Showing papers by "University of Oviedo published in 2000"

Absence of dc-conductivity in lambda-DNA.

Abstract: The electrical conductivity of biomaterials on a molecular scale is of fundamental interest in the life sciences. We perform first principles electronic structure calculations, which clearly indicate that lambda-DNA chains should present large resistance values. We also present two direct procedures to measure electrical currents through DNA molecules adsorbed on mica. The lower limit for the resistivity is 10(6) Omega . cm, in agreement with our calculations. We also show that low energy electron bombardment induces a rapid contamination and dramatically affects the measured conductivity, thus providing an explanation to recent reports of high DNA conductivity.

Induction of micronuclei and other nuclear abnormalities in European minnow Phoxinus phoxinus and mollie Poecilia latipinna: an assessment of the fish micronucleus test.

Abstract: In this work, we have measured both micronuclei and other nuclear abnormalities in renal erythrocytes from European minnow Phoxinus phoxinus and mollie Poecilia latipinna, with the aim to contribute to the standardisation of the micronucleus test for fish species. Intraperitoneal injections of colchicine (10 mg/kg), cyclophosphamide (40 mg/kg), or mitomycin C (20 mg/kg) for 24 h induced diverse nuclear abnormalities in minnow erythrocytes, therefore nuclear abnormalities should be added to micronuclei as genotoxicity indicators in fish micronucleus tests. The adequacy of administration protocols based on intraperitoneal injections has been evaluated by injecting saline solution to both species: single or double injections have not induced neither micronuclei nor other nuclear abnormalities in any case. Finally, the differential sensitivity of both species to toxic heavy metals was evaluated by exposing individuals of both species to different doses (0.17, 1.7, 2x1.7, and 3.4 mg/kg) of cadmium and mercury for 24 h; we concluded that the mollie is sensitive to both metals whereas the minnow is not sensitive to mercury.

High-pressure polymorphs of anatase TiO 2

Abstract: The equation of state of anatase ${\mathrm{TiO}}_{2}$ has been determined experimentally---using polycrystalline as well as single-crystal material---and compared with theoretical calculations using the ab initio perturbed ion model. The results are highly consistent, the zero-pressure bulk modulus being 179(2) GPa from experiment and 189 GPa from theory. Single-crystal tetragonal anatase transforms to the orthorhombic $\ensuremath{\alpha}\ensuremath{-}{\mathrm{PbO}}_{2}$ structure at about 4.5 GPa. This transition is suppressed in the polycrystalline material at room temperature, probably due to the presence of grain boundaries and other crystal defects. Polycrystalline anatase is found to transform to the monoclinic baddeleyite structure at about 13 GPa. Upon decompression, the baddeleyite phase transforms to the $\ensuremath{\alpha}\ensuremath{-}{\mathrm{PbO}}_{2}$ phase at about 7 GPa. The experimental zero-pressure bulk moduli are 258(8) GPa for the $\ensuremath{\alpha}\ensuremath{-}{\mathrm{PbO}}_{2}$ phase and 290(10) GPa for the baddeleyite phase.

Matrilysin-2, a New Matrix Metalloproteinase Expressed in Human Tumors and Showing the Minimal Domain Organization Required for Secretion, Latency, and Activity

Abstract: We have identified a human placenta cDNA coding for a new member of the matrix metalloproteinase (MMP) family. The isolated cDNA encodes a polypeptide of 261 amino acids, the smallest MMP identified to date, which contains several structural features of MMPs including the signal sequence, the prodomain involved in enzyme latency, and the catalytic domain with the zinc-binding site. However, it lacks the hinge region and hemopexin-domain present in most MMPs. According to these structural characteristics, the human MMP described herein has been called matrilysin-2 (MMP-26), because it exclusively shares with matrilysin this minimal domain organization required for secretion, latency, and activity. The amino acid sequence of matrilysin-2 also contains a threonine residue adjacent to the Zn-binding site that has been defined as a specific feature of matrilysin. Chromosomal location of the matrilysin-2 gene showed that it maps to the short arm of chromosome 11, a location distinct to that of other MMP genes. Matrilysin-2 was expressed in Escherichia coli, and, after purification and refolding, the recombinant protein was found to degrade synthetic substrates commonly used for assaying MMPs. Furthermore, this protein hydrolyzed type IV collagen, fibronectin, fibrinogen, and gelatin, which indicated that matrilysin-2 is a potent enzyme with a wide substrate specificity. In addition, it was found that matrilysin-2 is able to activate progelatinase B. Proteolytic activity of matrilysin-2 against all of these substrates was abolished by synthetic inhibitors and by tissue inhibitors of metalloproteinases. Expression analysis revealed that matrilysin-2 is detected not only in placenta and uterus but is widely expressed in malignant tumors from different sources as well as in diverse tumor cell lines. These data together with its broad spectrum of proteolytic activity, suggest that matrilysin-2 may play a role in some of the tissue-remodeling events associated with tumor progression.

