Bisphenol A induces otolith malformations during vertebrate embryogenesis

Background  

The plastic monomer and plasticizer bisphenol A (BPA), used for manufacturing polycarbonate plastic and epoxy resins, is produced at over 2.5 million metric tons per year. Concerns have been raised that BPA acts as an endocrine disruptor on both developmental and reproductive processes and a large body of evidence suggests that BPA interferes with estrogen and thyroid hormone signaling. Here, we investigated BPA effects during embryonic development using the zebrafish and Xenopus models.     

Porphyromonas gingivalis participates in pathogenesis of human abdominal aortic aneurysm by neutrophil activation. Proof of concept in rats

Background

Abdominal Aortic Aneurysms (AAAs) represent a particular form of atherothrombosis where neutrophil proteolytic activity plays a major role. We postulated that neutrophil recruitment and activation participating in AAA growth may originate in part from repeated episodes of periodontal bacteremia.

Methods and Findings

Our results show that neutrophil activation in human AAA was associated with Neutrophil Extracellular Trap (NET) formation in the IntraLuminal Thrombus, leading to the release of cell-free DNA. Human AAA samples were shown to contain bacterial DNA with high frequency (11/16), and in particular that of Porphyromonas gingivalis (Pg), the most prevalent pathogen involved in chronic periodontitis, a common form of periodontal disease. Both DNA reflecting the presence of NETs and antibodies to Pg were found to be increased in plasma of patients with AAA. Using a rat model of AAA, we demonstrated that repeated injection of Pg fostered aneurysm development, associated with pathological characteristics similar to those observed in humans, such as the persistence of a neutrophil-rich luminal thrombus, not observed in saline-injected rats in which a healing process was observed.

Conclusions

Thus, the control of periodontal disease may represent a therapeutic target to limit human AAA progression.     

LINGO1 variants in the French-Canadian population

Essential tremor (ET) is a complex genetic disorder for which no causative gene has been found. Recently, a genome-wide association study reported that two variants in the LINGO1 locus were associated to this disease. The aim of the present study was to test if this specific association could be replicated using a French-Canadian cohort of 259 ET patients and 479 ethnically matched controls. Our genotyping results lead us to conclude that no association exists between the key variant rs9652490 and ET (P_corr = 1.00).     

Putting into practice domain-linear motif interaction predictions for exploration of protein networks

PDZ domains recognise short sequence motifs at the extreme C-termini of proteins. A model based on microarray data has been recently published for predicting the binding preferences of PDZ domains to five residue long C-terminal sequences. Here we investigated the potential of this predictor for discovering novel protein interactions that involve PDZ domains. When tested on real negative data assembled from published literature, the predictor displayed a high false positive rate (FPR). We predicted and experimentally validated interactions between four PDZ domains derived from the human proteins MAGI1 and SCRIB and 19 peptides derived from human and viral C-termini of proteins. Measured binding intensities did not correlate with prediction scores, and the high FPR of the predictor was confirmed. Results indicate that limitations of the predictor may arise from an incomplete model definition and improper training of the model. Taking into account these limitations, we identified several novel putative interactions between PDZ domains of MAGI1 and SCRIB and the C-termini of the proteins FZD4, ARHGAP6, NET1, TANC1, GLUT7, MARCH3, MAS, ABC1, DLL1, TMEM215 and CYSLTR2. These proteins are localised to the membrane or suggested to act close to it and are often involved in G protein signalling. Furthermore, we showed that, while extension of minimal interacting domains or peptides toward tandem constructs or longer peptides never suppressed their ability to interact, the measured affinities and inferred specificity patterns often changed significantly. This suggests that if protein fragments interact, the full length proteins are also likely to interact, albeit possibly with altered affinities and specificities. Therefore, predictors dealing with protein fragments are promising tools for discovering protein interaction networks but their application to predict binding preferences within networks may be limited.     

