Showing papers by "Université libre de Bruxelles published in 1985"

Note-A Preference Ranking Organisation Method: The PROMETHEE Method for Multiple Criteria Decision-Making

Abstract: Principles for a new family of outranking methods are given. The main aim of the proposed PROMETHEE approach is to be as easily understood as possible by the decision-maker. It is based on extensions of the notion of criterion. Six possible extensions are considered. These extensions can easily be identified by the decision-maker because the parameters to be defined at most 2 have an economic significance. A valued outranking graph is constructed by using a preference index. Two possibilities are considered to solve the ranking problem by using this valued graph. PROMETHEE I provides a partial preorder and PROMETHEE II a total preorder on the set of the possible actions.

Spaces for the assessment of knowledge

Abstract: The information regarding a particular field of knowledge is conceptualized as a large, specified set of questions (or problems). The knowledge state of an individual with respect to that domain is formalized as the subset of all the questions that this individual is capable of solving. A particularly appealing postulate on the family of all possible knowledge states is that it is closed under arbitrary unions. A family of sets satisfying this condition is called a knowledge space. Generalizing a theorem of Birkhoff on partial orders, we show that knowledge spaces are in a one-to-one correspondence with AND/OR graphs of a particular kind. Two types of economical representations of knowledge spaces are analysed: bases, and Hasse systems, a concept generalizing that of a Hasse diagram of a partial order. The structures analysed here provide the foundation for later work on algorithmic procedures for the assessment of knowledge.

Nitrogen catabolite repression in yeasts and filamentous fungi.

Abstract: Publisher Summary This chapter provides a brief description of nitrogen catabolite repression in Saccharomyces cerevisiae. The ancestral use of yeasts in industry has led to the selection of many wild-type strains of Saccharomyces cerevisiae. Saccharomyces spp. are very different from bacteria, although in vegetative growth they can be handled in a similar way. This is probably the origin of the choice of these organisms when prokaryotic cellular physiologists became interested in eukaryotic organisms. Anabolism, catabolism, and regulation of arginine metabolism have also been studied in parallel in Saccharomyces cerevisiae. The chapter also discusses the nitrogen metabolite repression in filamentous fungi. A number of filamentous fungi are able to utilize a wide range of nitrogen sources. This metabolic versatility implies a strong selective pressure for a mechanism to ensure preferential utilization of the favorable nitrogen sources. This mechanism, nitrogen metabolite repression of the syntheses of many enzymes and permeases involved in nitrogen nutrition, has been extensively studied in two filamentous fungi, the ascomycetes Aspergillus nidulans and Neurospora crassa.

Primary structure of bovine thyroglobulin deduced from the sequence of its 8,431-base complementary DNA.

Abstract: In mammals, an adequate supply of thyroid hormones is essential for normal growth and neurological development. The biosynthesis of thyroid hormones involves an iodinated precursor protein, thyroglobulin, which may be considered an extreme example of a pro-hormone. Thyroglobulin is a dimeric glycoprotein of relative molecular mass (Mr) 660,000 (660K), which is secreted by the thyrocyte and stored in the lumen of the thyroid follicle. The hormonogenic reaction is extracellular, and involves iodination of tyrosyl residues of thyroglobulin and the intramolecular coupling of a subset of these into thyroxine (T4) and triiodothyronine (T3), which remain part of the polypeptide chain. Secretion of hormones results from the endocytosis of thyroglobulin followed by its complete hydrolysis in lysosomes. Considering that the maximum yield of hormones is approximately 6-8 per 660K protein, the whole process is apparently wasteful. However, the efficiency of thyroglobulin as a thyroid hormone precursor is extremely high when the supply of iodine is short; in such conditions, almost all the iodine incorporated is found in iodothyronine. Hence it is suggested that the thyroglobulin structure has evolved to allow for the preferential and efficient iodination and coupling of the hormonogenic tyrosines. Here we report the complete primary structure of bovine thyroglobulin, derived from the sequence of its 8,431-base-pair complementary DNA. The 2,769-amino-acid sequence is characterized by a pattern of imperfect repeats derived from three cysteine-rich motifs. Four hormonogenic tyrosines have been precisely localized near the amino and carboxyl ends of the protein.

Rate of bacterial mortality in aquatic environments

Abstract: A method is proposed which provides a minimum estimate of the rate of bacterial mortality in growing natural populations of planktonic bacteria. This estimate is given by the rate of decrease of radioactivity from the DNA of a [3H]thymidine-labeled natural assemblage of bacteria after all added thymidine has been exhausted from the medium. Results obtained from river water, estuarine water, and seawater show overall bacterial mortality rates in the range 0.010 to 0.030 h−1, in good agreement with the range of growth rates measured in the same environments. Use of selective filtration through Nuclepore filters (pore size, 2 μm) allowed us to determine the contribution of microzooplankton grazing to overall bacterial mortality. Grazing rates estimated by this method ranged from 0 to 0.02 h−1.

