Magnetoencephalography demonstrates multiple asynchronous generators during human sleep spindles.

Sleep spindles are approximately 1 s bursts of 10-16 Hz activity that occur during stage 2 sleep. Spindles are highly synchronous across the cortex and thalamus in animals, and across the scalp in humans, implying correspondingly widespread and synchronized cortical generators. However, prior studies have noted occasional dissociations of the magnetoencephalogram (MEG) from the EEG during spindles, although detailed studies of this phenomenon have been lacking. We systematically compared high-density MEG and EEG recordings during naturally occurring spindles in healthy humans. As expected, EEG was highly coherent across the scalp, with consistent topography across spindles. In contrast, the simultaneously recorded MEG was not synchronous, but varied strongly in amplitude and phase across locations and spindles. Overall, average coherence between pairs of EEG sensors was approximately 0.7, whereas MEG coherence was approximately 0.3 during spindles. Whereas 2 principle components explained approximately 50% of EEG spindle variance, >15 were required for MEG. Each PCA component for MEG typically involved several widely distributed locations, which were relatively coherent with each other. These results show that, in contrast to current models based on animal experiments, multiple asynchronous neural generators are active during normal human sleep spindles and are visible to MEG. It is possible that these multiple sources may overlap sufficiently in different EEG sensors to appear synchronous. Alternatively, EEG recordings may reflect diffusely distributed synchronous generators that are less visible to MEG. An intriguing possibility is that MEG preferentially records from the focal core thalamocortical system during spindles, and EEG from the distributed matrix system.

Regulation of monocyte functional heterogeneity by miR-146a and Relb.

Monocytes serve as a central defense system against infection and injury but can also promote pathological inflammatory responses. Considering the evidence that monocytes exist in at least two subsets committed to divergent functions, we investigated whether distinct factors regulate the balance between monocyte subset responses in vivo. We identified a microRNA (miRNA), miR-146a, which is differentially regulated both in mouse (Ly-6C(hi)/Ly-6C(lo)) and human (CD14(hi)/CD14(lo)CD16(+)) monocyte subsets. The single miRNA controlled the amplitude of the Ly-6C(hi) monocyte response during inflammatory challenge whereas it did not affect Ly-6C(lo) cells. miR-146a-mediated regulation was cell-intrinsic and depended on Relb, a member of the noncanonical NF-κB/Rel family, which we identified as a direct miR-146a target. These observations not only provide mechanistic insights into the molecular events that regulate responses mediated by committed monocyte precursor populations but also identify targets for manipulating Ly-6C(hi) monocyte responses while sparing Ly-6Clo monocyte activity.

The alpha v beta 3 integrin as a tumor homing ligand for lymphocytes.

Despite the presence of tumor-specific effector cells in the circulation of cancer patients, the immune response of the majority of these patients is not sufficient to prevent the growth and spread of their tumors. That tumor cells can be killed in vitro by tumor-reactive cytotoxic T cells is testimony to the fact that the tumors are not inherently resistant to T cell killing, but rather that there is a failure in immune recognition and effector cell activation. Many reasons for this failure of the body's defense system have been suggested, including the inability of tumor-reactive lymphocytes to migrate to tumor tissue. Here we designed a strategy to improve homing of primary lymphocytes into vascularized tumors. As a homing molecule we selected the integrin alpha v beta 3 since it is expressed by angiogenic vascular endothelium in tumors. To promote lymphocyte adhesion to alpha v beta 3 we "painted" primary lymphocytes with a recombinant, glycosylphosphatidylinositol-linked high-affinity ligand for alpha v beta 3. These painted lymphocytes specifically bound to alpha v beta 3 in vitro and homed to vascularized, solid tumors in vivo. This novel strategy may provide a significant advance in anti-tumor treatment such as adoptive immune therapy.

