A Naturally Occurring Canine Model of Autosomal Recessive Congenital Stationary Night Blindness

Congenital stationary night blindness (CSNB) is a non-progressive, clinically and genetically heterogeneous disease of impaired night vision. We report a naturally-occurring, stationary, autosomal recessive phenotype in beagle dogs with normal daylight vision but absent night vision. Affected dogs had normal retinas on clinical examination, but showed no detectable rod responses. They had “negative-type” mixed rod and cone responses in full-field ERGs. Their photopic long-flash ERGs had normal OFF-responses associated with severely reduced ON-responses. The phenotype is similar to the Schubert-Bornschein form of complete CSNB in humans. Homozygosity mapping ruled out most known CSNB candidates as well as CACNA2D4 and GNB3. Three remaining genes were excluded based on sequencing the open reading frame and intron-exon boundaries (RHO, NYX), causal to a different form of CSNB (RHO) or X-chromosome (NYX, CACNA1F) location. Among the genes expressed in the photoreceptors and their synaptic terminals, and mGluR6 cascade and modulators, reduced expression of GNAT1, CACNA2D4 and NYX was observed by qRT-PCR in both carrier (n = 2) and affected (n = 2) retinas whereas CACNA1F was down-regulated only in the affecteds. Retinal morphology revealed normal cellular layers and structure, and electron microscopy showed normal rod spherules and synaptic ribbons. No difference from normal was observed by immunohistochemistry (IHC) for antibodies labeling rods, cones and their presynaptic terminals. None of the retinas showed any sign of stress. Selected proteins of mGluR6 cascade and its modulators were examined by IHC and showed that PKCα weakly labeled the rod bipolar somata in the affected, but intensely labeled axonal terminals that appeared thickened and irregular. Dendritic terminals of ON-bipolar cells showed increased Goα labeling. Both PKCα and Goα labeled the more prominent bipolar dendrites that extended into the OPL in affected but not normal retinas. Interestingly, RGS11 showed no labeling in the affected retina. Our results indicate involvement of a yet unknown gene in this canine model of complete CSNB.     

Large-Scale Patterns of Turnover and Basal Area Change in Andean Forests

General patterns of forest dynamics and productivity in the Andes Mountains are poorly characterized. Here we present the first large-scale study of Andean forest dynamics using a set of 63 permanent forest plots assembled over the past two decades. In the North-Central Andes tree turnover (mortality and recruitment) and tree growth declined with increasing elevation and decreasing temperature. In addition, basal area increased in Lower Montane Moist Forests but did not change in Higher Montane Humid Forests. However, at higher elevations the lack of net basal area change and excess of mortality over recruitment suggests negative environmental impacts. In North-Western Argentina, forest dynamics appear to be influenced by land use history in addition to environmental variation. Taken together, our results indicate that combinations of abiotic and biotic factors that vary across elevation gradients are important determinants of tree turnover and productivity in the Andes. More extensive and longer-term monitoring and analyses of forest dynamics in permanent plots will be necessary to understand how demographic processes and woody biomass are responding to changing environmental conditions along elevation gradients through this century.     

Polyphenol‐solubility alters amyloid fibril formation of α‐synuclein

Amyloid fibril formation is associated with various amyloidoses, including neurodegenerative diseases such as Alzheimer''s and Parkinson''s diseases. Amyloid fibrils form above the solubility of amyloidogenic proteins or peptides upon breaking supersaturation, followed by a nucleation and elongation mechanism, which is similar to the crystallization of solutes. Many additives, including salts, detergents, and natural compounds, promote or inhibit amyloid formation. However, the underlying mechanisms of the opposing effects are unclear. We examined the effects of two polyphenols, that is, epigallocatechin gallate (EGCG) and kaempferol‐7─O─glycoside (KG), with high and low solubilities, respectively, on the amyloid formation of α‐synuclein (αSN). EGCG and KG inhibited and promoted amyloid formation of αSN, respectively, when monitored by thioflavin T (ThT) fluorescence or transmission electron microscopy (TEM). Nuclear magnetic resonance (NMR) analysis revealed that, although interactions of αSN with soluble EGCG increased the solubility of αSN, thus inhibiting amyloid formation, interactions of αSN with insoluble KG reduced the solubility of αSN, thereby promoting amyloid formation. Our study suggests that opposing effects of polyphenols on amyloid formation of proteins and peptides can be interpreted based on the solubility of polyphenols.     

