PubMed Health⌕ Search

Biomedical subjects

G Merlin

Publications and source records attributed to G Merlin.

At least 19 recordsLinked to original sources
PubMed2005

How to treat raw sewage with constructed wetlands: an overview of the French systems.

The development of vertical flow constructed wetlands treating raw wastewater in France has proved to be very successful over the last 20 years. In view of this a survey was carried out on more than 80 plants in order to study their performance and correct the design if necessary. This study shows that such systems perform well in terms of respecting the goals of both low level outlet COD and SS and nitrification. Pollutant removal performance in relation to the loads handled and the specific characteristics of the plants were investigated. Nitrification is shown to be the most sensitive process in such systems and performance in relation to sizing is discussed. Such systems, if well designed, can achieve an outlet level of 60 mg L(-1) in COD, 15 mg L(-1) in SS and 8 mg L(-1) in TKN with an area of 2 - 2.5 m2.PE(-1). The sludge deposit on the first stage must be removed after about 10-15 years.

Biodegradation, Environmental↗
PubMed2005

Influence of surface layer on hydrology and biology of gravel bed vertical flow constructed wetlands.

In France, gravel vertical flow constructed wetlands (gVFCWs) were adapted to treat raw wastewater, which led to important accumulations of matter in filters (organic and mineral). To prevent clogging, large gravel sizes were employed (O 2-6 mm). The aim of this paper was to present the influences of matter accumulation on the hydraulic and biological behaviour of the system. A one-year survey of accumulated matter content and potential respiration activities was completed in three gVFCWs (operating for 3, 4 and 8 years). Cores were sampled into filters. Results showed a vertical stratification of accumulated matter and respiration rates. Dry accumulated matter quantities ranged from 20 kg m(-2) (3 and 4 years operating) to 80 kg m(-2) in the oldest plant (8 years). Potential respiration was larger in the oldest plant (75g O2m(-2)h(-1)) than in the most recent one (15g O2m(-2)h(-1)). Accumulated matter seemed to play a role both on the water retention (enhancing initial percolation time by 5 times) and biological profile (enhancing microfauna's diversity). Contrary to what is generally proposed in the literature, accumulated matter in French gVFCWs seemed to provide better treatment efficiency without leading to surface clogging compared to systems using sand.

Data Collection↗
PubMed2004

A mechanistic model for m-xylene treatment with a peat-bed biofilter.

The painting of vehicles in the automobile industry generates large quantities of gaseous emissions which contain volatile organic compounds (VOC) like xylenes. This polluted air has a high moisture content and a temperature around 15-20 degrees C. It is thus possible to consider its treatment by a biological way. In this paper, laboratory tests are described which led to the choice of packing material to make a biofilter having good removal efficiency. Moreover this technique is known for its simplicity and low energy cost. The maximum treatment capacity was obtained with peat. A mathematical model which makes it possible to specify the different limiting steps of the process was carried out. This considered both physical parameters of the biofilter and properties of the biofilm. By choosing a lower Henry's constant than typical air:water system, we obtain a better simulation of the xylenes concentration according to the biofilter length and applied load.

Air Pollutants↗
PubMed2001

Design and performance of experimental constructed wetlands treating coke plant effluents.

Reed beds were chosen to treat effluents from a coke plant in France (Usinor-Sollac, Fos/mer). The pilot is composed by a two-stage gravel bed with subsurface flow and Phragmites australis as plant. This experimental constructed wetland was monitored for one year at steady-state conditions. The composition of influent shows high concentrations of organic compounds. The hydraulic residence time was close to 10-12 days with a plug flow with longitudinal dispersion. Results show that global removal of nitrogen ranged from 54 to 94% of load removal efficiency, but corresponds easily to the regulation recommendations. Because of wintertime, the denitrification process was inhibited by aerobic conditions observed in the gravel bed with oxygen concentrations higher than 2-3 mg/L, and by small amounts of biodegradable carbon. The fate of mineral pollutants are linked to the complex ferric hydroxides balance and a lack of phosphorus was observed for reed plants, as this nutrient is dependent on iron compounds. Some necrosis was observed on plant tissues corresponding with anthocyanic pigments accumulation caused by phosphorus absorption deficiency due to its co-precipitation with iron.

Coke↗
PubMed2000

LdARL-3A, a Leishmania promastigote-specific ADP-ribosylation factor-like protein, is essential for flagellum integrity.

