Showing papers by "University of Montpellier published in 1992"

DNA sequence variation of the mitochondrial control region among geographically and morphologically remote European brown trout Saltno trutta populations

Abstract: Summary Throughout its natural range, the brown trout Salmo trutta L. exhibits a complex pattern of morphological and life-history variation. This has led to considerable taxonomic confusion, hampering the understanding of the evolutionary history of the species. To document the phylogenetic relationships among morphologically and geographically remote brown trout populations across western Europe, we determined the DNA sequence variation in segments of the mitochondrial control region for 151 individuals representing 24 populations. DNA was prepared for double-stranded sequencing by the polymerase chain reaction (PCR). Twenty-one variable nucleotide positions within a 640-bp fragment surveyed defined 12 genotypes differing by a mean of 7 nucleotide substitutions (range 1–12). Five major phylogenetic assemblages differing by mean sequence divergence estimates of 0.96 to 1.44% were identified. These groupings exhibited a strong spatial partitioning but lacked congruence with either ecological or morphological differentiation. Complete mitochondrial DNA (mtDNA) monomorphism across all Atlantic basin populations contrasted with the high interdrainage genetic diversity observed in more southerly populations. This study exemplified the usefulness of mitochondrial DNA sequence analysis for estimating phylogenetic relationships within S. trutta populations.

Simple analytical method for calculating exciton binding energies in semiconductor quantum wells.

Abstract: We present a very simple method for calculating exciton binding energies in quantum-confined semiconductor structures. The aim of the model calculation, which is developed in the framework of the fractional-dimensional space, is not to compete with the very advanced ones already proposed, but, on the contrary, to avoid tedious and expensive calculations, to obtain, with good accuracy, the exciton binding energy in most of the confined structures where the exciton can be associated with a specific pair of electron and hole subbands. Our main result is an analytical expression for the exciton binding energy, free of any adjustable parameter. Furthermore, in the cases where the 1s and 2s transition energies can be experimentally measured, the method permits one to obtain the exciton binding energy without any hypothesis or calculation.

Modern tectonic stress field in the Mediterranean region: evidence for variation in stress directions at different scales

Abstract: SUMMARY A compilation of more than one thousand stress indicators (which include in situ stress measurements, focal mechanisms, microtectonic and other geological data) allowed us to reconstruct the modern stress field in the Mediterranean region and the surrounding area. Average stress directions at different scales have been reconstructed by means of a linear interpolation method. This method takes into account the distribution, scale and quality of stress data. The results of the interpolation at plate scale, allow us to recognize slightly deformed regions such as the northwestern European platform, where average maximum horizontal stress direction is oriented roughly NNW-SSE, subparallel to absolute and relative plate velocity directions. Other regions such as the Caucasus, Alps and Pyrenees, where recent tectonic deformation and seismicity are present, display important variations of stress directions. The reconstruction of the average stress directions at different scales within the French Alps pointed out that the average stress field pattern may vary from one scale to another. Nevertheless, variations of stress directions at a given scale are consistent with the kinematics of faults of the same scale.

New protein texturization processes by extrusion cooking at high moisture levels

Abstract: Although primarily used at low moisture levels, extrusion cooking with twin‐screw extruders also applies to food mixes with 40–80% moisture Such levels reduce or prevent viscous dissipation of energy and product expansion, but facilitate operations such as fat emulsification, sterilization, protein gelation, restructuring and shaping of comminuted meat or fish, and microcoagulation and/or fibrillation of specific protein constituents Fibrous gelled structures are obtained from (a) defatted soy flours or concentrates; (b) wheat gluten; and (c) mixes containing 70–80% surimi plus 30–20% soy concentrate or gluten, by extrusion cooking at 50–70% moisture, at barrel temperatures above 140°C, using long cooling dies The continuous gelled bands are highly resistant to stretching in the longitudinal direction They display a multilayer and partly fibrous structure An extruded crab analog with a finely fibrous texture, made from Alaska pollack surimi plus egg white and 1% starch, is already commercial

