Dans ce cas, il est montré théoriquement et vérifié expérimentalement que le milieu absolument instable, se comporte comme un oscillateur