Differential stability of DNA crossovers in solution mediated by divalent cations

The assembly of DNA duplexes into higher-order structures plays a major role in many vital cellular functions such as recombination, chromatin packaging and gene regulation. However, little is currently known about the molecular structure and stability of direct DNADNA interactions that are required for such functions. In nature, DNA helices minimize electrostatic repulsion between double helices in several ways. Within crystals, B-DNA forms either right-handed crossovers by groovebackbone interaction or left-handed crossovers by groovegroove juxtaposition. We evaluated the stability of such crossovers at various ionic concentrations using large-scale atomistic molecular dynamics simulations. Our results show that right-handed DNA crossovers are thermodynamically stable in solution in the presence of divalent cations. Attractive forces at short-range stabilize such crossover structures with inter-axial separation of helices less than 20 . Right-handed crossovers, however, dissociate swiftly in the presence of monovalent ions only. Surprisingly, left-handed crossovers, assembled by sequence-independent juxtaposition of the helices, appear unstable even at the highest concentration of Mg2+studied here. Our study provides new molecular insights into chiral association of DNA duplexes and highlights the unique role divalent cations play in differential stabilization of crossover structures. These results may serve as a rational basis to understand the role DNA crossovers play in biological processes

Sur deux points aveugles de la doctrine juridique: nouvelles considérations sur le dialogisme normatif

C’est ainsi. Je ne me souviens pas que depuis ce déjeuner de la fin de l’hiver 90, depuis cette rencontre et nos premières discussions à l’ombre du Panthéon évoquées par André Lajoie au début de son étude intitulée « dans l’angle mort de l’analyse systémale », nous ayons jamais vraiment interrompu la conversation qui nous avait réunis ce jour-là et qui, depuis, se poursuit autour des thèmes qu’elle sait si bien cerner et auxquels elle apporte toujours, à la fois, toute sa rigueur critique et toute sa créativité théorique. Je voudrais donc que l’article qui suit soit un des moments de ce dialogue – de ce dialogue et de cet échange amical que j’entretiens avec Andrée Lajoie et qui, sous toutes ses formes, se prolonge – pour mon plus grand plaisir et mon plus grand profit – depuis maintenant plus de quinze ans

Les principes généraux du droit français de la fonction publique

In France, public service rests upon the fundamental rule of the specialization of the law applicable to public servants. This entails that public servants are given a special status that singles them out from others in the other economic or social sectors. That special legal status of the French public service is however being diminished under the influence of external factors. Economic factors tend to subject public servants to the general law of labour contracts. Political factors tend to give public servants the complete enjoyment of fundamental rights and civil liberties. Finally, administrative factors such as policies favouring mobility and promotion tend to lessen the importance of rigid classification and grading. On the eve of major statutory changes in the law of the public service in Québec, Professor Timsit’s study provides an interesting comparative viewpoint

Helical Chirality: a Link between Local Interactions and Global Topology in DNA

DNA supercoiling plays a major role in many cellular functions. The global DNA conformation is however intimately linked to local DNA-DNA interactions influencing both the physical properties and the biological functions of the supercoiled molecule. Juxtaposition of DNA double helices in ubiquitous crossover arrangements participates in multiple functions such as recombination, gene regulation and DNA packaging. However, little is currently known about how the structure and stability of direct DNA-DNA interactions influence the topological state of DNA. Here, a crystallographic analysis shows that due to the intrinsic helical chirality of DNA, crossovers of opposite handedness exhibit markedly different geometries. While right-handed crossovers are self-fitted by sequence-specific groove-backbone interaction and bridging Mg2+ sites, left-handed crossovers are juxtaposed by groove-groove interaction. Our previous calculations have shown that the different geometries result in differential stabilisation in solution, in the presence of divalent cations. The present study reveals that the various topological states of the cell are associated with different inter-segmental interactions. While the unstable left-handed crossovers are exclusively formed in negatively supercoiled DNA, stable right-handed crossovers constitute the local signature of an unusual topological state in the cell, such as the positively supercoiled or relaxed DNA. These findings not only provide a simple mechanism for locally sensing the DNA topology but also lead to the prediction that, due to their different tertiary intra-molecular interactions, supercoiled molecules of opposite signs must display markedly different physical properties. Sticky inter-segmental interactions in positively supercoiled or relaxed DNA are expected to greatly slow down the slithering dynamics of DNA. We therefore suggest that the intrinsic helical chirality of DNA may have oriented the early evolutionary choices for DNA topology

The population-attributable fraction for time-dependent exposures and competing risks - A discussion on estimands

