Éditeur(s) : HAL CCSD Frontiers
Résumé : International audience
Estrogens can induce rapid, short-lived physiological and behavioral responses, in addition to their slow, but long-term, effects at the transcriptional level. To be functionally relevant, these effects should be associated with rapid modulations of estrogens concentrations. 17β-estradiol is synthesized by the enzyme aromatase, using testosterone as a substrate, but can also be degraded into catechol-estrogens via hydroxylation by the same enzyme, leading to an increase or decrease in estrogens concentration, respectively. The first evidence that aromatase activity (AA) can be rapidly modulated came from experiments performed in Japanese quail hypothalamus homogenates. This rapid modulation is triggered by calcium-dependent phosphorylations and was confirmed in other tissues and species. The mechanisms controlling the phosphorylation status, the targeted amino acid residues and the reversibility seem to vary depending of the tissues and is discussed in this review. We currently do not know whether the phosphorylation of the same amino acid affects both aromatase and/or hydroxylase activities or whether these residues are different. These processes provide a new general mechanism by which local estrogen concentration can be rapidly altered in the brain and other tissues.
ISSN: 1662-4548

Droits : http://creativecommons.org/licenses/by/
hal-01142062
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01142062
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01142062/document
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01142062/file/fnins-09-00083.pdf
PUBMED : 25852459

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Demerara plateau, located offshore French Guiana and Suriname, is part of a passive transform continental margin particularly prone to develop slope instabilities, probably in relation to the presence of a free distal border along its steep continental slope. Slope failure occurred at different periods (Cretaceous to Neogene) and shows an overall retrogressive evolution through time. Upslope these failure headscarp, an enigmatic regional Mio-Pliocene unconformity has been discovered through the interpretation of new academic and industrial datasets. The aim of this work is to describe and understand the origin of this surface. Our analysis shows that this unconformity is made of a series of valleys that cross-cut sedimentary strata. Each one of these valleys has a short lateral extent and is closed along two perpendicular directions, which suggests that it could correspond to a highly meandering system, or to some sub-circular depressions. The infill of these features is equivalent to the regional stratigraphic strata found outside the structures, but in a subdued position. This seems to imply that the structures have originated by a local loss of sediments at their base or by sliding processes. Furthermore, these depressions intersect each other through time, while migrating progressively downslope.We discuss a series of hypotheses that try to explain the onset and evolution of these depressions forming the Mio-Pliocene unconformity (Canyons? Slope failures? Contourite moats? Hydrate pockmarks?). Having established that these structures are depressions formed by collapse, and have many similarities with structures recently described in the literature as pockmarks associated with gas hydrate dissolution, we favor this hypothesis.We propose that these hydrate pockmarks form with a mass failure that was triggered by fluid-overpressure development at the base of the hydrate stability zone.
ISSN: 0025-3227

hal-01365920
https://hal.archives-ouvertes.fr/hal-01365920
DOI : 10.1016/j.margeo.2015.04.001