Leaf litter stoichiometry affects decomposition rates and nutrient dynamics in tropical forests under restoration in Costa Rica

Active restoration strategies increase the production of leaf litter in tropical forests, but little is known about their effect on litter decomposition and subsequent nutrient release. We quantified changes in leaf litter stoichiometry during decomposition in former pasture sites under contrasting restoration strategies (natural regeneration, applied nucleation/islands tree planting and plantation), as well as in nearby primary forest. Litterbags were employed to evaluate decomposition. We used a leaf mixture of either the four planted tree species in the plantation and island treatments or the nearby primary forest and compared them under a factorial design. Decomposition rates were similar between restoration treatments (p > 0.5), but leaves decomposed faster in the forest mixture than in the plantation mixture (p < 0.01). The content of Ca, Mg, K, P, and the C:N ratio were higher in the forest mixture at the beginning and during decomposition (p < 0.05); the N content in the plantation mixture was higher at the beginning but lower during decomposition (p < 0.05), which meant greater mobilization of nitrogen per unit of carbon lost. K and P had a strong initial release, while Mg was released more gradually. N and Ca had an irregular pattern of initial fast release, immobilization, and re‐release in the later stages. We conclude that the differences in rates of decomposition and nutrient release in these systems under restoration were at least partly determined by the floristic heterogeneity and chemical quality of the leaf litter that reaches the soil.     

Augmented Reticular Thalamic Bursting and Seizures in Scn1a-Dravet Syndrome

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Amberlite IRA 900 versus calcium alginate in immobilization of a novel,engineered β-fructofuranosidase for short-chain fructooligosaccharide synthesis from sucrose

The immobilization of β-fructofuranosidase for short-chain fructooligosaccharide (scFOS) synthesis holds the potential for a more efficient use of the biocatalyst. However, the choice of carrier and immobilization technique is a key to achieving that efficiency. In this study, calcium alginate (CA), Amberlite IRA 900 (AI900) and Dowex Marathon MSA (DMM) were tested as supports for immobilizing a novel engineered β-fructofuranosidase from Aspergillus japonicus for scFOS synthesis. Several immobilization parameters were estimated to ascertain the effectiveness of the carriers in immobilizing the enzyme. The performance of the immobilized biocatalysts are compared in terms of the yield of scFOS produced and reusability. The selection of carriers and reagents was motivated by the need to ensure safety of application in the production of food-grade products. The CA and AI900 both recorded impressive immobilization yields of 82 and 62%, respectively, while the DMM recorded 47%. Enzyme immobilizations on CA, AI900 and DMM showed activity recoveries of 23, 27, and 17%, respectively. The CA, AI900 immobilized and the free enzymes recorded their highest scFOS yields of 59, 53, and 61%, respectively. The AI900 immobilized enzyme produced a consistent scFOS yield and composition for 12 batch cycles but for the CA immobilized enzyme, only 6 batch cycles gave a consistent scFOS yield. In its first record of application in scFOS production, the AI900 anion exchange resin exhibited potential as an adequate carrier for industrial application with possible savings on cost of immobilization and reduced technical difficulty.     

Synthesis of non-glycosidic 4,6'-thioether-linked disaccharides as hydrolytically stable glycomimetics

