14 research outputs found
A High Throughput Genetic Screen Identifies New Early Meiotic Recombination Functions in Arabidopsis thaliana
Meiotic recombination is initiated by the formation of numerous DNA double-strand breaks (DSBs) catalysed by the widely conserved Spo11 protein. In Saccharomyces cerevisiae, Spo11 requires nine other proteins for meiotic DSB formation; however, unlike Spo11, few of these are conserved across kingdoms. In order to investigate this recombination step in higher eukaryotes, we took advantage of a high-throughput meiotic mutant screen carried out in the model plant Arabidopsis thaliana. A collection of 55,000 mutant lines was screened, and spo11-like mutations, characterised by a drastic decrease in chiasma formation at metaphase I associated with an absence of synapsis at prophase, were selected. This screen led to the identification of two populations of mutants classified according to their recombination defects: mutants that repair meiotic DSBs using the sister chromatid such as Atdmc1 or mutants that are unable to make DSBs like Atspo11-1. We found that in Arabidopsis thaliana at least four proteins are necessary for driving meiotic DSB repair via the homologous chromosomes. These include the previously characterised DMC1 and the Hop1-related ASY1 proteins, but also the meiotic specific cyclin SDS as well as the Hop2 Arabidopsis homologue AHP2. Analysing the mutants defective in DSB formation, we identified the previously characterised AtSPO11-1, AtSPO11-2, and AtPRD1 as well as two new genes, AtPRD2 and AtPRD3. Our data thus increase the number of proteins necessary for DSB formation in Arabidopsis thaliana to five. Unlike SPO11 and (to a minor extent) PRD1, these two new proteins are poorly conserved among species, suggesting that the DSB formation mechanism, but not its regulation, is conserved among eukaryotes
SCEP1 and SCEP2 are two new components of the synaptonemal complex central element
International audienceThe synaptonemal complex (SC) is a proteinaceous structure that forms between homologous chromosomes during meiosis prophase. The SC is widely conserved across species, but its structure and roles during meiotic recombination are still debated. While the SC central region is made up of transverse filaments and central element proteins in mammals and fungi, few central element proteins have been identified in other species. Here we report the identification of two coiled-coil proteins, SCEP1 and SCEP2, that form a complex and localize at the centre of the Arabidopsis thaliana SC. In scep1 and scep2 mutants, chromosomes are aligned but not synapsed (the ZYP1 transverse filament protein is not loaded), crossovers are increased compared with the wild type, interference is lost and heterochiasmy is strongly reduced. We thus report the identification of two plant SC central elements, and homologues of these are found in all major angiosperm clades
Redox-active ions unlock substitutional doping in halide perovskites
International audienceElectrical doping of metal halide perovskites (MPHs) is a key step towards the use of this efficient and cost-effective semiconductor class in modern electronics. In this work, we demonstrate n-type doping of methylammonium lead iodide (CH3NH3PbI3) by the postfabrication introduction of Sm2+. The ionic radius of the latter is similar to that of Pb2+ and can replace it without altering the perovskite crystal lattice. It s demonstrated that once incorporated, Sm2+ can act as a dopant by undergoing oxidation to Sm3+. This results in the release of a negative charge that n-dopes the material, resulting in an increase of conductivity of almost 3 orders of magnitude. Unlike substitution doping with heterovalent ions, furtive dopants do not require counterions to maintain charge neutrality with respect to the ions they replace and are thus more likely to be incorporated into the crystalline structure. The incorporation of the dopant throughout the material is evidenced by XPS and ToF-SIMS, while the XRD pattern shows no phase separation at low andmedium doping concentrations. A shift of the Fermi level towards a conduction energy of 0.52 eV confirms the doping to be n-type with a charge carrier density, calculated using the MottâSchottky method, estimated to be nearly 1017 cm 3 for the most conductive samples. Variable-temperature conductivity experiments show that thedopant is only partially ionized at room temperature due to dopant freeze-out
