1,721,092 research outputs found
Co-regulation of iron uptake system and exopolysaccharide biosynthetic operons in a biofilm-forming mutant of E.coli
No full textAppropriate use of positron emission tomography with [18F]fluorodeoxyglucose for staging of oncology patients
No full textPositron emission tomography (PET) was developed in the mid-1970, and its initial applications were for heart and brain imaging research. Nowadays, this technology is aimed mainly at staging or restaging tumours as it allows the assessment of biochemical processes that are either specific or associated with tumour biology. The full appreciation of PET potentials and limitations among general practitioners and internists cannot be considered achieved and the appropriate use of PET especially when coupled to X-ray computed tomography (CT) is still suboptimal. The majority of PET studies rely on the use of fluorodeoxyglucose labelled with fluorine-18 (FDG), which is a radiopharmaceutical specific for glucose transport and metabolism. PET with FDG is amenable for studying most type of tumours, including those of the head and neck, lung, oesophagus, colo-rectal, gastrointestinal stromal tumours, pancreas, some types of lymphomas and melanoma, whereas in some tumours, including those of the reproductive system, brain, breast and bones, there is a limited role for PET and there is no substantial role for FDG-PET for the bronchoalveolar, hepatocellular, urinary system, testicular, neuroendocrine, carcinoids and adrenal tumours, differentiated thyroid cancers, and several subtypes of malignant lymphoma. Thus, the limits of FDG have stimulated the use and development of other radiopharmaceuticals. These tracers represent the opportunity for expanding the use of PET to other areas in oncology in the near future
THE SUBTLE BIOFILM REGULATION IN ESCHERICHIA COLI: CSGD AND THE YDDV-DOS OPERON
Full text linkIn this PhD thesis work I investigated the expression modulation of the major adhesion factors in Escherichia coli; in particular I focused on the role of GGDEF and EAL proteins, on their modulation in E. coli biofilm formation in response to environmental signals and on regulation of curli fibers, cellulose and poly-N-acetylglucosamine (PNAG), the most important biofilm determinants in E. coli.
E. coli is an Enterobacterium, normally living inside the mammalian gut, at temperature of 37° C and in relatively nutrient-rich environment. Once outside the host, bacteria usually face much lower temperatures (< 30°C) and a nutrient-limiting environment. The biofilm determinants studied in this thesis are all expressed in response to environmental conditions such as low temperature, low osmolarity and starvation, suggesting that E. coli bacteria switch to a biofilm mode of growth as part of their adaptation to the natural environment. In response to reduction in growth rates, E. coli seems to canalize its energy consumption into production of extracellular features such as curli or exopolysaccharides. Biofilms can be thus considered as a “resistance form” of growth able to withstand stress conditions more efficiently than cells living in a planktonic mode of growth. The CsgD protein is the master regulator of E. coli biofilm formation. It is a transcriptional factor necessary for curli genes transcription and, through the AdrA protein, for cellulose biosynthesis. Gene regulation by CsgD is tightly connected to production and sensing of cyclic di-GMP, a bacterial second messenger involved in various cellular processes, including biosynthesis of extracellular polysaccharides (Simm et al., 2004), biofilm formation (Hickman et al., 2005), and virulence (Pratt et al., 2007; Tischler and Camilli, 2005), as well as morphological and physiological differentiation (Paul et al., 2004). The CsgD-dependent adrA gene, involved in cellulose biosynthesis (Zogaj et al., 2001), encodes a cyclic di-GMP synthase (Simm et al., 2004). CsgD can also activate yoaD, whose gene product is a cyclic di-GMP phosphodiesterase, suggesting that CsgD is directly involved in feedback regulation of cyclic di-GMP intracellular levels and of cellulose biosynthesis (Brombacher et al., 2006). CsgD is also able to activate the iraP gene: IraP acts as a stabilization factor for the σs protein, an alternative sigma factor of RNA polymerase which directs transcription of genes involved in adaptation to slow growth and to cellular stresses. Here I showed that CsgD transcription activation of the iraP gene does result in a significant increase of σs intracellular concentration by positively affecting σs protein stability, thus leading to altered expression of σs-dependent genes. CsgD-mediated increase of σs cellular concentrations via the iraP gene would trigger an autoactivation loop leading to an increased production of CsgD-dependent adhesion determinants such as curli fibers and cellulose. This autoregulatory circuitry might be further fueled by σs-dependent induction of genes encoding di-guanylate cyclases, i.e., proteins able to synthesize the second messenger di-cyclic- GMP, which, in turn, can positively affect csg gene expression (Kader et al., 2006; Weber et al., 2002). The yddV-dos operon is the most expressed among c-di-GMP-related genes showing dependence on σs (Weber et al., 2006; Sommerfeldt et al., 2009). It encodes, respectively, a