Geochemical evidence for melt migration and reaction in the upper mantle

Abstract: THE segregation of melts from the Earth's upper mantle into the crust is an important process in the chemical evolution of the crust–mantle system. The processes of melt formation and migration in the upper mantle are inadequately understood, but some important characteristics of these processes can be inferred from upper-mantle rocks exposed at the Earth's surface. The Horoman peridotite body in northern Japan is a layered upper-mantle rock. The major-element compositions of the layers are consistent with their formation as residues from varying extents of melting; however, abundances of rare-earth elements (REE) require additional processes to have occurred1, such as post-melting enrichment (metasomatism) resulting from reaction with a migrating fluid phase. We report here that chondrite-normalized REE patterns in clinopyroxenes show abrupt changes in slope, which vary with stratigraphic position and rock type. These data can be modelled by chromatographic fractionation as melts migrated through and interacted with peridotite, creating compositional heterogeneities in the upper mantle. In the Horoman peridotite these heterogeneities occur on a scale length of tens of metres.

Very high rates of cooling and uplift in the Alpine belt of the Betic Cordilleras, southern Spain

Abstract: Cooling-rate estimates of 150-350 °C/m.y., suggesting magnitudes of uplift and exhumation of ∼15-20 km at rates of 5-10 km/m.y., are proposed for the final stage of the orogenic development in a major part of the Betic Cordilleras. The results are based on a combination of radiometric and paleontological dates. Six isotopic chronometers (muscovite and biotite whole-rock Rb-Sr, muscovite and biotite 40 Ar/ 39 Ar, biotite K-Ar, and whole-rock Rb-Sr) yield analytical ages between 23 and 18.5 Ma for rocks from Alpine nappe complexes. Nappe-sealing marine sedimentary rocks contain early Miocene foraminifera and nannoplankton indicating minimum ages of 18-15.5 Ma. The very high estimates of cooling and uplift-exhumation rates suggest tectonic unroofing, which is tentatively connected geodynamically to lithospheric slab detachment and concomitant diapirism in the upper mantle, and extensional tectonics in the crustal section.

Tensegrity Systems: The State of the Art:

Abstract: Tensegrity systems are space structures of a special nature and their industrial use has not yet been fully developed. The article describes the state of the art. The systems examined are geometric...

p53 Mutations occur in aggressive breast cancer

Abstract: Using a polymerase chain reaction-single strand conformation polymorphism approach we analyzed 96 human primary breast tumors for the presence of mutations in exons 2, 5, 6, 7, 8, and 9 of the p53 gene. These exons have been shown to comprise highly conserved sequences and the portion including exons 5 through 9 is believed to be the target for over 90% of the acquired mutations in human cancer. Eighteen tumors of the 96 (18.7%) tested showed reproducibly a variant band indicative of a mutation. Most (15 tumors) of the mutations were single nucleotide substitutions and G:C to A:T transitions were prevalent (6 tumors), G:C to T:A transversions came next (4 tumors), and guanines were always on the nontranscribed strand. Concomitant loss of the wild type allele and mutation of the other copy was observed in only 3 of 18 mutated cases; this is consistent with the heterogeneous cellular composition of breast tumors. Furthermore p53 mutations were correlated to estrogen and/or progesterone receptor negative tumors, thus indicating their relationships to aggressive breast cancer. No association could be observed with DNA amplification events in these tumors.

Parasitism as a constraint on the rate of life‐history evolution

Abstract: There are a number of ways in which a host can respond in evolutionary time to reductions in survival and reproduction due to a virulent parasite. These include evolving physiological morphological, or behavioural mechanisms of resistance to infection (or to proliferation, once infection has occurred). But a more unexpected tactic is also possible. This is for hosts to reproduce (slightly) sooner when in the presence of a virulent parasite as compared to when the parasite is less virulent or absent. As such, hosts which reproduce younger may be at a selective advantage, since they can both evade parasitism in time and, even when parasitised, can reduce the likely impact of the parasite on survival and reproductive success. We employ a simple mathematical model to propose that parasites and pathogens can act as important agents in the evolution of the timing of reproduction and associated life-history characters (e.g. body size). Once established in a semelparous host population, evolutionary increases in parasite virulence should result in the evolution of shorter lived hosts; whereas the evolution of less virulent forms of the parasite should be accompanied by the evolution of longer lived hosts. We argue that in the presence of a sufficiently virulent parasite the evolution of longer pre-reproductive life-spans should require the previous or concomitant evolution of morphological, behavioural or physiological resistance to parasitic infection and proliferation.