The HEM Lines: a new library of homozygous Arabidopsis thaliana EMS mutants and its potential to detect meiotic phenotypes
Genetic screens have been crucial for deciphering many important biological processes, including meiosis. In Arabidopsis thaliana, previous forward screens have likely identified almost all the meiotic genes that when mutated lead to a pronounced decrease in fertility. However, the increasing number of genes identified in reverse genetics studies that play crucial roles in meiosis, but do not exhibit strong phenotypes when mutated, suggests that there are still many genes with meiotic function waiting to be discovered. In this study, we produced 897 A. thaliana homozygous mutant lines using Ethyl Methyl Sulfonate (EMS) mutagenesis followed by either single seed descent or haploid doubling. Whole genome sequencing of a subset of lines showed an average of 696 homozygous mutations per line, 195 of which (28%) modify a protein sequence. To test the power of this library, we carried out a forward screen looking for meiotic defects by observing chromosomes at metaphase I of male meiosis. Among the 649 lines analyzed, we identified 43 lines with meiotic defects. Of these, 21 lines had an obvious candidate causal mutation, namely a STOP or splicing site mutation in a gene previously shown to play a role in meiosis (ATM, MLH3, MLH1, MER3, HEI10, FLIP, ASY4, FLIP, PRD2, REC8, FANCL, and PSS1). Interestingly, this was the first time that six of these genes were identified in a forward screen in Arabidopsis (MLH3, MLH1, SGO1, PSS1, FANCL, and ASY4). These results illustrate the potential of this mutant population for screening for any qualitative or quantitative phenotype. Thus, this new mutant library is a powerful tool for functional genomics in A. thaliana. The HEM (Homozygote EMS Mutants) lines are available at the Versailles Arabidopsis stock center
La mort en Ăle-de-France
La mort est un sujet tabou dans notre sociĂ©tĂ©. Pourtant, câest Ă sa maniĂšre dâenvisager ou de reprĂ©senter la mort quâune sociĂ©tĂ© montre sa face cachĂ©e, ses angoisses profondes. Pour conjurer la crainte de ce franchissement, quoi de plus salutaire que dâĂ©crire un livre Ă son sujet et de croiser des regards diffĂ©rents sur un phĂ©nomĂšne souvent vĂ©cu de maniĂšre trĂšs, voire trop, personnelle. ...Les archĂ©ologues voient dans les sĂ©pultures et les nĂ©cropoles un tĂ©moignage prĂ©cieux des mentalitĂ©s du passĂ©. ...Les amĂ©nageurs ont Ă rĂ©soudre les problĂšmes posĂ©s par les cimetiĂšres dans les grandes mĂ©tropoles. ...Les juristes tentent de dĂ©finir les droits et obligations des vivants face Ă la mort des autres et aux procĂ©dures qui sâensuivent. ...Les artistes dĂ©sacralisent les reprĂ©sentations habituelles en « truquant » la mort quand le cadavre devient travesti.Du moment que quelqu'un est neÌ, a veÌcu, il en restera toujours quelque chose, meÌme si on ne peut dire quoi ; nous ne pouvons plus faire deÌsormais comme si ce quelqu'un eÌtait inexistant en geÌneÌral, ou n'avait jamais eÌteÌ. Jusqu'aux sieÌcles des sieÌcles, il faudra tenir compte de ce mysteÌrieux « avoir-eÌteÌ Â». Vladimir JankeÌleÌvitch, La mort, Flammarion, 1977 *** Quand on habite rue Belgrand ou rue des PyrĂ©nĂ©es, On ne peut Ă©viter dâapercevoir souvent Les deux Ă©normes cheminĂ©es DâoĂč chaque jour des corps sâĂ©chappent en fumĂ©es Que disperse le vent. Les Ăąmes ont sans doute pris de lâavance ; Ă©tonnĂ©es, Elles regardent fuir ce nuage mouvant : La chair qui durant tant dâannĂ©es Les tint dans sa chaleur dĂ©lectable enfermĂ©es. Jacques RĂDA, FumĂ©es, in La Course, Gallimard, 199
Membrane and Nuclear Estrogen Receptor Alpha Actions: From Tissue Specificity to Medical Implications