Pathogenesis-related proteins and the jasmonate signaling pathway

Résumé Etant une importante source d'énergie, les plantes sont constamment attaquées par des pathogènes. Ne pouvant se mouvoir, elles ont développé des systèmes de défense sophistiqués afin de lutter contre ces prédateurs. Parmi ces systèmes, les voies de signalisation mettant en jeu des éliciteurs endog8nes tels que les jasmonates permettent d'induire la production de protéines de défense telles que les protéines dites "liées à la pathogénèse". Les gènes codant pour ces protéines appartiennent à des familles multigéniques. Le premier but de cette thèse est d'évaluer le nombre de ces gènes dans le génome d'Arabidopsis thaliana et d'estimer la part de ce système de défense, dépendant de la voie de signalisation des jasmonates. Nous avons défini un cluster de seulement 1S gènes sur 266, "liés à la pathogénèse", exclusivement régulés par les jasmonates. De multiples membres des familles des lectines de type jacaline et des inhibiteurs de trypsines semblent dépendre du jasmonate. Présente dans tous les systèmes immunitaires des eucaryotes, la famille des défensines est une famille très intéressante. Chez Arabidopsis thaliana, 317 protéines similaires aux défensines ont été définies, cependant seulement 15 défensines (PDF) sont bien annotées. Ces 15 défensines sont séparées en deux groupes dont un semble avoir évolué plus récemment. Le second but de cette thèse est d'étudier ce groupe de défensines à l'aide de la bioinformatique et des techniques de biologie moléculaire (gêne rapporteur, PCR en temps réel). Nous avons montré que ce groupe contenait une défensine acide intéressante, PDF1.5, qui semblait avoir subi une sélection positive. Cette protéine n'avait encore jamais été étudiée. Contrairement à ce que nous pensions, nous avons établi que cette protéine pouvait avoir une activité biologique liée à la défense. Ce travail de thèse a permis de préciser le nombre de gènes "liées à la pathogénèse" induits par la voie des jasmonates et d'apporter des éléments de réponse sur la question de la redondance des gènes de défense. En conclusion, même si de nombreuses familles de gènes intervenant dans la défense sont bien définies chez Arabidopsis, il reste encore de nombreuses études à faire sur chacun de ces membres. Abstract Being an important source of energy, plants are constantly attacked by herbivores and pathogens. As sessile organisms, they have developed sophisticated defense responses to cope with attack. Among these responses, signalling pathways, using endogenous elicitors including jasmonates (JA), allow the plant to induce the production of defense proteins such as pathogenesis-related (PR) proteins. The genes encoding these proteins belong to multigenic families. The first goal of this thesis was to evaluate the number of PR genes in the genome of Arabidopsis thaliana and estimate how much of this plant defense system was dependent on the jasmonate signaling pathway in leaves. Surprisingly a cluster of only 1S genes out of 2ó6 PR genes was exclusively regulated by JA. Multiple members of the jacalin lectin and trypsin inhibitor gene families were shown to be regulated by JA. Present in all eukaryotic immune systems, defensins are an attractive PR family to study. In Arabidopsis thaliana, 317 defensin-related proteins have been found but just 1S defensins (i.e. PDF family) are well annotated. These defensins are split into 2 groups. One of these groups may have appeared and diversified recently. The second goal of this thesis was to study this defensin gene group combining bioinformatic, reporter gene and quantitative PCR techniques. We have shown that this group contains an interesting acidic defensin, PDF1.S, which seems to have undergone positive selection. No information was known on this protein. We have established that this protein may have a biological activity in plant defense. This thesis allowed us to define the number of PR genes induced by the jasmonate pathway and gave initial leads to explain the redundancy of the PR genes in the genome of Arabidopsis. In conclusion, even if many defense gene families are already defined in the Arabidopsis genome, much work remains to be done on individual members.

A novel Nrf2-miR-29-desmocollin-2 axis regulates desmosome function in keratinocytes.

