Showing papers by "University of Lausanne published in 1995"

Hypertension caused by a truncated epithelial sodium channel γ subunit: genetic heterogeneity of Liddle syndrome

Abstract: Sensitivity of blood pressure to dietary salt is a common feature in subjects with hypertension. These features are exemplified by the mendelian disorder, Liddle's syndrome, previously shown to arise from constitutive activation of the renal epithelial sodium channel due to mutation in the β subunit of this channel. We now demonstrate that this disease can also result from a mutation truncating the carboxy terminus of the γ subunit of this channel; this truncated subunit also activates channel activity. These findings demonstrate genetic heterogeneity of Liddle's syndrome, indicate independent roles of β and γ subunits in the negative regulation of channel activity, and identify a new gene in which mutation causes a salt–sensitive form of human hypertension.

Statistics and the Evaluation of Evidence for Forensic Scientists

Abstract: Preface to the first edition. Preface to the second edition. Uncertainty in forensic science. Variation. The evaluation of evidence. Historical review. Bayesian inference. Sampling. Interpretation. Transfer evidence. Discrete data. Continuous data. Multivariate analysis. Fibres. DNA profiling. Bayesian networks. References. Notation. Cases.

Long-Term Contracts, Short-Term Investment and Monitoring

Abstract: term contracts, asymmetric information between investors and firms can make it impossible to implement profitable long-term projects. The paper characterizes the structure of optimal, renegotiation-proof contracts for unmonitored and monitored finance. Monitoring by investors, although itself subject to distorting incentive constraints, is shown to be able to overcome the short-term bias of investment and thus to lengthen the firms' planning horizon. I. INTRODUCTION An important question in the literature on corporate finance in the recent years has been whether the dependence on outside finance can force firms to undertake inefficient amounts of investment. Little work has been done, however, on the impact of outside finance on the quality of investment. The present paper studies this issue in the context of a question which has attracted considerable attention in the financial press and in the economic policy debate: can the dependence on outside finance lead a firm to undertake inefficient myopic investments?' To do this, the paper studies a dynamic model of financial contracting that allows one to characterize the choice of a firm's investment horizon. It points to information asymmetries as responsible for investment myopia, discusses the costs and benefits of monitoring as a reaction to it, and characterizes the optimal dynamic debt structure for unmonitored, as well as for monitored finance. According to standard financial theory, the market sees through the corporate veil and encourages the choice of efficient projects. In response to this, an important recent literature has developed more explicit theories of financial contracts and their role for the behaviour of imperfectly informed and strategically acting economic agents.2 This paper builds on this literature and analyses the problem of optimal financial contracting for a firm that wants to raise capital for a risky long-term investment project. The framework used to study the issue is a simple two-period contracting model, complicated by the interplay of hidden-characteristics and hidden-action problems on the side of the firm. More specifically, the probability distribution of project returns is assumed to depend on the intrinsic quality of the project, as well as on the investment horizon and effort chosen

Regional Convergence in the European Community

Abstract: This article assesses convergence in output per head across regions in the European Community, for the period 1975–90. We use three alternative methodologies to measure convergence, which yield consistent results. We observe that there are strong differences in the pattern of convergence across sub-periods and across subsets of regions. If the south of Europe seems to catch up in the early 1980s, it stagnates, at best, in the second part of the eighties. At the opposite end, the regions in the north of Europe tend to stagnate or diverge in the first part of the eighties but converge strongly thereafter. This pattern is consistent with the view that northern European countries have adjusted better to the main change in policy regime which occurred in the mid-1980s, namely the implementation of the internal market programme and the entry of the Iberian peninsula in the Community in 1985. This evidence also lends support to the view that trade liberalization can exacerbate disparities. Finally, our evidence indicates that the distinction between the north and the south of the EC is likely to be more relevant in the analysis of growth patterns than the distinction between the centre and the periphery. Preliminary evidence on migration indicates that the population of the southern regions responds much more slowly to wage and unemployment differences. This may explain partly why southern regions have not converged after 1985.

A Controlled Trial of Zidovudine in Primary Human Immunodeficiency Virus Infection

Abstract: Background It is possible that antiretroviral treatment given early during primary infection with the human immunodeficiency virus (HIV) may reduce acute symptoms, help preserve immune function, and improve the long-term prognosis. Methods To assess the effect of early antiviral treatment, we conducted a multicenter, double-blind, placebo-controlled trial in which 77 patients with primary HIV infection were randomly assigned to receive either zidovudine (250 mg twice daily; n = 39) or placebo (n = 38) for six months. Results The mean time from the onset of symptoms until enrollment in the study was 25.1 days. Among the 43 patients who were still symptomatic at the time of enrollment, there was no appreciable difference in the mean (±SE) duration of the retroviral syndrome between the zidovudine group (15.0±4.1 days) and the placebo group (15.8±3.6 days). During a mean follow-up period of 15 months, minor opportunistic infections developed in eight patients: oral candidiasis in four, herpes zoster in two, ...