The effect of genetic variation on the lipid response to dietary change: recent findings

PURPOSE OF REVIEW: Dyslipidaemia is an important risk factor for cardiovascular disease, and can be modified by diet. However, the lipid response to dietary change may be influenced by genetic variation. This review examines recent research (published since August 2003) on the effect of genetic variation on the lipid response to dietary change. RECENT FINDINGS: In 10 reports describing intervention studies and seven reports describing observational studies, the lipid response to diet was modified by polymorphisms within the genes for apoE, apoB, apoCIII, lipoprotein lipase, hepatic lipase, endothelial lipase, the liver fatty acid-binding protein, the beta3-adrenergic receptor, adipsin and the peroxisome proliferator-activated receptor gamma. The studies varied widely in terms of the number and type of study participants, the composition and duration of the dietary interventions, the nutrients studied and dietary assessment methods used in the observational studies, and the polymorphisms analysed--some of which had not been studied before with regard to the lipid response to diet. SUMMARY: The lipid response to dietary change is highly complex. Future studies will have to be large in order to assess the effects of multiple polymorphisms, and will have to control for many factors other than diet. At present, it is premature to recommend the use of genotyping in the design of therapeutic diets. However, such studies may be useful in identifying the mechanisms by which dietary components influence lipid levels.     

Dual expression system suitable for high-throughput fluorescence-based screening and production of soluble proteins

Many studies that aim to characterize the proteome structurally or functionally require the production of pure protein in a high-throughput format. We have developed a fast and flexible integrated system for cloning, protein expression in Escherichia coli, solubility screening and purification that can be completely automated in a 96-well microplate format. We used recombination cloning in custom-designed vectors including (i) a (His)(6) tag-encoding sequence, (ii) a variable solubilizing partner gene, (iii) the DNA sequence corresponding to the TEV protease cleavage site, (iv) the gene (or DNA fragment) of interest, (v) a suppressible amber stop codon, and (vi) an S.tag peptide-encoding sequence. First, conditions of bacterial culture in microplates (250 microL) were optimized to obtain expression and solubility patterns identical to those obtained in a 1-L flask (100-mL culture). Such conditions enabled the screening of various parameters in addition to the fusion partners (E. coli strains, temperature, inducer...). Second, expression of fusion proteins in amber suppressor strains allowed quantification of soluble and insoluble proteins by fluorescence through the detection of the S.tag. This technique is faster and more sensitive than other commonly used methods (dot blots, Western blots, SDS-PAGE). The presence of the amber suppressor tRNA was shown to affect neither the expression pattern nor the solubility of the target proteins. Third, production of the most interesting soluble fusion proteins, as detected by our screening method, could be performed in nonsuppressor strains. After cleavage with the TEV protease, the target proteins were obtained in a native form with a unique additional N-terminal glycine.     

A unique voltage sensor sensitizes the potassium channel AKT2 to phosphoregulation

Among all voltage-gated K+ channels from the model plant Arabidopsis thaliana, the weakly rectifying K+ channel (K(weak) channel) AKT2 displays unique gating properties. AKT2 is exceptionally regulated by phosphorylation: when nonphosphorylated AKT2 behaves as an inward-rectifying potassium channel; phosphorylation of AKT2 abolishes inward rectification by shifting its activation threshold far positive (>200 mV) so that it closes only at voltages positive of +100 mV. In its phosphorylated form, AKT2 is thus locked in the open state in the entire physiological voltage range. To understand the molecular grounds of this unique gating behavior, we generated chimeras between AKT2 and the conventional inward-rectifying channel KAT1. The transfer of the pore from KAT1 to AKT2 altered the permeation properties of the channel. However, the gating properties were unaffected, suggesting that the pore region of AKT2 is not responsible for the unique K(weak) gating. Instead, a lysine residue in S4, highly conserved among all K(weak) channels but absent from other plant K+ channels, was pinpointed in a site-directed mutagenesis approach. Substitution of the lysine by serine or aspartate abolished the "open-lock" characteristic and converted AKT2 into an inward-rectifying channel. Interestingly, phosphoregulation of the mutant AKT2-K197S appeared to be similar to that of the K(in) channel KAT1: as suggested by mimicking the phosphorylated and dephosphorylated states, phosphorylation induced a shift of the activation threshold of AKT2-K197S by about +50 mV. We conclude that the lysine residue K197 sensitizes AKT2 to phosphoregulation. The phosphorylation-induced reduction of the activation energy in AKT2 is approximately 6 kT larger than in the K197S mutant. It is discussed that this hypersensitive response of AKT2 to phosphorylation equips a cell with the versatility to establish a potassium gradient and to make efficient use of it.