Cohesin regulates homology search during recombinational DNA repair.

Homologous recombination repairs DNA double-strand breaks (DSB) using an intact dsDNA molecule as a template. It entails a homology search step, carried out along a conserved RecA/Rad51-ssDNA filament assembled on each DSB end. Whether, how and to what extent a DSB impacts chromatin folding, and how this (re)organization in turns influences the homology search process, remain ill-defined. Here we characterize two layers of spatial chromatin reorganization following DSB formation in Saccharomyces cerevisiae. Although cohesin folds chromosomes into cohesive arrays of ~20-kb-long chromatin loops as cells arrest in G2/M, the DSB-flanking regions interact locally in a resection- and 9-1-1 clamp-dependent manner, independently of cohesin, Mec1ATR, Rad52 and Rad51. This local structure blocks cohesin progression, constraining the DSB region at the base of a loop. Functionally, cohesin promotes DSB-dsDNA interactions and donor identification in cis, while inhibiting them in trans. This study identifies multiple direct and indirect ways by which cohesin regulates homology search during recombinational DNA repair.

Infrared thermography investigation of an evaporating sessile water droplet on heated substrates.

The present study is an experimental investigation of the thermal evolution of millimeter-sized sessile water droplets deposited on heated substrates. Infrared thermography is used to record temperature profiles on the droplet interface in time as evaporation takes place. The local measurements of the interface temperature allowed us to deduce the local evaporation rate and its evolution in time. To our knowledge, this is the first time that such measurements have been performed. The deduced evaporation rate using thermography data has been validated with optical measurements. Temperature evolution is used to reveal the contact line location and transient temperature fields. Temperature differences between the apex of the droplet and the contact line are shown to decrease in time. The rate of local temperature increase at the interface is found to behave linearly with time. The slope of this linear increase turns out to be more pronounced as the substrate temperature is increased. A generalized linear trend, using dimensionless properties for the interface temperature rise, is deduced from the measurements.

Influence of substrate heating on the evaporation dynamics of pinned water droplets.

The dynamics of evaporating water droplets deposited on a heated substrate is investigated numerically. Droplets are pinned with a contact line radius of R = 1 mm. Evaporative mass flow and convection occurring inside the droplets are studied for different heating substrate sizes L S and heating temperatures T S. A simplified model neglecting hydrodynamics in air and evaporative cooling and assuming droplets to be spherical caps is simulated with a finite element method. A toruslike convective cell appears inside the droplets as evaporation takes place. For L S/ R > 1, the contact line is warmer than the apex of the droplets, and convection generates a downstream flow in the vicinity of the symmetry axis of the droplets. For L S/ R < 1, it is the apex that is warmer. Convection then generates an upstream flow. The overall evaporation time is described. It slows when L S/ R > 1.

Evaporation and Marangoni driven convection in small heated water droplets.

Evaporation dynamics of small sessile water droplets under microgravity conditions is investigated numerically. The water-air interface is free, and the surrounding air is assumed to be quasisteady. The droplet is described by Navier-Stokes and heat equations and its surrounding water/air gaseous phase with Laplace equation. In the thermodynamic conditions of the simulations presented herein, the evaporative mass flow is nonlinear. It shows a minimum that indicates the existence of qualitative changes in the evaporative regimes although the droplet is sessile. Due to temperature gradients on the free interface, Marangoni motion occurs and generates inside the droplet convection cells that furthermore exhibit small fluctuating motion as evaporation goes on.

Inhibition of crotoxin phospholipase A(2) activity by manoalide associated with inactivation of crotoxin toxicity and dissociation of the heterodimeric neurotoxic complex.

Crotoxin (CACB complex) is a convulsant heterodimeric neurotoxic phospholipase A(2) (PLA(2)). The role of phospholipid hydrolysis in its epileptogenic properties remains unresolved. We, thus, studied the effect of manoalide (MLD), a PLA(2) inhibitor, on the toxin catalytic activity and its central and peripheral toxicity. Incubation of crotoxin with MLD fully and irreversibly inactivated its enzymatic activity. Interestingly, crotoxin also lost its central neurotoxicity after intracerebroventricular injection and peripheral toxicity after intravenous administration. MLD-treated crotoxin prevented the high affinity binding of [125I]-radiolabeled crotoxin on rat cortex synaptic plasma membranes. Further analysis of MLD-treated crotoxin by non-denaturing PAGE and surface plasmon resonance indicated that the crotoxin complex was dissociated after MLD treatment. Although the loss of MLD-treated crotoxin peripheral neurotoxicity could not be attributed to this dissociation, the presence of free CA subunit might explain the observed competition in binding experiments. In conclusion, the dissociation of the crotoxin complex by MLD, as demonstrated in this study, did not permit to specify the role of the enzymatic activity in crotoxin epileptogenic properties. Other approaches would be required to resolve this question.