Benthic diatom communities from two salt marshes of the St. Lawrence Estuary (Canada)

Microphytobenthic diatom communities were investigated in the high and low sections of two salt marshes of the Lower St. Lawrence Estuary (eastern Canada): one featuring a sandy low marsh zone (Pointe-aux-Épinettes; PE) and one with a muddy low marsh area (Pointe-au-Père; PP). Based on diatom composition and diversity, bacterial abundance, chlorophyll-a, phaeopigments and geochemical analyses (Corg, Ntot, granulometry, extracellular polymeric substances), the PP high marsh area appeared to be singular compared to the other sampling sites. Estimated surface biomass ranged from 11 to 71 g C•m-2 in the PE marsh and from 24 to 486 g C•m-2 in the PP marsh. A higher diversity of diatom species was observed in the PP high marsh area with a dominance of epipelic forms, in opposition to the dominant epipsammic forms at the other sites. Statistical analyses showed that diatom density was mainly affected by nutrient availability while the relative abundance of epipelic and epipsammic species was related to sediment grain size. This study provides original data on the composition of benthic diatoms in surface sediments in St. Lawrence saltmarshes during summer time that represent the first step to the determination of the DBI (Diatom biological index) of these northern environments.La composition des communautés de diatomées benthiques a été étudiée dans les zones supérieures et inférieures de deux marais côtiers de l’estuaire maritime du Saint-Laurent (Québec, Canada), l’un possédant un estran sableux (marais de Pointe-aux-Épinette; PE) et l’autre possédant un estran vaseux (marais de Pointe-au-Père; PP). En nous penchant sur l’abondance et la diversité des diatomées benthiques ainsi que sur les caractéristiques biogéochimiques du sédiment (abondance bactérienne totale, granulométrie, composition élémentaire, concentration de pigments, de polysaccharides), nous avons observé que la zone supérieure du marais PP constituait un milieu singulier. Une plus grande diversité de diatomées a été observée dans cette zone avec une dominance des formes épipéliques alors qu’aux autres sites, nous avons observé une prédominance des formes épipsammiques. Nos analyses statistiques ont montré que l’abondance totale de diatomées est corrélée à la disponibilité des nutriments, alors que l’abondance relative de cellules de types épipélique et épisammique est corrélée à la taille des particules de sédiment. Selon nos estimations, la biomasse associée aux diatomées variait de 11 à 71 g C•m-2 dans le marais PE et de 24 à 486 g C•m-2 dans le marais PP. Cette étude décrit pour la première fois la composition détaillée des communautés de diatomées établies dans les sédiments des marais côtiers nordiques en saison estivale et constitue un premier pas vers la détermination de l’indice biologique diatomique de ces environnements nordiques

On Buffon Machines and Numbers

Largely revised version with references and figures added. 12 pages.International audienceThe well-know needle experiment of Buffon can be regarded as an analog (i.e., continuous) device that stochastically "computes" the number 2/pi ~ 0.63661, which is the experiment's probability of success. Generalizing the experiment and simplifying the computational framework, we consider probability distributions, which can be produced perfectly, from a discrete source of unbiased coin flips. We describe and analyse a few simple Buffon machines that generate geometric, Poisson, and logarithmic-series distributions. We provide human-accessible Buffon machines, which require a dozen coin flips or less, on average, and produce experiments whose probabilities of success are expressible in terms of numbers such as, exp(-1), log 2, sqrt(3), cos(1/4), aeta(5). Generally, we develop a collection of constructions based on simple probabilistic mechanisms that enable one to design Buffon experiments involving compositions of exponentials and logarithms, polylogarithms, direct and inverse trigonometric functions, algebraic and hypergeometric functions, as well as functions defined by integrals, such as the Gaussian error function

