Eicosanoids and the stomach

Eicosanoids are arachidonic acid derivatives that include prostaglandins, thromboxanes, and leukotrienes. During the last three decades, it has become evident that these bioactive lipids play a pivotal role in gastric physiology. The goal of the present review is to describe their involvement in the normal regulation of gastric secretion and gastric motility, as well as in gastric mucosal defense. Their role in gastric mucosal mitogenesis, apoptosis, inflammation, and immune modulatory responses is also discussed.     

Cross-hybridizing snake satellite, Drosophila, and mouse DNA sequences may have arisen independently

Previous reports have interpreted hybridization between snake satellite DNA and DNA clones from a variety of distant taxonomic groups as evidence for evolutionary conservation, which implies common ancestry (homology) and/or convergence (analogy) to produce the cross- hybridizing sequences. We have isolated 11 clones from a genomic library of Drosophila melanogaster, using a cloned 2.5-kb snake satellite probe of known nucleotide sequence. We have also analysed published sequence data from snakes, mice, and Drosophila. These data show that (1) all of the cross-hybridization between the snake, fly, and mouse clones can be accounted for by the presence of either of two tandem repeats, [GATA]n and [GACA]n and (2) these tandem repeats are organized differently among the different species. We find no evidence that these sequences are homologous apart from the existence of the simple repeat itself, although their divergence from a common ancestral sequence cannot be ruled out. The sequences contain a variety of homogeneous clusters of tandem repeats of CATA, GA, TA, and CA, as well as GATA and GACA. We suggest that these motifs may have arisen by a self-accelerating process involving slipped-strand mispairing of DNA. Homogeneity of the clusters might simply be the result of a rate of accumulation of tandem repeats that exceeds that of other mutations.      

Intracellular fate of Francisella tularensis within arthropod-derived cells

Since transmission of Francisella tularensis into the mammalian host occurs via arthropod vectors such as ticks, mosquitoes, horseflies and deerflies, recent studies have established Drosophila melanogaster as an arthropod vector model system. Nothing is known about the intracellular fate of F. tularensis within arthropod‐derived cells, and the role of this host‐parasite adaptation in the evolution of this pathogen to infect mammals. In this report, we explored intracellular trafficking of F. tularensis ssp. novicida in D. melanogaster‐derived S2 cells. First, we show that similar to the F. tularensis ssp. holarctica‐derived LVS strain, F. tularensis ssp. novicida is highly infectious, replicates exponentially within S2 cells and within adult flies, and is fatal to adult fruit flies in a dose‐dependent manner, while the iglC, iglD and mglA mutants are defective. Using electron and fluorescence microscopy‐based phagosome integrity assays, we show that the wild‐type strain escapes into the cytosol of S2 cells within 30–60 min post infection and by 6 h, 90% were cytosolic. In contrast, approximately 40–50% of the iglC and iglD mutants escape into the cytosol by 6 h while the other subpopulation becomes enclosed within multilamellar vesicles (MLVs). Pre‐treatment of S2 cells with the autophagy inhibitor methyl adenine blocks formation of the MLVs and all the vacuolar subpopulation of the iglC and iglD mutant bacteria become enclosed within single membrane‐surrounded vacuoles. Endocytic trafficking studies of F. tularensis within S2 cells show transient colocalization of the bacterial phagosome with D. melanogaster LAMP2–GFP fusion but not with lysosomes pre‐loaded with fluorescent dextran. Our data show that MLVs harbouring the iglC mutant acquire Lamp2 and dextran while MLVs harbouring the iglD mutant exclude these late endosomal and lysosomal markers. Our data indicate crucial differences in the role of the pathogenicity island‐encoded proteins in modulating intracellular trafficking within human macrophages and arthropod vector‐derived cells.     

An Algorithm to Automate Yeast Segmentation and Tracking

Our understanding of dynamic cellular processes has been greatly enhanced by rapid advances in quantitative fluorescence microscopy. Imaging single cells has emphasized the prevalence of phenomena that can be difficult to infer from population measurements, such as all-or-none cellular decisions, cell-to-cell variability, and oscillations. Examination of these phenomena requires segmenting and tracking individual cells over long periods of time. However, accurate segmentation and tracking of cells is difficult and is often the rate-limiting step in an experimental pipeline. Here, we present an algorithm that accomplishes fully automated segmentation and tracking of budding yeast cells within growing colonies. The algorithm incorporates prior information of yeast-specific traits, such as immobility and growth rate, to segment an image using a set of threshold values rather than one specific optimized threshold. Results from the entire set of thresholds are then used to perform a robust final segmentation.     

