Isolation of Cell Nuclei Using Inert Macromolecules to Mimic the Crowded Cytoplasm

Cell nuclei are commonly isolated and studied in media which include millimolar concentrations of cations, which conserve the nuclear volume by screening the negative charges on chromatin and maintaining its compaction. However, two factors question if these ionic conditions correctly reproduce the environment of nuclei in vivo: the small-scale motion and conformation of chromatin in vivo are not reproduced in isolated nuclei, and experiments and theory suggest that small ions in the cytoplasm are not free in the soluble phase but are predominantly bound to macromolecules. We studied the possible role in maintaining the structure and functions of nuclei in vivo of a further but frequently overlooked property of the cytoplasm, the crowding or osmotic effects caused by diffusible macromolecules whose concentration, measured in several studies, is in the range of 130 mg/ml. Nuclei which conserved their volume in the cell and their ultrastructure seen by electron microscopy were released from K562 cells in media containing the inert polymer 70 kDa Ficoll (50% w/v) or 70 kDa dextran (35% w/v) to replace the diffusible cytoplasmic molecules which were dispersed on cell lysis with digitonin, with 100 µM K-Hepes buffer as the only source of ions. Immunofluorescence labelling and experiments using cells expressing GFP-fusion proteins showed that internal compartments (nucleoli, PML and coiled bodies, foci of RNA polymerase II) were conserved in these nuclei, and nascent RNA transcripts could be elongated. Our observations are consistent with the hypothesis that crowding by diffusible cytoplasmic macromolecules is a crucial but overlooked factor which supports the nucleus in vivo by equilibrating the opposing osmotic pressure cause by the high concentration of macromolecules in the nucleus, and suggest that crowded media provide more physiological conditions to study nuclear structure and functions. They may also help to resolve the long-standing paradox that the small-scale motion and irregular conformation of chromatin seen in vivo are not reproduced in nuclei isolated in conventional ionic media

What Drives Stock Market Development in Arab Countries?

Arab stock exchanges have witnessed tremendous growth in recent decades, and the number of listed companies and the size of stock market capitalization have increased. In the light of this remarkable growth, this study aims to find out what are the most important determinants and economic factors affecting this development during the period 2006– 2017. By employing panel data models, we find that trade openness; market liquidity, money supply and economic growth have positive impacts on stock market development, whereas the global financial crisis has negative impact. Based on these results, measures should be taken to improve market liquidity, control of money supply, and maintain a balanced economic growth rate to promote the development of Arab stock exchanges. Policy recommendations are provided based on these findings

Driving factors of the potentially toxic and harmful species of Prorocentrum Ehrenberg in a semi-enclosed Mediterranean lagoon (Tunisia, SW Mediterranean)

We analysed the dynamics of the potentially toxic and harmful species of Prorocentrum Ehrenberg in Bizerte lagoon (important aquaculture area, Northern Tunisia), substantiating the possible driving forces (temperature, salinity and nutrients), based on a two years database. We revealed that Prorocentrum spp. blooms of high magnitude (104 - 105 cells l-1) occurred mostly during the period of late winter to early spring. We found five species of Prorocentrum, two of which, P. lima and P. cordatum, the most common during the field, are confirmed agents of Diarrhetic Shellfish Poisoning in various regions of the world ocean. Prorocentrum sp., P. micans, and P. gracile were however present only sporadically but with high cell abundances, exemplifying bloom densities. Canonical correspondence analysis revealed that P. minimum and P. lima were much more abundant in eutrophied waters characterized here by high Chl a biomass, while P. gracile species occurred principally in warm waters. Furthermore, Prorocentrum sp. and P. micans seemed more likely to proliferate in saline waters with high concentrations of inorganic nutrients (nitrate, ammonia and phosphate). Our study calls attention to a possible intensification of DSP events in the Bizerte lagoon, given the propensity of Prorocentrum spp. to proliferate in a eutrophied system

Spectral Composition of Sunlight Affects the Microbial Functional Structure of Beech Leaf Litter During the Initial Phase of Decomposition

Aims This study tests whether different spectral regions of sunlight affect the microbial decomposer assemblage in surface leaf litter in a beech understorey over the first 6 months following leaf senescence. Methods We performed a litterbag experiment employing filters attenuating combinations of UV-B, UV-A, blue, and green light as well as the whole spectrum of sunlight. We measured changes in microbial biomass and community structure, litter mass loss and litter chemistry during the first 6 months of decomposition. Results Fungal and total microbial biomass were highest in the treatment excluding UV radiation, blue and green light. Exclusion of UV-B radiation decreased the fungal:bacterial biomass ratio and litter nitrogen content. Bacterial biomass was lower in the dark treatment compared to treatments receiving at least part of the solar spectrum. Our filter treatments affected microbial functional structure from the beginning of the experiment, whereas mass loss was only significantly affected after 6 months of decomposition and no effect was found on litter carbon content. Conclusions This study proves that sunlight, in a spectrally dependent manner, affects both microbial functional structure and biomass in temperate deciduous forests early in the decomposition process, with bacteria tending to dominate in sunlight and fungi in dark conditions. We found sunlight to be important in the decomposition in temperate forest understoreys despite the low irradiance characterizing these environments. However, long-term studies are required to estimate the relative contribution of sunlight among factors affecting the eventual incorporation of decomposing leaf litter into forest soils.Peer reviewe