Tanycytes: morphology and functions: a review.

Abstract: Publisher Summary The chapter presents a review of the morphology and functions of tanycytes. The name “tanycyte,” derived from the Greek word “tanus,” which means “elongated,” was chosen to stress the shape of these bipolar cells, in relation at their apical pole with the infundibular recess of the third ventricle and, at their distal pole, with the portal vessels of the median eminence and the floor of the brain. The morphology of tanycytes has been thoroughly explored by means of photonic observations as well as by transmission (TEM) and scanning (SEM) electron microscopy. The review of the chapter will be restricted to the tanycytes lining the ventral region of the third ventricle in mammals, thus, excluding the study of similar cells lining the circumventricular organs (subfornical organ, subcommissural organ, organum vasculosum of the lamina terminalis), the aqueduct, and the floor of the fourth ventricle. The possible functions of the tanycytes will also be reviewed. The Golgi impregnation has been used by several authors to study the morphology of the tanycytes in mammals. Because of the thickness of the sections impregnated by this method, it is possible in favorable incidences to follow the entire length of these elongated cells, allowing a dissection in situ. This method demonstrates two main types of tanycytes according to their location and their morphology. The ventral tanycytes are located on the floor and lower third of the infundibular recess. Dorsal tanycytes have a longer tail process, starting from the base of the tanycyte and arching ventrolaterally in the neuropil of the arcuate nucleus. Glycerophosphate dehydrogenase (GPDH), lactic dehydrogenase (LDH), and glucosed-phosphate dehydrogenase (G6PD) are more active in the perikaryons of β tanycytes as compared to α.

Biochemical fractionation of primary production by phytoplankton in Belgian coastal waters during short- and long-term incubations with 14C-bicarbonate - I. Mixed diatom population

Abstract: Short- and long-term, light-dark, time-course studies of radiocarbon accumulation in the major intracellular end-products of photosynthesis (proteins, polysaccharides, lipids, small metabolites) and extracellular monomers and polymers were conducted at natural light intensity in Belgian coastal waters and in the English Channel on Phaeocystis poucheti colonies growing under depleted and non-limited, inorganic nitrogen concentration. Evidence is given that the exopolymeric substances which compose the colony envelope, massively secreted during the photoperiod, are used during the dark, together with the intracellular reserve products, to cover the carbon and energetic needs of the colonies either for the maintenance or for pursuing protein synthesis, according to the external inorganic nitrogen level.

Mutations affecting the enzymes involved in the utilization of 4-aminobutyric acid as nitrogen source by the yeast Saccharomyces cerevisiae.

Abstract: We present genetic evidence for the enzymes 4-aminobutyrate: 2-oxoglutarate aminotransferase (EC 2.6.1.19) and succinate-semialdehyde dehydrogenase [NAD(P)+] (EC 1.2.1.16) constituting the functional pathway for the utilization of 4-aminobutyric acid as a nitrogen source by Saccharomyces cerevisiae. We show that the pathway is induced by 4-aminobutyric acid and that the presence of the pathway enzymes probably requires the integrity of a positive control element.

Pharmacokinetics and pharmacodynamics of vecuronium (ORG NC 45) in patients with cirrhosis

Abstract: To evaluate the effect of liver cirrhosis on the pharmacokinetics and the pharmacodynamics of vecuronium, 12 patients with cirrhosis, aged (mean +/- SD) 52 +/- 12 yr, and 14 control patients, 42 +/- 15 yr, undergoing elective surgery under general anesthesia were studied. The simultaneous time courses of the plasma concentration of vecuronium and of the neuromuscular blockade were studied after the administration of a bolus dose of 0.2 mg X kg-1. Vecuronium plasma concentration declined biexponentially in both groups. Vecuronium plasma clearance was reduced significantly (P less than 0.01) from 4.26 +/- 1.38 ml X min-1 X kg-1 in the controls to 2.73 +/- 1.19 ml X min-1 X kg-1 in the patients with cirrhosis. The elimination half-life was 58 +/- 19 min in the controls and was prolonged significantly to 84 +/- 23 min (P less than 0.01) in the patients with cirrhosis. The total apparent volume of distribution was unchanged in patients with cirrhosis (0.253 +/- 0.086 1 X kg-1 vs. 0.246 +/- 0.092 1 X kg-1 in the controls). Cirrhosis caused a prolongation of the neuromuscular blockade induced by vecuronium: the duration of effect from injection to 50% recovery of the twitch height was prolonged by 100% (P less than 0.01) from 62 +/- 16 min in the controls to 130 +/- 52 min in patients with cirrhosis. The recovery rate (TH 25-75) also was prolonged (P less than 0.05) from 21 +/- 7 min in the controls to 44 +/- 18 min in patients with cirrhosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Constant pressure-constant temperature molecular dynamics for rigid and partially rigid molecular systems