Biological and Clinical Significance of Cathepsin D in Breast Cancer

Abstract: Cathepsin D, an aspartyl protease of lysosomes, is overproduced and hypersecreted by breast cancer cells. The prognostic value of its immunoassay in breast cancer cytosol is reviewed from the first retrospective clinical studies available, which show a strong correlation between high concentrations of cathepsin D in the cytosol of primary tumor and further occurrence of metastasis. This new prognostic factor is induced by estrogen in hormone dependent breast cancer but expressed at a high level in hormone independent breast cancer and appears to be independent of other more classical factors. Its value in node negative patients varies according to the studies. In nude mice, transfection of cathepsin D cDNA into tumor cells increases their metastatic potential, suggesting that overexpression of this protease may be one of the factors responsible for metastasis in human breast cancer. The mechanism by which this protease might facilitate metastasis in vivo is still unknown, even though cathepsin D has the potential to initiate a proteolytic cascade, to degrade extracellular matrix and to liberate FGFs like growth factors from the matrix. These studies should stimulate the search for new therapeutical agents in order to inhibit cathepsin D action.

Growth-regulated expression of rhoG, a new member of the ras homolog gene family

Abstract: Cellular transition from the resting state to DNA synthesis involves master switches genes encoding transcriptional factors (e.g., fos, jun, and egr genes), whose targets remain to be fully characterized. To isolate coding sequences specifically accumulated in late G1, a differential screening was performed on a cDNA library prepared from hamster lung fibroblasts stimulated for 5 h with serum. One of the positive clones which displayed a sevenfold induction, turned out to code for a protein sharing homology to Ras-like products. Cloning and sequence analysis of the human homolog revealed that this putative new small GTPase, referred to as rhoG, is more closely related to the rac, CDC42, and TC10 members of the rho (ras homolog) gene family and might have diverged very early during evolution. rhoG mRNA accumulates in proportion to the mitogenic strength of various purified growth factors used for the stimulation, as a consequence of transcriptional activation. G1-specific RNA accumulation is impaired upon addition of antimitogenic cyclic AMP and is enhanced when protein synthesis is inhibited, mainly as a result of RNA stabilization. rhoG mRNA expression is observed in a wide variety of human organs but reaches a particularly high level in lung and placental tissues.

Thermal redistribution reactions in crosslinked polysiloxanes

Abstract: The thermolysis under argon of various polysiloxane resins containing D, T, DH, or TH units was investigated using thermogravimetric analysis combined with mass spectroscopy (TG/MS analysis) and solid-state 29Si-NMR Redistribution reactions involving the exchange of SiC/SiO bonds or SiH/SiO bonds were evidenced in addition to the exchange of SiO/SiO bonds reported to date These reactions significantly modify the initial siloxane units and lead to an escape of volatile silanes or siloxanes The exchange of SiH/SiO bonds takes place at lower temperatures (300°C) than the exchange of SiC/SiO bonds (500°C)

The efficiency of cell targeting by recombinant retroviruses depends on the nature of the receptor and the composition of the artificial cell-virus linker.

Abstract: Using streptavidin-bound antibodies specific for both viral and cell membrane epitopes, we have reported previously that human cells may be infected by murine ecotropic retroviruses through an interaction with major histocompatibility complex class I and class II antigens, and thus have demonstrated that cell targeting by recombinant retroviruses is feasible. We report here that (i) growth factor or hormone receptors, such as those for epidermal growth factor (EGF) and insulin, can also mediate infection of human cells; (ii) a biotinylated cytokine or hormone can substitute for the anti-cell antibody in bispecific antibody complexes, thus extending the versatility of the method; (iii) although yields are low in our assay, infection efficiency clearly appears to depend upon the biochemical composition of molecular bridges because bi-functional antibody complexes are more efficient than cytokine-antibody complexes in the case of the EGF receptor. Finally, our study indicates that different cell membrane molecules are not equally efficient in allowing infection of human cells because targeting of the transferrin, high density lipoprotein and galactose receptors, as well as that of various membrane glycoconjugates, by murine ecotropic retroviruses did not lead to the establishment of a proviral state.

