From dormant to germinating spores of Streptomyces coelicolor A3(2): new perspectives from the crp null mutant

The complete understanding of the morphological differentiation of streptomycetes is an ambitious challenge as diverse sensors and pathways sensitive to various environmental stimuli control the process. Germination occupies a particular position in the life cycle as the good achievement of the process depends on events occurring both during the preceding sporulation and during germination per se. The cyclic AMP receptor protein (crp) null mutant of Streptomyces coelicolor, affected in both sporulation and germination, was therefore presented as a privileged candidate to highlight new proteins involved in the shift from dormant to germinating spores. Our multidisciplinary approach-combining in vivo data, the analysis of spores morphological properties, and a proteome study-has shown that Crp is a central regulatory protein of the life cycle in S. coelicolor; and has identified spores proteins with statistically significant increased or decreased expression that should be listed as priority targets for further investigations on proteins that trigger both ends of the life cycle.     

Acetylation-dependent chromatin reorganization by BRDT,a testis-specific bromodomain-containing protein

The association between histone acetylation and replacement observed during spermatogenesis prompted us to consider the testis as a source for potential factors capable of remodelling acetylated chromatin. A systematic search of data banks for open reading frames encoding testis-specific bromodomain-containing proteins focused our attention on BRDT, a testis-specific protein of unknown function containing two bromodomains. BRDT specifically binds hyperacetylated histone H4 tail depending on the integrity of both bromodomains. Moreover, in somatic cells, the ectopic expression of BRDT triggered a dramatic reorganization of the chromatin only after induction of histone hyperacetylation by trichostatin A (TSA). We then defined critical domains of BRDT involved in its activity. Both bromodomains of BRDT, as well as flanking regions, were found indispensable for its histone acetylation-dependent remodelling activity. Interestingly, we also observed that recombinant BRDT was capable of inducing reorganization of the chromatin of isolated nuclei in vitro only when the nuclei were from TSA-treated cells. This assay also allowed us to show that the action of BRDT was ATP independent, suggesting a structural role for the protein in the remodelling of acetylated chromatin. This is the first demonstration of a large-scale reorganization of acetylated chromatin induced by a specific factor.     

Endothelial autophagic flux hampers atherosclerotic lesion development

Blood flowing in arteries generates shear forces at the surface of the vascular endothelium that control its anti-atherogenic properties. However, due to the architecture of the vascular tree, these shear forces are heterogeneous and atherosclerotic plaques develop preferentially in areas where shear is low or disturbed. Here we review our recent study showing that elevated shear forces stimulate endothelial autophagic flux and that inactivating the endothelial macroautophagy/autophagy pathway promotes a proinflammatory, prosenescent and proapoptotic cell phenotype despite the presence of atheroprotective shear forces. Specific deficiency in endothelial autophagy in a murine model of atherosclerosis stimulates the development of atherosclerotic lesions exclusively in areas of the vasculature that are normally resistant to atherosclerosis. Our findings demonstrate that adequate endothelial autophagic flux limits atherosclerotic plaque formation by preventing endothelial apoptosis, senescence and inflammation.     

Epileptogenesis caused by the kindling effect in diving at 3 ATA of air

The kindling effect is an experimental model of epilepsy which results from an intermittent application of focal electrical stimulations to certain regions of the brain. Generalized seizures are usually obtained after about fifteen stimulations of amygdala in the rat. We studied the kindling effect in hyperbaric-hyperoxic conditions. Eleven Wistar rats were stimulated daily in a caisson and all stimulations were delivered after 30 min of diving at 3 ATA of air. Diving inhibited kindling in half animals. In the others, which all presented generalised convulsions, diving produced a reduction in seizure duration, especially during the generalisation phase.     

Genetic analysis of phenotypic variation for ectomycorrhiza formation in an interspecific F1 poplar full-sib family

A plants capability to develop ectomycorrhizal symbiosis is under the control of both genetic and environmental factors. In order to determine the roles played by these different factors, we have performed a quantitative genetic analysis of the ability of poplar trees to form ectomycorrhizas. Quantitative genetics were applied to an interspecific family of poplar for which the two parental genetic maps had already been described, and for which data analyses concerning fungal aggressors were obtained. Quantitative trait loci (QTL) related to ectomycorrhiza formation were identified and located in the genetic maps of the two parents. One QTL was located at a linkage group of the genetic map of Populus trichocarpa showing a high concentration of several QTL involved in the pathogenic interaction with the fungus Melampsora larici-populina, the causal agent of leaf rust.     

Variation in the ability to form ectomycorrhizas in the F1 progeny of an interspecific poplar (Populus spp.) cross

The aim of this study was to determine the existence of a genetic basis for the ability to form ectomycorrhiza on a model angiosperm tree (Populus, poplar). Parental clones and 18 progeny from a controlled interspecific cross between Populus deltoides and Po- pulus trichocarpa were grown in a glasshouse and inoculated with mycelium of the ectomycorrhizal fungus Laccaria bicolor. Three months after inoculation, the percentage of mycorrhizal root tips was determined for each inoculated plant. The data indicate variability in the ability to form ectomycorrhizas among the F1 progeny, including individual progeny which are different to either parent. This suggests a genetic basis for mycorrhiza formation. Accepted: 6 November 2000     

Approche ph��nom��nologique du n��ant

In this article, we address the issue of nothingness on the basis of perceptive experience in its phenomenological dimension. Through an analysis of the visual perception and various types of memories related to it, we will try to answer three questions: what is phenomenological nothingness? What role does it play in the emergence of determinations within the consciousness? What are its relationships with disappearance and forgetting involved in all the stages of object donation in consciousness?