Localized DNA Demethylation at Recombination Intermediates during Immunoglobulin Heavy Chain Gene Assembly

Multiple epigenetic marks have been proposed to contribute to the regulation of antigen receptor gene assembly via V(D)J recombination. Here we provide a comprehensive view of DNA methylation at the immunoglobulin heavy chain (IgH) gene locus prior to and during V(D)J recombination. DNA methylation did not correlate with the histone modification state on unrearranged alleles, indicating that these epigenetic marks were regulated independently. Instead, pockets of tissue-specific demethylation were restricted to DNase I hypersensitive sites within this locus. Though unrearranged diversity (DH) and joining (JH) gene segments were methylated, DJH junctions created after the first recombination step were largely demethylated in pro-, pre-, and mature B cells. Junctional demethylation was highly localized, B-lineage-specific, and required an intact tissue-specific enhancer, Eμ. We propose that demethylation occurs after the first recombination step and may mark the junction for secondary recombination

Analysis of Mice Lacking DNaseI Hypersensitive Sites at the 5′ End of the IgH Locus

The 5′ end of the IgH locus contains a cluster of DNaseI hypersensitive sites, one of which (HS1) was shown to be pro-B cell specific and to contain binding sites for the transcription factors PU.1, E2A, and Pax5. These data as well as the location of the hypersensitive sites at the 5′ border of the IgH locus suggested a possible regulatory function for these elements with respect to the IgH locus. To test this notion, we generated mice carrying targeted deletions of either the pro-B cell specific site HS1 or the whole cluster of DNaseI hypersensitive sites. Lymphocytes carrying these deletions appear to undergo normal development, and mutant B cells do not exhibit any obvious defects in V(D)J recombination, allelic exclusion, or class switch recombination. We conclude that deletion of these DNaseI hypersensitive sites does not have an obvious impact on the IgH locus or B cell development

AID-Targeting and Hypermutation of Non-Immunoglobulin Genes Does Not Correlate with Proximity to Immunoglobulin Genes in Germinal Center B Cells

Upon activation, B cells divide, form a germinal center, and express the activation induced deaminase (AID), an enzyme that triggers somatic hypermutation of the variable regions of immunoglobulin (Ig) loci. Recent evidence indicates that at least 25% of expressed genes in germinal center B cells are mutated or deaminated by AID. One of the most deaminated genes, c-Myc, frequently appears as a translocation partner with the Ig heavy chain gene (Igh) in mouse plasmacytomas and human Burkitt's lymphomas. This indicates that the two genes or their double-strand break ends come into close proximity at a biologically relevant frequency. However, the proximity of c-Myc and Igh has never been measured in germinal center B cells, where many such translocations are thought to occur. We hypothesized that in germinal center B cells, not only is c-Myc near Igh, but other mutating non-Ig genes are deaminated by AID because they are near Ig genes, the primary targets of AID. We tested this “collateral damage” model using 3D-fluorescence in situ hybridization (3D-FISH) to measure the distance from non-Ig genes to Ig genes in germinal center B cells. We also made mice transgenic for human MYC and measured expression and mutation of the transgenes. We found that there is no correlation between proximity to Ig genes and levels of AID targeting or gene mutation, and that c-Myc was not closer to Igh than were other non-Ig genes. In addition, the human MYC transgenes did not accumulate mutations and were not deaminated by AID. We conclude that proximity to Ig loci is unlikely to be a major determinant of AID targeting or mutation of non-Ig genes, and that the MYC transgenes are either missing important regulatory elements that allow mutation or are unable to mutate because their new nuclear position is not conducive to AID deamination

LES PROTOCOLES IMMUNOSUPPRESSEURS EN TRANSPLANTATION CARDIAQUE ET PULMONAIRE.DEUX CAS PARTICULIERS D'ADAPTATION

CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocSudocFranceF

Influence of cement type on transport properties and chemical degradation: application to nuclear waste storage

International audienceThe geological repository of nuclear waste in concrete containers is a possible storage method explored by ANDRA (Agence Nationale pour la gestion des Déchets RAdioactifs). The concrete must display a high confinement capacity for long periods, characterized by transport properties and by the acido-basic buffer of hydrated cement. During service life, these properties can be endangered by chemical attack of underground water. The cement type has an important influence on the concrete's performances. Then, it is essential to establish appropriate mixtures and select accurate components. In this work an ordinary Portland cement and fly ash and blast furnace slag blended cement are compared. To determine confinement capacities, transfer properties and mortars pore size distributions were investigated. To predict the long term structure behavior, an ammonium nitrate test has been developed to enhance decalcification and to accelerate hydrolysis of cementitious materials. Measurement of degraded depth with time regarding calcium content was carried out. Impact of decalcification on transport properties was evaluated. Fly ash and blast furnace slag provide better properties for native mortars, and more principally diffusion properties, but not as much as necessary to limit leaching in degraded material by chemical attack. Keywords: Fly ash, blast furnace slag, gas permeability, chloride diffusion, mercury intrusion porosimetry, ammonium nitrate degradation. Résumé : Le stockage de déchets radioactifs en formation géologique profonde est une voie d'investigation de l'ANDRA (Agence Nationale pour la gestion des Déchets RAdioactifs). La barrière ouvragée cimentaire doit assurer une capacité de confinement pendant de longues périodes, caractérisée par ses propriétés de transfert et le maintien du tampon acido-basique du ciment hydraté. Pendant la durée de service de l'ouvrage, ces propriétés sont modifiées par l'attaque acide des eaux souterraines. La nature du ciment influençant majoritairement les performances du béton, il apparaît essentiel de sélectionner les composants adéquats pour établir des formulations performantes. Dans cette étude les performances en terme de durabilité d'un ciment Portland ordinaire et un ciment aux cendres volantes et aux laitiers sont comparées. 2 /22 Les propriétés de transfert et la microstructure des mortiers sont mesurées pour en évaluer les capacités de confinement. Afin d'estimer le comportement à long terme de la structure, un essai de dégradation par le nitrate d'ammonium a été développé pour accélérer la décalcification des matériaux cimentaires. L'évolution de l'épaisseur dégradée au cours de l'attaque ramenée à la teneur en calcium est suivie. L'impact de la décalcification sur les propriétés de transfert est évalué. Les cendres volantes et les laitiers semblent améliorer les propriétés des mortiers, notamment en terme de diffusion, mais pas assez pour résister à l'attaque chimique