The small G protein-encoding LdARL-3A gene, a homologue of the human ARL-3 gene, was isolated from Leishmania donovani, and its protein product characterised. It is unique in the Leishmania genome and expressed only in the extracellular promastigote insect form, but not in the intracellular amastigote mammalian form, as shown by northern blots and western blots developed with a specific anti-C terminus immune serum. Indirect immunofluorescence microscopy revealed distinct labelled spots regularly distributed on the plasma membrane, including the part lining the flagellum and the flagellar pocket. By transfection experiments, it was found that wild-type LdARL-3A-overexpressing promastigotes reached higher densities in culture, but released significantly less secreted acid phosphatase in the extracellular medium than the parental strain. When LdARL-3A blocked under the GDP-bound 'inactive' form or with an inactivated potential myristoylation site was overexpressed, the cells displayed an apparent wild-type phenotype, but died earlier in the stationary phase; in contrast to parental cells, they showed a diffuse pattern of fluorescence labelling in the cytoplasm and on the cell membrane. Strikingly, when a constitutively 'active' form of LdARL-3A (blocked under the GTP-bound form) was overexpressed, the promastigotes were immobile with a very short flagellum, a slow growth rate and a low level of acid phosphatase secretion; the length of the flagellum was inversely proportional to mutant protein expression. We concluded that LdARL-3A could be an essential gene involved in flagellum biogenesis; it may provide new approaches for control of the parasite at the insect stage.

ADP-Ribosylation Factors↗
PubMed1999

Xanthine phosphoribosyltransferase from Leishmania donovani. Molecular cloning, biochemical characterization, and genetic analysis.

Xanthine phosphoribosyltransferase (XPRT) from Leishmania donovani is a unique enzyme that lacks a mammalian counterpart and is, therefore, a potential target for antiparasitic therapy. To investigate the enzyme at the molecular and biochemical level, a cDNA encoding the L. donovani XPRT was isolated by functional complementation of a purine auxotroph of Escherichia coli that also harbors deficiencies in the prokaryotic phosphoribosyltransferase (PRT) activities. The cDNA was then used to isolate the XPRT genomic clone. XPRT encodes a 241-amino acid protein exhibiting approximately 33% amino acid identity with the L. donovani hypoxanthine-guanine phosphoribosyltransferase (HGPRT) and significant homology with other HGPRT family members. Southern blot analysis revealed that XPRT was a single copy gene that co-localized with HGPRT within a 4.3-kilobase pair (kb) EcoRI fragment, implying that the two genes arose as a result of an ancestral duplication event. Sequencing of this EcoRI fragment confirmed that HGPRT and XPRT were organized in a head-to-tail arrangement separated by an approximately 2.2-kb intergenic region. Both the 3.2-kb XPRT mRNA and XPRT enzyme were significantly up-regulated in Deltahgprt and Deltahgprt/Deltaaprt L. donovani mutants. Genetic obliteration of the XPRT locus by targeted gene replacement indicated that XPRT was not an essential gene under most conditions and that the Deltaxprt null strain was competent of salvaging all purines except xanthine. XPRT was overexpressed in E. coli and the recombinant protein purified to homogeneity. Kinetic analysis revealed that the XPRT preferentially phosphoribosylated xanthine but could also recognize hypoxanthine and guanine. K(m) values of 7.1, 448.0, and >100 microM and k(cat) values of 3.5, 2.6, and approximately 0.003 s(-1) were calculated for xanthine, hypoxanthine, and guanine, respectively. The XPRT gene and XPRT protein provide the requisite molecular and biochemical reagents for subsequent studies to validate XPRT as a potential therapeutic target.

Amino Acid Sequence↗
PubMed1998

Conserved organization of genes in trypanosomatids.

Trypanosomatids are unicellular protozoan parasites which constitute some of the most primitive eukaryotes. Leishmania spp, Trypanosoma cruzi and members of the Trypanosoma brucei group, which cause human diseases, are the most studied representatives of this large family. Here we report a comparative analysis of a large genomic region containing glucose transporter genes in three Salivarian trypanosomes (T. brucei, T. congolense and T. vivax), T. cruzi and Leishmania donovani. In T. brucei, the 8 kb (upstream) and 14 kb (downstream) regions flanking the glucose transporter genes cluster contain two and six new genes, respectively, six of them encoding proteins homologous to known eukaryotic proteins (phosphatidylinositol 3 kinase, ribosomal protein S12, DNAJ and three small G-proteins--Rab1, YPT6 and ARL3). This gene organization is identical in T. brucei, T. congolense and T. vivax suggesting that Salivarian trypanosomes have a high level of conservation in gene organization. In T. cruzi and Leishmania, the overall organization of this cluster is conserved, with insertion of additional genes when compared with T. brucei. Phylogenetic reconstitution based on glucose transporters is in accord with the monophyly of the genus Trypanosoma and the early separation of T. vivax within Salivarian trypanosomes. On the basis of gene organization, biochemical characteristics of isoforms and phylogeny, we discuss the genesis of the glucose transporter multigene family in Salivarian trypanosomes.

