Modeling actin filament reorganization in endothelial cells subjected to cyclic stretch

Hemodynamic forces affect endothelial cell morphology and function. In particular, circumferential cyclic stretch of blood vessels, due to pressure changes during the cardiac cycle, is known to affect the endothelial cell shape, mediating the alignment of the cells in the direction perpendicular to stretch. This change in cell shape proceeds a drastic reorganization at the internal level. The cellular scaffolding, mainly composed of actin filaments, reorganize in the direction which later becomes the cell's long axis. How this external mechanical stimulus is 'sensed' and transduced into the cell is still unknown. Here, we develop a mathematical model depicting the dynamics of actin filaments, and the influence of the cyclic stretch of the substratum based on the experimental evidence that external stimuli may be transduced inside the cell via transmembrane proteins which are coupled with actin filaments on the cytoplasmic side. Based on this view, we investigate two approaches describing the formulation of the transduction mechanisms involving the coupling between filaments and the membrane proteins. As a result, we find that the mechanical stimulus could cause the experimentally observed reorganization of the entire cytoskeleton simply by altering the dynamics of the filaments connected with the integral membrane proteins, as described in our model. Comparison of our results with previous studies of cytoskeletal dynamics reveals that the cytoskeleton, which, in the absence of the effect of stretch would maintain its isotropic distribution, slowly aligns with the precise direction set by the external stimulus. It is found that even a feeble stimulus, coupled with a strong internal dynamics, is sufficient to align actin filaments perpendicular to the direction of stretc

Altération des biotites dans les arènes des pays tempérés, tropicaux et équatoriaux

Neue Untersuchungen über die Verwitterung von Glimmer (Biotit) in Frankreich, in verschiedenen afrikanischen Staaten und in Madagaskar haben gezeigt, dass es zwei Möglichkeiten beim Abbau dieses Minerals gibt. Der erste Weg führt zur Bildung von Kaolinit über ein mehr oder weniger vorübergehendes Vermikulit-Stadium. Dieser Abbau spielt sich in einem gut drainierten, ausgewaschenen Milieu ab, welches man oft im tropischfeuchten Klimagebiet vorfindet. Erreicht die Entwässerung ein Übermass, so bildet sich Gibbsit als Endprodukt der Biotit-Verwitterung. In gemässigtem, feucht-kühlem Klima dauert das vorübergehende Vermikulit-Stadium länger an. Der zweite Weg führt zur Montmorillonit-Bildung, welche in leicht aridem Klima beobachtet wird. Sie kann sich nur in kieselsäurereichem Milieu entwickeln. Die Berechnung der Strukturformeln scheint darauf hinzudeuten, dass während dieser Umwandlung das Aluminium aus den tetraedrischen in die oktaedischen Lagen wandert und dass die hierdurch frei gewordenen Lagen durch Kieselsäure besetzt werden.Резюме ВЫВЕТРИВАНИЕ БИОТИТОВ В ГРАНИТНОЙ ДРЕСВЕ СТРАН УМЕРЕННОГО, ТРОПИЧЕСКОГО И ЭКВАТОРИАЛЬНОГО ДЛИМАГА Иисследования выветривания биотитов во Франции, в некоторых странах Африки и на о. Мадагаскаре позволяют утРвеРжАать, что существует два пути в эволюции этого минерала. Первый путь ведет к образованию каолинита с переходом через промежуточную, олее или менее скоропреходящую, стадию вермикулита. Такая деградация происходит в выщелачивающей и хорошо дренированной среде, часто встречающейся в странах с тропическим влажным климатом. Если дренаж становится чрезмерным, то конечным продуктом выветривания биотита может быть гиббсит. В умеренно влажном и прохладном климате, переходная стадия вермикулита удлинняется. Второй путь ведет к монтмориллониту. Такое преобразование, наблюдаемое в климате с аридны оттенком, может происходить исключительное в замкнутой среде с кремнеземом. Приближенные расчеты структурных формул наводят на мысль, что в процессе такого преобразования алюминий мигрирует из тетраэдрических п октаэдрические узлы и что создавшиеся таким образом свободные места, занимаются кремнеземом.The study of the weathering of biotites from different origins (France, Africa and Malagasy) shows two ways of evolution of this mineral. The first way leads to kaolinite with an intermediate stage of vermiculite, more or less ephemeral. This degradation takes place in a leached and well drained environment usually typical of humid tropical regions. If drainage becomes excessive, the final product of the evolution of biotite can be gibbsite. Under humid and cool temperate climates, the intermediate stage of vermiculite is prolonged. The second way leads to montmorillonite. This transformation, pointed out under arid climates, can take place only in the environments where solutions are rich in silica. Some approaches of structural formula calculations show that, during this transformation, aluminium migrates from tetrahedral sites towards octahedral ones and that silica can occupy the vacant tetrahedral sites.L'examen de l'évolution géochimique des diorites en région tempérée a été entrepris sur des exemples de profils pris dans le Limousin, Tout comme pour les granites et les roches cristallophylliennes on enregistre dans les massifs dioritiques une intense arénisation, mais avec production de matériaux dans l'ensemble plus fins. Quant à l'altération chimique globale, elle est également ménagée et caractérisée par des séquences d'altération comparables. Par contre, ce qui différencie profondément les arènes et les sols dioritiques des formations équivalentes sur les autres roches cristallines, c'est l'extrême complication de la composition de leurs phases fines < 2µ, 2-10µ et 10-20µ, entraînée par la constitution minéralogique des roches mères. Ici plagioclases, biotite et hornblende sont les minéraux fondamentaux dont l'évolution au cours des processus d'altération peut être très variée et conduit à des mélanges très complexes de matériaux argileux.Novikoff André, Tsawlassou Gatien, Gac Jean-Yves, Bourgeat Fernand, Tardy Yves. Altération des biotites dans les arènes des pays tempérés, tropicaux et équatoriaux. In: Sciences Géologiques. Bulletin, tome 25, n°4, 1972. Sédimentologie et géochimie de la surface. pp. 287-305

