m6A‐mediated alternative splicing coupled with nonsense‐mediated mRNA decay regulates SAM synthetase homeostasis

Alternative splicing of pre‐mRNAs can regulate gene expression levels by coupling with nonsense‐mediated mRNA decay (NMD). In order to elucidate a repertoire of mRNAs regulated by alternative splicing coupled with NMD (AS‐NMD) in an organism, we performed long‐read RNA sequencing of poly(A)⁺ RNAs from an NMD‐deficient mutant strain of Caenorhabditis elegans, and obtained full‐length sequences for mRNA isoforms from 259 high‐confidence AS‐NMD genes. Among them are the S‐adenosyl‐L‐methionine (SAM) synthetase (sams) genes sams‐3 and sams‐4. SAM synthetase activity autoregulates sams gene expression through AS‐NMD in a negative feedback loop. We furthermore find that METT‐10, the orthologue of human U6 snRNA methyltransferase METTL16, is required for the splicing regulation in␣vivo, and specifically methylates the invariant AG dinucleotide at the distal 3′ splice site (3′SS) in␣vitro. Direct RNA sequencing coupled with machine learning confirms m⁶A modification of endogenous sams mRNAs. Overall, these results indicate that homeostasis of SAM synthetase in C. elegans is maintained by alternative splicing regulation through m⁶A modification at the 3′SS of the sams genes.     

Recognition of heptoses and the inner core of bacterial lipopolysaccharides by surfactant protein d

Lipopolysaccharides (LPS) of Gram-negative bacteria are important mediators of bacterial virulence that can elicit potent endotoxic effects. Surfactant protein D (SP-D) shows specific interactions with LPS, both in vitro and in vivo. These interactions involve binding of the carbohydrate recognition domain (CRD) to LPS oligosaccharides (OS); however, little is known about the mechanisms of LPS recognition. Recombinant neck+CRDs (NCRDs) provide an opportunity to directly correlate binding interactions with a crystallographic analysis of the binding mechanism. In these studies, we examined the interactions of wild-type and mutant trimeric NCRDs with rough LPS (R-LPS). Although rat NCRDs bound more efficiently than human NCRDs to Escherichia coli J-5 LPS, both proteins exhibited efficient binding to solid-phase Rd2-LPS and to Rd2-LPS aggregates presented in the solution phase. Involvement of residues flanking calcium at the sugar binding site was demonstrated by reciprocal exchange of lysine and arginine at position 343 of rat and human CRDs. The lectin activity of hNCRDs was inhibited by specific heptoses, including l-glycero-alpha-d-manno-heptose (l,d-heptose), but not by 3-deoxy-alpha-d-manno-oct-2-ulosonic acid (Kdo). Crystallographic analysis of the hNCRD demonstrated a novel binding orientation for l,d-heptose, involving the hydroxyl groups of the side chain. Similar binding was observed for a synthetic alpha1-->3-linked heptose disaccharide corresponding to heptoses I and II of the inner core region in many LPS. 7-O-Carbamoyl-l,d-heptose and d-glycero-alpha-d-manno-heptose were bound via ring hydroxyl groups. Interactions with the side chain of inner core heptoses provide a potential mechanism for the recognition of diverse types of LPS by SP-D.     

Inhibitory effects of methylglyoxal on light-induced stomatal opening and inward K+ channel activity in Arabidopsis

Methylglyoxal (MG) is a reactive aldehyde derived by glycolysis. In Arabidopsis, MG inhibited light-induced stomatal opening in a dose-dependent manner. It significantly inhibited both inward-rectifying potassium (K(in)) channels in guard-cell protoplasts and an Arabidopsis K(in) channel, KAT1, heterologously expressed in Xenopus oocytes. Thus it appears that MG inhibition of stomatal opening involves MG inhibition of K(+) influx into guard cells.     

Synthesis of the non-peptidic snail toxin 6-bromo-2-mercaptotryptamine dimer (BrMT)2, its lower and higher thio homologs and their ability to modulate potassium ion channels

The first synthesis of the non-peptidic snail toxin 6-bromo-2-mercaptotryptamine dimer (BrMT)₂ is described, along with the preparation of its lower and higher thio homologs. The synthetic (BrMT)₂ and its derivatives reported herein are all capable of slowing the activation of the K_v1.1 potassium ion channel. Only the monosulfide variant shows significant slowing of the deactivation process. This synthetic strategy can now be applied to creating a more extensive set of compounds that vary in the length of the linker connecting the two monomers, the substituents on the indole ring core, and terminal amine.     

Glycoconjugates for the recognition of Bacillus spores

Carbohydrates act as ligands in many biological processes, including the folding and secretion of proteins, cell-cell recognition, adhesion, and sporulation in the Bacillus genus. Fluorescent-labeled disaccharide glycoconjugates have been applied to evaluate binding to bacterial spores assuming that the spore surface is covered with carbohydrates. This study has shown that specific recognition of bacterial spores is based on interactions between disaccharide glycoconjugates acting as ligands and monosaccharide units expressed on the exterior of bacterial spores. Using fluorophore-assisted carbohydrate electrophoresis (FACE), carbohydrates that are expressed on the exterior of the spores were enumerated. The findings have an impact on how to improve ligand selection, essential for sensor development. In addition, the findings provide new information for inhibition of bacterial spores, and in general, demonstrate how carbohydrates function as recognition signals in nature.     