The Nrf2 transcription factor controls the expression of genes involved in the antioxidant defense system. Here, we identified Nrf2 as a novel regulator of desmosomes in the epidermis through the regulation of microRNAs. On Nrf2 activation, expression of miR-29a and miR-29b increases in cultured human keratinocytes and in mouse epidermis. Chromatin immunoprecipitation identified the Mir29ab1 and Mir29b2c genes as direct Nrf2 targets in keratinocytes. While binding of Nrf2 to the Mir29ab1 gene activates expression of miR-29a and -b, the Mir29b2c gene is silenced by DNA methylation. We identified desmocollin-2 (Dsc2) as a major target of Nrf2-induced miR-29s. This is functionally important, since Nrf2 activation in keratinocytes of transgenic mice causes structural alterations of epidermal desmosomes. Furthermore, the overexpression of miR-29a/b or knockdown of Dsc2 impairs the formation of hyper-adhesive desmosomes in keratinocytes, whereas Dsc2 overexpression has the opposite effect. These results demonstrate that a novel Nrf2-miR-29-Dsc2 axis controls desmosome function and cutaneous homeostasis.

Performance comparison of an active matrix flat panel imager, computed radiography system, and a screen-film system at four standard radiation qualities.

Four standard radiation qualities (from RQA 3 to RQA 9) were used to compare the imaging performance of a computed radiography (CR) system (general purpose and high resolution phosphor plates of a Kodak CR 9000 system), a selenium-based direct flat panel detector (Kodak Direct View DR 9000), and a conventional screen-film system (Kodak T-MAT L/RA film with a 3M Trimax Regular screen of speed 400) in conventional radiography. Reference exposure levels were chosen according to the manufacturer's recommendations to be representative of clinical practice (exposure index of 1700 for digital systems and a film optical density of 1.4). With the exception of the RQA 3 beam quality, the exposure levels needed to produce a mean digital signal of 1700 were higher than those needed to obtain a mean film optical density of 1.4. In spite of intense developments in the field of digital detectors, screen-film systems are still very efficient detectors for most of the beam qualities used in radiology. An important outcome of this study is the behavior of the detective quantum efficiency of the digital radiography (DR) system as a function of beam energy. The practice of users to increase beam energy when switching from a screen-film system to a CR system, in order to improve the compromise between patient dose and image quality, might not be appropriate when switching from screen-film to selenium-based DR systems.

Hypotensive effect of the active fragment derived from factor XII is mediated by an activation of the plasma kallikrein-kinin system.

Plasma protein fraction (PPF) contaminated by factor XII active fragment (XIIf) may cause hypotensive reactions when infused to patients. This study was planned to assess in conscious normotensive rats whether the blood pressure response to the factor XIIf is mediated by an activation of the plasma kallikrein-kinin system or by stimulation of prostaglandin synthesis. To test whether the factor XIIf-induced blood pressure fall is due partially to an enhanced generation of vasodilating prostaglandins, the blood pressure effect of XIIf (1 microgram i.v.) was investigated 15 min after treatment with indomethacin (5 mg i.v.), an inhibitor of cyclo-oxygenase. Factor XIIf reduced mean blood pressure similarly in indomethacin- and vehicle-treated rats (-23 +/- 4 mmHg, n = 5, and -23 +/- 5 mmHg, n = 4, respectively). Other rats received factor XIIf 15 min after depletion of circulating prekallikrein by the administration of dextran sulfate. Thirty minutes after a 0.25 mg i.v. dose of this agent, plasma prekallikrein activity averaged 0.12 +/- 0.015 mumol/min/ml (n = 6) as compared to 2.48 +/- 0.31 mumol/min/ml in control rats (n = 4, P less than .001). Factor XIIf decreased mean blood pressure by only 4 +/- 2 mm Hg in rats pretreated with dextran sulfate. Thus, it was possible to blunt the acute hypotensive effect of factor XIIf by depleting circulating prekallikrein, but not by inhibiting prostaglandin production. This strongly suggests that the blood pressure effects of factor XIIf is mediated by a stimulation of the plasma kallikrein-kinin system.