Femoral Bone Mineral Density, Neck-Shaft Angle and Mean Femoral Neck Width as Predictors of Hip Fracture in Men and Women.

Abstract: The effect of femoral bone mineral density (BMD) and several parameters of femoral neck geometry (hip axis length, neck-shaft angle and mean femoral neck width) on hip fracture risk in a Spanish population was assessed in a cross-sectional study. All parameters were determined by dual-energy X-ray absorptiometry. There were 411 patients (116 men, 295 women; aged 60-90 years) with hip fractures in whom measurements were taken in the contralateral hip. Controls were 545 persons (235 men, 310 women; aged 60-90 years) who participated in a previous study on BMD in a healthy Spanish population. Femoral neck BMD was significantly lower, and neck-shaft angle and mean femoral neck width significantly higher, in fracture cases than in controls. The logistic regression analysis adjusted by age, height and weight showed that a decrease of 1 standard deviation (SD) in femoral neck BMD was associated with an odds ratio of hip fracture of 4.52 [95% confidence interval (CI) 2.93 to 6.96] in men and 4.45 (95% CI 3.11 to 6.36) in women; an increase of 1 SD in neck-shaft angle of 2.45 (95% CI 1.73 to 3.45) in men and 3.48 (95% CI 2.61 to 4.65) in women; and an increase of 1 SD in mean femoral neck width of 2.15 (95% CI 1.55 to 2.98) in men and 2.40 (95% CI 1.79 to 3.22) in women. The use of a combination of femoral BMD and geometric parameters of the femoral neck except for hip axis length may improve hip fracture risk prediction allowing a better therapeutic strategy for hip fracture prevention.

A Production Model With Firm-Specific Temporal Variation in Technical Inefficiency: With Application to Spanish Dairy Farms

Abstract: This paper introduces a stochastic frontier production model which accommodates firm-specific temporal variation in technical inefficiency. Unlike Cornwell, Schmidt and Sickles (1990), technical inefficiency is not modeled through the intercept of the production frontier, but through an error component model. The proposed model is a generalization of the Battese and Coelli (1992) model, which imposed a common temporal pattern upon all firms. In our application involving Spanish dairy farms, we find that the new model is preferred to the Battese and Coelli (1992) model on the basis of the likelihood ratio test. Results provide a new source of information on the different patterns of technical inefficiency change among the 82 farms in the sample.

Human MT6-matrix metalloproteinase: identification, progelatinase A activation, and expression in brain tumors.