International audienceEstrogen receptor alpha (ERα) has been recognized now for several decades as playing a key role in reproduction and exerting functions in numerous nonreproductive tissues. In this review, we attempt to summarize the in vitro studies that are the basis of our current understanding of the mechanisms of action of ERα as a nuclear receptor and the key roles played by its two activation functions (AFs) in its transcriptional activities. We then depict the consequences of the selective inactivation of these AFs in mouse models, focusing on the prominent roles played by ERα in the reproductive tract and in the vascular system. Evidence has accumulated over the two last decades that ERα is also associated with the plasma membrane and activates non-nuclear signaling from this site. These rapid/nongenomic/membrane-initiated steroid signals (MISS) have been characterized in a variety of cell lines, and in particular in endothelial cells. The development of selective pharmacological tools that specifically activate MISS and the generation of mice expressing an ERα protein impeded for membrane localization have begun to unravel the physiological role of MISS in vivo. Finally, we discuss novel perspectives for the design of tissue-selective ER modulators based on the integration of the physiological and pathophysiological roles of MISS actions of estrogens
Mutation of Arginine 264 on ERα (Estrogen Receptor Alpha) Selectively Abrogates the Rapid Signaling of Estradiol in the Endothelium Without Altering Fertility
International audienceObjective - ERα (estrogen receptor alpha) exerts nuclear genomic actions and also rapid membrane-initiated steroid signaling. The mutation of the cysteine 451 into alanine in vivo has recently revealed the key role of this ERα palmitoylation site on some vasculoprotective actions of 17ÎČ-estradiol (E2) and fertility. Here, we studied the in vivo role of the arginine 260 of ERα which has also been described to be involved in its E2-induced rapid signaling with PI-3K (phosphoinositide 3-kinase) as well as G protein in cultured cell lines. Approach and Results: We generated a mouse model harboring a point mutation of the murine counterpart of this arginine into alanine (R264A-ERα). In contrast to the , the females are fertile with standard hormonal serum levels and normal control of hypothalamus-pituitary ovarian axis. Although R264A-ERα protein abundance was normal, the well-described membrane ERα-dependent actions of estradiol, such as the rapid dilation of mesenteric arteries and the acceleration of endothelial repair of carotid, were abrogated in mice. In striking contrast, E2-regulated gene expression was highly preserved in the uterus and the aorta, revealing intact nuclear/genomic actions in response to E2. Consistently, 2 recognized nuclear ERα-dependent actions of E2, namely atheroma prevention and flow-mediated arterial remodeling were totally preserved. Conclusions - These data underline the exquisite role of arginine 264 of ERα for endothelial membrane-initiated steroid signaling effects of E2 but not for nuclear/genomic actions. This provides the first model of fertile mouse with no overt endocrine abnormalities with specific loss-of-function of rapid ERα signaling in vascular functions
Metabolic causes of nonimmune hydrops fetalis: A next-generation sequencing panel as a first-line investigation.
International audienceHydrops fetalis is a life-threatening fetal condition, and 85% of all cases are classified as nonimmune hydrops fetalis (NIHF). Up to 15% of NIHF cases may be due to inborn errors of metabolism (IEM), but a large proportion of cases linked to metabolic disorders remains undiagnosed. This lack of diagnosis may be related to the limitations of conventional biological procedures, which involve sequential investigations and require multiple samples and steps. In addition, this approach is time consuming. We have developed a next-generation sequencing (NGS) panel to investigate metabolic causes of NIHF, ascites, and polyhydramnios associated to another fetal abnormality