A mutation in the epithelial sodium channel causing Liddle disease increases channel activity in the Xenopus laevis oocyte expression system

Abstract: We have studied the functional consequences of a mutation in the epithelial Na+ channel that causes a heritable form of salt-sensitive hypertension, Liddle disease. This mutation, identified in the original kindred described by Liddle, introduces a premature stop codon in the channel beta subunit, resulting in a deletion of almost all of the C terminus of the encoded protein. Coexpression of the mutant beta subunit with wild-type alpha and gamma subunits in Xenopus laevis oocytes resulted in an approximately 3-fold increase in the macroscopic amiloride-sensitive Na+ current (INa) compared with the wild-type channel. This change in INa reflected an increase in the overall channel activity characterized by a higher number of active channels in membrane patches. The truncation mutation in the beta subunit of epithelial Na+ channel did not alter the biophysical and pharmacological properties of the channel--including unitary conductance, ion selectivity, or sensitivity to amiloride block. These results provide direct physiological evidence that Liddle disease is related to constitutive channel hyperactivity in the cell membrane. Deletions of the C-terminal end of the beta and gamma subunits of rat epithelial Na+ channel were functionally equivalent in increasing INa, suggesting that the cytoplasmic domain of the gamma subunit might be another molecular target for mutations responsible for salt-sensitive forms of hypertension.

Physical Activity Assessment Using a Pedometer and Its Comparison with a Questionnaire in a Large Population Survey

Abstract: The aim of this study was to evaluate the use of the pedometer in epidemiologic research on physical activity. Within the framework of a health examination survey in 1988-1989, physical activity was assessed in a representative population sample of 493 men and women aged 25-74 years who were residents of Switzerland. They wore a pedometer for 1 week at work and during leisure time, and the results, converted into steps per day, were compared with answers to a questionnaire. The average number of steps per day decreased from 11,900 to 6,700 and from 9,300 to 7,300 for men and women, respectively, in the youngest to the oldest age groups. For men, categorized according to type of physical activity at work, there was a highly significant difference in the number of steps (p < 0.001), whereas in women the results were associated with leisure-time physical activity (p = 0.003). For both sexes, practicing sports more than once a week was associated with an important increase in steps per day. Analyzing the number of steps according to the day of the week and occupational category produced an unexpected result : Men with a physically active job engaged in more leisure-time physical activity on the weekend. The pedometer proved to be useful in assessing physical activity in a large, free-living population.

Social life: the paradox of multiple-queen colonies.

Abstract: The evolution of animal societies in which some individuals forego their own reproductive opportunities to help others to reproduce poses an evolutionary paradox that can be traced to Darwin. Altruism may evolve through kin selection when the donor and recipient of altruistic acts are related to each other, as generally is the case in social birds and mammals. Similarly, social insect workers are highly related to the brood they rear when colonies are headed by a single queen. However, recent studies have shown that insect colonies frequently contain several queens, with the effect of decreasing relatedness among colony members. How can one account for the origin and maintenance of such colonies? This evolutionary enigma presents many of the same theoretical challenges as does the evolution of cooperative breeding and eusociality.

Ratio-Dependent Predation: An Abstraction That Works

Abstract: Recent papers opposing ratio dependence focus on four main criticisms: (1) the empirical evidence we present is insufficient or biased, (2) ratio-dependent models exhibit pathological behavior, (3) ratio dependence lacks a logical or mechanistic base, and (4) more general models incorporate both prey and ratio dependence and there is no need for either of the two simplifications. We review these arguments in the light of empirical evidence from field and experimental studies. We argue that (1) empirical evidence shows that most natural systems are closer to ratio dependence than to prey dependence, (2) pathological dynamics in a mathematical sense is not only realistic, but the lack of such dynamics in prey-dependent models actually makes them pathological in a biological sense, (3) the mechanistic base of ratio dependence is (direct and indirect) interference and resource sharing, and (4) although more general models (with extra parameters) can never fit natural patterns worse than either prey- or ratio-dependent models, there are theoretical, practical, and pedagogical reasons for attempting to find simpler models that can capture the essential dynamics of natural systems.