Mutations of the p53 gene in human myeloma cell lines.

Abstract: Mutations affecting the p53 gene have been found associated with many human malignancies, but little is as yet known about multiple myeloma We investigated p53 gene alterations in 10 human myeloma cell lines (HMCL), half of these being dependent upon exogenous interleukin 6 (IL-6) for in vitro growth, similar to freshly explanted myeloma cells Using a polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) approach, eight of the 10 HMCL were found to bear a mutated p53 gene All the mutations were single base substitutions with a predominance of G:C to A:T transitions There was no apparent relation between the presence of a mutation and IL-6 requirement of the cell line Interestingly, in two cell lines (XG-2 and XG-4) the SSCP pattern showed the presence of both the wild-type and the mutated allele and, upon reverse PCR on RNA, both alleles were found to be concomitantly expressed at the RNA level Moreover, three freshly explanted tumor samples had the same p53 gene status (mutated versus wild type) as the HMCL that were derived from them These results show that p53 mutations are frequent in HMCL Although no apparent relation could be evidenced with the loss of exogenous IL-6 requirement, it may prove interesting to investigate further potential relations between the presence of a mutated p53 allele and gradual autonomy for cell growth

Preparation of monolithic gels from silicon halides by a non-hydrolytic sol-gel process

Abstract: Reactions of organic oxygen compounds, such as ter-butanol, benzylalcohol, dibenzylether and benzaldehyde, with silicon halides provide a novel non-hydrolytic sol-gel route to silica.

Earliest known simian primate found in Algeria

Abstract: THE record of early fossil Simiiformes (Anthropoidea1) from the Late Eocene and Early Oligocene of Africa and the Arabian Peninsula has increased dramatically in recent years2–6. We report here the discovery of a new, diminutive and much older (Early or Middle Eocene) simian from an Algerian locality, Glib Zegdou. This species is smaller than any other living or fossil African simiiform. Derived similarities shared with Aegyptoplthecus suggest that the new genus is more closely related to propliopithecines than to oligopithecines, implying that these two subfamilies differentiated during the Early Eocene. The new discovery confirms predictions about the great antiquity of Simiiformes7–9 and emphasizes a long and endemic African history for higher primates.

Corrosion resistant sol-gel ZrO2 coatings on stainless steel

Abstract: Corrosion resistant ZrO2 coatings on 316L stainless steel sheets have been fabricated utilizing sonocatalysis of precursors sols. The solutions were prepared from zirconium alkoxide Zr(OC3H7)4, isopropanol alcohol, glacial acetic acid and water, and submitted to ultrasonic agitation. Their composition varied between 0.025 and 0.9 mol/l ZrO2. Single thin films were thermally treated between 40 and 1100°C in unoxidizing atmosphere. The coatings characteristics were determined by X-ray diffraction, optical reflection, ellipsometry and scanning electron microscopy. At temperatures higher than 700°C, the films are polycrystalline with a tetragonal structure and show a blue-green color. Depending on the composition, the thickness varied from 5.5 to 35 nm. When treated under a slow and controlled heating rate, the ZrO2 films with the smallest thickness show outstanding corrosion resistance to acid attack and to oxidation as no weight change was observed after 30 h treatment in H2SO4 at 81°C or 10 h treatment in air at 800°C. The thicker films as well as the films treated with a rapid heating rate tend to crack during the densification process and are less corrosion resistant.

Allozyme variation in turbot (Psetta maxima) and brill (Scophthalmus rhombus) (Osteichthyes, Pleuronectoformes, Scophthalmidae) throughout their range in Europe

Abstract: Two species of coastal flatfish (brill and turbot, Scophthalmidae) were analysed electrophoretically at 17 common enzymatic loci in samples taken from 11 sites representing the species ranges in Europe. Brill showed a mean heterozygosity (H) of 0·11 while that of turbot was 0·02. The virtual absence of genetic diversity in turbot is probably due to a very low evolutionary rate, and provides little evidence for population substructure even if various signs indicate the possibility of a hidden differentiation (presence of the taxon maoetica in the Black Sea and differentiation of a species-specific cestode parasite on either side of the Strait of Gibraltar). On the other hand, the weak geographic structure in brill seems to result from rapid recolonization following the last ice age.