Reduction of dNTP levels enhances DNA replication fidelity in vivo

ATP is the most important energy source for the maintenance and growth of living cells. Here we report that the impairment of the aerobic respiratory chain by inactivation of the ndh gene, or the inhibition of glycolysis with arsenate, both of which reduce intracellular ATP, result in a significant decrease in spontaneous mutagenesis in Escherichia coli. The genetic analyses and mutation spectra in the ndh strain revealed that the decrease in spontaneous mutagenesis resulted from an enhanced accuracy of the replicative DNA polymerase. Quantification of the dNTP content in the ndh mutant cells and in the arsenate-treated cells showed reduction of the dNTP pool, which could explain the observed broad antimutator effects. In conclusion, our work indicates that the cellular energy supply could affect spontaneous mutation rates and that a reduction of the dNTP levels can be antimutagenic.     

Mapping of a novel QTL for resistance to cereal cyst nematode in wheat

Cereal cyst nematode (CCN; Heterodera avenae Woll.) is a root pathogen of cereals that can cause severe yield losses in intolerant wheat cultivars. Loci for resistance to CCN, measured by a seedling bioassay, were identified by creating a genetic map based on a Trident/Molineux doubled haploid population of 182 lines. A novel locus accounting for up to 14% of the resistance to CCN was mapped to chromosome 1B of Molineux by association with microsatellite marker loci Xwmc719 and Xgwm140. This locus acts additively with the previously identified CCN resistance loci identified on chromosomes 6B (Cre8) and 2A (Cre5 on the VPM1 segment) in this population to explain 44% of the genetic variance for this major wheat pathogen.     

Proteomic-based analysis of nuclear signaling: PLCbeta1 affects the expression of the splicing factor SRp20 in Friend erythroleukemia cells

An extensive body of evidence links inositide-specific phospholipase C (PLC) to the nucleus and the main isoform located in the nucleus is PLCbeta(1). Constitutive overexpression of nuclear PLCbeta(1) has been previously shown to inhibit Friend erythroleukemia cells differentiation and to induce cell cycle progression targeting cyclin D3. The aim of this study was to identify new proteins regulated by PLCbeta(1) overexpression, given the role exerted by its signaling in the nucleus during cell growth and differentiation. To identify novel downstream effectors of nuclear PLCbeta(1)-dependent signaling in Friend erythroleukemia cells, we performed the high-resolution 2-DE-based proteomic analysis. Using a proteomic approach we found that SRp20, a member of the highly conserved SR family of splicing regulators, was down-regulated in cells overexpressing nuclear PLCbeta(1) as compared with wild-type cells. Reduction in SRp20 was confirmed by 2-D Western blotting. Moreover, we have shown that nuclear PLCbeta(1) is bound to the SRp20 splicing factor. Indeed, by immunoprecipitation and subcellular fractioning, we have demonstrated that endogenous PLCbeta(1) and SRp20 physically interact in the nucleus. Here we show the existence of a PLCbeta(1)-specific target, the splicing factor SRp20, whose expression is specifically down-regulated by the nuclear signaling evoked by PLCbeta(1).     

aP2-Cre-Mediated Inactivation of Estrogen Receptor Alpha Causes Hydrometra

In this study we describe the reproductive phenotypes of a novel mouse model in which Cre-mediated deletion of ERα is regulated by the aP2 (fatty acid binding protein 4) promoter. ERα-floxed mice were crossed with transgenic mice expressing Cre-recombinase under the control of the aP2 promoter to generate aP2-Cre/ERα^flox/flox mice. As expected, ERα mRNA levels were reduced in adipose tissue, but in addition we also detected an 80% reduction of ERα levels in the hypothalamus of aP2-Cre/ERα^flox/flox mice. Phenotypic analysis revealed that aP2-Cre/ERα^flox/flox female mice were infertile. In line with this, aP2-Cre/ERα^flox/flox female mice did not cycle and presented 3.8-fold elevated estrogen levels. That elevated estrogen levels were associated with increased estrogen signaling was evidenced by increased mRNA levels of the estrogen-regulated genes lactoferrin and aquaporin 5 in the uterus. Furthermore, aP2-Cre/ERα^flox/flox female mice showed an accumulation of intra-uterine fluid, hydrometra, without overt indications for causative anatomical anomalies. However, the vagina and cervix displayed advanced keratosis with abnormal quantities of accumulating squamous epithelial cells suggesting functional obstruction by keratin plugs. Importantly, treatment of aP2-Cre/ERα^flox/flox mice with the aromatase inhibitor Letrozole caused regression of the hydrometra phenotype linking increased estrogen levels to the observed phenotype. We propose that in aP2-Cre/ERα^flox/flox mice, increased serum estrogen levels cause over-stimulation in the uterus and genital tracts resulting in hydrometra and vaginal obstruction.     

