112 research outputs found
Transitional forms between the three domains of life and evolutionary implications
The question as to the origin and relationship between the three domains of life is lodged in a phylogenetic impasse. The dominant paradigm is to see the three domains as separated. However, the recently characterized bacterial species have suggested continuity between the three domains. Here, we review the evidence in support of this hypothesis and evaluate the implications for and against the models of the origin of the three domains of life. The existence of intermediate steps between the three domains discards the need for fusion to explain eukaryogenesis and suggests that the last universal common ancestor was complex. We propose a scenario in which the ancestor of the current bacterial Planctomycetes, Verrucomicrobiae and Chlamydiae superphylum was related to the last archaeal and eukaryotic common ancestor, thus providing a way out of the phylogenetic impasse
Renormalon disappearance in Borel sum of the 1/N expansion of the Gross-Neveu model mass gap
The exact mass gap of the O(N) Gross-Neveu model is known, for arbitrary ,
from non-perturbative methods. However, a "naive" perturbative expansion of the
pole mass exhibits an infinite set of infrared renormalons at order 1/N,
formally similar to the QCD heavy quark pole mass renormalons, potentially
leading to large perturbative ambiguities. We examine the
precise vanishing mechanism of such infrared renormalons, which avoids this
(only apparent)contradiction, and operates without need of (Borel) summation
contour prescription, usually preventing unambiguous separation of perturbative
contributions. As a consequence we stress the direct Borel summability of the
(1/N) perturbative expansion of the mass gap. We briefly speculate on a
possible similar behaviour of analogous non-perturbative QCD quantities.Comment: 16 pp., 1 figure. v2: a few paragraphs and one appendix added, title
and abstract slightly changed, essential results unchange
Functionally Distinct Subsets of Lineage-Biased Multipotent Progenitors Control Blood Production in Normal and Regenerative Conditions.
Despite great advances in understanding the mechanisms underlying blood production, lineage specification at the level of multipotent progenitors (MPPs) remains poorly understood. Here, we show that MPP2 and MPP3 are distinct myeloid-biased MPP subsets that work together with lymphoid-primed MPP4 cells to control blood production. We find that all MPPs are produced in parallel by hematopoietic stem cells (HSCs), but with different kinetics and at variable levels depending on hematopoietic demands. We also show that the normally rare myeloid-biased MPPs are transiently overproduced by HSCs in regenerating conditions, hence supporting myeloid amplification to rebuild the hematopoietic system. This shift is accompanied by a reduction in self-renewal activity in regenerating HSCs and reprogramming of MPP4 fate toward the myeloid lineage. Our results support a dynamic model of blood development in which HSCs convey lineage specification through independent production of distinct lineage-biased MPP subsets that, in turn, support lineage expansion and differentiation.This work was supported by NIH awards F32HL106989 and K01DK098315 to E.M.P,
grants from Leukaemia and Lymphoma Research, Cancer Research UK and core support by the Wellcome Trust to B.G.; and NIH grant R01HL092471, Rita Allen
Scholar Award and Leukemia Lymphoma Society Scholar Award to E.P.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Elsevier/Cell Press
Evaluating 3D hydraulic conditions to favor sediment transport and erosion trough a reservoir: the case study of Champagneux run-of-river dam on the Rhöne River, France
Water Qualit
In Situ Fe and S isotope analyses in pyrite from the 3.2 Ga Mendon Formation (Barberton Greenstone Belt, South Africa): Evidence for early microbial iron reduction
International audienceOn the basis of phylogenetic studies and laboratory cultures, it has been proposed that the ability of microbes to metabolize iron has emerged prior to the Archaea/ Bacteria split. However, no unambiguous geochemical data supporting this claim have been put forward in rocks older than 2.7-2.5 giga years (Gyr). In the present work, we report in situ Fe and S isotope composition of pyrite from 3.28-to 3.26-Gyr-old cherts from the upper Mendon Formation, South Africa. We identified three populations of microscopic pyrites showing a wide range of Fe isotope compositions, which cluster around two ÎŽ 56 Fe values of â1.8â° and +1â°. These three pyrite groups can also be distinguished based on the pyrite crystallinity and the S isotope mass-independent signatures. One pyrite group displays poorly crystallized pyrite minerals with positive Î 33 S values > +3â°, while the other groups display more variable and closer to 0â° Î 33 S values with recrystallized pyrite rims. It is worth to note that all the pyrite groups display positive Î 33 S values in the pyrite core and similar trace element compositions