Amino Acid Sequence↗
PubMed1997

The gene for the ligand binding chain of the human interferon gamma receptor.

In order to characterize the gene encoding the ligand binding (1(st); alpha) chain of the human IFN-gamma receptor, two overlapping cosmid clones were analyzed. The gene spans over 25 kilobases (kb) of the genomic DNA and has seven exons. The extracellular domain is encoded by exons 1 to 5 and by part of exon 6. The transmembrane region is also encoded by exon 6. Exon 7 encodes the intracellular domain and the 3' untranslated portion. The gene was located on chromosome 6q23.1, as determined by in situ hybridization. The 4 kb region upstream (5') of the gene was sequenced and analyzed for promoter activity. No consensus-matching TATA or CAAT boxes in the 5' region were found. Potential binding sites for Sp1, AP-1, AP-2, and CREB nuclear factors were identified. Compatible with the presence of the Sp1/AP-2 sites and the lack of TATA box, S1-nuclease mapping experiments showed multiple transcription initiation sites. Promoter activity of the 5' flanking region was analyzed with two different reporter genes: the Escherichia coli chloramphenicol acetyltransferase and human growth hormone. The smallest 5' region of the gene that still had full promoter activity was 692 base pairs in length. In addition, we found sequences belonging to the oldest family of Alu repeats, 2 - 3 kb upstream of the gene, which could be useful for genetic studies.

Amino Acid Sequence↗
PubMed1995

Isolation of an ubiquitously expressed cDNA encoding human dynamin II, a member of the large GTP-binding protein family.

Dynamin (Dyn) is a member of a novel group of GTPases which was initially identified as a microtubule-binding protein with a role in vectorial movement. Three distinct Dyn-encoding genes (DYN I, II and III), with a neuronal-, ubiquitous or testis-specific expression, respectively, have been identified in rat. In man, only DYN I has so far been characterized. We have previously isolated a genomic DNA fragment implicated in the correction of mitomycin C hypersensitivity of cells from a Fanconi anemia patient belonging to genetic complementation group D (FA(D)). Using this probe, we have cloned a human complementary DNA designated hDYN II encoding a ubiquitous Dyn isoform. The predicted protein consists of 866 amino acids (97.5 kDa). Dyn proteins exhibit a high degree of evolutionary conservation: hDyn II is 98% identical to rat Dyn II and 73% identical to hDyn I. A unique 3.6-kb transcript is found in all human tissues examined and it is more abundant in skeletal muscle and heart. This transcript is also expressed in tissue-culture cells. The hDYN II message is present and not mutated in the FA(D) patient studied. In addition to the GTP-binding domain and motifs associated with regulatory function, the hDyn II protein contains a noticeable number of concensus motifs for p34Cdc2 kinase phosphorylation which may indicate a potential role at the G2/mitosis transition. The sequence reported here should allow a more complete analysis of Dyn function(s) in man.

Amino Acid Sequence↗
PubMed1995

Increased expression of LD1 genes transcribed by RNA polymerase I in Leishmania donovani as a result of duplication into the rRNA gene locus.

Eukaryotic protein-coding genes are generally transcribed by RNA polymerase II (Pol II), which has a lower transcription rate than that of Pol I. We report here the duplication of two LD1 genes into the rRNA locus and their resultant transcription by Pol I. The multigenic LD1 locus is present in a 2.2-Mb chromosome in all stocks of Leishmania spp. and is also present in multicopy 200- to 450-kb linear chromosomes or multicopy circular DNAs in over 15% of stocks examined. Genomic rearrangement in Leishmania donovani LSB-51.1 resulted in duplication of a 3.9-kb segment of LD1 containing two genes (orfF and orfG) and of a 1.3-kb segment from approximately 10 kb downstream into the rRNA gene repeat region of the 1.2-Mb chromosome. Short sequences (12 or 13 bp) common to the 2.2-Mb LD1 and 1.2-Mb rRNA loci suggest that this gene conversion occurred by homologous recombination. Transcription of the duplicated genes is alpha-amanitin resistant, indicating transcription by Pol I, in contrast to the alpha-amanitin-sensitive (Pol II) transcription of the genes in the 2.2-Mb LD1 locus. This results in higher transcript abundance than expected from the gene copy number in LSB-51.1 and in elevated expression of at least the orfF gene product.

