72 research outputs found
La relation de l’esprit et du monde
Fil: Lavelle, Louis.
Collège de France (ParĂs
Interleukin-33 regulates metabolic reprogramming of the retinal pigment epithelium in response to immune stressors
It remains unresolved how retinal pigment epithelial cell metabolism is regulated following immune activation to maintain retinal homeostasis and retinal function. We exposed retinal pigment epithelium (RPE) to several stress signals, particularly Toll-like receptor stimulation, and uncovered an ability of RPE to adapt their metabolic preference on aerobic glycolysis or oxidative glucose metabolism in response to different immune stimuli. We have identified interleukin-33 (IL-33) as a key metabolic checkpoint that antagonizes the Warburg effect to ensure the functional stability of the RPE. The identification of IL-33 as a key regulator of mitochondrial metabolism suggests roles for the cytokine that go beyond its extracellular “alarmin” activities. IL-33 exerts control over mitochondrial respiration in RPE by facilitating oxidative pyruvate catabolism. We have also revealed that in the absence of IL-33, mitochondrial function declined and resultant bioenergetic switching was aligned with altered mitochondrial morphology. Our data not only shed new light on the molecular pathway of activation of mitochondrial respiration in RPE in response to immune stressors but also uncover a potentially novel role of nuclear intrinsic IL-33 as a metabolic checkpoint regulator
Diversity and Abundance of Arbuscular–Mycorrhizal Fungus Spores in Tropical Forest and Pasture 1
As Neotropical forests are increasingly converted to agriculture (especially pastures), little is known about the impacts on microbial biodiversity. To assess such impacts, I compared spore abundance and diversity of arbuscular mycorrhizal fungi (AMF) in soils from lowland evergreen forests and pastures in Nicaragua and Costa Rica. Species composition, dominance–diversity curves, and Simpson's diversity indices were similar for both forest and pasture soils. Of 28 distinct fungus morphospecies, 11 produced more spores in pasture, while only 1 produced more spores in forest. According to species–accumulation curves, local AMF species richness did not significantly decline following conversion of forest to pasture. Because pastures contained a surprising abundance and diversity of AMF spores compared to native forest, a lack of mycorrhizal fungi is unlikely to limit plant succession, restoration, or reforestation in the pastures studied. At the regional scale, however, species-accumulation curves showed significantly greater gamma (G) diversity of spores in forest. In addition to these trends in diversity, species that sporulated more in pasture tended to have small spores, while the one species that sporulated more in forest had the largest spores. Similarly, only largespored fungi (>300 Μm) showed any seasonal variation in spore abundance, being more common in the wet season.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71602/1/j.1744-7429.2000.tb00522.x.pd
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Casting a wider net: Immunosurveillance by nonclassical MHC molecules
Most studies of T lymphocytes focus on recognition of classical major histocompatibility complex (MHC) class I or II molecules presenting oligopeptides, yet there are numerous variations and exceptions of biological significance based on recognition of a wide variety of nonclassical MHC molecules. These include αβ and γδ T cells that recognize different class Ib molecules (CD1, MR-1, HLA-E, G, F, et al.) that are nearly monomorphic within a given species. Collectively, these T cells can be considered “unconventional,” in part because they recognize lipids, metabolites, and modified peptides. Unlike classical MHC-specific cells, unconventional T cells generally exhibit limited T-cell antigen receptor (TCR) repertoires and often produce innate immune cell-like rapid effector responses. Exploiting this system in new generation vaccines for human immunodeficiency virus (HIV), tuberculosis (TB), other infectious agents, and cancer was the focus of a recent workshop, “Immune Surveillance by Non-classical MHC Molecules: Improving Diversity for Antigens,” sponsored by the National Institute of Allergy and Infectious Diseases. Here, we summarize salient points presented regarding the basic immunobiology of unconventional T cells, recent advances in methodologies to measure unconventional T-cell activity in diseases, and approaches to harness their considerable clinical potential
Self-Assemblage and Quorum in the Earthworm Eisenia fetida (Oligochaete, Lumbricidae)
Despite their ubiquity and ecological significance in temperate ecosystems, the behavioural ecology of earthworms is not well described. This study examines the mechanisms that govern aggregation behaviour specially the tendency of individuals to leave or join groups in the compost earthworm Eisenia fetida, a species with considerable economic importance, especially in waste management applications. Through behavioural assays combined with mathematical modelling, we provide the first evidence of self-assembled social structures in earthworms and describe key mechanisms involved in cluster formation. We found that the probability of an individual joining a group increased with group size, while the probability of leaving decreased. Moreover, attraction to groups located at a distance was observed, suggesting a role for volatile cues in cluster formation. The size of earthworm clusters appears to be a key factor determining the stability of the group. These findings enhance our understanding of intra-specific interactions in earthworms and have potential implications for extraction and collection of earthworms in vermicomposting processes
Nucleosome Chiral Transition under Positive Torsional Stress in Single Chromatin Fibers
Using magnetic tweezers to investigate the mechanical response of single
chromatin fibers, we show that fibers submitted to large positive torsion
transiently trap positive turns, at a rate of one turn per nucleosome. A
comparison with the response of fibers of tetrasomes (the (H3-H4)2 tetramer
bound with ~50 bp of DNA) obtained by depletion of H2A-H2B dimers, suggests
that the trapping reflects a nucleosome chiral transition to a metastable form
built on the previously documented righthanded tetrasome. In view of its low
energy, <8 kT, we propose this transition is physiologically relevant and
serves to break the docking of the dimers on the tetramer which in the absence
of other factors exerts a strong block against elongation of transcription by
the main RNA polymerase.Comment: 33 pages (double spacing), 7 figure
Structural plasticity of single chromatin fibers revealed by torsional manipulation
Magnetic tweezers are used to study the mechanical response under torsion of
single nucleosome arrays reconstituted on tandem repeats of 5S positioning
sequences. Regular arrays are extremely resilient and can reversibly
accommodate a large amount of supercoiling without much change in length. This
behavior is quantitatively described by a molecular model of the chromatin 3-D
architecture. In this model, we assume the existence of a dynamic equilibrium
between three conformations of the nucleosome, which are determined by the
crossing status of the entry/exit DNAs (positive, null or negative). Torsional
strain, in displacing that equilibrium, extensively reorganizes the fiber
architecture. The model explains a number of long-standing topological
questions regarding DNA in chromatin, and may provide the ground to better
understand the dynamic binding of most chromatin-associated proteins.Comment: 18 pages, 7 figures, Supplementary information available at
http://www.nature.com/nsmb/journal/v13/n5/suppinfo/nsmb1087_S1.htm
French Roadmap for complex Systems 2008-2009
This second issue of the French Complex Systems Roadmap is the outcome of the
Entretiens de Cargese 2008, an interdisciplinary brainstorming session
organized over one week in 2008, jointly by RNSC, ISC-PIF and IXXI. It
capitalizes on the first roadmap and gathers contributions of more than 70
scientists from major French institutions. The aim of this roadmap is to foster
the coordination of the complex systems community on focused topics and
questions, as well as to present contributions and challenges in the complex
systems sciences and complexity science to the public, political and industrial
spheres
Reading Redaction: Symptomatic Metadata, Erasure Poetry, and Mark Blacklock’s I’m Jack
In this article, through a reading of Mark Blacklock’s 2015 novel, I’m Jack, alongside the history of erasure poetry, I suggest that an apt literary-critical metaphor for reading redaction in contemporary literature comes from the term “metadata”. The article schematizes the ways in which redaction can work in literary contexts and points to the modalities through which supposedly blank surfaces are, in fact, textured depths that can be read
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