Heparin promotes ß-secretase cleavage of the Alzheimer''s amyloid precursor protein

In Alzheimer's disease, abnormal processing of the amyloid precursor protein (APP) is thought to play an important role in amyloid deposition. We investigated the effect of heparin, a highly sulfated glycosaminoglycan related to heparan sulfate, on the secretion of the ß-secretase cleavage product of APP (sAPPß) in a human neuroblastoma cell line. Heparin induced an increase in the secretion of total APP, and an even greater relative increase in the secretion of sAPPß. The effect on sAPPß was specific to heparin. These data support the hypothesis that highly sulfated heparan sulfate proteoglycans may promote amyloidogenic pathways of APP metabolism.     

Failure prediction of the total hip prosthesis system

The mechanical failure of the prosthesis-cement-femur system is analyzed by using a two-dimensional finite element model. The strain energy density (SED) criterion is applied to locate potential failure sites in the PMMA and prosthesis stem for five different prosthesis positions.

Medial and lateral failure sites in the proximal regions of the cement are found to be the most sensitive to prosthesis position. According to the SED criterion, these are the weakest regions of the cement. Additional bilateral failure sites are also located at the distal end of the prosthesis, but are less likely to fail. The overall structural integrity of the total hip system is found to be adequate for the ideal case considered herein. In practice, the combination of energy concentration coupled with imperfections such as voids and cracks in the cement are potential sites of failure initiation.

On the basis of clinical evidence on cement and prosthesis stem fracture, local reductions in the cement elastic modulus were introduced into the finite element model in order to model cement defects. The bilateral reduction of modulus by 40% in the cement adjacent to the distal portion of the prosthesis stem can lead to an increase of the strain energy density by 19%.     

Running worms: C. elegans self-sorting by electrotaxis

The nematode C. elegans displays complex dynamical behaviors that are commonly used to identify relevant phenotypes. Although its maintenance is straightforward, sorting large populations of worms when looking for a behavioral phenotype is difficult, time consuming and hardly quantitative when done manually. Interestingly, when submitted to a moderate electric field, worms move steadily along straight trajectories. Here, we report an inexpensive method to measure worms crawling velocities and sort them within a few minutes by taking advantage of their electrotactic skills. This method allows to quantitatively measure the effect of mutations and aging on worm's crawling velocity. We also show that worms with different locomotory phenotypes can be spatially sorted, fast worms traveling away from slow ones. Group of nematodes with comparable locomotory fitness could then be isolated for further analysis. C. elegans is a growing model for neurodegenerative diseases and using electrotaxis for self-sorting can improve the high-throughput search of therapeutic bio-molecules.     

Effects of anthrax lethal toxin on human primary keratinocytes

Aims: To investigate the effects of anthrax lethal toxin (LeTx) on human primary keratinocytes. Methods and Results: We show here that human primary keratinocytes are resistant to LeTx‐triggered cytotoxicity. All but one of the MEKs (mitogen‐activated protein kinase kinases) are cleaved within 3 h, and the cleavage of MEKs in keratinocytes leads to their subsequent proteasome‐mediated degradation at different rates. Moreover, LeTx reduced the concentration of several cytokines except RANTES in culture. Conclusions: Our results indicate that primary keratinocytes are resistant to LeTx cytotoxicity, and MEK cleavage does not correlate with LeTx cytotoxicity. Although LeTx is considered as an anti‐inflammatory agent, it upregulates RANTES. Significance and Impact of the Study: According to a current view, the action of LeTx results in downregulation of the inflammatory response, as evidenced by diminished expression of several inflammatory biomarkers. Paradoxically, LeTx has been reported to attract neutrophils to cutaneous infection sites. This paper, which shows that RANTES, a chemoattractant for immune cells, is upregulated after exposure of keratinocytes to LeTx, although a number of other markers of the inflammatory response are downregulated. Our results might explain why the exposure of keratinocytes to LeTx results in the recruitment of neutrophils to cutaneous infection sites, while the expression of several inflammatory biomarkers is diminished.     

Clostridium difficile in seafood and fish

The objective of this study was to determine the prevalence of Clostridium difficile contamination in retail seafood and fish from Canadian grocery stores. C.?difficile was found in 4.8% (5/119) of the samples. This study, combined with studies of other food sources, suggests that widespread contamination of food is common.     

Absolute SILAC-compatible expression strain allows Sumo-2 copy number determination in clinical samples

Quantitative mass spectrometry-based proteomics is a vital tool in modern life science research. In contrast to the popularity of approaches for relative protein quantitation, the widespread use of absolute quantitation has been hampered by inefficient and expensive production of labeled protein standards. To optimize production of isotopically labeled standards, we genetically modified a commonly employed protein expression Escherichia coli strain, BL21 (DE3), to construct an auxotroph for arginine and lysine. This bacterial strain allows low-cost, high-level expression of fully labeled proteins with no conversion of labeled arginine to proline. In combination with a fluorescence-based quantitation of standards and nontargeted LC-MS/MS analysis of unfractionated total cell lysates, this strain was used to determine the copy number of a post-translational modifier, small ubiquitin-like modifier (SUMO-2), in HeLa, human sperm, and chronic lymphocytic leukemia cells. By streamlining and improving the generation of labeled standards, this production system increases the breadth of absolute quantitation by mass spectrometry and will facilitate a far wider uptake of this important technique than previously possible.