Implication des peptides RALFs dans les communications cellulaires lors du développement du gamétophyte femelle chez Solanum chacoense et Arabidopsis thaliana

Chez les angiospermes, la reproduction passe par la double fécondation. Le tube pollinique délivre deux cellules spermatiques au sein du gamétophyte femelle. Une cellule féconde la cellule œuf pour produire un zygote; l’autre féconde la cellule centrale pour produire l’endosperme. Pour assurer un succès reproductif, le développement du gamétophyte femelle au sein de l’ovule doit établir un patron cellulaire qui favorise les interactions avec le tube pollinique et les cellules spermatiques. Pour ce faire, un dialogue doit s’établir entre les différentes cellules de l’ovule lors de son développement, de même que lors de la fécondation. D’ailleurs, plusieurs types de communications intercellulaires sont supposées suite à la caractérisation de plusieurs mutants développementaux. De même, ces communications semblent persister au sein du zygote et de l’endosperme pour permettre la formation d’un embryon viable au sein de la graine. Malgré les développements récents qui ont permis de trouver des molécules de signalisation supportant les modèles d’interactions cellulaires avancés par la communauté scientifique, les voies de signalisation sont de loin très incomplètes. Dans le but de caractériser des gènes encodant des protéines de signalisation potentiellement impliqués dans la reproduction chez Solanum chacoense, l’analyse d’expression des gènes de type RALF présents dans une banque d’ESTs (Expressed Sequence Tags) spécifiques à l’ovule après fécondation a été entreprise. RALF, Rapid Alcalinization Factor, est un peptide de 5 kDa qui fait partie de la superfamille des «protéines riches en cystéines (CRPs)», dont les rôles physiologiques au sein de la plante sont multiples. Cette analyse d’expression a conduit à une analyse approfondie de ScRALF3, dont l’expression au sein de la plante se limite essentiellement à l’ovule. L’analyse de plantes transgéniques d’interférence pour le gène ScRALF3 a révélé un rôle particulier lors de la mégagamétogénèse. Les plantes transgéniques présentent des divisions mitotiques anormales qui empêchent le développement complet du sac embryonnaire. Le positionnement des noyaux, de même que la synchronisation des divisions au sein du syncytium, semblent responsables de cette perte de progression lors de la mégagamétogénèse. L’isolement du promoteur de même que l’analyse plus précise d’expression au sein de l’ovule révèle une localisation sporophytique du transcrit. La voie de signalisation de l’auxine régule également la transcription de ScRALF3. De surcroît, ScRALF3 est un peptide empruntant la voie de sécrétion médiée par le réticulum endoplasmique et l’appareil de Golgi. En somme, ScRALF3 est un important facteur facilitant la communication entre le sporophyte et le gamétophyte pour amener à maturité le sac embryonnaire. L’identification d’un orthologue potentiel chez Arabidopsis thaliana a conduit à la caractérisation de AtRALF34. L’absence de phénotype lors du développement du sac embryonnaire suggère, cependant, de la redondance génétique au sein de la grande famille des gènes de type RALF. Néanmoins, les peptides RALFs apparaissent comme d’importants régulateurs lors de la reproduction chez Solanum chacoense et Arabidopsis thaliana.In angiosperms, reproduction occurs through double fertilization. The pollen tube delivers two sperm cells into the female gametophyte. A first sperm cell fertilizes the egg cell to produce a zygote, while the other fertilizes the central cell to produce the endosperm. To ensure reproductive success, the development of the female gametophyte within the ovule must establish a cellular pattern allowing interaction with the pollen tube and sperm cells. To this end, a dialogue must be established amongst the various cells of the ovule during its development, as well as during fertilization. Several types of communication are suggested by the analysis of developmental mutants. These communications must persist in the zygote and endosperm to allow the formation of a viable embryo within the seed. Recent developments have helped to find signaling molecules that support cell interaction models developed by the scientific community, but the signaling pathways are far from complete. In order to characterise genes encoding signaling proteins which are potentially active during reproduction in Solanum chacoense, I undertook the expression analysis of the RALF-like genes present in a bank of ESTs (Expressed Sequence Tags) specific to the ovule after fertilization. RALF, Rapid Alcalinization Factor, is a 5 kDa peptide that is part of the superfamily of Cysteine Rich Proteins (CRPs), which play a wide variety physiological roles within the plant. This expression analysis led to a detailed analysis of ScRALF3, whose expression in the plant is largely restricted to the ovule. The analysis of ScRALF3 RNAi transgenic plants revealed a function during megagametogenesis. The transgenic plants exhibit abnormal mitotic divisions that prevent the maturity of the embryo sac. The positioning of the nuclei, as well as the timing of divisions in the syncytium, appear to be responsible for the arrest of development during megagametogenesis. Isolation of the promoter as well as more accurate analysis of transcript expression reveals localisation within the ovule sporophytic tissue. The auxin signaling pathway is also involved in the regulation of ScRALF3 expression. ScRALF3 is a secreted peptide passing via the endoplasmic reticulum and the Golgi apparatus. In summary, ScRALF3 may be an important factor facilitating communication between the gametophyte and the sporophyte to allow maturation of the embryo sac. The identification of a potential orthologue in Arabidopsis thaliana led to the characterisation of AtRALF34. The lack of a phenotype during embryo sac development, however, suggests that genetic redundancy within the family of RALF-like genes is very complex. Nevertheless, the RALF peptides appear to be important regulators during reproduction in Solanum chacoense and Arabidopsis thaliana

