Çédille, revista de estudios franceses

Presentació

Hairpins in a DNA site for topoisomerase II studied by 1H- and 31P-NMR.

1H- and 31P-NMR and UV-absorption studies were carried out with the oligonucleotide strands d(AGCT-TATC-ATC-GATAAGCT) (-ATC-) and d(AGCTTATC-GAT-GATAAGCT) (-GAT-) contained in the strongest and salt resistant cleavage site for topoisomerase II in pBR322 DNA. We found that the two oligonucleotides were stabilized under a hairpin structure characterized by a eight base pair stem and a three base loop at low DNA and salt concentrations. In such experimental conditions, only the -GAT- oligonucleotide displayed a partial homoduplex structure in slow equilibrium with its folded structure. Temperature dependencies of imino protons showed that the partial homoduplex of -GAT- melted at a lower temperature than the hairpin structure. It was suggested that the appearance of the partial homoduplex in -GAT- is related to the formation of two stabilizing (G.T) mismatched base pairs in the central loop of this structure. Finally, it was inferred from the dispersion of chemical shifts in the 31P-NMR spectra that the distortions affecting the backbone of the hairpin loop are larger in the case of -ATC- compared with -GAT-. At the same time NOEs proved that the base stacking was stronger within the loop of the -ATC- hairpin

Effects of a germ-free environment on gut immune regulation and diabetes progression in non-obese diabetic (NOD) mice

Aims/hypothesisMicrobial factors influence the development of diabetes in NOD mice. Studies in germ-free animals have revealed important roles of microbiota in the regulation of Th17 and forkhead box P3 (FOXP3)(+) T regulatory (Treg) activation in the intestine. However, the effects of intestinal microbiota in immune regulation and diabetes development in NOD mice are still poorly understood.MethodsA colony of germ-free NOD mice was established to evaluate the effects of intestinal microbiota on regulatory immunity in the gut, and on the development of insulitis and diabetes in NOD mice.ResultsDiabetes developed in roughly equal numbers in germ-free and specific pathogen-free NOD mice. Insulitis was accentuated in germ-free NOD mice; yet insulin preservation was unaltered. Germ-free NOD mice showed increased levels of Il17 (also known as Il17a) mRNA in the colon, and of Th17 and Th1 cells in the mesenteric and pancreatic lymph nodes, while Foxp3 mRNA and FOXP3(+) Tregs were reduced. In the islet infiltrates, FOXP3(+)CD4(+) T cells were slightly increased in germ-free mice. B cells appeared less activated in the peritoneum and were less abundant in islet infiltrates.Conclusions/interpretationThese results indicate that lack of intestinal microbiota promotes an imbalance between Th1, Th17 and Treg differentiation in the intestine. This imbalance is associated with accelerated insulitis, but intact recruitment of FOXP3(+) Tregs into islets, suggesting: (1) a microbial dependence of local induction of Treg in the gut and draining lymph nodes; but (2) a potentially compensatory function of naturally occurring Tregs in the islets, which may help control diabetogenic T cells

CPMG measurements and ultrafast imaging in human lungs with hyperpolarized helium-3 at low field (0.1 T).

International audienceThis work reports the use of single-shot spin echo sequences to achieve in vivo diffusion gas measurements and ultrafast imaging of human lungs, in vivo, with hyperpolarized He-3 at 0.1 T. The observed transverse relaxation time of He-3 lasted up to 10 s, which made it possible to use long Carr-Purcelf-Meiboom-Gill echo trains. Preliminary NMR studies showed that the resolution of lung images acquired with hyperpolarized He-3 and single-shot sequences is limited to about 6 mm because of the diffusion of the gas in applied field gradients. Ultrafast images of human lungs in normal subjects, achieved in less than 0.4 s with the equivalent of only 130 mu mol of fully polarized He-3, are presented. Comparison with other studies shows that there is no SNR penalty by using low fields in the hyperpolarized case. Advantage was taken of the self diffusion-weighting of the rapid acquisition with relaxation enhancement (RARE) sequence to acquire apparent diffusion coefficient (ADC) images of the lungs. Time scales of seconds could be explored for the first time because there is no hindrance from T-2(star) as with the usual approaches. At 0.1 T, 180 degrees RF pulses can be repeated every 10 ms without exceeding specific absorption rate limits, which would not be the case for higher fields. Moreover, at low field, susceptibility-induced phenomena are expected to be milder. This supports the idea that low-field imagers can be used for hyperpolarized noble gas MRI of lungs and may be preferred for ADC measurements. Magn Reson Med 47:75-81, 2002. (C) 2002 Wiley-Liss, Inc

Gene Expression Profiling Reveals Clear Differences Between EBV-Positive and EBV-Negative Posttransplant Lymphoproliferative Disorders

Posttransplant patients are at risk of developing a potentially life-threatening posttransplantation lymphoproliferative disorder (PTLD), most often of diffuse large B cell lymphoma (DLBCL) morphology and associated with Epstein-Barr Virus (EBV) infection. The aim of this study was to characterize the clinicopathological and molecular-genetic characteristics of posttransplant DLBCL and to elucidate whether EBV(+) and EBV(-) posttransplant DLBCL are biologically different. We performed gene expression profiling studies on 48 DLBCL of which 33 arose posttransplantation (PT-DLBCL; 72% EBV+) and 15 in immunocompetent hosts (IC-DLBCL; none EBV+). Unsupervised hierarchical analysis showed clustering of samples related to EBV-status rather than immune status. Except for decreased T cell signaling these cases were inseparable from EBV(-) IC-DLBCL. In contrast, a viral response signature clearly segregated EBV(+) PT-DLBCL from EBV(-) PT-DLBCL and IC-DLBCL cases that were intermixed. The broad EBV latency profile (LMP1+/EBNA2+) was expressed in 59% of EBV(+) PT-DLBCL and associated with a more elaborate inflammatory response compared to intermediate latency (LMP1+/EBNA2-). Inference analysis revealed a role for innate and tolerogenic immune responses (including VSIG4 and IDO1) in EBV(+) PT-DLBCL. In conclusion we can state that the EBV signature is the most determining factor in the pathogenesis of EBV(+) PT-DLBCL.status: publishe