Abstract: The method of molecular dynamics at fixed pressure and/or temperature is adapted to rigid or partly rigid molecular systems with geometrical constraints using the cartesian coordinate approach. Both isotropic and anisotropic volume fluctuations, allowing for shape variation, are considered. The simulation of a benzene crystal at zero pressure and various temperatures is given as an illustration.

Antagonistic effects of thyrotropin and epidermal growth factor on thyroglobulin mRNA level in cultured thyroid cells

Abstract: Both thyrotropin (TSH) and epidermal growth factor (EGF) are potent mitogenic agents when added to dog thyroid cells in primary culture [Roger, P. P. and Dumont, J. E. (1984) Mol. Cell. Endocrinol. 36, 79-93]. The concomitant effect of these agents on the differentiation state of the cells was appreciated using cell morphology, iodide trapping, thyroglobulin synthesis and cytoplasmic thyroglobulin mRNA content as markers. Together with previous results [Mol. Cell. Endocrinol. 36, 79-93 (1984)] it is shown that cells cultured in the continuous presence of TSH maintain all the parameters at a near normal level. In the absence of TSH, thyroglobulin mRNA decreased to very low, though still detectable levels. Addition of TSH restored subnormal mRNA levels. Culture of cells in the presence of EGF for 4-6 days affected profoundly their morphology, abolished iodide trapping and decreased thyroglobulin synthesis and cytoplasmic mRNA content to undetectable levels. Addition of TSH to cells previously exposed to EGF reversed the growth factor effect on all four indexes. The redifferentiating effect of TSH was well observed within 3-4 days and was mimicked by the adenylate cyclase activators, forskolin and cholera toxin. When administered simultaneously, TSH and EGF achieved an intermediate situation, EGF antagonizing partially the effect of TSH on the expression of thyroglobulin gene. Another growth factor, fibroblast growth factor, while promoting thyroid cell proliferation also, did not interfere at all with TSH effects on cytoplasmic thyroglobulin mRNA content. Our results make the dog thyroid cell in primary culture an appropriate model to study the mechanisms involved in gene regulation by cyclic AMP and growth factors.

An unusually long poly(purine)-poly(pyrimidine) sequence is located upstream from the human thyroglobulin gene

Abstract: A region of human genomic DNA encompassing the 5' end of the thyroglobulin gene has been sequenced and the position of the transcriptional start site has been determined. The 5' non-translated portion of the mRNA displays a quasi-palindromic sequence which could allow this region to adopt a hairpin structure. The first exon of the gene encodes a 19 amino-acids signal peptide and the 3 first amino acids of the mature protein. Apart from the canonical TATA-Box and from a CAAT-Box homology, the promoter region contains a 209 bp-long poly(purine)-poly (pyrimidine) sequence located between positions-512 and -304 relative to the transcription start. When contained in a supercoiled plasmid, this sequence exhibits sensitivity to S1 nuclease at two distinct positions. A precise mapping of the borders of the sensitive regions was achieved by extending primers from both ends of the sequence after digestion by the enzyme. The resulting data can be explained by a model involving the formation of a triple helix structure.

Cell kinetic indicators of premalignant stages of colorectal cancer

Abstract: Using an in vitro double labeling technique with two different levels of 3H-thymidine, the duration of the phase of DNA synthesis (S) and the labeling index (LI) were measured in the colorectal mucosa of three groups of patients: patients with colorectal neoplasms (adenomas and/or adenocarcinomas), patients with inflammatory bowel disease, and a control group of patients without gastrointestinal pathology. In those patients with colorectal neoplasms, samples were obtained from both the neoplastic mucosa and from the normal appearing mucosa at various distances from the lesions. One-way analyses of variance were used to test the equality of mean S-phase duration and LI in the various types of tissues. S-phase duration was significantly longer in the tumor than in the unaffected mucosa of patients with adenocarcinoma (18.65 hours +/- 2.3 versus 10.13 hours +/- 1.26 P less than 0.0001). However, S-phase duration was significantly longer in the unaffected mucosa of cancer patients than in the mucosa of patients without gastrointestinal pathology (10.58 hours +/- 1.84 versus 7.91 hours +/- 0.46, P = 0.013). Similarly, LI was significantly higher in the unaffected mucosa of patients with adenoma and adenocarcinoma than in the mucosa of patients without gastrointestinal pathology (19.1% +/- 3.0 versus 9.5% +/- 2.2, P less than 0.0001). There was a highly significant trend to a progressive increase of LI from flat histologically normal appearing mucosas to inflammatory mucosas, adenomas, and adenocarcinomas (P less than 0.0001). These results suggest that increased S-phase duration is specifically related to cancer. In mucosa without histologic sign of malignancy, an increased S-phase duration would indicate that the malignant process has started. An increased LI would appear to relate to the selective advantage that rapidly proliferating cells hold over less proliferating ones.