Michael addition of 1,2:3,4-di-O-isopropylidene-6-thio-alpha-D-galactose (2) to 2-propyl 6-O-acetyl-3,4-dideoxy-alpha-D-glycero-hex-3-enopyranosid-2-ulose (1) afforded, as the major diastereoisomer, 2-propyl 6-O-acetyl-3-deoxy-4-S-(6-deoxy-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranos-6-yl)-4-thio-alpha-D-threo-hexopyranosid-2-ulose (3, 91% yield). Reduction of the carbonyl group of 3, followed by O-deacetylation gave the two epimers 7 (alpha-D-lyxo) and 8 (alpha-D-xylo) in a 1:2 ratio. On removal of the protecting groups of 8 by acid hydrolysis, formation of an 1,6-anhydro bridge was observed in the 3-deoxy-4-thiohexopyranose unit (10). The free non-glycosidic thioether-linked disaccharide 3-deoxy-4-S-(6-deoxy-alpha,beta-D-galactopyranos-6-yl)-4-thio-alpha,beta-D-xylo-hexopyranose (11) was obtained by acetolysis of 10 followed by O-deacetylation. A similar sequence starting from the enone 1 and methyl 2,3,4-tri-O-benzoyl-6-thio-alpha-D-glucopyranoside (12) led successfully to 2-propyl 3-deoxy-4-S-(methyl 6-deoxy-alpha-D-glucopyranos-6-yl)-4-thio-alpha-D-lyxo-hexopyranoside (17) and its alpha-D-xylo analog (19, major product). In this synthetic route, orthogonal sets of protecting groups were employed to preserve the configuration of both reducing ends and to avoid the formation of the 1,6-anhydro ring.     

Detoxification of olefinic epoxides and nucleotide excision repair of epoxide-mediated DNA damage: Insights from animal models examining human sensitivity to 1,3-butadiene

1,3-Butadiene (BD) is a well-documented mutagen and carcinogen in rodents and is currently classified as a probable carcinogen in humans. Studies investigating workers exposed to BD indicate that, in some plants, there may be an increased genetic risk, and that polymorphisms in biotransformation and DNA repair proteins may modulate genetic susceptibility. To investigate the role of genetic polymorphisms in microsomal epoxide hydrolase (mEH) or nucleotide excision repair (NER) in contributing to the mutagenicity of BD, we conducted a series of experiments in which mice lacking mEH or NER activity were exposed to BD by inhalation or to the reactive epoxide metabolites of BD (epoxybutene-EB or diepoxybutane-DEB) by i.p. injection. Genetic susceptibility was measured using the Hprt cloning assay. Both deficient strains of mouse were significantly more sensitive to the mutagenic effects of BD and the injected epoxides. These studies provide support for the critical role that mEH plays in the biotransformation of BD, and the role that NER plays in maintaining genomic integrity following exposure to BD. Additional studies are needed to examine the importance of base excision repair (BER) in maintaining genomic integrity, the differential formation of DNA and protein adducts in deficient strains, and the potential for enhanced sensitivity to BD genotoxicity in mice either lacking or deficient in both biotransformation and DNA repair activity.     

Leishmania amazonensis: Anionic currents expressed in oocytes upon microinjection of mRNA from the parasite

Transport mechanisms involved in pH homeostasis are relevant for the survival of Leishmania parasites. The presence of chloride conductive pathways in Leishmania has been anticipated since anion channel inhibitors limit the proton extrusion mediated by the H+ATPase, which is the major regulator of intracellular pH in amastigotes. In this study, we used Xenopus laevis oocytes as a heterologous expression system in which to study the expression of ion channels upon microinjection of polyA mRNA from Leishmania amazonensis. After injection of polyA mRNA into the oocytes, we measured three different types of currents. We discuss the possible origin of each, and propose that Type 3 currents could be the result of the heterologous expression of proteins from Leishmania since they show different pharmacological and biophysical properties as compared to endogenous oocyte currents.     

Cytosolic hydroxymethyldihydropterin pyrophosphokinase/dihydropteroate synthase from Arabidopsis thaliana: a specific role in early development and stress response