Detection and characterization of hydraulically active fractures in a carbonate aquifer: Results from self-potential, temperature and fluid conductivity logging along a 260-m-deep borehole in the Combioula hydrothermal system in the southwestern Swiss Alps

A geophysical and geochemical study has been conducted in a fractured carbonate aquifer located at Combioula in the southwestern Swiss Alps with the objective to detect and characterize hydraulically active fractures along a 260-m-deep borehole. Hydrochemical analyses, borehole diameter, temperature and fluid electrical conductivity logging data were integrated in order to relate electrokinetic self-potential signals to groundwater flow inside the fracture network. The results show a generally good, albeit locally variable correlation of variations of the self-potential signals with variations in temperature, fluid electrical conductivity and borehole diameter. Together with the hydrochemical evidence, which was found to be critical for the interpretation of the self-potential data, these measurements not only made it possible to detect the hydraulically active fractures but also to characterize them as zones of fluid gain or fluid loss. The results complement the available information from the corresponding litholog and illustrate the potential of electrokinetic self-potential signals in conjunction with temperature, fluid electrical conductivity and hydrochemical analyses for the characterization of fractured aquifers, and thus may offer a perspective for an effective quantitative characterization of this increasingly important class of aquifers and geothermal reservoirs.

The role of the hypothalamic kisspeptin/GPR54 system in the control of GnRH neurons