Abstract: The localization of proteolytic enzymes at the cell surface is a widely used strategy for facilitating tumor invasion. In this study, we have cloned a new member of the membrane-type subfamily of matrix metalloproteinases (MT-MMPs), a group of enzymes associated with tumor progression. The cloned cDNA encodes a protein of 562 amino acids with a domain organization similar to that of other MT-MMPs, including a prodomain with a cysteine switch, a catalytic domain with the zinc-binding site, a hemopexin-like domain, and a COOH-terminal extension rich in hydrophobic residues. The predicted protein sequence also contains a short insertion of basic residues located between the propeptide and the catalytic domain and involved in the proteolytic activation of MT-MMPs by furin-like enzymes. Furthermore, immunofluorescence and Western blot analysis of COS-7 cells transfected with the isolated cDNA revealed that the encoded protein is localized at the cell surface. Based on these properties, this novel human matrix metalloproteinase has been called MT6-MMP because it is the sixth identified member of this subfamily of matrix metalloproteinase. Cotransfection of expression plasmids encoding MT6-MMP and progelatinase A resulted in activation of COS-7-secreted progelatinase A, as demonstrated by gelatin zymography. In contrast, transfection of progelatinase A cDNA alone did not lead to the activation of the proenzyme. Northern blot analysis of polyadenylated RNAs isolated from human tissues demonstrated that MT6-MMP is predominantly expressed in leukocytes, lung, and spleen. MT6-MMP was also detected at high levels in SW480 colon carcinoma cells as well as in some anaplastic astrocytomas and glioblastomas, but not in normal colon or brain or in meningiomas. On the basis of these results, we propose that MT6-MMP may facilitate tumor progression through its ability to activate progelatinase A at the membrane of cells from colon carcinomas or brain tumors.

A survey of concepts of independence for imprecise probabilities

Abstract: Our aim in this paper is to clarify the notion of independence for imprecise probabilities. Suppose that two marginal experiments are each described by an imprecise probability model, i.e., by a convex set of probability distributions or an equivalent model such as upper and lower probabilities or previsions. Then there are several ways to define independence of the two experiments and to construct an imprecise probability model for the joint experiment. We survey and compare six definitions of independence. To clarify the meaning of the definitions and the relationships between them, we give simple examples which involve drawing balls from urns. For each concept of independence, we give a mathematical definition, an intuitive or behavioural interpretation, assumptions under which the definition is justified, and an example of an urn model to which the definition is applicable. Each of the independence concepts we study appears to be useful in some kinds of application. The concepts of strong independence and epistemic independence appear to be the most frequently applicable.

Influence of incubation temperature on morphology, locomotor performance, and early growth of hatchling wall lizards (Podarcis muralis)

Abstract: Eggs of wall lizards (Podarcis muralis) were incubated at three temperatures ap- proaching the upper limit of viability for embryonic development in this species (26, 29, and 32°C) to assess the influence of temperature on various aspects of hatchling phenotype likely affecting fitness. The thermal environment affected size and several morphometric characteristics of hatchling lizards. Hatchlings from eggs incubated at 32°C were smaller (snout-vent length, SVL) than those from 26 and 29°C and had smaller mass residuals (from the regression on SVL) as well as shorter tail, head, and femur relative to SVL. Variation in the level of fluctuating asymmetry in meristic and morphometric traits associated with incubation temperatures was quite high but not clearly consistent with the prediction that environmental stress associated with the highest incubation temperatures might produce the highest level of asymmetry. When tested for locomotor capacity in trials developed at body temperatures of 32 and 35°C, hatchlings from the 32°C incubation treatment exhibited the worst performance in any aspect considered (burst speed, maximal length, and number of stops in the complete run). Repeated measures ANCOVAs (with initial egg mass as covariate) of snout-vent length and mass of lizards at days 0 and 20 revealed significant effects of incubation temperature only for mass, being again the hatchlings from eggs incubated at 32°C those exhibiting the smallest final size. All together, our results evidenced a pervasive effect of thermal regime during incubation (and hence of nest site selection) on hatchling phenotypes. How- ever, incubation temperature does not affect hatchling phenotypes in a continuous way; for most of the analysed traits a critical threshold seems to exist between 29 and 32°C, so that hatch- lings incubated at 32°C exhibited major detrimental effects. J. Exp. Zool. 286:422-433, 2000. © 2000 Wiley-Liss, Inc.

Genetic variation in the renin-angiotensin system and athletic performance.

