Cadmium stress: an oxidative challenge

At the cellular level, cadmium (Cd) induces both damaging and repair processes in which the cellular redox status plays a crucial role. Being not redox-active, Cd is unable to generate reactive oxygen species (ROS) directly, but Cd-induced oxidative stress is a common phenomenon observed in multiple studies. The current review gives an overview on Cd-induced ROS production and anti-oxidative defense in organisms under different Cd regimes. Moreover, the Cd-induced oxidative challenge is discussed with a focus on damage and signaling as downstream responses. Gathering these data, it was clear that oxidative stress related responses are affected during Cd stress, but the apparent discrepancies observed in between the different studies points towards the necessity to increase our knowledge on the spatial and temporal ROS signature under Cd stress. This information is essential in order to reveal the exact role of Cd-induced oxidative stress in the modulation of downstream responses under a diverse array of conditions.     

Critical oxygen partial pressures and maximal tracheal conductances for Drosophila melanogaster reared for multiple generations in hypoxia or hyperoxia

In Drosophila melanogaster and other insects, increases in atmospheric oxygen partial pressure (aPO₂) tend to increase adult body size and decrease tracheal diameters and tracheolar proliferation. If changes in tracheal morphology allow for functional compensation for aPO₂, we would predict that higher aPO₂ would be associated with higher critical PO₂ values (CritPO₂) and lower maximal tracheal conductances (G_max). We measured CritPO₂ and G_max for adult and larval vinegar flies reared for 7-9 generations in 10, 21 or 40 kPa O₂. The CritPO₂, CO₂ emission rates and G_max values were generally independent of the rearing PO₂ these flies had experienced, suggesting that minimal functional changes in tracheal capacities occurred in response to rearing PO₂. Larvae were able to continue activity during 20 min of anoxia. The lack of multigenerational rearing PO₂ effects on tracheal function suggests that the functional compensation at the whole-body level due to tracheal morphological changes in response to aPO₂ may be minimal; alternatively the benefits of such compensation may occur in specific tissues or during processes not assessed by these methods. In larvae, the CritPO₂ and the capacity for movement in anoxia suggest adaptations for life in hypoxic organic matter.     

Neuroligin Trafficking Deficiencies Arising from Mutations in the α/β-Hydrolase Fold Protein Family

Despite great functional diversity, characterization of the α/β-hydrolase fold proteins that encompass a superfamily of hydrolases, heterophilic adhesion proteins, and chaperone domains reveals a common structural motif. By incorporating the R451C mutation found in neuroligin (NLGN) and associated with autism and the thyroglobulin G2320R (G221R in NLGN) mutation responsible for congenital hypothyroidism into NLGN3, we show that mutations in the α/β-hydrolase fold domain influence folding and biosynthetic processing of neuroligin3 as determined by in vitro susceptibility to proteases, glycosylation processing, turnover, and processing rates. We also show altered interactions of the mutant proteins with chaperones in the endoplasmic reticulum and arrest of transport along the secretory pathway with diversion to the proteasome. Time-controlled expression of a fluorescently tagged neuroligin in hippocampal neurons shows that these mutations compromise neuronal trafficking of the protein, with the R451C mutation reducing and the G221R mutation virtually abolishing the export of NLGN3 from the soma to the dendritic spines. Although the R451C mutation causes a local folding defect, the G221R mutation appears responsible for more global misfolding of the protein, reflecting their sequence positions in the structure of the protein. Our results suggest that disease-related mutations in the α/β-hydrolase fold domain share common trafficking deficiencies yet lead to discrete congenital disorders of differing severity in the endocrine and nervous systems.     

Endophytic bacterial diversity in poplar trees growing on a BTEX-contaminated site: the characterisation of isolates with potential to enhance phytoremediation

The diversity of endophytic bacteria found in association with poplar was investigated as part of a larger study to assess the possibility and practicality of using endophytic bacteria to enhance in situ phytoremediation. Endophytic bacteria were isolated from the root, stem and leaf of two cultivars of poplar tree growing on a site contaminated with BTEX compounds. They were further characterised genotypically by comparative sequence analysis of partial 16S rRNA genes and BOX-PCR genomic DNA fingerprinting, and phenotypically by their tolerance to a range of target pollutants, heavy metals and antibiotics. One hundred and 21 stable, morphologically distinct isolates were obtained, belonging to 21 genera, although six isolates could not be identified with confidence to a genus. The endophytic bacteria exhibited marked spatial compartmentalisation within the plant, suggesting there are likely to be species-specific and non-specific associations between bacteria and plants. A number of isolates demonstrated the ability to degrade BTEX compounds or to grow in the presence of TCE. This study demonstrates that within the diverse bacterial communities found in poplar several endophytic strains are present that have the potential to enhance phytoremediation strategies.     

DsrB gene-based DGGE for community and diversity surveys of sulfate-reducing bacteria

A denaturing gradient gel electrophoresis (DGGE) method was developed to assess the diversity of dsrB (dissimilatory sulfite reductase beta-subunit)-genes in sulfate-reducing communities. For this purpose a PCR primer pair was optimized for the amplification of a approximately 350 bp dsrB gene fragment that after DGGE gel electrophoresis enabled us to discriminate between dsrB genes of different SRB-subgroups,-genera and -species. The dsrB-DGGE method revealed considerable genetic diversity when applied to DNA extracts obtained from aquifer samples that were derived from monitoring wells of an in situ metal precipitation (ISMP) pilot project conducted at the site of a non-ferrous industry or from environmental heavy metal contaminated samples. The sequences of the excised and sequenced DGGE bands represented dsrB genes of different SRB-subgroups,-genera and -species, thus confirming the broad applicability of the PCR primer pair. Linking the results of the physico-chemical follow-up of the field and lab experiments to the dsrB-DGGE data will provide a better understanding of the contribution of the SRB populations to the ongoing ISMP processes.     