Promising Antibacterial Effects of Silver Nanoparticle-Loaded Tea Tree Oil Nanoemulsion: a Synergistic Combination Against Resistance Threat

Highly resistant pathogens may be developed in patients with immune disorders after prolonged exposure to antibiotics, a growing threat worldwide. In order to overcome these problems, this study introduces a new class of engineered nanosystems comprising of tea tree oil nanoemulsion (TTO NE) loaded with Ag nanoparticles (NPs). Silver shows a strong toxicity towards a wide range of microorganisms. Also, TTO NE could be employed as a promising and safe antimicrobial agent for local therapies of bacterial infections. The nanosystem was prepared by low-energy method. Mean droplet size of the NE was found to be 17.7 nm. Results of the antibacterial assays showed promising ability of the designed nanosystem for eradication of Gram-positive and Gram-negative bacteria (95%). Also, it was shown that introducing colloidal Ag NPs to the TTO NE exerted a synergistic effect against Escherichia coli (FIC 0.48) while only an additive effect was observed against Staphylococcus aureus (FIC 0.75). The antibacterial effects of TTO NE+Ag NPs together with their compatibility with human cells can present them as a suitable candidate to fight against the antibacterial resistance threat.     

Enhanced tolerance of transgenic tall fescue plants overexpressing 2-Cys peroxiredoxin against methyl viologen and heat stresses

Plant 2-Cys peroxiredoxins (2-Cys Prx) has both peroxidase and chaperon function. We overexpressed an Arabidopsis 2-Cys Prx in transgenic tall fescue (Festuca arundinacea) plants to confer tolerance against heat and methyl viologen (MV) stress. Transgenic plants were generated by Agrobacterium-mediated genetic transformation, and integration and expression of the transgene was confirmed by Southern, northern and western blot analyses. Compared to control plants, transgenic plants had significantly less electrolyte leakage and thiobarbituric acid-reactive substances (TBARS) when exposed to heat or MV. Under heat stress (42°C), transgenic plants maintained their chlorophyll fluorescence (Fv/Fm) for 24 h while control plants lost chlorophyll fluorescence very quickly. We conclude that the high levels of 2-Cys Prx proteins in transgenic plants protect leaves from oxidative damage probably due to chaperon activity.     

Acrolein produced from polyamines as one of the uraemic toxins

It is well known that the addition of spermine or spermidine to culture medium containing ruminant serum inhibits cellular proliferation. This effect is caused by the products of oxidation of polyamines that are generated by serum amine oxidase. Among the products, we found that acrolein is a major toxic compound produced from spermine and spermidine by amine oxidase. We then analysed the level of polyamines (putrescine, spermidine and spermine) and amine oxidase activity in plasma of patients with chronic renal failure. It was found that the levels of putrescine and the amine oxidase activity were increased, whereas spermidine and spermine were decreased in plasma of patients with chronic renal failure. The levels of free and protein-conjugated acrolein were also increased in plasma of patients with chronic renal failure. An increase in putrescine, amine oxidase and acrolein in plasma was observed in all cases such as diabetic nephropathy, chronic glomerulonephritis and nephrosclerosis. These results suggest that acrolein is produced during the early stage of nephritis through kidney damage and also during uraemia through accumulation of polyamines in blood due to the decrease in their excretion into urine.     

Regional Variation in the Prevalence of E. coli O157 in Cattle: A Meta-Analysis and Meta-Regression

Background

Escherichia coli O157 (EcO157) infection has been recognized as an important global public health concern. But information on the prevalence of EcO157 in cattle at the global and at the wider geographical levels is limited, if not absent. This is the first meta-analysis to investigate the point prevalence of EcO157 in cattle at the global level and to explore the factors contributing to variation in prevalence estimates.

Methods

Seven electronic databases- CAB Abstracts, PubMed, Biosis Citation Index, Medline, Web of Knowledge, Scirus and Scopus were searched for relevant publications from 1980 to 2012. A random effect meta-analysis model was used to produce the pooled estimates. The potential sources of between study heterogeneity were identified using meta-regression.

Principal findings

A total of 140 studies consisting 220,427 cattle were included in the meta-analysis. The prevalence estimate of EcO157 in cattle at the global level was 5.68% (95% CI, 5.16–6.20). The random effects pooled prevalence estimates in Africa, Northern America, Oceania, Europe, Asia and Latin America-Caribbean were 31.20% (95% CI, 12.35–50.04), 7.35% (95% CI, 6.44–8.26), 6.85% (95% CI, 2.41–11.29), 5.15% (95% CI, 4.21–6.09), 4.69% (95% CI, 3.05–6.33) and 1.65% (95% CI, 0.77–2.53), respectively. Between studies heterogeneity was evidenced in most regions. World region (p<0.001), type of cattle (p<0.001) and to some extent, specimens (p = 0.074) as well as method of pre-enrichment (p = 0.110), were identified as factors for variation in the prevalence estimates of EcO157 in cattle.

Conclusion

The prevalence of the organism seems to be higher in the African and Northern American regions. The important factors that might have influence in the estimates of EcO157 are type of cattle and kind of screening specimen. Their roles need to be determined and they should be properly handled in any survey to estimate the true prevalence of EcO157.