Amanitins↗
PubMed1994

Fate of a volatile chlorinated solvent in indoor aquatic microcosms: sublethal and static exposure to [14C]dichloromethane. Groupe pour l'Etude du Devenir de Xénobiotiques dans l'Environnement (GEDEXE).

The goal of this work was to study the fate of dichloromethane in indoor aquatic microcosms after a sublethal and static exposure to simulate the accidental contamination of a lenitic ecosystem such as littoral lake zone or a pond. This kind of ecosystem is characterized by high productive capacity and rich biocoenose, and are usually first affected by acute or chronic pollution. Microcosms containing immersed bryophytes (Fontinalis antipyretica), macrophytes (Lemna minor, Groenlendia densa, Elodea canadensis), molluscs (Physa fontinalis), crustaceans (Daphnia magna), and unicellular green algae (Scenedesmus subspicatus) were contaminated with sublethal concentrations of dichloromethane or [14C]dichloromethane. The initial mean concentration was 9.9 +/- 3.7 microM. The mean concentration exposure for organisms was 4.5 +/- 1.5 microM. The fate of 14C radioactivity was monitored by measuring the radioactivity of the sediment, water, macro- and microorganism, and atmospheric compartments. Radioactivity in the water disappeared quickly from the microcosms, most likely as [14C]dichloromethane (t1/2 = 5.31 +/- 0.41 days). At the end of the experiments, radioactivity was mainly located in the atmosphere, with traces remaining in the biomass. Under static conditions, the bioaccumulation of 14C radioactivity from the radiolabeled dichloromethane was negligible.

Animals↗
PubMed1994

An amplified DNA element in Leishmania encodes potential integral membrane and nucleotide-binding proteins.

LD1 is a 27.5-kb sequence that occurs in an approx. 2.2-Mb chromosome in all species and strains of Leishmania. In Leishmania infantum MHOM/BL/67/ITMAP263, LD1 is also present as an inverted dimeric repeat in multicopy, 55-kb circular molecules. Sequence analysis of a 7873-nt segment derived from the circular DNA reveals 4 open reading frames (ORFs) with potential protein coding function. One ORF predicts a protein with an ATP/GTP binding site motif. Another ORF predicts a protein with 10-12 potential membrane-spanning domains, suggesting that it encodes an integral membrane protein. This protein also has homology with that predicted by the ESAG10 gene of Trypanosoma brucei.

Adenosine Triphosphate↗
PubMed1992

Tumor necrosis factor-alpha and IL-6 up-regulate IFN-gamma receptor gene expression in human monocytic THP-1 cells by transcriptional and post-transcriptional mechanisms.

IFN-gamma is a potent activator of monocytic cell functions, including the stimulation of TNF-alpha and the control of IL-6 synthesis. These cytokines might act as autocrine or paracrine factors together with IFN-gamma in inducing biologic responses. In this study, we addressed the question of whether or not TNF-alpha and IL-6 play a role in modulating of IFN-gamma binding. Expression of IFN-gamma surface receptor was measured in the human monocytic THP-1 cells. The capacity of these cells to bind IFN-gamma increased with time after treatment with each cytokine. The number of IFN-gamma R per cell rose by three- and fourfold after 16 h of treatment with TNF-alpha and IL-6, respectively. Scatchard analysis of binding data showed that neither TNF-alpha nor IL-6 affected the affinity of IFN-gamma for its receptor. The increased surface expression of IFN-gamma R induced by TNF-alpha and IL-6 correlated with the rise in IFN-gamma mRNA receptor levels. TNF-alpha-mediated up-regulation of IFN-gamma R was due to an increase in transcriptional activity of the IFN-gamma R gene, as shown by run-on experiments. No significant modulation of IFN-gamma R gene transcription was observed in nuclei from cells treated with IL-6, whose effect appeared to be related to IFN-gamma mRNA receptor stabilization. Taken together, the present results provide, to our knowledge, the first evidence for cytokine-mediated up-regulation of IFN-gamma R in human monocytic cells. This up-regulation by TNF-alpha and IL-6, which are both produced by monocytes, occurs through different mechanisms, and may be of physiologic relevance in host defense.

Cell Line↗
PubMed1992

Functional characterization of a hybrid human-mouse interferon gamma receptor: evidence for species-specific interaction of the extracellular receptor domain with a putative signal transducer.