Abstract: The D allele at the angiotensin-I-converting enzyme (ACE)-insertion/deletion polymorphism has been associated with an increased risk of developing several pathological processes, such as coronary heart disease and ventricular hypertrophy. Individuals with the DD genotype show a significantly increased left-ventricular mass in response to physical training, compared to the II genotype (which would be associated with the lowest plasma ACE levels) and the ID genotype. The II genotype has been linked to a greater anabolic response. In accordance with a role for ACE in the response to rigorous physical training, a higher frequency of the I allele has been reported to exist among elite rowers and high-altitude mountaineers. Sixty elite (professional) athletes (25 cyclists, 20 long-distance runners, and 15 handball players), and 400 healthy controls were genotyped for the DNA polymorphisms of the ACE, angiotensinogen (Ang) and angiotensin receptor type 1 (AT1) genes. Plasma ACE levels showed a strong correlation with the I/D genotype in our population. The I-allele occurred at a significantly higher frequency in athletes compared to controls (P=0.0009). Gene and genotype frequencies for the Ang and AT1 polymorphisms did not differ between athletes and controls. Since the frequency of the ACE I allele was significantly increased among our elite athletes, we conclude that the ACE polymorphism represents a genetic factor that contributes to the development of an elite athlete.

Worst-case utilization bound for EDF scheduling on real-time multiprocessor systems

Abstract: Presents the utilization bound for earliest deadline first (EDF) scheduling on homogeneous multiprocessor systems with partitioning strategies. Assuming that tasks are pre-emptively scheduled on each processor according to the EDF algorithm, and allocated according to the first-fit (FF) heuristic, we prove that the worst-case achievable utilization is 0.5(n+1), where n is the number of processors. This bound is valid for arbitrary utilization factors. Moreover, if all the tasks have utilization factors under a value /spl alpha/, the previous bound is raised, and the new utilization bound considering /spl alpha/ is calculated. In addition, we prove that no uniprocessor scheduling algorithm/allocation algorithm pair can provide a higher worst-case achievable utilization than that of EDF-FF. Finally, simulation provides the average-case achievable utilization for EDF-FF.

The genetic structure of Spanish Celtic horse breeds inferred from microsatellite data.

Abstract: Partition of the genetic variability, genetic structure and relationships among seven Spanish Celtic horse breeds were studied using PCR amplification of 13 microsatellites on 481 random individuals. In addition, 60 thoroughbred horses were included. The average observed heterozygosity and the mean number of alleles were higher for the Atlantic horse breeds than for the Balearic Islands breeds. Only eight percentage of the total genetic variability could be attributed to differences among breeds (mean FST approximately 0.08; P < 0.01). Atlantic breeds clearly form a separate cluster from the Balearic Islands breeds and among the former only two form a clear clustering, while the rest of Atlantic breeds (Jaca Navarra, Caballo Gallego and Pottoka) are not consistently differentiated. Multivariate analysis showed that Asturcon populations, Losina and Balearic Islands breeds are clearly separated from each other and from the rest of the breeds. In addition to this, the use of the microsatellites proved to be useful for breed assignment.

EMS1 gene amplification correlates with poor prognosis in squamous cell carcinomas of the head and neck.

Abstract: The relationship between CCND1 and/or EMS1 amplification and disease outcome was studied in a prospective series of 104 head and neck squamous cell carcinomas treated by surgical resection. The CCND1 and EMS1 copy number in tumor samples was estimated by differential PCR. The presence or absence of amplification was analyzed in relation to clinicopathological variables, tumor recurrence, and patient survival. CCND1 amplification occurred in 32 cases (31%) and was associated with increased lymph node stage (P = 0.005) and advanced disease stage (P = 0.003). EMS1 amplification was identified in 21 cases (20%) and was related with advanced T stages (P = 0.001), increased lymph node stage (P = 0.02), advanced disease stage (P = 0.041), poor histological differentiation (P = 0.018), recurrent disease (P = 0.0004), and reduced disease-specific survival (P < 0.0001). Coamplification of both genes occurred in 11 cases (11.5%). Multivariate analysis confirmed that in addition to regional lymph node status, EMS1 amplification is an independent predictor of death from the tumor (P = 0.0027). CCND1 amplification was not prognostic. These data indicate that EMS1 amplification, but not CCND1 amplification, predicts early recurrence and reduced survival in squamous cell carcinoma of the head and neck. The prognostic significance previously attributed to CCND1 amplification may be attributable to its frequent coamplification with EMS1.