A mutation linked with autism reveals a common mechanism of endoplasmic reticulum retention for the alpha,beta-hydrolase fold protein family

A mutation linked to autistic spectrum disorders encodes an Arg to Cys replacement in the C-terminal portion of the extracellular domain of neuroligin-3. The solvent-exposed Cys causes virtually complete retention of the protein in the endoplasmic reticulum when the protein is expressed in transfected cells. An identical Cys substitution was reported for butyrylcholinesterase through genotyping patients with post-succinylcholine apnea. Neuroligin, butyrylcholinesterase, and acetylcholinesterase are members of the alpha,beta-hydrolase fold family of proteins sharing sequence similarity and common tertiary structures. Although these proteins have distinct oligomeric assemblies and cellular dispositions, homologous Arg residues in neuroligin-3 (Arg-451), in butyrylcholinesterase (Arg-386), and in acetylcholinesterase (Arg-395) are conserved in all studied mammalian species. To examine whether an homologous Arg to Cys mutation affects related proteins similarly despite their differing capacities to oligomerize, we inserted homologous mutations in the acetylcholinesterase and butyrylcholinesterase cDNAs. Using confocal fluorescence microscopy and analysis of oligosaccharide processing, we find that the homologous Arg to Cys mutation also results in endoplasmic reticulum retention of the two cholinesterases. Small quantities of mutated acetylcholinesterase exported from the cell retain activity but show a greater K(m), a much smaller k(cat), and altered substrate inhibition. The nascent proteins associate with chaperones during processing, but the mutation presumably restricts processing through the endoplasmic reticulum and Golgi apparatus, because of local protein misfolding and inability to oligomerize. The mutation may alter the capacity of these proteins to dissociate from their chaperone prior to oligomerization and processing for export.     

Understanding the development of roots exposed to contaminants and the potential of plant-associated bacteria for optimization of growth

Background and Scope

Plant responses to the toxic effects of soil contaminants, such as excess metals or organic substances, have been studied mainly at physiological, biochemical and molecular levels, but the influence on root system architecture has received little attention. Nevertheless, the precise position, morphology and extent of roots can influence contaminant uptake. Here, data are discussed that aim to increase the molecular and ecological understanding of the influence of contaminants on root system architecture. Furthermore, the potential of plant-associated bacteria to influence root growth by their growth-promoting and stress-relieving capacities is explored.

Methods

Root growth parameters of Arabidopsis thaliana seedlings grown in vertical agar plates are quantified. Mutants are used in a reverse genetics approach to identify molecular components underlying quantitative changes in root architecture after exposure to excess cadmium, copper or zinc. Plant-associated bacteria are isolated from contaminated environments, genotypically and phenotypically characterized, and used to test plant root growth improvement in the presence of contaminants.

Key Results

The molecular determinants of primary root growth inhibition and effects on lateral root density by cadmium were identified. A vertical split-root system revealed local effects of cadmium and copper on root development. However, systemic effects of zinc exposure on root growth reduced both the avoidance of contaminated areas and colonization of non-contaminated areas. The potential for growth promotion and contaminant degradation of plant-associated bacteria was demonstrated by improved root growth of inoculated plants exposed to 2,4-di-nitro-toluene (DNT) or cadmium.

Conclusions

Knowledge concerning the specific influence of different contaminants on root system architecture and the molecular mechanisms by which this is achieved can be combined with the exploitation of plant-associated bacteria to influence root development and increase plant stress tolerance, which should lead to more optimal root systems for application in phytoremediation or safer biomass production.     

African Perceptions of Female Attractiveness

Little is known about mate choice preferences outside Western, educated, industrialised, rich and democratic societies, even though these Western populations may be particularly unrepresentative of human populations. To our knowledge, this is the first study to test which facial cues contribute to African perceptions of African female attractiveness and also the first study to test the combined role of facial adiposity, skin colour (lightness, yellowness and redness), skin homogeneity and youthfulness in the facial attractiveness preferences of any population. Results show that youthfulness, skin colour, skin homogeneity and facial adiposity significantly and independently predict attractiveness in female African faces. Younger, thinner women with a lighter, yellower skin colour and a more homogenous skin tone are considered more attractive. These findings provide a more global perspective on human mate choice and point to a universal role for these four facial cues in female facial attractiveness.     

Centromere mitotic recombination in mammalian cells

Centromeres are special structures of eukaryotic chromosomes that hold sister chromatid together and ensure proper chromosome segregation during cell division. Centromeres consist of repeated sequences, which have hindered the study of centromere mitotic recombination and its consequences for centromeric function. We use a chromosome orientation fluorescence in situ hybridization technique to visualize and quantify recombination events at mouse centromeres. We show that centromere mitotic recombination occurs in normal cells to a higher frequency than telomere recombination and to a much higher frequency than chromosome-arm recombination. Furthermore, we show that centromere mitotic recombination is increased in cells lacking the Dnmt3a and Dnmt3b DNA methyltransferases, suggesting that the epigenetic state of centromeric heterochromatin controls recombination events at these regions. Increased centromere recombination in Dnmt3a,3b-deficient cells is accompanied by changes in the length of centromere repeats, suggesting that prevention of illicit centromere recombination is important to maintain centromere integrity in the mouse.