The human interferon gamma (IFN-gamma) receptor expressed in mouse cells displays binding properties indistinguishable from those of the resident receptor on human cells. Still, mouse cells expressing the human IFN-gamma receptor remain insensitive to human IFN-gamma. It is widely accepted that at least one species-specific cofactor encoded within human chromosome 21 is required for signal transduction. To define structural domains of the human IFN-gamma receptor responsible for this species-specific interaction, a hybrid between the human and the murine receptor was constructed and expressed in mouse L929 cells or in mouse L cell-derived SCC16-5 cells, which contain human chromosome 21. This hybrid receptor, which consisted of the extracellular domain of the human IFN-gamma receptor and the transmembrane and cytoplasmic domains of the murine IFN-gamma receptor, was found to bind human IFN-gamma with high affinity. However, only SCC16-5 cells expressing the human/mouse hybrid receptor were responsive to human IFN-gamma as revealed by enhanced expression of major histocompatibility complex class I antigens, induction of the transcription factor IRF-1, and induction of a partial antiviral state. These findings strongly suggest that IFN-gamma-mediated signal transduction requires a species-specific interaction of the extracellular portion of the known ligand-binding IFN-gamma receptor chain with an additional, presumably membrane-anchored receptor subunit.

Animals↗
PubMed1992

Pentoxifylline inhibits certain constitutive and tumor necrosis factor-alpha-induced activities of human normal dermal fibroblasts.

Pentoxifylline (PFN), analog of theobromine, which phenotypically and functionally alters various cell types including dermal fibroblasts, has been reported to inhibit tumor necrosis factor-alpha (TNF alpha) activation of neutrophils. We investigated the ability of PFN to alter constitutive and TNF alpha-induced biosynthetic activities of human normal dermal fibroblasts. The sixteenfold increase over constitutive intracellular 2'-5' oligo-adenylate synthetase (2'-5' A synthetase) activity induced by TNF alpha (400 U/ml) failed to occur when PFN (1 mg/ml) was added prior to cytokine treatment. This loss of biologic activity paralleled a reduction in 2'-5' A synthetase proteins and 2'-5' A synthetase-specific m-RNA. PFN failed to inhibit constitutive or TNF alpha-induced IL-6 hybridoma proliferative activity, IL-6 protein, or IL-6-specific m-RNA levels. The presence of PFN (1 mg/ml) in fibroblast cultures reduced constitutive synthesis of collagen and glycosaminoglycan (GAG) by 87% and 45%, respectively, and blocked induction of their synthesis by TNF alpha (10(4) U/ml). Total non-collagenous protein synthesis was not inhibited following PFN treatment (1 mg/ml). PFN did not inhibit TNF alpha induction of only those biosynthetic activities also susceptible to PFN in the constitutive state, with PFN failing to reduce constitutive collagenolytic activity but reducing TNF alpha-induced enhanced collagenolytic activity by 26% and collagenase m-RNA by 51%. Furthermore, PFN did inhibit, by 98%, TNF alpha-dependent murine and human fibroblast cytotoxicity. The selective nature of PFN inhibition of certain TNF alpha activities, the failure of PFN (1 mg/ml) to alter constitutive and TNF alpha-induced levels of type 1 and 2 TNF alpha receptor m-RNA, and the finding that PFN-treated fibroblasts express a similar number of receptors, of similar molecular weight and high affinity for TNF alpha as control, untreated cells, suggest that inhibitory activities of PFN are mediated at a locus other than receptors for TNF alpha.

2',5'-Oligoadenylate Synthetase↗
PubMed1991

Identification and characterization of a functional receptor for interferon-gamma on a megakaryocytic cell line.

We have previously shown that human interferon-gamma (Hu-IFN-gamma) induces platelets to become efficient effector cells, capable of killing young larvae of the parasite Schistosoma mansoni. Recently, binding sites for IFN-gamma on platelets have been characterized. We show here the presence of high-affinity receptors for IFN-gamma on the surface of the human megakaryocytic Dami cell line. Scatchard analysis indicated the presence of about 11,000 binding sites per cell, with a kd of 3 +/- 0.5 x 10(-10) mol/L; the apparent molecular weight of the receptor was 90 Kd. Receptor-bound 125I Hu-recombinant IFN-gamma was rapidly internalized and degraded when the temperature was increased from 4 degrees C to 37 degrees C. The half-life of this receptor was about 7 hours, and pretreatment of cells with IFN-gamma or phorbol myristate acetate had very little effect on the surface receptor number and no detectable effect on IFN-gamma receptor messenger RNA (mRNA) expression. The receptor was functional, because 24 hours of treatment with IFN-gamma led to the increase of HLA class I mRNA expression and to the initiation of HLA class II mRNA expression. These effects were selective because platelet glycoprotein Ib, IIb, or IIIa mRNA expression and cell proliferation were unaffected.

Blotting, Northern↗