Summary : The hypothalamus represents less than 1 % of the total volume of the brain tissue, yet it plays a crucial role in endocrine regulations. Puberty is defined as a process leading to physical, sexual and psychosocial maturation. The hypothalamus is central to this process, via the activation of GnRH neurons. Pulsatile GnRH secretion, minimal during childhood, increases with the onset of puberty. The primary function of GnRH is to regulate the growth, development and function of testes in boys and ovaries in girls, by stimulating the pituitary gland secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Several factors contribute to the timing of puberty, including sex and ethnicity, genetics, dietary intake and energy expenditure. Kisspeptins constitute a family of small peptides arising from the proteolytic cleavage of metastin, a peptide with 54 amino acids initially purified from human placenta. These kisspeptins were the subject of much attention following their discovery because of their antimetastatic properties, but it was more recently that their determining role in the reproductive function was demonstrated. It was shown that kisspeptins are ligands of a receptor, GPR54, whose natural inactivating mutation in humans, or knockout in the mouse, lead to infertility. GnRH neurons play a pivotal role in the central regulation of fertility. Kisspeptin greatly increases GnRH release and GnRH neuron firing activity, but the neurobiological mechanisms for these actions are unknown. Gprotein-coupled receptor 54, the receptor for kisspeptin, is expressed by GnRH neurons as well as other hypothalamic neurons, suggesting that both direct and indirect effects are possible. In the first part of my thesis, we investigated a possible connection between the acceleration of sexual development induced by leptin and hypothalamic metastin neurons. However, the data generated by our preliminary experiments confirmed that the commercially available antibodies are non-specific. This finding constituted a major drawback for our studies, which relied heavily upon the neuroanatomical study of the hypothalamic metastinergic pathways to elucidate their sensitivity to exogenous leptin. Therefore, we decided to postpone any further in vivo experiment until a better antibody becomes available, and focused on in vitro studies to better understand the mechanisms of action of kisspeptins in the modulation of the activity of GnRH neurons. We used two GnRH-expressing neuronal cell lines to investigate the cellular and molecular mechanisms of action of metastin in GnRH neurons. We demonstrated that kisspeptin induces an early activation of the MAP kinase intracellular signaling pathway in both cell lines, whereas the SAP/JNK or the Akt pathways were unaffected. Moreover, we found an increase in GnRH mRNA levels after 6h of metastin stimulation. Thus, we can conclude that kisspeptin regulates GnRH neurons both at the secretion and the gene expression levels. The MAPK pathway is the major pathway activated by metastin in GnRH expressing neurons. Taken together, these data provide the first mechanism of action of kisspeptin on GnRH neurons. Résumé : L'hypothalamus est une zone située au centre du cerveau, dont il représente moins de 1 du volume total. La puberté est la période de transition entre l'enfance et l'age adulte, qui s'accompagne de transformations somatiques, psychologiques, métaboliques et hormonales conduisant à la possibilité de procréer. La fonction principale de la GnRH est la régulation de la croissance, du développement et de la fonction des testicules chez les hommes, et des ovaires chez les femmes en stimulant la sécrétion de l'hormone lutéinisante (LH) et de l'hormone folliculostimulante (FSH) par la glande hypophysaire. Plusieurs facteurs contribuent au déclanchement de la puberté, y compris le sexe et l'appartenance ethnique, la génétique, l'apport alimentaire et la dépense énergétique. Les Kisspeptines constituent une famille de peptides résultant de la dissociation proteolytique de la métastine, un peptide de 54 acides aminés initialement purifié à partir de placenta humain. Ces kisspeptines ont fait l'objet de beaucoup d'attention à la suite de leur découverte en raison de leurs propriétés anti-metastatiques, et c'est plus récemment que leur rôle déterminant dans la fonction reproductive a été démontré. Les kisspeptines sont des ligands du récepteur GPR54, dont la mutation inactivatrice chez l'homme, ou le knockout chez la souris, conduisent à l'infertilité par hypogonadisme hypogonadotrope. Les neurones à GnRH jouent un rôle central dans le règlement des fonctions reproductrices et la kisspeptine stimule l'activité des neurones à GnRH et la libération de GnRH par ces neurones. Toutefois, les mécanismes neurobiologiques de ces actions ne sont pas connus. Dans la première partie de ma thèse, nous avons étudié le lien potentiel entre l'accélération du développement sexuel induite par la leptine et les neurones hypothalamiques à metastine. Les données générées dans cette première série d'expériences ont malheureusement confirmé que les anticorps anti-metastine disponibles dans le commerce sont aspécifiques. Ceci a constitué un inconvénient majeur pour nos études, qui devaient fortement s'appuyer sur l' étude neuroanatomique des neurones hypothalamiques à metastine pour évaluer leur sensibilité à la leptine exogène. Nous avons donc décidé de focaliser nos travaux sur une étude in vitro des mécanismes d'action de la kisspeptine pour moduler l'activité des neurones à GnRH. Nous avons utilisé deux lignées de cellules neuronales exprimant la GnRH pour étudier les mécanismes d'action cellulaires et moléculaires de la metastine dans des neurones. Nous avons ainsi pu démontrer que la kisspeptine induit une activation précoce de la voie f de signalisation de la MAP kinase dans les deux lignées cellulaires, alors que nous n'avons observé aucune activation de la voie de signalisation de la P13 Kinase et de la SAP/JNK. Nous avons en outre démontré une augmentation de l'expression de la GnRH par la stimulation avec la Kisspeptine. L'ensemble de ces données contribue à élucider le mécanisme d'action avec lequel la kisspeptine agit dans les neurones à GnRH, en démontrant un effet sur l'expression génique de la GnRH. Nous pouvons également conclure que la voie de la MAPK est la voie principale activée par la metastine dans les neurones exprimant la GnRH.

Automatic Mallampati Classification Using Active Appearance Models

Difficult tracheal intubation assessment is an important research topic in anesthesia as failed intubations are important causes of mortality in anesthetic practice. The modified Mallampati score is widely used, alone or in conjunction with other criteria, to predict the difficulty of intubation. This work presents an automatic method to assess the modified Mallampati score from an image of a patient with the mouth wide open. For this purpose we propose an active appearance models (AAM) based method and use linear support vector machines (SVM) to select a subset of relevant features obtained using the AAM. This feature selection step proves to be essential as it improves drastically the performance of classification, which is obtained using SVM with RBF kernel and majority voting. We test our method on images of 100 patients undergoing elective surgery and achieve 97.9% accuracy in the leave-one-out crossvalidation test and provide a key element to an automatic difficult intubation assessment system.

Small ubiquitin-like modifier conjugating enzyme with active site mutation acts as dominant negative inhibitor of SUMO conjugation in arabidopsis(F).