New bonded assembly configuration for dynamic mechanical analysis of adhesives

A new sample configuration has been developed in order to study molecular mobility of an adhesive in a bonded assembly configuration by dynamic mechanical analysis. The torsional rectangular mode is used to provide a shear solicitation all along the adherend/adhesive interface. The initial mechanical properties of each assembly's constituent are first investigated as reference. The modulus of aluminum foils used as substrates exhibits a classic elastic component and a slight viscous part due to microstructural changes or stress relaxation. Four relaxation modes are highlighted and identified for epoxy adhesive tested as a bulk material. Its viscoelastic behavior is compared to the one of adhesive tested in assembly configuration. The relaxation modes of the adhesive remain visible in spite of the sample stiffening by aluminum foils. Relaxation modes comparison shows that the temperature of loss modulus associated with the mechanical manifestation of glass transition slightly increases for the assembly configuration. Energy losses during this relaxation are much higher in the assembly configuration. Influence of rigid aluminum substrates is discussed in terms of the adhesively bonded joint solicitation mode

Identification of the Mechanical Properties of Particle Boards and Stochastic Simulation of the Behavior of Furniture

International audienceIn furniture industry, the numerical simulation allows the design and optimization of wood-based structures, thus avoiding expensive experimental campaigns. Most of wood-based furniture present some particular features in terms of material properties and geometries. On the one hand, the properties of timber materials (such as particule boards) are strongly heterogeneous and anisotropic. On the other hand, the furniture are often made of simply-shaped elements and then can be represented by an assembly of plates and/or beams. The present work deals with those specific features and presents the identification of the elastic properties of particle boards from digital image correlation (DIC) [1] as well as the simulation of the mechanical behavior of furniture.First, three-point bending tests based on Timoshenko's beam theory are performed on different samples cut from a prototype desk for the identification of the material properties using DIC techniques. Secondly, a probabilistic model for the uncertain material parameters is constructed by using the Maximum Entropy (MaxEnt) principle [2] combined with a Markov Chain Monte-Carlo (MCMC) method based on Metropolis-Hastings algorithm for generating realizations of the underlying random variables. Thirdly, numerical virtual tests are performed to propagate the uncertainties in the material properties through the model and assess the impact of such variabilities on the response of the structure. Lastly, several real tests were previously conducted on the desk in order to validate the proposed numerical approach. Quite good agreement is observed between the numerical computations and the experimental measurements.[1] L. Chevalier, S. Calloch, F. Hild and Y. Marco, Digital image correlation used to ana- lyze the multiaxial behavior of rubber-like materials. European Journal of Mechanics- A/Solids. Vol. 20(2), pp. 169–187, 2001.[2] C. Soize, Uncertainty Quantication: An Accelerated Course with Advanced Applica- tions in Computational Engineering. Springer, Vol. 47, 2017

