(dC-dA)n.(dG-dT)n sequences have evolutionarily conserved chromosomal locations in Drosophila with implications for roles in chromosome structure and function.

In situ hybridization of (dC-dA)n.(dG-dT)n to the polytene chromosomes of Drosophila melanogaster reveals a clearly non-random distribution of chromosomal sites for this sequence. Sites are distributed over most euchromatic regions but the density of sites along the X chromosome is significantly higher than the density over the autosomes. All autosomes show approximately equal levels of hybridization except chromosome 4 which has no detectable stretches of (dC-dA)n.(dG-dT)n. Another striking feature is the lack of hybridization of the beta-heterochromatin of the chromocenter. The specific sites are conserved between different strains of D. melanogaster. The same overall chromosomal pattern of hybridization is seen for the other Drosophila species studied, including D. simulans, a sibling species with a much lower content of middle repetitive DNA, and D. virilis, a distantly related species. The evolutionary conservation of the distribution of (dC-dA)n.(dG-dT)n suggests that these sequences are of functional importance. The distribution patterns seen for D. pseudoobscura and D. miranda raise interesting speculations about function. In these species a chromosome equivalent to an autosomal arm of D. melanogaster has been translocated onto the X chromosome and acquired dosage compensation. In each species the new arm of the X also has a higher density of (dC-dA)n.(dG-dT)n similar to that seen on other X chromosomes. In addition to correlations with dosage compensation, the depletion of (dC-dA)n.(dG-dT)n in beta-heterochromatin and chromosome 4 may also be related to the fact that these regions do not normally undergo meiotic recombination.     

Ultrastructural neurohistochemical evidence for a neuro-endocrine link in the regulation of the extra-hepatic biliary dynamics.

Electron microscopical neurohistochemical studies of the choledocho-duodenal junction of the cat revealed acetylcholinesterase-positve nerve terminals closely abutting on ("ectopic"), mono-amine(s)-containing alpha-cells (of the islets of Langerhans) scattered in small clusters between bundles of the sphincteric smooth muscle (of Oddi). The cell membrane of the alpha-cells at and near the site of the neuro-effector contacts was reactive, too. This finding may be considered as some evidence for cholinergic innervation of cholinoceptive neuro-endocrine cells, and obviously represents one of the neuro-endocrine links involved in the regulation of the extra-hepatic biliary dynamics, demonstrated earlier in physiological and pharmacological studies.     

A change in the stability of globin mRNA during the induction of murine erythroleukemia cells

The stability of globin mRNA in murine erythroleukemia cells (Friend cells) before and during DMSO-induced differentiation was investigated. Cells were exposed to 3H-uridine for 2 hr and then transferred to medium without the radioactive precursor. The loss of radioactivity in total RNA, poly(A)-containing RNA and globin mRNA was followed. The globin mRNA was isolated using a highly specific globin cDNA column. In uninduced cells and cells early in differentiation, the globin mRNA decays with a half-life of less than 50 hr. After 4 days of induction, the globin mRNA decays with a half-life of 17 hr, demonstrating a change in stability during the induction process. Although the stability of globin mRNA changes during induction, this is not true for total poly(A)-containing RNA. At all times of induction, the poly(A)-containing RNA decays as two populations, one with a half-life of 6 hr and the other with a half-life of 36 hr. The half-life of the rRNA also remains unchanged during differentiation.     

From geochemical background determination to pollution assessment of heavy metals in sediments and soils

Establishing geochemical background concentrations to distinguish the natural background from anthropogenic concentrations of heavy metals in sediments and soils is necessary to develop guidelines for environmental legislation. Due to the fact that the background concentrations strongly depend on geological characteristics such as mineral composition, grain size distribution and organic matter content, several normalization methods have been developed. Empirical (geochemical), theoretical (statistical) and integrated methods (combining both empirical and theoretical methods) are the main approaches described in literature for determination of geochemical background concentrations. In this review paper, the different approaches as well as the main normalization methods for heavy metal concentrations in sediments and soils will be discussed. Both geochemical background concentrations and added risk level (maximum permissible addition) should be taken into account for setting up legal threshold limits. Moreover, different approaches to evaluate the pollution status of heavy metals in sediments and soils, from Sediment/Soil Quality Guidelines to quantitative indices (Geo-accumulation Index-I_geo, Enrichment Factor-EF, Pollution Load Index-PLI and Risk assessment Code-RAC) will be presented. Although guidelines to establish whether a sediment or soil is polluted or not are generally only related to total metal concentrations, the available/reactive pool i.e., availability/reactivity of metals should be taken into account for sediment/soil pollution assessment.     

Harvesting and seeding of stochastic populations: analysis and numerical approximation

Journal of Mathematical Biology - We study an ecosystem of interacting species that are influenced by random environmental fluctuations. At any point in time, we can either harvest or seed...     

Sequence‐independent processing site of the C‐terminal domain (CTD) influences maturation of the RgpB protease from Porphyromonas gingivalis

The Gram‐negative periodontal pathogen Porphyromonas gingivalis produces a family of outer membrane‐anchored proteases, the gingipains, shown to play an essential role in virulence of the organism. The C‐terminal domain (CTD) of gingipains and other secreted proteins is known to be the targeting signal for maturation and translocation of the protein through the outer membrane. The CTD is subsequently cleaved during the secretion process. Multiple alignment of various CTDs failed to define a consensus sequence at the putative CTD processing site. Using mutagenesis, we were able to show that cleavage at the site is not dependent on a specific residue and that recognition of the site is independent of local sequence. Interestingly, length of the junction between the CTD and adjacent Ig‐like subdomain has a critical influence on post‐translational glycan modification of the protein, whereby insertion of additional residues immediately N‐terminal to the cleavage site results in failure of glycan modification and release of soluble protease into the culture medium. Various hypotheses are presented to explain these phenomena. Knowledge of the role CTDs play in maturation of gingipains has broader application for understanding maturation of CTD homologues expressed by bacteria of the Bacteriodetes phylum.     

Antisense expression of carnation cDNA encoding ACC synthase or ACC oxidase enhances polyamine content and abiotic stress tolerance in transgenic tobacco plants

The amount of polyamines (such as putrescine, spermidine, and spermine) increased under environmental stress conditions. We used transgenic technology in an attempt to evaluate their potential for mitigating the adverse effects of several abiotic stresses in plants. Because there is a metabolic competition for S-adenosylmethionine as a precursor between polyamine (PA) and ethylene biosyntheses, it was expected that the antisense-expression of ethylene biosynthetic genes could result in an increase in PA biosynthesis. Antisense constructs of cDNAs for senescence-related 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (CAS) and ACC oxidase (CAO) were isolated from carnation flowers that were introduced into tobacco by Agrobacterium-mediated transformation. Several transgenic lines showed higher PA contents than wild-type plants. The number and weight of seeds also increased. Stress-induced senescence was attenuated in these transgenic plants in terms of total chlorophyll loss and phenotypic changes after oxidative stress with hydrogen peroxide (H2O2), high salinity, acid stress (pH 3.0), and ABA treatment. These results suggest that the transgenic plants with antisense CAS and CAO cDNAs are more tolerant to abiotic stresses than wild-type plants. This shows a positive correlation between PA content and stress tolerance in plants.