Cloning of histidine genes of Azospirillum brasilense: organization of the ABFH gene cluster and nucleotide sequence of the hisB gene

Summary A cluster of four Azospirillum brasilense histidine biosynthetic genes, hisA, hisB, hisF and hisH, was identified on a 4.5 kb DNA fragment and its organization studied by complementation analysis of Escherichia coli mutations and nucleotide sequence. The nucleotide sequence of a 1.3 kb fragment that complemented the E. coli hisB mutation was determined and an ORF of 624 nucleotides which can code for a protein of 207 amino acids was identified. A significant base sequence homology with the carboxyterminal moiety of the E. coli hisB gene (0.53) and the Saccharomyces cerevisiae HIS3 gene (0.44), coding for an imidazole glycerolphosphate dehydratase activity was found. The amino acid sequence and composition, the hydropathic profile and the predicted secondary structures of the yeast, E. coli and A. brasilense proteins were compared. The significance of the data presented is discussed.Abbreviations IGP imidazole glycerolphosphate - HP histidinolphosphate     

Pull-push neuromodulation of LTP and LTD enables bidirectional experience-induced synaptic scaling in visual cortex

Neuromodulatory input, acting on G protein-coupled receptors, is essential for the induction of experience-dependent cortical plasticity. Here we report that G-coupled receptors in layer II/III of visual cortex control the polarity of synaptic plasticity through a pull-push regulation of LTP and LTD. In slices, receptors coupled to Gs promote LTP while suppressing LTD; conversely, receptors coupled to Gq11 promote LTD and suppress LTP. In vivo, the selective stimulation of Gs- or Gq11-coupled receptors brings the cortex into LTP-only or LTD-only states, which allows the potentiation or depression of targeted synapses with visual stimulation. The pull-push regulation of LTP/LTD occurs via direct control of the synaptic plasticity machinery and it is independent of changes in NMDAR activation or neuronal excitability. We propose these simple rules governing the pull-push control of LTP/LTD form a general metaplasticity mechanism that may contribute to neuromodulation of plasticity in other cortical circuits.     

Helicobacter pylori virulence genes and host IL-1RN and IL-1beta genes interplay in favouring the development of peptic ulcer and intestinal metaplasia

Helicobacter pylori infection outcome might depend on genotypic polymorphisms of both the bacterium and the host. We ascertained: (1) the functionality of H. pylori oipA gene; (2) the polymorphism of the hostinterleukin (IL-1beta) gene (-31 C/T) and of the IL-1RN gene (intron 2 VNTR); (3) the association between the above genes and the histological and pathological outcome of H. pylori infection. One hundred and sixty-five H. pylori positive and 137 H. pylori negative subjects (23 gastric adenocarcinoma, 58 peptic ulcer, 221 gastritis) were studied. oipA was sequenced, IL-1beta was RFLP analysed. Antral and body mucosal biopsies were histologically evaluated. Functional oipA genes were correlated with cagA gene; both genes were significantly associated with gastritis activity, peptic ulcer and gastric adenocarcinoma. In these patients heterozygousIL-1RN 1/2 and IL-1beta C/T genotypes were more frequent than in gastritis patients. Intestinal metaplasia was associated with cagA, functional oipA and IL-1RN 2 allele. In conclusion, peptic ulcer and the preneoplastic intestinal metaplasia are associated with H. pylori virulence genes and with IL-1RN 2 host allele. An interplay between bacterial virulence factors and cytokines genotypes, is probably the main route causing H. pylori infection to lead to benign mild disease, benign severe disease or preneoplastic lesions.     

Re-infestation of houses by Triatoma dimidiata after intra-domicile insecticide application in the Yucatán peninsula, Mexico

In most countries, Chagas disease transmission control remains based on domestic insecticide application. We thus evaluated the efficacy of intra-domicile cyfluthrin spraying for the control of Triatoma dimidiata, the only Chagas disease vector in the Yucatán peninsula, Mexico, and monitored potential re-infestation every 15 days for up to 9 months. We found that there was a re-infestation of houses by adult bugs starting 4 months after insecticide application, possibly from sylvatic/peridomicile areas. This points out the need to take into account the potential dispersal of sylvatic/peridomestic adult bugs into the domiciles as well as continuity action for an effective vector control.     

A model of visual perception

In this paper we propose a model of visual perception in which a positive feedback mechanism can reproduce the pattern stimulus on a neurons screen. The pattern stimulus reproduction is based on informations coming from the spatial derivatives of visual pattern. This information together with the response of the feature extractors provides to the reproduction of the visual pattern as neuron screen electric activity. We simulate several input patterns and prove that the model reproduces the percept.     

Secondary production and richness of native and non-native macroinvertebrates are driven by human-altered shoreline morphology in a large river

Animals living in extreme environments with predictable seasonality may have important life history events correlated to favourable periods. These animals pass critical life stages in protected habitats, especially during early life, often receiving parental care. It is thus hypothesized that juveniles rely on protective microhabitats provided by their parents, becoming independent only during favourable seasons. Semi-terrestrial crayfish Parastacus pugnax inhabit burrows in highly seasonal and predictable environments, thus being well suited to test this hypothesis. Following marked burrows and individual crayfish we examined the life history patterns of P. pugnax in their natural environment to test the predictions that (i) burrowing activity is higher during the wet season, (ii) reproductive events occur during favourable seasons and (iii) juveniles only disperse after reaching larger sizes. There was little or no burrowing activity during the dry season, when soil was more compact, but burrows became wider and had more openings during the wet season. After hatching, juveniles cohabited with adults for at least 4 months during the dry season. During this period juveniles grew considerably, starting independent lives during the wet season. These results suggest that the prolonged parent-offspring cohabitation evolved in response to the predictable seasonal variations in the crayfish habitat.