In plants, 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase/7,8-dihydropteroate synthase (mitHPPK/DHPS) is a bifunctional mitochondrial enzyme, which catalyzes the first two consecutive steps of tetrahydrofolate biosynthesis. Mining the Arabidopsis genome data base has revealed a second gene encoding a protein that lacks a potential transit peptide, suggesting a cytosolic localization of the isoenzyme (cytHPPK/DHPS). When the N-terminal part of the cytHPPK/DHPS was fused to green fluorescent protein, the fusion protein appeared only in the cytosol, confirming the above prediction. Functionality of cytHPPK/DHPS was addressed by two parallel approaches: first, the cytHPPK/DHPS was able to rescue yeast mutants lacking corresponding activities; second, recombinant cytHPPK/DHPS expressed and purified from Escherichia coli displayed both HPPK and DHPS activities in vitro. In contrast to mitHPPK/DHPS, which was ubiquitously expressed, the cytHPPK/DHPS gene was exclusively expressed in reproductive tissue, more precisely in developing seeds as revealed by histochemical analysis of a transgenic cytHPPK/DHPS promoter-GUS line. In addition, it was observed that expression of cytHPPK/DHPS mRNA was induced by salt stress, suggesting a potential role of the enzyme in stress response. This was supported by the phenotype of a T-DNA insertion mutant in the cytHPPK/DHPS gene, resulting in lower germination rates as compared with the wild-type upon application of oxidative and osmotic stress.     

Radial mass density, charge, and epitope distribution in the Cryptococcus neoformans capsule

Exposure of Cryptococcus neoformans cells to gamma radiation results in a gradual release of capsular polysaccharide, in a dose-dependent manner. This method allows the systematic exploration of different capsular regions. Using this methodology, capsule density was determined to change according to the radial distribution of glucuronoxylomannan and total polysaccharide, becoming denser at the inner regions of the capsule. Scanning electron microscopy of cells following gamma radiation treatment confirmed this finding. The zeta potential of the capsule also increased as the capsule size decreased. However, neither charge nor density differences were correlated with any change in sugar composition (xylose, mannose, and glucuronic acid) in the different capsular regions, since the proportions of these sugars remained constant throughout the capsule. Analysis of the capsular antigenic properties by monoclonal antibody binding and Scatchard analysis revealed fluctuations in the binding affinity within the capsule but not in the number of antibody binding sites, suggesting that the spatial organization of high- and low-affinity epitopes within the capsule changed according to radial position. Finally, evidence is presented that the structure of the capsule changes with capsule age, since the capsule of older cells became more resistant to gamma radiation-induced ablation. In summary, the capsule of C. neoformans is heterogeneous in its spatial distribution and changes with age. Furthermore, our results suggest several mechanisms by which the capsule may protect the fungal cell against exogenous environmental factors.     

Evaluation of the developmental toxicity of lenalidomide in rabbits

BACKGROUND: Lenalidomide, a thalidomide analog, is indicated for treatment of patients with deletion-5q myelodysplastic syndromes or multiple myeloma. NZW rabbits were used because of sensitivity to thalidomide's teratogenicity. METHODS: Range-finding and pulse-dosing studies preceded a full developmental toxicity study in New Zealand white (NZW) rabbits (25/group) given lenalidomide (0, 3, 10, or 20 mg/kg/day) or thalidomide (180 mg/kg/day) by stomach tube on gestation days (GD) 7-19. Clinical signs, body weights, and feed consumption were recorded daily from GD 7. On GD 29, standard maternal necropsy, uterine content, and fetal evaluations were carried out. RESULTS: In all studies, thalidomide was selectively toxic to development. In the pulse-dosing study, lenalidomide did not affect development at 100 mg/kg/day. Increases in C(max) and AUC(0-24 hr) values for lenalidomide were slightly less than dose-proportional; lenalidomide occurred in the fetuses. At 10 and 20 mg/kg/day, lenalidomide was maternally toxic (reduced body weight gain and feed consumption; at 20 mg/kg/day, weight loss and one abortion). Developmental toxicity at 10 and 20 mg/kg/day included reduced fetal body weights and increased postimplantation losses and fetal variations (morbidity/purple-discolored skin, undeveloped intermediate lung lobe, irregular nasal-frontal suture, and delayed metacarpal ossification). Thalidomide selectively reduced fetal body weight, increased postimplantation loss and caused characteristic limb and other dysmorphology. CONCLUSIONS: The maternal and developmental NOAELs for lenalidomide are 3 mg/kg/day. Unlike thalidomide, lenalidomide affected embryo-fetal development only at maternally toxic dosages, confirming that structure-activity relationships may not predict maternal or developmental effects. No fetal malformations were attributable to lenalidomide.