Small ubiquitin-like modifier (SUMO) conjugation affects a broad range of processes in plants, including growth, flower initiation, pathogen defense, and responses to abiotic stress. Here, we investigate in vivo and in vitro a SUMO conjugating enzyme with a Cys to Ser change in the active site, and show that it has a dominant negative effect. In planta expression significantly perturbs normal development, leading to growth retardation, early flowering and gene expression changes. We suggest that the mutant protein can serve as a probe to investigate sumoylation, also in plants for which poor genetic infrastructure precludes analysis via loss-of-function mutants.

The costs of parasitism and anti-parasitic defense in the common vole

Résumé : Les relations entre un parasite et son hôte sont avant tout marquées par le coût pour l'hôte que représente la ponction de ressources au profit du parasite et ses conséquences sur les traits d'histoires de vie de l'hôte. Pour contenir la réduction de leur valeur reproductive, les hôtes ont acquis au cours de l'évolution des mécanismes soit de lutte contre les parasites, soit de réallocations des ressources. Curieusement les effets des ectoparasites sur la biologie de mammifères ont été peu étudiés. Dans une première expérience à long terme, nous avons examiné sous un angle intégratif si les puces Nosopsyllus fasciatus affectent certains paramètres physiologiques des campagnols des champs Microtus arvalis. Nous avons également testé si les puces peuvent réduire la longévité et si oui, si ce pourrait être dû à une accélération de la sénescence. Ensuite nous avons testé si la simple activation répétée du système immunitaire comme lors d'une infestation chronique pouvait aussi réduire la longévité. Dans une dernière expérience, nous avons d'abord testé si l'infestation par des puces de jeunes campagnols au stade néonatal (21 jours) pouvait modifier leur développement et leur phénotype adulte. Puis nous avons testé si la modification du phénotype adulte est une réponse prédite et potentiellement adaptative pour minimiser les effets des puces à l'âge adulte. Nos résultats montrent que l'infestation par des puces réduit la croissance subadulte, induit une forte anémie et une immunodépression, et augmente le métabolisme de repos. De plus les puces réduisent la longévité et la taille des testicules, réduisant fortement le succès reproducteur potentiel des individus parasités. La taille finale, c'est-à-dire le développement pré-adulte, détermine en grande part la longévité. La réduction de longévité ne devrait pas être due à l'investissement au profit du système immunitaire car l'activation chronique seule du système immunitaire ne réduit pas la longévité. L'infestation néonatale retarde légèrement le développement mais surtout modifie l'hématocrite et réduit les performances locomotrices des campagnols plus de 3 mois après l'infestation. Les effets immédiats du parasitisme sur la physiologie semblent bien supérieurs comparés aux effets à long terme. Nous n'avons pas d'éléments permettant d'affirmer que le parasitisme néonatal prépare les campagnols à faire face aux puces à l'âge adulte. Au contraire, le parasitisme néonatal interagit sur le parasitisme adulte pour augmenter le métabolisme de repos. Cette thèse offre une vision intégrative des mécanismes par lesquels les puces peuvent affecter la valeur reproductive de leurs hôtes. De façon générale, ces résultats 35 montrent l'importance des puces comme force de sélection chez les campagnols. Il est indispensable de prendre en compte les ectoparasites dans l'étude de l'écologie et des dynamiques de populations chez les mammifères. Summary : The relationship between a parasite and its host is fundamentally marked by the costs for host of the withdrawals of resources by parasite and the subsequent reduction in host life-history traits. Hosts have evolved a number of strategies to reduce these costs, either by fighting against the parasite directly or by reallocating resources to reduce costs on lifetime reproductive value. The effects of ectoparasites on burrowing mammals have been scarcely studied. In a first long-term experiment, we examined how fleas Nosopsyllus fasciatus affect physiological levels of the common vole, Microtus arvalis. We also examined whether fleas reduce longevity and if so, if it is due to an early senescence pattern. Then we tested if experimental activation of the immune system by repeated injections of an antigen could result in a shorter longevity. In the last experiment, we tested if short-lasting neonatal parasitism can have long-term effects on phenotype, and if these effects could induce a predictive response to reduce damages when parasitized at the adult stage. We found that parasitism by flea reduced subadult growth, induced anaemia and immunodepression, and increased energy consumption even when resting. Moreover fleas reduce longevity and testes size associated to splenomegaly, suggesting an overall reduction in fitness but we did not find any pattern of accelerated senescence explaining the early death of parasitized voles compared to non-parasitzed. The cost of mounting an immune response throughout life does not impair longevity, suggesting that it is the cost of parasitism that limits the longevity and not the immune investment. Neonatal infestation by fleas has long-term effects on physiology and reduces motor activity more than 3 months after infestation. The modification of physiology due to long-term effects seems weak compared to the immediate effects of adult infestation. We found no evidence that neonatal parasitism prepares voles to mount a predictive adaptive response in order to reduce effects of fleas on fitness components. On the contrary, neonatal parasitism seems to worsen the effect of adult parasitism. This thesis offers an integrative view of mechanisms by which fleas affect their host at the individual level. Overall, our results demonstrate the importance of fleas as a selective force in voles. These results highlight the importance of ectoparasitism in ecology of micromarnrnals and suggest a role in the dynamic of host populations.