Fungi associated with rice at entre rios province, Argentina. toxigenic capacity offusarium graminearum andmicrodochium nivale isolates

A mycological survey was carried out on rice samples harvested in 1997 and 1998 from Entre Ríos province, belonging to the main production area of Argentina. The relative density and isolation frequency of the prevalent fungi were statistically compared between locations and harvest seasons. The genusAlternaria was the most prevalent component of the internal seedborne mycoflora in the two harvest seasons. Fungi belonging to the generaPhoma, Fusarium, Microdochium, Penicillium andAspergillus were also isolated. The predominant species of these genera wereAlternaria alternata, Phoma glomerata, Fusarium graminearum, Microdochium nivale, Penicillium citrinum and Aspergillus flavus.     

Plasma Levels of Trace Elements Have an Implication on Interferon Treatment of Children with Chronic Hepatitis B Infection

This study evaluated the plasma levels of trace elements in children with chronic hepatitis B virus (HBV) infection and assessed whether they can be a factor that affects the response to interferon alpha (IFN-α) treatment. The study included 35 cases (ten girls, 25 boys) aged 3–13 years with chronic HBV infection and the control group. Plasma levels of copper (Cu), manganese (Mn), molybdenum (Mo), selenium (Se), and zinc (Zn) were measured before IFN-α treatment and biochemical, virological, and histopathologic response to treatment were assessed. Children were followed for at least 15 months. Although plasma Cu levels showed no difference between the groups, Mn, Mo, Se, and Zn levels were significantly lower in the study group before treatment. Fourteen cases (40%) showed biochemical response; 17 (48.6%) showed virological response; 16 (47.6%) showed histopathologic response, and ten (28.6%) showed response according to all three parameters. Plasma Cu and Mn levels of patients with triple response showed no difference; but Mo, Se, and Zn levels were significantly lower (p?<?0.001) in the study group. No difference was observed between responders and nonresponders (p?>?0.05). Plasma levels of Mn, Mo, Se, and Zn are lower in children with chronic HBV infection compared to healthy children. The pretreatment levels of these elements did not show difference between responders and nonresponders to IFN-α.     

Evolution of the secondary structures and compensatory mutations of the ribosomal RNAs of Drosophila melanogaster

This paper examines the effects of DNA sequence evolution on RNA secondary structures and compensatory mutations. Models of the secondary structures of Drosophila melanogaster 18S ribosomal RNA (rRNA) and of the complex between 2S, 5.8S, and 28S rRNAs have been drawn on the basis of comparative and energetic criteria. The overall AU richness of the D. melanogaster rRNAs allows the resolution of some ambiguities in the structures of both large rRNAs. Comparison of the sequence of expansion segment V2 in D. melanogaster 18S rRNA with the same region in three other Drosophila species and the tsetse fly (Glossina morsitans morsitans) allows us to distinguish between two models for the secondary structure of this region. The secondary structures of the expansion segments of D. melanogaster 28S rRNA conform to a general pattern for all eukaryotes, despite having highly divergent sequences between D. melanogaster and vertebrates. The 70 novel compensatory mutations identified in the 28S rRNA show a strong (70%) bias toward A-U base pairs, suggesting that a process of biased mutation and/or biased fixation of A and T point mutations or AT-rich slippage-generated motifs has occurred during the evolution of D. melanogaster rDNA. This process has not occurred throughout the D. melanogaster genome. The processes by which compensatory pairs of mutations are generated and spread are discussed, and a model is suggested by which a second mutation is more likely to occur in a unit with a first mutation as such a unit begins to spread through the family and concomitantly through the population. Alternatively, mechanisms of proofreading in stem-loop structures at the DNA level, or between RNA and DNA, might be involved. The apparent tolerance of noncompensatory mutations in some stems which are otherwise strongly supported by comparative criteria within D. melanogaster 28S rRNA must be borne in mind when compensatory mutations are used as a criterion in secondary-structure modeling. Noncompensatory mutation may extend to the production of unstable structures where a stem is stabilized by RNA- protein or additional RNA-RNA interactions in the mature ribosome. Of motifs suggested to be involved in rRNA processing, one (CGAAAG) is strongly overrepresented in the 28S rRNA sequence. The data are discussed both in the context of the forces involved with the evolution of multigene families and in the context of molecular coevolution in the rDNA family in particular.      

Genetic engineering of Bacillus subtilis for the commercial production of riboflavin

Recombinant DNA engineering was combined with mutant selection and fermentation improvement to develop a strain of Bacillus subtilis that produces commercially attractive levels of riboflavin. The B. subtilis riboflavin production strain contains multiple copies of a modified B. subtilis riboflavin biosynthetic operon (rib operon) integrated at two different sites in the B. subtilis chromosome. The modified rib operons are expressed constitutively from strong phage promoters located at the 5′ end and in an internal region of the operon. The engineered strain also contains purine analog-resistant mutations designed to deregulate the purine pathway (GTP is the precursor for riboflavin), and a riboflavin analog-resistant mutation in ribC that deregulates the riboflavin biosynthetic pathway. Received 22 June 1998/ Accepted in revised form 6 November 1998