Trans activation of the bovine leukemia virus long terminal repeat in BLV-infected cells.

Abstract: The transcription initiation signals for retroviruses lie within the long terminal repeat (LTR) sequences that flank the integrated provirus. This study shows that factors present in cells infected with bovine leukemia virus (BLV) mediate transcriptional trans activation of the BLV LTR. This phenomenon is similar to that reported for the human T-cell leukemia virus LTR and establishes both structural and functional criteria for inclusion of BLV and human T-cell leukemia viruses in the same family of transforming retroviruses.

The freezing of hard spheres: The density functional theory revisited

Abstract: We have analysed the recent theories of freezing and found that all results obtained hitherto are biased numerically by the early truncation of slowly converging series. As a result the local density of the solid is shown to become very negative in the interstitial regions. Therefore we have reconsidered the theory of freezing starting from formally exact equations, making three physical approximations and testing all numerical methods for the case of the freezing of hard spheres. A fluid-solid transition is found which is in fair agreement with the known computer experiments.

Suicidal behaviour in major depressive illness.

Abstract: We investigated past suicidal behaviour and family history of suicide in 713 inpatients with major depressive illness. A familial history of suicide (mainly violent) significantly increased the frequency of violent suicidal behaviour in depressive women; bipolar patients being more affected than unipolars. In depressed men, the presence of suicidal behaviour was not significantly affected by polarity. The occurrence of familial suicide significantly increased the risk of violent suicidal behaviour in male depressed attempters. The present study indicates that a familial history of violent suicide is associated with the presence of violent suicidal behaviour in major depressive patients.

Kinetic Study of The Dissolution of Albite with a Continuous Flow-Through Fluidized Bed Reactor

Abstract: The dissolution kinetics of albite were studied using a continuous flow reactor based on the fluidized bed technique. The influence of pH and concentration of dissolved Na, Al and Si was investigated. The results indicate that the mechanism in- volves three successive steps: 1) rapid exchange of Na+ with H+, 2) build-up of a residual layer depleted in Na and also depleted in Al under acidic conditions, and 3) a steady-state and congruent dissolution stage where the rate is controlled by a surface reaction between the residual layer and the solution. It might be possible to describe the kinetics of this steady-state stage in terms of activated surface complexes, but their nature is certainly more complicated than previously considered.

Telomeric reciprocal recombination as a possible mechanism for antigenic variation in trypanosomes.

Abstract: In African trypanosomes, antigenic variation is achieved through differential gene activation, with one antigen gene being expressed at a time among a large collection of antigen-specific sequences. Transcription of the antigen gene always takes place in a telomere, but different telomeres can alternatively act as the expression site. Telomeric antigen genes can be expressed without apparent DNA rearrangement, but they can also, like non-telomeric genes, have access to the telomeric expression site through a duplicative transposition mechanism resembling gene conversion. We report here that, as previously suggested, telomeric genes may use another route to be activated. This mechanism of gene activation is by reciprocal crossing-over upstream from the gene, in the so-called 'barren' region. This allows the antigen gene to be placed in the previously activated telomere, while inactivating the formerly expressed gene by recombination into a silent environment. At least for the telomeric antigen gene described here, three possible activation mechanisms coexist.

Large scale instability of nonlinear standing waves

Abstract: We present the nonlinear phase equations describing the stability of a time-periodic one-dimensional spatial pattern, that arises in a system which is invariant by space and time translations and space reflection symmetry. We show that a large scale oscillatory instability can occur, leading to a quasiperiodic temporal regime with two different spatial scales On etablit les equations aux derivees partielles non lineaires qui gouvernent la stabilite a grande echelle d'une structure cellulaire unidimensionnelle oscillante, apparaissant dans un systeme hors equilibre, invariant par translations d'espace et de temps, et par reflexion d'espace. Existence d'une instabilite oscillatoire, conduisant a un regime quasi periodique, possedant deux echelles spatiales distinctes