Immune system's role in viral encephalitis.

Viral infections can be a major thread for the central nervous system (CNS), therefore, the immune system must be able to mount a highly proportionate immune response, not too weak, which would allow the virus to proliferate, but not too strong either, to avoid collateral damages. Here, we aim at reviewing the immunological mechanisms involved in the host defense in viral CNS infections. First, we review the specificities of the innate as well as the adaptive immune responses in the CNS, using several examples of various viral encephalitis. Then, we focus on three different modes of interactions between viruses and immune responses, namely human Herpes virus-1 encephalitis with the defect in innate immune response which favors this disease; JC virus-caused progressive multifocal leukoencephalopathy and the crucial role of adaptive immune response in this example; and finally, HIV infection with the accompanying low grade chronic inflammation in the CNS in some patients, which may be an explanation for the presence of cognitive disorders, even in some well-treated HIV-infected patients. We also emphasize that, although the immune response is generally associated with viral replication control and limited cellular death, an exaggerated inflammatory reaction can lead to tissue damage and can be detrimental for the host, a feature of the immune reconstitution inflammatory syndrome (IRIS). We will briefly address the indication of steroids in this situation.

A gene-rich, transcriptionally active environment and the pre-deposition of repressive marks are predictive of susceptibility to KRAB/KAP1-mediated silencing.

AbstractBACKGROUND: KRAB-ZFPs (Krüppel-associated box domain-zinc finger proteins) are vertebrate-restricted transcriptional repressors encoded in the hundreds by the mouse and human genomes. They act via an essential cofactor, KAP1, which recruits effectors responsible for the formation of facultative heterochromatin. We have recently shown that KRAB/KAP1 can mediate long-range transcriptional repression through heterochromatin spreading, but also demonstrated that this process is at times countered by endogenous influences.METHOD: To investigate this issue further we used an ectopic KRAB-based repressor. This system allowed us to tether KRAB/KAP1 to hundreds of euchromatic sites within genes, and to record its impact on gene expression. We then correlated this KRAB/KAP1-mediated transcriptional effect to pre-existing genomic and chromatin structures to identify specific characteristics making a gene susceptible to repression.RESULTS: We found that genes that were susceptible to KRAB/KAP1-mediated silencing carried higher levels of repressive histone marks both at the promoter and over the transcribed region than genes that were insensitive. In parallel, we found a high enrichment in euchromatic marks within both the close and more distant environment of these genes.CONCLUSION: Together, these data indicate that high levels of gene activity in the genomic environment and the pre-deposition of repressive histone marks within a gene increase its susceptibility to KRAB/KAP1-mediated repression.