Updated survey of the steroid-converting enzymes in human adipose tissues

Over the past decade, adipose tissues have been increasingly known for their endocrine properties, that is, their ability to secrete a number of adipocytokines that may exert local and/or systemic effects. In addition to these hormonal peptides, adipose tissues have long been recognized as significant sites for steroid hormone transformation and action. We hereby provide an updated survey of the many steroid-converting enzymes that may be detected in human adipose tissues, their activities and potential roles. In addition to the now well-established role of aromatase and 11β-hydroxysteroid dehydrogenase (HSD) type 1, many enzymes have been reported in adipocyte cell lines, isolated mature cells and/or preadipocytes. These include 11βHSD type 2, 17β-HSDs, 3β-HSD, 5α-reductases, sulfatases and glucuronosyltransferases. Some of these enzymes are postulated to bear relevance for adipose tissue physiology and perhaps for the pathophysiology of obesity. This elaborate set of steroid-converting enzymes in the cell types of adipose tissue deserves further scientific attention. Our work on 20α-HSD (AKR1C1), 3αHSD type 3 (AKR1C2) and 17β-HSD type 5 (AKR1C3) allowed us to clarify the relevance of these enzymes for some aspects of adipose tissue function. For example, AKR1C2 expression down-regulation in preadipocytes seems to potentiate the inhibitory action of dihydrotestosterone on adipogenesis in this model. Many additional studies are warranted to assess the impact of intra-adipose steroid hormone conversions on adipose tissue functions and chronic conditions such as obesity, diabetes and cancer

17β-HSD type 2 activity and localization in human adipose tissue

Testosterone can be converted into androstenedione (4-dione) by 17β-hydroxysteroid dehydrogenase (HSD) activity likely performed by 17β-HSD type 2. Our objective was to evaluate the rate of testosterone conversion to 4-dione as well as expression and localization of 17β-HSD type 2 in omental (OM) vs. subcutaneous (SC) adipose tissues of men. Formation of 4-dione from testosterone was significantly higher in homogenates (p ≤ 0.001) and explants (p ≤ 0.01) of OM than SC tissue. Microscopy analyses and biochemical assays in cell fractions localized the enzyme in the vasculature/endothelial cells of adipose tissues. Conversion of testosterone to 4-dione was weakly detected in most OM and/or SC preadipocyte cultures. Positive correlations were found between 17β-HSD type 2 activity in whole tissue and BMI or SC adipocyte diameter. We conclude that conversion of testosterone to 4-dione detected in abdominal adipose tissue is caused by 17β-HSD type 2 which is localized in the vasculature of the adipose compartment

MicroRNA and Target Protein Patterns Reveal Physiopathological Features of Glioma Subtypes

Gliomas such as oligodendrogliomas (ODG) and glioblastomas (GBM) are brain tumours with different clinical outcomes. Histology-based classification of these tumour types is often difficult. Therefore the first aim of this study was to gain microRNA data that can be used as reliable signatures of oligodendrogliomas and glioblastomas. We investigated the levels of 282 microRNAs using membrane-array hybridisation and real-time PCR in ODG, GBM and control brain tissues. In comparison to these control tissues, 26 deregulated microRNAs were identified in tumours and the tissue levels of seven microRNAs (miR-21, miR-128, miR-132, miR-134, miR-155, miR-210 and miR-409-5p) appropriately discriminated oligodendrogliomas from glioblastomas. Genomic, epigenomic and host gene expression studies were conducted to investigate the mechanisms involved in these deregulations. Another aim of this study was to better understand glioma physiopathology looking for targets of deregulated microRNAs. We discovered that some targets of these microRNAs such as STAT3, PTBP1 or SIRT1 are differentially expressed in gliomas consistent with deregulation of microRNA expression. Moreover, MDH1, the target of several deregulated microRNAs, is repressed in glioblastomas, making an intramitochondrial-NAD reduction mediated by the mitochondrial aspartate-malate shuttle unlikely. Understanding the connections between microRNAs and bioenergetic pathways in gliomas may lead to identification of novel therapeutic targets

Caractérisation de la fonction NA+/K+- atpasique branchiale chez des ombles de fontaine (Salvelinus fontinalis) anadromes et résidents de la rivière Laval