Inoculation and nitrate alter phytohormone levels in soybean roots: differences between a supernodulating mutant and the wild type.

Abstract: The levels of different cytokinins. indole-3-acetic acid (IAA) and abscisic acid (ABA) in roots of Glycine max [L.] Merr. cv. Bragg and its supermodulating mutant nts382 were compared for the first time. Forty-eight hours after inoculation with Bradyrhizobium, quantitative and qualitative differences were found in the root's endogenous hormone status between cultivar Bragg and the mutant nts382. The six quantified cytokinins, ranking similarly in each genotype, were present at higher concentrations (30-196% on average for isopentenyl adenosine and dihydrozeatin riboside, respectively) in mutant roots. By contrast, the ABA content was 2-fold higher in Bragg, while the basal levels of IAA [0.53 mu mol (g DW)(-1), on average] were similar in both genotypes. In 1 mM NO3--fed Bragg roots 48 h post-inoculation, IAA, ABA and the cytokinins isopentenyl adenine, and isopentenyl adenosine quantitatively increased with respect to uninoculated controls. However, only the two cytokinins increased in the mutant. High NO3- (8 mM) markedly reduced root auxin concentration, and neither genotypic differences nor the inoculation-induced increase in auxin concentration in Bragg was observed under these conditions. Cytokinins and ABA, on the other hand, Were little affected by 8 mM NO3-. Root IAA/cytokinin and ABA/cytokinin ratios were always higher in Bragg relative to the mutant, and responded to inoculation (mainly in Bragg) and nitrate (both genotypes). The overall results are consistent with the auxin-burst-control hypothesis for the explanation of autoregulation and supernodulation in soybean. However, they are still inconclusive with respect to the inhibitory effect of NO3-.

Antimicrobial Resistance and Spread of Class 1 Integrons among Salmonella Serotypes

Abstract: The resistance profiles, for 15 antimicrobial agents, of 333 Salmonella strains representing the most frequent nontyphoidal serotypes, isolated between 1989 and 1998 in a Spanish region, and 9 reference strains were analyzed. All strains were susceptible to amikacin, ceftazidime, ciprofloxacin, and imipenem, and 31% were susceptible to all antimicrobials tested. The most frequent types of resistance were to sulfadiazine, tetracycline, streptomycin, spectinomycin, ampicillin, and chloramphenicol (ranging from 46 to 22%); 13% were resistant to these six drugs. This multidrug resistance pattern was found alone or together with other resistance types within serotypes Typhimurium (45%), Panama (23%), and Virchow (4%). Each isolate was also screened for the presence of class 1 integrons and selected resistance genes therein; seven variable regions which carried one (aadA1a, aadA2, or pse-1) or two (dfrA14-aadA1a, dfrA1-aadA1a, oxa1-aadA1a, or sat1-aadA1a) resistance genes were found in integrons.

Coccolith Sr/Ca as a new indicator of coccolithophorid calcification and growth rate

Abstract: [1] Polyspecific coccolith separates from core top sediments in the eastern equatorial Pacific show variations of ∼15% in Sr/Ca ratios across the equatorial upwelling zone, with Sr/Ca highest at the equator and decreasing off-axis. These variations cannot be due to changes in the Sr/Ca of seawater, which varies by less than 2% in the surface ocean. Variations in Sr/Ca of coccolith sediments are similar to variations in primary productivity and alkenone-estimated coccolithophorid growth rates in overlying surface waters and to CaCO3 rain rates measured in sediment traps. Because of these relationships and because calcification rate exerts a strong control on Sr/Ca in abiogenic calcites, we suggest that the observed Sr/Ca variations in coccoliths may be strongly controlled by coccolithophorid growth and calcification rates, although temperature may also influence coccolith Sr/Ca to a lesser degree. Changes in dissolution intensity and coccolith assemblages appear to exert a minor influence, if any, on coccolith Sr/Ca in these sediment core tops. If further work confirms relationships between coccolith Sr/Ca and coccolithophorid productivity, Sr/Ca records of past changes in coccolithophorid productivity may be useful in reconstructing past variations in the rain ratio of organic to carbonate carbon, an important control on deep ocean pH and partitioning of CO2 between the atmosphere and ocean. In addition, coccolith Sr/Ca might provide an independent record of past changes in coccolithophorid growth rates, which in combination with data on the carbon isotopic fractionation in coccolithophorid organic matter may permit more reliable calculations of past dissolved CO2 in the surface ocean.