Granzyme A is an interleukin 1 beta-converting enzyme.

Abstract: Apoptosis is critically dependent on the presence of the ced-3 gene in Caenorhabditis elegans, which encodes a protein homologous to the mammalian interleukin (IL)-1 beta-converting enzyme (ICE). Overexpression of ICE or ced-3 promotes apoptosis. Cytotoxic T lymphocyte-mediated rapid apoptosis is induced by the proteases granzyme A and B. ICE and granzyme B share the rare substrate site of aspartic acid, after which amino acid cleavage of precursor IL-1 beta (pIL-1 beta) occurs. Here we show that granzyme A, but not granzyme B, converts pIL-1 beta to its 17-kD mature form. Major cleavage occurs at Arg120, four amino acids downstream of the authentic processing site, Asp116. IL-1 beta generated by granzyme A is biologically active. When pIL-1 beta processing is monitored in lipopolysaccharide-activated macrophage target cells attacked by cytotoxic T lymphocytes, intracellular conversion precedes lysis. Prior granzyme inactivation blocks this processing. We conclude that the apoptosis-inducing granzyme A and ICE share at least one downstream target substrate, i.e., pIL-1 beta. This suggests that lymphocytes, by means of their own converting enzyme, could initiate a local inflammatory response independent of the presence of ICE.

Signaling cross-talk between peroxisome proliferator-activated receptor/retinoid x receptor and estrogen receptor through estrogen response elements

Abstract: Peroxisome proliferator-activated receptors (PPARs) and retinoid X receptors (RXRs) are nuclear hormone receptors that are activated by fatty acids and 9-cis-retinoic acid, respectively. PPARs and RXRs form heterodimers that activate transcription by binding to PPAR response elements (PPREs) in the promoter of target genes. The PPREs described thus far consist of a direct tandem repeat of the AGGTCA core element with one intervening nucleotide. We show here that the vitellogenin A2 estrogen response element (ERE) can also function as a PPRE and is bound by a PPAR/RXR heterodimer. Although this heterodimer can bind to several other ERE-related palindromic response elements containing AGGTCA half-sites, only the ERE is able to confer transactivation of test reporter plasmids, when the ERE is placed either close to or at a distance from the transcription initiation site. Examination of natural ERE-containing promoters, including the pS2, very-low-density apolipoprotein II and vitellogenin A2 genes, revealed ...

Structural genes for salicylate biosynthesis from chorismate in Pseudomonas aeruginosa

Abstract: Salicylate is a precursor of pyochelin in Pseudomonas aeruginosa and both compounds display siderophore activity. To elucidate the salicylate biosynthetic pathway, we have cloned and sequenced a chromosomal region of P. aeruginosa PAO1 containing two adjacent genes, designated pchB and pchA, which are necessary for salicylate formation. The pchA gene encodes a protein of 52 kDa with extensive similarity to the chorismate-utilizing enzymes isochorismate synthase, anthranilate synthase (component I) and p-aminobenzoate synthase (component I), whereas the 11 kDa protein encoded by pchB does not show significant similarity with other proteins. The pchB stop codon overlaps the presumed pchA start codon. Expression of the pchA gene in P. aeruginosa appears to depend on the transcription and translation of the upstream pchB gene. The pchBA genes are the first salicylate biosynthetic genes to be reported. Salicylate formation was demonstrated in an Escherichia coli entC mutant lacking isochorismate synthase when this strain expressed both the pchBA genes, but not when it expressed pchB alone. By contrast, an entB mutant of E. coli blocked in the conversion of isochorismate to 2,3-dihydro-2,3-dihydroxybenzoate formed salicylate when transformed with a pchB expression construct. Salicylate formation could also be demonstrated in vitro when chorismate was incubated with a crude extract of P. aeruginosa containing overproduced PchA and PchB proteins; salicylate and pyruvate were formed in equimolar amounts. Furthermore, salicylate-forming activity could be detected in extracts from a P. aeruginosa pyoverdin-negative mutant when grown under iron limitation, but not with iron excess. Our results are consistent with a pathway leading from chorismate to isochorismate and then to salicylate plus pyruvate, catalyzed consecutively by the iron-repressible PchA and PchB proteins in P. aeruginosa.

