Éditeur(s) : HAL CCSD National Institute of Environmental Health Sciences
Résumé : International audience
BACKGROUND: Women of reproductive age can be exposed to endocrine-disrupting chemicals (EDCs) at work, and exposure to EDCs in pregnancy may affect fetal growth. OBJECTIVES: We assessed whether maternal occupational exposure to EDCs during pregnancy as classified by application of a job exposure matrix was associated with birth weight, term low birth weight (LBW), length of gestation, and preterm delivery. METHODS: Using individual participant data from 133,957 mother-child pairs in 13 European cohorts spanning births from 1994 through 2011, we linked maternal job titles with exposure to 10 EDC groups as assessed through a job exposure matrix. For each group, we combined the two levels of exposure categories (possible and probable) and compared birth outcomes with the unexposed group (exposure unlikely). We performed meta-analyses of cohort-specific estimates. RESULTS: Eleven percent of pregnant women were classified as exposed to EDCs at work during pregnancy, based on job title. Classification of exposure to one or more EDC group was associated with an increased risk of term LBW [odds ratio (OR) = 1.25; 95% CI: 1.04, 1.49], as were most specific EDC groups; this association was consistent across cohorts. Further, the risk increased with increasing number of EDC groups (OR = 2.11; 95% CI: 1.10, 4.06 for exposure to four or more EDC groups). There were few associations (p < 0.05) with the other outcomes; women holding job titles classified as exposed to bisphenol A or brominated flame retardants were at higher risk for longer length of gestation. CONCLUSION: Results from our large population-based birth cohort design indicate that employment during pregnancy in occupations classified as possibly or probably exposed to EDCs was associated with an increased risk of term LBW.
ISSN: 0091-6765

hal-01405823
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01405823
DOI : 10.1289/EHP208
PUBMED : 27152464

Éditeur(s) : HAL CCSD
Résumé : The recent accumulation of genomic sequence data has shown that gene evolution is not strictly tree-Like. Many evolutionary processes, like exon shuffling, gene fusion or nonhomologous recombination remodel genes by creating composite structures that are made from parts with different evolutionary histories. The development of sequence similarity networks provides an analytical framework to study the impact of these processes on molecular evolution, by structuring the resemblance relationships between sequences and by formalizing, in terms of graph theory, the detection of composite genes (intransitive triplets) and gene families (clique minimal separators). The size of current data sets, typically several million sequences, has also required the development of new tools and methods: sequence comparison parallelization, large networks visualization with Louvain communities and large cycles identification. When applied to eukaryotic and viral genome data sets, these methods have shown that composite genes are found throughout cellular organisms and mobile genetic elements. Proportionally, composite genes are more numerous in eukaryotic genomes; in absolute number, they are more numerous in viruses. In the latter, composite genes functional distribution is biased (enrichment of genes families that are essential for the perpetuation of the viral cycle), and the various parts of composite genes sometimes even originate from the genetic material of different viral classes. More generally, the extent of combinatorial processes, by unravelling other evolutionary bonds than homology bonds in the strictest sense, legitimates a pluralistic study of similarity relationships between sequences.
L’accumulation récente de données de séquences génomiques a montré que l’évolution des gènes n’est pas strictement arborescente. De nombreux processus évolutifs, comme l’exon shuffling, la fusion de gènes ou la recombinaison illégitime remodèlent les gènes, créant des structures composites, formées de parties dont les histoires évolutives sont différentes. Le développement de réseaux de similarité de séquences fournit un cadre analytique permettant d’étudier l’impact de ces processus sur l’évolution moléculaire, en structurant les relations de ressemblance entre séquences et en formalisant en termes de graphes la détection de gènes (triplets intransitifs) et de familles de gènes (cliques minimales séparatrices) composites. La taille des jeux de données actuels, de l’ordre de plusieurs millions de séquences, a également requis le développement de nouveaux outils et méthodes : parallélisation des comparaisons de séquences, visualisation de très grands réseaux par simplification en communautés de Louvain et identification de grands cycles. Appliquées à des jeux de données de génomes eucaryotes et viraux, ces méthodes ont démontré la présence de gènes composites dans tout le vivant et les éléments génétiques mobiles. En proportion, les gènes composites sont plus nombreux dans les génomes eucaryotes ; en nombre absolu, ils sont plus nombreux à être portés par des virus. Chez ces derniers, la distribution fonctionnelle des gènes composites est biaisée (enrichissement dans les familles essentielles pour la perpétuation du cycle viral), et les éléments des gènes composites trouvent même parfois leurs origines dans le matériel génétique de classes virales différentes. Plus généralement, l’étendue des processus combinatoires, en révélant des liens évolutionnaires autres que les liens d’homologie au sens fort, justifie une étude pluraliste des relations de similarité entre séquences.
https://tel.archives-ouvertes.fr/tel-01127379