Multiple paternity increases effective size of southern Atlantic salmon populations.

Abstract: Genetic analyses were performed on the progeny of Atlantic salmon (Salmo salar L.) sampled in natural redds of three rivers flowing into the Bay of Biscay, the Nivelle, the Mandeo and the Sella. These rivers are at the southern limit of the European distribution of the species and their populations are small and endangered by human activities. Nine variable number of tandem repeat (VNTR) loci (five minisatellites and four microsatellites) were used for parentage analysis. Multiple male participation was recognized in the fertilization of eggs. A large proportion was fertilized by precociously mature parr. We demonstrate that multiple paternity derived from mature parr is crucial for the conservation of genetic variability in small populations of Atlantic salmon.

Local compressibilities in crystals

Abstract: An application of the atoms in molecules theory to the partitioning of static thermodynamic properties in condensed systems is presented. Attention is focused on the definition and the behavior of atomic compressibilities. Inverses of bulk moduli are found to be simple weighted averages of atomic compressibilities. Two kinds of systems are investigated as examples: four related oxide spinels and the alkali halide family. Our analyses show that the puzzling constancy of the bulk moduli of these spinels is a consequence of the value of the compressibility of an oxide ion. A functional dependence between ionic bulk moduli and ionic volume is also proposed.

The use of quality expectations to segment a service market

Abstract: Reports some findings with respect to the possibility of classifying service consumers on the basis of their quality expectations. After reviewing traditional types of market segmentation, two hypotheses related to the applicability of service quality expectations as a grouping variable are formulated. Then, findings from a study developed in the tourism industry are presented, using the Chow test to verify the mentioned hypotheses. The study indicates that the segmentation proposed is operational and that, in general, the aspects for which the customers have greater expectations are those which influence their satisfaction to a greater extent. Finally, managerial implications are discussed based on the results of the study

ADAM 23/MDC3, a Human Disintegrin That Promotes Cell Adhesion via Interaction with the αvβ3 Integrin through an RGD-independent Mechanism

Abstract: ADAM 23 (a disintegrin and metalloproteinase domain)/MDC3 (metalloprotease, disintegrin, and cysteine-rich domain) is a member of the disintegrin family of proteins expressed in fetal and adult brain. In this work we show that the disintegrin-like domain of ADAM 23 produced in Escherichia coli and immobilized on culture dishes promotes attachment of different human cells of neural origin, such as neuroblastoma cells (NB100 and SH-Sy5y) or astrocytoma cells (U373 and U87 MG). Analysis of ADAM 23 binding to integrins revealed a specific interaction with avb3, mediated by a short amino acid sequence present in its putative disintegrin loop. This sequence lacks any RGD motif, which is a common structural determinant supporting avb3-mediated interactions of diverse proteins, including other disintegrins. avb3 also supported adhesion of HeLa cells transfected with a full-length cDNA for ADAM 23, extending the results obtained with the recombinant protein containing the disintegrin domain of ADAM 23. On the basis of these results, we propose that ADAM 23, through its disintegrin-like domain, may function as an adhesion molecule involved in avb3-mediated cell interactions occurring in normal and pathological processes, including progression of malignant tumors from neural origin.

Causes of subcontracting: evidence from panel data on construction firms

Abstract: This paper examines factors explaining subcontracting decisions in the construction industry. Rather than the more common cross-sectional analyses, we use panel data to evaluate the influence of all relevant variables. We design and use a new index of the closeness to small numbers situations to estimate the extent of hold-up problems. Results show that as specificity grows, firms tend to subcontract less. The opposite happens when output heterogeneity and the use of intangible assets and capabilities increase. Neither temporary shortage of capacity nor geographical dispersion of activities seem to affect the extent of subcontracting. Finally, proxies for uncertainty do not show any clear effect.