Time-Dependence of the Mass Accretion Rate in Cluster Cooling Flows

We analyze two time-dependent cluster cooling flow models in spherical symmetry. The first assumes that the intracluster gas resides in a static external potential, and includes the effects of optically thin radiative cooling and mass deposition. This corresponds to previous steady-state cooling flow models calculated by White & Sarazin (1987). Detailed agreement is found between steady-state models and time-dependent models at fixed times in the simulations. The mass accretion rate is found either to increase or remain nearly constant once flows reach a steady state. The time rate of change of the accretion rate is strongly sensitive to the value of the mass deposition parameter q, but only mildly sensitive to the ratio beta of gravitational binding energy to gas temperature. We show that previous scaling arguments presented by Bertschinger (1988) and White (1988) are valid only for mature cooling flows with weak mass deposition (q ~< 1). The second set of models includes the effects of a secularly deepening cluster potential and secondary infall of gas from the Hubble flow. We find that such heating effects do not prevent the flows from reaching a steady state within an initial central cooling time.Comment: 22 pages (AASTeX) with 16 EPS figures; accepted for publication in The Astrophysical Journa

Enthalpy relaxation phenomena of epoxy adhesive in operational configuration: Thermal, mechanical and dielectric analyses

Thermal cycling in space environment can cause physical aging of polymers used in structural adhesive bonded joint. Later, they can initiate failure. A methodology to follow physical aging effects on their thermal, mechanical and dielectric properties is applied to a commercial epoxy adhesive. The analytic description, using Tool, Narayanaswamy and Moynihan model gives a good description of the enthalpy relaxation. It is completed by a phenomenological analysis of the evolution of the adhesive thermal transitions, mechanical properties and molecular mobility. Testedsamples with bondedassembly are representative ofin service configurations. The influence of physical aging on the adhesive and the associated bonded assemblies is analyzed

Aneurysm of the Pancreaticoduodenal Arteries Associated with a Cœliac Artery Lesion

IntroductionA ruptured aneurysm of the pancreaticoduodenalarteries without acute or chronic pancreatitis butassociated with a median arcuate ligament divisionis an exceptional event described in only 11 cases. Thecase of a ruptured pancreaticoduodenal artery aneur-ysm, associated with a cœliac artery lesion which wedescribe, illustrates the difficulty in diagnosing theserare events promptly and in instituting urgent treat-ment to arrest the bleeding followed by an electiveprocedure to prevent recurrence.Case ReportA 54-year-old man with no history of vascular diseasewas admitted to a district hospital for investigation ofvague abdominal pain mainly affecting the rightabdomen, hypotension corrected by infusion ofcrystalloid and no fever. Laboratory blood chemicalfindings including a normal hemoglobin, raisedleukocyte count and high C-reactive protein concen-tration. This presentation raised the suspicion of a gallbladder infection and the patient was kept under closeobservation overnight. The next day, hypotensiondeveloped and the patient complained of pain in theright iliac quadrant. An abdominal ultrasound scanshowed a large iliac fluid collection, but no lesionsinvolving the gall bladder or liver. Appendicitis wasdiagnosed and the patient underwent a McBurneyoperation. During surgery blood was found in theabdomen. An exploratory laparotomy revealed a largeretroperitoneal hematoma. The patient was trans-ferred to our vascular surgery unit. A CT scan aftercontrast injection revealed an intact retroperitonealhematoma (16 £ 9 £ 15 cm), with no bleeding from theaorta or the visceral arteries, and a median arcuateligament division that compressed the origin of thecœliac trunk. Because these findings suggested aruptured pancreaticoduodenal artery aneurysm arter-iography was planned to confirm the diagnosis andtreat the aneurysm by embolization. The patient, whowas by now haemodynamically stable, was kept underobservation in the ITU and transferred to the vascularsurgical unit. On day 1, a CT scan showed that thehematoma had enlarged. The patient was kept undersurveillance in the vascular unit and arteriographywas planned for the following day. During the night,the patient collapsed but responded to more IVcrystalloid and was immediately transferred to theradiological unit. While the patient was being pre-pared for arteriography, a new CT scan showed thehematoma had now increased in size and had spreadto the intraperitoneal space, filling the peri-hepaticand peri-splenic areas as well as the pelvis.The patient underwent selective arteriography tovisualize the stenosis caused by compression of thecœliac axis, to localize the bleeding pancreaticoduo-denal artery aneurysm and to proceed to treatment byembolization. Under local anesthesia, a 5-F introduce