Éditeur(s) : HAL CCSD Portland Press
Résumé : International audience
Lutheran (Lu) blood group and Basal Cell Adhesion Molecule (BCAM) antigens both reside on two glycoprotein (gp) isoforms, Lu and Lu(v13), that differ by the size of their cytoplasmic tail. They are receptors of laminin-10/11 and are expressed in red blood cells (RBCs), epithelial cells of multiple tissues and vascular endothelial cells. To gain more insights into the biological function of Lu/BCAM gps, we looked for potential partners of their cytoplasmic tail. We isolated Ubc9 (Ubiquitin-conjugating enzyme 9) protein by screening a human kidney library using the yeast two-hybrid system. Lu/Ubc9 interaction was validated by GST pull-down and co-immunoprecipitation experiments. Endogenous Ubc9 formed a complex with endogenous or recombinant Lu gp in A498 and MDCK epithelial cells, respectively. Substitution of lysine 585 by alanine in the Lu gp, abolished in vitro and ex vivo interaction of Lu gp with Ubc9 protein. Lu K585A mutant transfected in MDCK cells exhibited a normal basolateral membrane expression but was overexpressed at the surface of polarized MDCK cells as compared to wild-type Lu. Pulse-chase experiments showed extended half-life of Lu K585A gp at the plasma membrane, suggesting an impaired endocytosis of this mutant leading to protein accumulation at the membrane. Furthermore, we showed that the ability of MDCK-Lu K585A cells to spread on immobilized laminin was dramatically decreased. Our data supports a physiological role for the direct interaction between Lu gp and Ubc9 protein, and reveals a role for this enzyme in regulating the stability of Lu gp at the cell membrane.
ISSN: 0264-6021

hal-00478614
https://hal.archives-ouvertes.fr/hal-00478614
https://hal.archives-ouvertes.fr/hal-00478614/document
https://hal.archives-ouvertes.fr/hal-00478614/file/PEER_stage2_10.1042%252FBJ20060861.pdf
DOI : 10.1042/BJ20060861

Éditeur(s) : HAL CCSD GIA - Gemological Institute of America
Résumé : A new opal deposit was discovered in 2008 near the village of Wegel Tena, in volcanic rocks of Ethiopia's Wollo Province. Unlike previous Ethiopian opals, the new material is mostly white, with some brown opal, fire opal, and colorless "crystal" opal. Some of it resembles Australian and Brazilian sedimentary opals, with play-of-color that is often very vivid. However, its properties are consistent with those of opal-CT and most volcanic opals. Inclusions consist of pyrite, barium-manganese oxides, and native carbon Some samples show "digit patterns", interpenetrating play-of-color and common opal, resembling fingers. The opaque-to-translucent Wegel Tena opals become transparent when soaked in water, showing a remarkable hydrophane character. White opals from this deposit contain an elevated Ba content, which has not been reported so far in opal-CT. The fire and crystal opals are prone to breakage, while the white, opaque-to-translucent opals are remarkably durable. The proportion of gem-quality material in the Wegel Tena deposit seems unusually high, and 1,500 kg have already been extracted using rudimentary mining techniques. The deposit may extend over several kilometers and could become a major source of gem-quality opal
ISSN: 0016-626X

hal-00560177
https://hal.archives-ouvertes.fr/hal-00560177

Éditeur(s) : HAL CCSD Geological Society
Résumé : Gem opals from Wegel Tena, Wollo Province, Ethiopia, occur in Oligocene rhyolitic ignimbrites. They display a unique geochemistry, with some samples yielding the highest Ba concentrations ever recorded. They are generally much richer in chemical impurities than opals from other localities. For example, the sum Al+Fe or the sum Na+Mg+Ca+K+Ba are often higher. These geochemical features make them easy to distinguish from other opals worldwide. We observed strong geochemical variations and some good positive correlations in our samples, such as Al+Fe vs. Na+Mg+Ca+K+Ba, Al vs Ca, or Ba vs Ca. This shows that the crystallography of opal has controlled, at least in part, the incorporation of chemical impurities, although opal is not well-crystallized. In addition, the multimodal distributions of several chemical impurities (e.g. U vs Sr, Al vs Ca, Ba vs Ca, etc.) suggest at least two origins of silica: weathering of feldspars and weathering of volcanic glass. In addition, opals from Wegel Tena contain numerous well-preserved microscopic plant fossils. Moreover, their host rock exhibits features typical of pedogenesis (abundant clays, desiccation cracks, and grain size sorting). We propose that the opals at Wegel Tena formed during the Oligocene period when volcanic emissions stopped for a time long enough to allow weathering of ingimbrites and therefore liberation of silica. This accompanied the formation of soil and development of plant life, and some plants were trapped in opal.
ISSN: 1467-7873

hal-00767555
https://hal.archives-ouvertes.fr/hal-00767555
DOI : 10.1144/1467-7873/10-MINDEP-058

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Excess gas phase in magmas erupting explosively is well known worldwide. However, the origin of this gas phase, in excess of what can be dissolved in the erupting magma at depth, and the rate of gas accumulation is less well defined. The 2010 mildly explosive eruption at Eyjafjallajökull, Iceland, produced mingled tephra of benmoreitic and trachytic composition whereas alkali basalt was emitted during preceding flank eruption. Tephra of the first explosive phase are composed of three glass types, alkaline rhyolite, mixed benmoreite, and basalt, which suggests that the basaltic magma intruded a pre-existing rhyolitic magma chamber, and ultimately triggered the eruption. The mixed benmoreitic tephra (erupted on 15 and 17 April 2010) had large 210Po in excess of 210Pb View the MathML source[(Po210/Pb210)0=1.88] at the time of eruption, and possibly a small 210Pb excess over its parent 226Ra. In contrast, the preceding flank eruption produced basalt with View the MathML source(Po210)0=0, upon eruption, and the final trachyte had lost most of its 210Po during open-system degassing. The 210Po excess in the first erupted benmoreites is interpreted to result from 210Po degassing of basaltic magma and the accumulation of 210Po-enriched gas, either in the upper part of the basaltic intrusion, below the rhyolite–basalt interface, or in the pre-existing residual rhyolitic magma chamber. From a simple model of radon and polonium accumulation in the rhyolitic reservoir, the ratio of the mass of basalt magma degassing over the mass of magma accumulating the excess gas decreased from 20 to 15 over 2 days, implying zoned magma reservoir, with the uppermost and gas-richest part erupting first. The duration of pre-eruptive gas accumulation in this model is approximately one year. This corresponds closely to the initiation of a seismic swarm beneath Eyjafjallajökull, early June 2009, which was the first pre-eruptive signal detected. The coincidence between initiation of gas accumulation at relatively shallow depth and deeper seismicity strongly suggests that the excess gas phase originated from a basalt magma batch intruded at depth, and that this gas phase reached the surface approximately a year later.
ISSN: 0012-821X

hal-01217142
https://hal.archives-ouvertes.fr/hal-01217142
DOI : 10.1016/j.epsl.2015.06.054