protein with DGC activity and a PDE that can degrade c-di- GMP to pGpG. Both Dos and YddV are heme-binding oxygen sensors, and interact to form a stable protein complex (Tuckerman et al., 2009). Although it has been reported that YddV overexpression can stimulate biofilm formation (Mendez-Ortiz et al., 2006), the targets of yddV-dependent biofilm induction had not yet been identified. Here I showed that YddV acts modulating curli and PNAG expression. Control of curli production by yddV-dos takes place at the level of transcription regulation of the csgBAC operon, encoding curli structural subunits, and is mediated by the DGC and PDE activities of YddV and Dos. In contrast, the YddV–Dos protein complex does not strongly influence csgDEFG expression, nor does it affect the expression of the CsgD-dependent adrA gene, encoding a positive effector for cellulose biosynthesis. Regarding PNAG production, we showed that YddV is able to prevent degradation of pgaABCD transcript in the MG1655csrA background, thus suggesting that a DGC might regulate gene expression by affecting mRNA stability in E. coli. YddV regulation of pgaABCD operon in a wild type contest is still controversial: pgaABCD genes are expressed at low levels in MG1655 (the standard laboratory strain of E. coli) and their mRNA half-life is lower than two minutes regardless of the growth conditions tested; thus, possible effects of yddV inactivation on destabilization of the pga transcript are not easy to evaluate in the wt contest. In the last part of my thesis I tried to characterize a biofilm-forming mutant of E. coli, able to express pgaABCD genes at high levels. Even if initial data suggested that a mutation in the csrA gene could be responsible for pga mRNA stabilization in this mutant, actual the mutation leading to the adhesive phenotype and to PNAG production is outside the csrA gene and is still unknown. Moreover my data suggest a connection between pga expression and iron regulation in E. coli strains: it is conceivable that pgaABCD expression and consequent biofilm formation and the adherent phenotype depends on concerted production of different determinants, whose expression is also affected by iron concentration. Thus, my research highlighted that biofilm production is the result of coordinated expression of different adhesion determinants, whose regulation is complex and not fully understood. In particular, the precise extent and the molecular mechanism of c-di-GMP adhesion factors regulation remains to be largely identified and represents an exciting challenge for future research in the biofilm field
High interaction regime Lockhart-Martinelli model for pressure drop in trickle-bed reactors
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Apparently dominant transmission of a recessive disease: deficiency of factor VII in Iranian Jews
No full textIn inherited disorders transmitted as autosomal recessive traits the children of affected individuals are usually asymptomatic and phenotypically normal because they are heterozygous for the defect. In an Iranian Jewish family with moderately severe deficiency of coagulation factor VII (an autosomal recessive bleeding disorder) the son of an affected woman was also affected. DNA analysis of the factor VII gene showed that this unusual situation was due to the fact that he inherited an abnormal allele with the Ala244Val missense mutation from both the homozygous mother and the heterozygous father. The parents, although not overtly consanguineous, belong to the same ethnic group of Iranian Jews, among whom this factor VII gene mutation reaches high frequencies (between 2 and 3%) in the heterozygous state
Biofilm formation-gene expression relay system in Escherichia coli: modulation of sigma(S)-dependent gene expression by the CsgD regulatory protein via sigma(S) protein stabilization
No full textBacteria can switch from a single-cell (planktonic) mode to a multicellular community (biofilm) mode via production of cell-cell aggregation and surface adhesion factors. In this report, we present evidence that the CsgD protein, a transcription regulator involved in biofilm formation in Escherichia coli, modulates the expression of the rpoS (sigmaS) regulon. Protein pattern analysis of E. coli cells in stationary phase shows that CsgD affects the expression of several proteins encoded by sigmaS-dependent genes. CsgD regulation of sigmaS-dependent genes takes place at gene transcription level, does not by-pass the need for rpoS and is abolished in an rpoS null mutant. Consistent with these results, we find that CsgD expression leads to an increase in sigmaS intracellular concentration. Increase in sigmaS cellular amount is mediated by CsgD-dependent transcription activation of iraP, encoding a factor involved in sigmaS protein stabilization. Our results strongly suggest that the CsgD regulatory protein plays a major role as a relay between adhesion factors production and sigmaS-dependent gene expression via sigmaS protein stabilization. Direct co-ordination between biofilm formation and expression of the rpoS regulon could positively impact important biological processes, such as host colonization or response to environmental stresses
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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