The population-attributable fraction (PAF) quantifies the public health impact of a harmful exposure. Despite being a measure of significant importance an estimand accommodating complicated time-to-event data is not clearly defined. We discuss current estimands of the PAF used to quantify the public health impact of an internal time-dependent exposure for data subject to competing outcomes. To overcome some limitations, we proposed a novel estimand which is based on dynamic prediction by landmarking. In a profound simulation study, we discuss interpretation and performance of the various estimands and their estimators. The methods are applied to a large French database to estimate the health impact of ventilator-associated pneumonia for patients in intensive care.Comment: A revision has been submitte

The population-attributable fraction for time-dependent exposures using dynamic prediction and landmarking

The public health impact of a harmful exposure can be quantified by the population-attributable fraction (PAF). The PAF describes the attributable risk due to an exposure and is often interpreted as the proportion of preventable cases if the exposure could be extinct. Difficulties in the definition and interpretation of the PAF arise when the exposure of interest depends on time. Then, the definition of exposed and unexposed individuals is not straightforward. We propose dynamic prediction and landmarking to define and estimate a PAF in this data situation. Two estimands are discussed which are based on two hypothetical interventions that could prevent the exposure in different ways. Considering the first estimand, at each landmark the estimation problem is reduced to a time-independent setting. Then, estimation is simply performed by using a generalized-linear model accounting for the current exposure state and further (time-varying) covariates. The second estimand is based on counterfactual outcomes, estimation can be performed using pseudo-values or inverse-probability weights. The approach is explored in a simulation study and applied on two data examples. First, we study a large French database of intensive care unit patients to estimate the population-benefit of a pathogen-specific intervention that could prevent ventilator-associated pneumonia caused by the pathogen Pseudomonas aeruginosa. Moreover, we quantify the population-attributable burden of locoregional and distant recurrence in breast cancer patients.Comment: A revised version has been submitte

Anticholinergic therapy for acute asthma in children.

Inhaled anticholinergics as single agent bronchodilators (or in combination with beta(2)-agonists) are one of the several medications available for the treatment of acute asthma in children

Year in review in Intensive Care Medicine 2012. II: Pneumonia and infection, sepsis, coagulation, hemodynamics, cardiovascular and microcirculation, critical care organization, imaging, ethics and legal issues.

Journal ArticleSCOPUS: re.jSCOPUS: re.jinfo:eu-repo/semantics/publishe

Comparison of four skin preparation strategies to prevent catheter-related infection in intensive care unit (CLEAN trial): a study protocol for a randomized controlled trial

International audienceBackgroundCatheter-related infection is the third cause of infections in intensive care units (ICU), increasing the length of stay in ICU and hospital, mortality, and costs. Skin antisepsis is one of the most prevalent preventive measures. In this respect, it would appear preferable to recommend the use of alcoholic povidone iodine or chlorhexidine rather than aqueous povidone iodine. However, the data comparing chlorhexidine to povidone-iodine, both of them in alcoholic solutions, remain limited. Moreover, the benefits of enhanced cleaning prior to disinfection of skin that is not visibly soiled have yet to be confirmed in a randomized study.MethodsA prospective multicenter, 2×2 factorial, randomized-controlled, assessor-blind trial will be conducted in 11 intensive care units in six French hospitals. All adult patients aged over 18 years requiring the insertion of at least one peripheral arterial catheter and/or a non-tunneled central venous catheter and/or a hemodialysis catheter and/or an arterial pulmonary catheter will be randomly assigned to have all their catheters cared with one of four skin preparation strategies (2% chlorhexidine/70% isopropyl alcohol or 5% povidone iodine/69% ethanol with or without prior skin scrubbing). At catheter removal, catheter tips will be quantitatively cultured. Sets of aerobic and anaerobic blood cultures will be routinely obtained when a patient has fever, hypothermia, or other indications. In case of suspected catheter-related infection the patient's form will be reviewed by an independent adjudication committee. We plan to enroll 2,400 patients (4,800 catheters). The main objective is to demonstrate that use of 2% alcoholic chlorhexidine compared to 5% alcoholic povidone iodine in skin preparation lowers the rate of catheter-related infection. The second endpoint is to demonstrate that enhanced skin cleaning prior to disinfection of skin that is not visibly soiled does not reduce catheter colonization. Other outcomes include comparison of skin colonization at catheter insertion site, comparison of catheter colonization and catheter-related bacteremia taking place during implementation of the four strategies of skin preparation, and cutaneous tolerance, length of hospitalization, mortality, and costs.DiscussionThis study will help to update recommendations on the choice of an antiseptic agent to use in skin preparation prior to insertion of a vascular catheter and, by extension, of an epidural catheter and it will likewise help to update recommendations on the usefulness of skin scrubbing prior to disinfection when the skin is not visibly soiled.Trial registrationClinicaltrials.gov number NCT0162955