NNT : 2014PA066358
tel-01127379
https://tel.archives-ouvertes.fr/tel-01127379
https://tel.archives-ouvertes.fr/tel-01127379/document
https://tel.archives-ouvertes.fr/tel-01127379/file/2014PA066358.pdf

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The upward oil migration in a transparent and rough fracture containing a liquid of higher density is studied experimentally using a light transmission technique. The aperture heterogeneity is also measured by light transmission. The injection of oil in a fracture containing a heavier fluid produces a gravitational fingering instability. Depending on the injection velocity (capillary number, Ca) and the density difference between the two fluids (Bond number, Bo), different patterns are observed during the oil displacements. The width of the finger and its velocity are measured as a function of Bo and Ca. A stability analysis of the interface, based on a generalised Darcy equation in a two-dimensional fracture, allows an accurate description of the experimental results. The order of magnitude of the finger width and its velocity are in good agreement with the calculations, with small disparities due to various unknown fluid flow parameters: capillary pressure, finger thickness in the gap of the fracture, finger tortuosity and oil velocity field into the finger. The theoretical approach allows constructing a (Ca, Bo) phase diagram of stability of the interface.
ISSN: 0169-3913

hal-00429329
https://hal.archives-ouvertes.fr/hal-00429329
DOI : 10.1007/s11242-009-9340-2

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Secondary migration is defined as the movement of hydrocarbons through relatively permeable rocks from source to trap: a two-phase flow within a porous medium. Depending on the geometry and capillary pressure distributions of carrier beds, secondary migration has both vertical and lateral components. The present paper focuses on that part of the migration where the movement is mainly vertical. Its objective is to propose a description of the dynamics governing the vertical part of secondary migration based on the main physical aspects of two-phase flow in a homogeneous porous medium. The study is illustrated by laboratory observations performed in a vertical, 2-D Hele-Shaw cell filled with a transparent porous medium where the flow of dyed oil invading a wetting fluid is visually observed. These observations help us to understand the effect of buoyant, capillary and viscous forces on the resulting flow, the relative importance of which is characterized by non-dimensional numbers. Extrapolating these observations to natural media, it is proposed that vertical secondary migration can be described as a percolation of disconnected and vertically-elongated stringers. These stringers do not move continuously but as a succession of snap-off and re-feeding events which result in a jerky upward movement. Using parameters characterizing the physical properties of the fluid and of the porous medium, the geometry and the dynamic behavior of the stringers are estimated. The width of stringers occurring during secondary migration in geological media is centimetric and their vertical size ranges from several centimeters to a few meters. An upper limit of the mean upward velocity of stringers is proposed, as well as an estimate of their spatial density and of the minimum, average horizontal distance (decametric) between two stringers. The stringers are sparsely distributed, resulting in a low average oil loss and a high efficiency of the vertical migration process.
ISSN: 0264-8172

hal-00831370
https://hal.archives-ouvertes.fr/hal-00831370
https://hal.archives-ouvertes.fr/hal-00831370/document
https://hal.archives-ouvertes.fr/hal-00831370/file/pekins-V-edited.pdf
DOI : 10.1016/j.marpetgeo.2013.04.020

Éditeur(s) : HAL CCSD Springer Verlag (Germany) Springer Verlag
Résumé : Dihydroceramide ?4-desaturase 1 (DES1) catalyzes the last step of the de novo ceramide biosynthesis, which consists of the introduction of a trans ?4-double bond in the carbon chain of the dihydroceramide. It was previously observed that myristic acid binds DES1 through N-myristoylation. This N-terminal modification significantly increased the activity of the recombinant DES1 in COS-7 cells and targeted part of the enzyme initially present in the endoplasmic reticulum to the mitochondrial outer membrane, leading to an increase in ceramide levels. Since these results were obtained in a recombinant COS-7 cell model with high expression of rat DES1, the purpose of the present study was to investigate if the native DES1 enzyme was really upregulated by its N-myristoylation in cultured rat hepatocytes. We first showed that DES1 was the main dihydroceramide desaturase isoform expressed in rat hepatocytes. In this model, the wild-type myristoylable recombinant form of rat DES1 was found in both the endoplasmic reticulum and the mitochondria whereas the mutated non-myristoylable recombinant form (N-terminal glycine replaced by an alanine) was almost exclusively localized in the endoplasmic reticulum, which evidenced the importance of the myristoylation. Then, we showed that compared to other fatty acids, myristic acid was the only one to increase native DES1 activity, in both total cell lysates and mitochondrial fractions. The myristic acid-associated increase in DES1 activity was not linked to elevated mRNA or protein expression but more likely to its N-terminal myristoylation. Finally, the myristic acid-associated increase in DES1 activity slightly enhanced the number of apoptotic cells.
ISSN: 0024-4201

hal-00808026
https://hal-agrocampus-ouest.archives-ouvertes.fr/hal-00808026
DOI : 10.1007/s11745-011-3638-x