Etude de proprietes thermiques de cristaux-liquides par deflexion photothermique

SIGLEINIST T 73558 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Cinetique reactionnelle en regime hydrodynamique dans l'oxygene: application a la production industrielle de l'ozone

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 78746 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Le critere d'appartenance a un certain groupe social dans la Convention Relative au Statut des Refugies de 1951

The need for a clear definition of the concept of a "refugee" arose with compelling urgency in the wake of the marked intensification in the flow of refugees that followed the Second World War. The 1951 Convention relating to the Status of Refugees responded to this exigency: providing criteria which make it possible to identify those individuals who could be classified as refugees. The Convention limits the recognition of refugee status to those individuals who "have a well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group or political opinion." Unlike the other criteria, the meaning of "membership of a particular social group" remains obscure. Since 1951, court judgements and scholarly publications have supplied various interpretations of this criterion: manifesting the need to have a clear definition so as to avoid weakening the very notion of a refugee. In this article Benbernou addresses the need to define this criterion 121 by analysing: (a) the historical evolution of the concept; (b) various theoretical interpretations; and (c) court judgements. Thus the author constructs a clear definition of this concept that highlights its progressive function, since it is the only criterion that can accommodate new situations that were not envisaged by the drafters of the Convention. The ejusdem generis theory is seen as providing the best interpretation of this criterion that satisfies scientific rigour as well as humanitarian exigencies. There is persecution motivated by "membership of a particular social group" when what are threatened are characteristics that are innate, immutable or such an intrinsic aspect of group identity, that forcing members to renounce to them would constitute a violation of their fundamental human rights.peer-reviewe

Etude de composites à base de nanotubes de carbone par la radiométrie photothermique infrarouge

Ce travail concerne l'étude des paramètres thermiques et électriques de matériaux composites. Nous avons développé différentes procédures autour de la radiométrie photothermique infrarouge qui permettent de mesurer avec précision l'ensemble des paramètres thermiques de tout type de matériau solide quelque soit sa nature. Ces procédures ont été développées à partir de l'expression de la température de surface de l'échantillon analysé. Elles permettent la détermination des paramètres thermiques de manière analytique sans recourir à une procédure d'ajustement numérique. Pour chacune des procédures propose es, une étude théorique a permis d'évaluer la précision sur la détermination des paramètres thermiques en fonction des différents paramètres expérimentaux. La sensibilité du signal aux paramètres thermiques a également été étudiée. Les méthodologies mises au point permettent d'étudier le comportement thermique à une température donnée ou en fonction de la température. Une partie de ce travail a porté sur la validation expérimentale de ces procédures par la mesure des paramètres thermique de divers échantillons : un carbone vitreux, un tantalate de lithium, une céramique PZT. L'évolution des paramètres thermiques de certains de ces échantillons a également été étudiée en fonction de la température. La dernière partie de ce travail a été consacrée à étudier le comportement thermique et électrique de composites à base de nanotubes de carbone. Après avoir passé en revue les caractéristiques physiques des nanotubes et de leurs applications, nous avons étudié l'évolution des paramètres thermiques de composites KBr/ nanotubes de carbone en fonction de leur concentration en nanotubes de carbone. La conductivité électrique de ces composites a été étudiée à l'aide de la méthode des 4 points et comparée au comportement thermique. Bien qu'une percolation électrique soit observée, aucune percolation thermique n'est à relever. Différentes hypothèses ont été formulées afin d'expliquer ce comportement. Plusieurs modèles disponibles dans la littérature ont été utilisés afin de modéliser et de comprendre les comportements électrique et thermique de ces composites.This work relates to the study of the thermal and electrical parameters of composites materials. We have developed various procedures around the infrared radiometry which make it possible to measure with precision all thermal parameters of any type of solids materials. These procedures were developed starting from the expression of the surface temperature of the analyzed sample. They allow the determination of the thermal parameters in an analytical way without resorting to a procedure of numerical adjustment. For each procedure suggested, a theoretical study evaluate the precision on the determination of the thermal parameters function of the various experimental parameters. The sensitivity of the signal to the thermal parameters was also studied. The methodologies developped make it possible to study the thermal behavior at a given temperature or according to the temperature. Part of this work is devoted to the experimental validation of these procedures by the measurement of the thermal parameters of various samples : vitreous carbon, lithium tantalate, PZT ceramic. The evolution of the thermal parameters of some of these samples was also studied according to the temperature. The last part of this work was devoted to study the thermal and electrical behavior of carbon nanotubes based composites. After having reviewed the physical characteristics of the nanotubes and their applications, we have studied the evolution of the thermal parameters of KBr/carbon nanotubes composites according to their concentration in carbon nanotubes. The electrical conductivity of these composites was studied using the four points prob method and was compared with the thermal behavior. Although an electrical percolation is observed, no thermal percolation is noted. Various assumptions were formulated in order to explain this behavior. Several models available in the literature were used in order to model and to understand the electrical and thermal behavior of these composites.DUNKERQUE-BU Lettres Sci.Hum. (591832101) / SudocSudocFranceF