Influence of plant species on disease suppression by Pseudomonas fluorescens strain CHAO with enhanced antibiotic production

Abstract: Introduction of the recombinant cosmid pME3090 into Pseudomonas fluorescens strain CHAO, a good biocontrol agent of various diseases caused by soilborne pathogens, increased three- to five-fold the production of the antibiotic metabolites pyoluteorin (Pit) and 2,4-diacetylphlorogIucinol (Phi) in vitro. Strain CHAO/pME3090 also overproduced Pit and Phi in the rhizosphere of wheat infected or not infected with Pythium ultimum. The biocontrol activity of the wild-type and recombinant Straitis was compared using various plant pathogen-host combinations in a gnotobiotic system. Antibiotic overproduction affected neither the protection of wheat against P. ultimum and Gaeumannomyces graminis var. tritici nor the growth of wheat plants. In contrast, strain CHA0/pME3090 showed an increased capacity to protect cucumber against Fusarium oxysporum f. sp. cucumerinum and Phomopsis sclerotioides, compared with the wild-type strain CHAO, The antibiotic overproducing strain protected tobacco roots significantly better against Thielaviopsis basicola than the wild-type strain but drastically reduced the growth of tobacco plants and was also toxic to the growth of sweet com. On King's B agar and on malt agar, the recombinant strain CHA0/pME3090 inhibited all pathogens more than did the parental strain CHAO. Synthetic Pit and Phi were toxic to all fungi tested. Tobacco and sweet com were more sensitive to synthetic Pit and Phi than were cucumber and wheat. There was no correlation between the sensitivity of the pathogens to the synthetic antibiotics and the degree of disease suppression by strain CHAO pME3090. However, there was a correlation between the sensitivity of the plants and the toxicity of the recombinant strain. We conclude that the plant species rather than the pathogen determines whether cosmid pME3090 in P. fluorescens strain CHAO leads to improved disease suppression.

Local Fas/APO-1(CD95) ligand-mediated tumor cell killing in vivo

Abstract: Fas/APO-1 (CD95) is a cell surface receptor which mediates apoptosis when ligated by specific antibodies or by its recently cloned natural ligand, FasL. We have studied the cytotoxic potential of FasL in vivo using Fas/APO-1-expressing Yac-1 cells as targets. Supernatant harvested from Neuro-2a cells transfected with the murine FasL cDNA contains FasL and transduces a potent apoptotic signal to Yac-1 cells in vitro. Specificity of FasL-mediated cytotoxicity was confirmed by competition assays using soluble Fas or anti-Fas/APO-1 F(ab')2 fragments which specifically interfere with FasL-Fas/APO-1 interactions. Intraperitoneal injection of FasL-containing supernatant efficiently killed Yac-1 target cells which had been implanted in capsules into the peritoneal cavity of mice. Analysis of the target cells revealed DNA fragmentation and nuclear changes typical of apoptosis. As previously shown, intraperitoneal injection of anti-Fas/APO-1 antibodies caused liver failure (Ogasawara, J., Watanabe, F.R., Adachi, M., Matsuzawa, A., Kasugai, T., Kitamura, Y., Itoh, N., Suda, T. and Nagata, S., Nature 1993. 364:806) and was observed at doses which did not reduce Yac-1 cell viability. In contrast, FasL did not induce histopathology in the liver when applied intraperitoneally at doses cytotoxic for Yac-1 cells. However, intravenous administration of FasL induced lethal liver hemorrhages and hepatocyte apoptosis. Thus, locally applied FasL kills tumor cells very efficiently without systemic toxicity and may therefore represent a candidate for local tumor treatment.

A recombinant Salmonella typhimurium vaccine induces local immunity by four different routes of immunization.

Abstract: Immunization of mice with an attenuated Salmonella typhimurium strain (Phopc) carrying a plasmid encoding a hybrid form of the hepatitis B virus core antigen (HBc) induced specific antibody responses against the bacterial lipopolysaccharide (LPS) and HBc. Different mucosal routes of immunization, i.e., oral, nasal, rectal, and vaginal, were compared for their ability to induce a systemic as well as a mucosal response at sites proximal or distant to the site of immunization. Anti-LPS and anti-HBc immunoglobulin A (IgA) antibodies were measured in saliva, in feces, and in genital, bronchial, and intestinal secretions. Specific antibodies in serum and secretions were observed after immunization via all routes; however, the response to LPS was independent of that against HBc. In serum, saliva, and genital and bronchial secretions, high amounts of anti-HBc IgA were obtained by the nasal route of immunization. Vaginal immunization resulted in two different responses in mice: high and low. We observed a correlation between the level of specific immune response and the estrous status of these mice at the time of immunization. Rectal immunization induced high amounts of IgA against HBc and LPS in colonorectal secretions and feces but not at distant sites. These data suggest that S. typhimurium is able to invade different mucosal tissues and induce long-lasting local IgA responses against itself and a carried antigen after a single immunization.