Predation on migrating eels (Anguilla anguilla L.) from the Western Mediterranean

Nineteen female silver European eels (Anguilla anguilla L.) were tagged with satellite tags and released in the Gulf of Lion in the Mediterranean during the migration seasons 2013 and 2015. Sixteen tags transmitted data: five in the Atlantic Ocean, and eleven in the Mediterranean. Of those, 50% of migrating eels were consumed by marine mammals in each year, all in the Mediterranean. The diving behaviour recorded by the tags after the eels were consumed indicated that the most likely predators were deep diving toothed whales. Measurements of the acoustic target strength of the tag showed a negligible effect on the detectability by whale biosonar. Overall, the observed predation rate was similar to that reported for eels escaping into the Atlantic. However, unlike eels in the Atlantic, which are most vulnerable to predators in the first week of escapement as they traverse the continental shelf and before they reach the refuge of the deep ocean, eels escaping from the Mediterranean were predated in deep water, months after release, likely as a consequence of their migration within a relatively narrow and deep corridor in the Alboran Sea. This emphasises the challenge of accounting for natural mortality in management plans for the long-term recovery of the European eel

Modeling actin filament reorganization in endothelial cells subjected to cyclic stretch

Hemodynamic forces affect endothelial cell morphology and function. In particular, circumferential cyclic stretch of blood vessels, due to pressure changes during the cardiac cycle, is known to affect the endothelial cell shape, mediating the alignment of the cells in the direction perpendicular to stretch. This change in cell shape proceeds a drastic reorganization at the internal level. The cellular scaffolding, mainly composed of actin filaments, reorganize in the direction which later becomes the cell's long axis. How this external mechanical stimulus is 'sensed' and transduced into the cell is still unknown. Here, we develop a mathematical model depicting the dynamics of actin filaments, and the influence of the cyclic stretch of the substratum based on the experimental evidence that external stimuli may be transduced inside the cell via transmembrane proteins which are coupled with actin filaments on the cytoplasmic side. Based on this view, we investigate two approaches describing the formulation of the transduction mechanisms involving the coupling between filaments and the membrane proteins. As a result, we find that the mechanical stimulus could cause the experimentally observed reorganization of the entire cytoskeleton simply by altering the dynamics of the filaments connected with the integral membrane proteins, as described in our model. Comparison of our results with previous studies of cytoskeletal dynamics reveals that the cytoskeleton, which, in the absence of the effect of stretch would maintain its isotropic distribution, slowly aligns with the precise direction set by the external stimulus. It is found that even a feeble stimulus, coupled with a strong internal dynamics, is sufficient to align actin filaments perpendicular to the direction of stretch

Integration of formal fault analysis in ASSERT: Case studies and lessons learnt

International audienceThe ASSERT European Integrated Project (Automated proof-based System and Software Engineering for Real-Time systems; EC FP6, IST-004033) has investigated, elaborated and experimented advanced methods based on the AltaRica language and support tool OCAS for architecture and fault approach propagation description analysis, and integrated in the complete ASSERT process. The paper describes lessons learnt from three case studies: safety critical spacecraft, autonomous deep exploration spacecraft, and civil aircraft

Rhinoplasty. The Difficult Nasal Tip: Total Resection of the Alar Cartilages

There are many ways to reconstruct and make nasal tips more attractive. Sometimes we cannot find the best way unless we at least remove all surplus from the tip. This may occur in primary or secondary rhinoplasty. In principle, anything is possible when relocating and reconstructing. However, sometimes we face reality when we uncover the tip: broken or bulging cartilages that are difficult to put right. For this reason, in 1987 we thought of totally resectioning the alar cartilages in a case of secondary rhinoplasty with an unsightly appearance. After a year the result was seen to be correct from an aesthetic and a functional perspective and is still so today. Aesthetically, it kept its shape and did not collapse with nasal respiratory failure. We covered the end of the crus medialis with a small, temporary, one- to two-layered fascia patch. Except in exceptional cases, we now use this procedure: Total sectioning of the alar cartilages including the domes, or maintenance of them by preserving the fibroadipose tip tissue with a suture in the middle of the end of the crus medialis and by covering this with temporary fascia, which usually has two layers depending on the thickness of the skin of the tip. This procedure is indicated mainly in secondary rhinoplasty when the cartilages of the tip are completely destroyed, and in primary rhinoplasty when the tip is excessively wide and bulbous. Our philosophy is, therefore, elegance and beauty of the nasal tip with a solid and equilateral base without prejudices