Influence of cement type on transport properties and chemical degradation: application to nuclear waste storage

International audienceThe geological repository of nuclear waste in concrete containers is a possible storage method explored by ANDRA (Agence Nationale pour la gestion des Déchets RAdioactifs). The concrete must display a high confinement capacity for long periods, characterized by transport properties and by the acido-basic buffer of hydrated cement. During service life, these properties can be endangered by chemical attack of underground water. The cement type has an important influence on the concrete's performances. Then, it is essential to establish appropriate mixtures and select accurate components. In this work an ordinary Portland cement and fly ash and blast furnace slag blended cement are compared. To determine confinement capacities, transfer properties and mortars pore size distributions were investigated. To predict the long term structure behavior, an ammonium nitrate test has been developed to enhance decalcification and to accelerate hydrolysis of cementitious materials. Measurement of degraded depth with time regarding calcium content was carried out. Impact of decalcification on transport properties was evaluated. Fly ash and blast furnace slag provide better properties for native mortars, and more principally diffusion properties, but not as much as necessary to limit leaching in degraded material by chemical attack. Keywords: Fly ash, blast furnace slag, gas permeability, chloride diffusion, mercury intrusion porosimetry, ammonium nitrate degradation. Résumé : Le stockage de déchets radioactifs en formation géologique profonde est une voie d'investigation de l'ANDRA (Agence Nationale pour la gestion des Déchets RAdioactifs). La barrière ouvragée cimentaire doit assurer une capacité de confinement pendant de longues périodes, caractérisée par ses propriétés de transfert et le maintien du tampon acido-basique du ciment hydraté. Pendant la durée de service de l'ouvrage, ces propriétés sont modifiées par l'attaque acide des eaux souterraines. La nature du ciment influençant majoritairement les performances du béton, il apparaît essentiel de sélectionner les composants adéquats pour établir des formulations performantes. Dans cette étude les performances en terme de durabilité d'un ciment Portland ordinaire et un ciment aux cendres volantes et aux laitiers sont comparées. 2 /22 Les propriétés de transfert et la microstructure des mortiers sont mesurées pour en évaluer les capacités de confinement. Afin d'estimer le comportement à long terme de la structure, un essai de dégradation par le nitrate d'ammonium a été développé pour accélérer la décalcification des matériaux cimentaires. L'évolution de l'épaisseur dégradée au cours de l'attaque ramenée à la teneur en calcium est suivie. L'impact de la décalcification sur les propriétés de transfert est évalué. Les cendres volantes et les laitiers semblent améliorer les propriétés des mortiers, notamment en terme de diffusion, mais pas assez pour résister à l'attaque chimique

Optical GEO Feeder Link Design

Abstract: Telecommunication satellites must follow the advances of terrestrial network capacities and increase their total throughputs in order to remain competitive. This paper shows how the terrestrial fibre technology at 1550-nm wavelength can be extended to support an optical feeder link between ground and a GEO satellite. With 100 Gb/s in a single direction, an optical uplink would outperform the near-term Ka-band systems. Mitigation techniques against clouds and turbulence are described. The impact of satellite transparency on the optical transmission system is discussed. To increase the profitability of the optical solution, cost and link availability associated with various ground station networks should be carefully assessed

Matrix regulation of skeletal cell apoptosis. Role of calcium and phosphate ions

Previously, we noted that inorganic phosphate (Pi), a major component of bone extracellular matrix, induced osteoblast apoptosis (Meleti, Z., Shapiro, I. M., and Adams, C. S. (2000) Bone (NY) 27, 359-366). Since Ca2+ along with Pi is released from bone during the resorption process, we advanced the hypothesis that Ca2+ modulates Pi-mediated osteoblast apoptosis. To test this hypothesis, osteoblasts were incubated with both ions, and cell death was determined. We noted that a modest increase in the medium Ca2+ concentrations ([Ca2+]e) of 0.1-1 mm caused a profound and rapid enhancement in Pi-dependent death of cultured osteoblasts. An elevation in [Ca2+]e alone had no effect on osteoblast viability, whereas Ca2+ channel blockers failed to inhibit killing of ion pair-treated cells. These results indicated that Pi-mediated cell death is not dependent on a sustained increase in the cytosolic Ca 2+ concentration. Terminal dUTP nick-end labeling analysis and measurement of caspase-3 activity of the ion pair-treated cells suggested that death was apoptotic. Apoptosis was confirmed using caspase-3 and endonuclease inhibitors. The mitochondrial membrane potential and cytosolic Ca2+ status of the treated cells were evaluated. After incubation with [Ca 2+]e and Pi, a decrease in mitochondrial fluorescence was noted, suggesting that the ions decreased the mitochondrial transmembrane potential. Subsequent to the fall in mitochondrial membrane potential, there was a transient elevation in the cytosolic Ca2+ concentration. Results of the study suggest that the ion pair conspire at the level of the plasma membrane to induce intracellular changes that result in loss of mitochondrial function. The subsequent increase in the cytosolic Ca 2+ concentration may trigger downstream events that transduce osteoblast apoptosis