RĂ©alisation dâun Contrat dâEtudes Prospectives des secteurs du transport: Rapport final
Le CEP a pour objectif de rĂ©aliser un Ă©tat des lieux du secteur, de conduire une analyse prospective qualitative et quantitative de lâĂ©volution des mĂ©tiers et des besoins de compĂ©tences du transport et de prĂ©coniser un plan dâactions pour les transports routiers, maritimes et fluviaux. A lâissue des travaux dâĂ©tude, le rapport final a Ă©tĂ© remis aux membres du ComitĂ© de pilotage (MinistĂšre de lâemploi - DGEFP, ReprĂ©sentants des branches des transports, lâOPCA Transports et Services, PĂŽle Emploi, MinistĂšre de lâĂ©cologie et du dĂ©veloppement durable, des transport et du logement)
MICROSCOPE mission analysis, requirements and expected performance
The MICROSCOPE mission aimed to test the Weak Equivalence Principle (WEP) to
a precision of . The WEP states that two bodies fall at the same rate
on a gravitational field independently of their mass or composition. In
MICROSCOPE, two masses of different compositions (titanium and platinum alloys)
are placed on a quasi-circular trajectory around the Earth. They are the
test-masses of a double accelerometer. The measurement of their accelerations
is used to extract a potential WEP violation that would occur at a frequency
defined by the motion and attitude of the satellite around the Earth. This
paper details the major drivers of the mission leading to the specification of
the major subsystems (satellite, ground segment, instrument, orbit...).
Building upon the measurement equation, we derive the objective of the test in
statistical and systematic error allocation and provide the mission's expected
error budget.Comment: References update
Community-Level Responses to Iron Availability in Open Ocean Plankton Ecosystems
Predicting responses of plankton to variations in essential nutrients is hampered by limited in situ measurements, a poor understanding of community composition, and the lack of reference gene catalogs for key taxa. Iron is a key driver of plankton dynamics and, therefore, of global biogeochemical cycles and climate. To assess the impact of iron availability on plankton communities, we explored the comprehensive bio-oceanographic and bio-omics data sets from Tara Oceans in the context of the iron products from two state-of-the-art global scale biogeochemical models. We obtained novel information about adaptation and acclimation toward iron in a range of phytoplankton, including picocyanobacteria and diatoms, and identified whole subcommunities covarying with iron. Many of the observed global patterns were recapitulated in the Marquesas archipelago, where frequent plankton blooms are believed to be caused by natural iron fertilization, although they are not captured in large-scale biogeochemical models. This work provides a proof of concept that integrative analyses, spanning from genes to ecosystems and viruses to zooplankton, can disentangle the complexity of plankton communities and can lead to more accurate formulations of resource bioavailability in biogeochemical models, thus improving our understanding of plankton resilience in a changing environment
MICROSCOPE mission: first results of a space test of the equivalence principle
According to the weak equivalence principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the 10â15 precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A nonvanishing result would correspond to a violation of the equivalence principle, or to the discovery of a new long-range force. Analysis of the first data gives ÎŽ(Ti,Pt)=[â1±9(stat)±9(syst)]Ă10â15 (1Ï statistical uncertainty) for the titanium-platinum Eötvös parameter characterizing the relative difference in their free-fall accelerations
Etude de la protéine SCL/TAL-1 au cours de l'hématopoïÚse humaine (implication de ce facteur de transcription dans l'autorenouvellement des cellules souches hématopoïétiques humaines)
La protéïne SCL/TAL-1 est un facteur de transcription appartenant à la famille bHLH. Ce facteur est un régulateur clé de l'hématopoïÚse. Lors de ce travail, nous avons étudié l'effet de l'expression ectopique de TAL-1 sur les potentialités hématopoïétiques des progéniteurs humains CD34+ issus de sang de cordon. Dans un premier temps, nous avons pu mettre en évidence diverses fonctions de TAL-1 sur les étapes initiales de la différenciation érythroïde générée "in vitro". Dans un second temps, nous démontrons que l'expressionde TAL-1 permet l'amplification des compartiments hématopoïétiques immatures détectés, "in vivo", lors d'expériences de transplantations xénogéniques, à long terme, chez des souris NOD-SCID. Dans ces conditions d' étude, nous avons en parallÚle, analysé l' importance du domaine de liaison à l' ADN, pour lesPARIS5-BU-Necker : Fermée (751152101) / SudocSudocFranceF
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