Superantigens of mouse mammary tumor virus.

Abstract: Superantigens (SAgs) are proteins of microbial origin that bind to major histocompatibility complex (MHC) class II molecules and stimulate T cells via interaction with the V beta domain of the T cell receptor (TCR). Mouse mammary tumor virus (MMTV) is a milk-transmitted type B retrovirus that encodes a SAg in its 3' long terminal repeat. Upon MMTV infection, B cells present SAg to the appropriate T cell subset, which leads to a strong "cognate" T-B interaction. This immune reaction results in preferential clonal expansion of infected B cells and differentiation of some of these cells into long-lived memory cells. In this way a stable MMTV infection is achieved that ultimately results in infection of the mammary gland and virus transmission via milk. Thus, in contrast to many microorganisms that attempt to evade the host immune system (reviewed in 1), MMTV depends upon a strong SAg-induced immune response for its survival. Because of their ability to stimulate very strong T cell responses in MHC-identical mice, minor lymphocyte stimulatory (Mls) antigens, discovered more than 20 years ago, are now known to be SAgs encoded by endogenous MMTV proviruses that have randomly integrated into germ cells. The aim of this review is to combine the extensive biology of Mls SAgs with our current understanding of the life cycle of MMTV.

Neuron death in vertebrate development: in vitro methods.

Abstract: Publisher Summary The study of neuronal death involves demonstrating that it occurs in a given situation, estimating the magnitude and timing of the loss, evaluating which particular neurons die, analyzing why and how they die, and understanding the role or purpose of the loss. A wide range of methods is available for achieving these ends; most involve the use of histological sections, although biochemical analysis of homogenized tissue can also provide useful information. Counting healthy neurons in histological sections is the most direct and widely used method for estimating the number of neurons that die, and the timing of their loss. Because most cases of neuronal death occur in postmitotic populations, there is rarely any need to consider complex tissue kinetics; the number of neurons lost is simply the initial number minus the final number in a defined population. However, the fact that subtraction is used makes the final estimation of neuronal death highly sensitive to errors in the estimations of total neuronal number. To meet the high standards of accuracy that are required in counting healthy neurons, it is essential to avoid two main sources of error: those because of inadequate definition of the population to be counted and those in counting.

Structure of a multisubunit complex that promotes DNA branch migration

Abstract: The RuvA and RuvB proteins of Escherichia coli, which are induced in response to DNA damage, are important in the formation of heteroduplex DNA during genetic recombination and related recombinational repair processes. In vitro studies show that RuvA binds Holiday junctions and acts as a specificity factor that targets the RuvB ATPase, a hexameric ring protein, to the junction. Together, RuvA and RuvB promote branch migration, an ATP-dependent reaction that increases the length of the heteroduplex DNA. Electron microscopic visualization of RuvAB now provides a new insight into the mechanism of this process. We observe the formation of a tripartite protein complex in which RuvA binds the crossover and is sandwiched between two hexameric rings of RuvB. The Holliday junction within this complex adopts a square-planar structure. We propose a molecular model for branch migration, a unique feature of which is the role played by the two oppositely oriented RuvB ring motors.

Effects of caffeine on energy metabolism, heart rate, and methylxanthine metabolism in lean and obese women

Abstract: The magnitude of coffee-induced thermogenesis and the influence of coffee ingestion on substrate oxidation were investigated in 10 lean and 10 obese women, over two 24-h periods in a respiratory ch...

Amplification of the housekeeping sigma factor in Pseudomonas fluorescens CHA0 enhances antibiotic production and improves biocontrol abilities.

Abstract: Pseudomonas fluorescens CHA0 produces a variety of secondary metabolites, in particular the antibiotics pyoluteorin and 2,4-diacetylphloroglucinol, and protects various plants from diseases caused by soilborne pathogenic fungi. The rpoD gene encoding the housekeeping sigma factor sigma 70 of P. fluorescens was sequenced. The deduced RpoD protein showed 83% identity with RpoD of Pseudomonas aeruginosa and 67% identity with RpoD of Escherichia coli. Attempts to inactivate the single chromosomal rpoD gene of strain CHA0 were unsuccessful, indicating an essential role of this gene. When rpoD was carried by an IncP vector in strain CHA0, the production of both antibiotics was increased severalfold and, in parallel, protection of cucumber against disease caused by Pythium ultimum was improved, in comparison with strain CHA0.