RÉSUMÉ: Les ombles de fontaine (Salvelinus fontinalis) anadromes et résidents de la rivière Laval (Côte-Nord, Québec) représentent deux populations génétiquement et physiologiquement distinctes vivant en sympatrie. L'anadromie implique un défi osmorégulatoire pour les poissons, entraînant plusieurs ajustements physiologiques, incluant l'augmentation de l'activité de la Na+/K+-ATPase branchiale. Cette dernière est considérée comme critique lors de l'acclimatation en eau salée chez les salmonidés. La présence de deux isoformes (a1a et a1b) de la sous-unité catalytique de la Na+/K+-ATPase branchiale, différemment exprimés en fonction de la salinité a récemment été démontrée chez d'autres espèces de salmonidés anadromes. Afin de vérifier s'il existe des différences de capacité osmorégulatoire en eau salée au niveau de la Na+/K+-ATPase branchiale entre les deux formes, des ombles de fontaine anadromes et résidents de la rivière Laval (l+) ont été graduellement transférés dans des eaux estuariennes de juin à août (augmentation de 2% par jour, salinité finale 28%) et comparés à un groupe contrôle demeuré en eau douce. Avant le transfert et 3, 7, 14 et 60 jours après le transfert en eau salée, des mesures d'activités enzymatiques absolue et spécifique de la Na+/K+-A TPase branchiale ont été réalisées. Les expressions relatives des deux isoformes a1a et a1b ont été mesurées à l'aide d'analyses peR quantitatives en temps réel. Les résultats démontrent des réponses enzymatique et d'expression génique Na+/K+-ATPasique branchiales similaires chez les deux formes; soit une augmentation des activités spécifique et absolue après 14 jours (28%), ainsi qu'une diminution de l'expression de l'isoforme ala après 14 jours (28%) et une augmentation de l'expression de l'isoforme a1b après 60 jours (28%). Ces résultats suggèrent la conservation chez les résidents de la rivière Laval d'une certaine capacité d'habileté hypo-osmorégulatoire en eau salée au niveau de cette enzyme. L'expression différentielle des deux isoformes en fonction de la salinité suggère une activité ou une régulation de transport différente reliée à l'absorption ou l'excrétion d'ions. Un décalage entre les réponses d'expression génique et d'activité enzymatique a été observé, traduisant peut-être des inhibitions de la traduction ou simplement des temps de réponses différents pour ces deux processus. -- Mots clés: Omble de fontaine, Na+/K+-A TPase branchiale, anadromie, acclimatation eau salée, régulation ionique. -- ABSTRACT: Anadromous and river-resident brook charr (Salvelinus fontinalis) from Laval river (Northem shore, Québec) representent two genetically and physiologically distinct populations, living in sympatry. Anadromy implies an osmoregulatory challenge for fish and several physiological adjustments must be set up, including the up regulation of gill Na+/K+-A TPase activity, considered as a critical physiological variable for successful seawater acclimation in salmonids. It has been recently demonstrated in other anadromous salmon id species, that the two isoforms (a1a and a1b) of this enzyme are differently expressed according to salinity. In order to verify if there are differences in the saItwater osmoregulatory capacity at the gill Na+/K+-A TPase level in both forms, anadromous and river-resident brook charr (1+) were gradually transferred in estuarine water from June to August (increase of 2% day"l, final 28%) and compared to a control group stayed in fresh water. Before the transfer and after 3, 7, 14 and 60 days following saltwater transfer, enzymatic gill Na+/K+-ATPase absolute and specifie activities were measured. Relative expression of the two isoforms a1a and a1b were analysed using quantitative real time PCR. The results showed similar gill Na+/K+-ATPase responses at enzymatic and genomic expression levels in both forms of brook charr: up regulation of absolute and specifie activity after 14 days (28%), down regulation of ala isoform after 14 days (28%) and up regulation of a1b isoform after 60 days (28%). These results suggest a certain conservation of the hypo-osmoregulatory capacity in river-resident charr from Laval river at the gill Na+/K+-A TPase level. The differential expression of these isoforms according to salinity suggest that a1a and a1b may differ in transport activity or regulation related to ion uptake and secretion, respectively. A time lapse between enzymatic and genomic expression responses has been observed and may indicate translation inhibition or different time response of these two mechanisms. -- Keywords : Brook charr, gill Na+/K+-ATPase, anadromy, seawater acclimation, ion regulation

Algorithms Seminar 2001–2002, F. Chyzak (ed.), INRIA, (2003), pp. 17–18. Random Generation from Boltzmann Principles

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