Extracellular monoenzyme deglycosylation system of 7-O-linked flavonoid β-rutinosides and its disaccharide transglycosylation activity from Stilbella fimetaria

We screened for microorganisms able to use flavonoids as a carbon source; and one isolate, nominated Stilbella fimetaria SES201, was found to possess a disaccharide-specific hydrolase. It was a cell-bound ectoenzyme that was released to the medium during conidiogenesis. The enzyme was shown to cleave the flavonoid hesperidin (hesperetin 7-O-α-rhamnopyranosyl-β-glucopyranoside) into rutinose (α-rhamnopyranosyl-β-glucopyranose) and hesperetin. Since only intracellular traces of monoglycosidase activities (β-glucosidase, α-rhamnosidase) were produced, the disaccharidase α-rhamnosyl-β-glucosidase was the main system utilized by the microorganism for hesperidin hydrolysis. The enzyme was a glycoprotein with a molecular weight of 42224 Da and isoelectric point of 5.7. Even when maximum activity was found at 70°C, it was active at temperatures as low as 5°C, consistent with the psychrotolerant character of S. fimetaria. Substrate preference studies indicated that the enzyme exhibits high specificity toward 7-O-linked flavonoid β-rutinosides. It did not act on flavonoid 3-O-β-rutinoside and 7-O-β-neohesperidosides, neither monoglycosylated substrates. In an aqueous medium, the α-rhamnosyl-β-glucosidase was also able to transfer rutinose to other acceptors besides water, indicating its potential as biocatalyst for organic synthesis. The monoenzyme strategy of S. fimetaria SES201, as well as the enzyme substrate preference for 7-O-β-flavonoid rutinosides, is unique characteristics among the microbial flavonoid deglycosylation systems reported.     

Synthesis and nootropic activity of some 2,3-dihydro-1H-isoindol-1-one derivatives structurally related with piracetam

Three 2,3‐dihydro‐1H‐isoindol‐1‐ones structurally related with piracetam (=2‐oxopyrrolidine‐1‐acetamide) have been synthesized and tested for their nootropic effects in the passive avoidance test in mice. Compounds (RS)‐ 2 , (R,R)‐ 3 , and (R,S)‐ 3 were obtained in good yields in only two steps starting from methyl dl ‐phthaloylalanine. Compound (RS)‐ 2 exhibited nootropic activity at lower doses than piracetam, used as reference drug, but it showed lower efficacy. Whereas diastereoisomers (R,R)‐ 3 and (R,S)‐ 3 were as potent as piracetam to revert amnesia induced by scopolamine, (R,S)‐ 3 showed lower efficacy than (R,R)‐ 3 . Only (R,R)‐ 3 showed myorelaxant effect at doses of 10 and 30 mg/kg; other compounds did not exhibit any anticonvulsant, sedative, myorelaxant, or impaired motor‐coordination effect in mice. These synthesized 2,3‐dihydro‐1H‐isoindol‐1‐one derivatives constitute a new kind of nootropic compounds.     

Kinetic model of the inhibition of respiration by endogenous nitric oxide in intact cells

Nitric oxide (NO) inhibits mitochondrial respiration by decreasing the apparent affinity of cytochrome c oxidase (CcO) for oxygen. Using iNOS-transfected HEK 293 cells to achieve regulated intracellular NO production, we determined NO and O₂ concentrations and mitochondrial O₂ consumption by high-resolution respirometry over a range of O₂ concentrations down to nanomolar. Inhibition of respiration by NO was reversible, and complete NO removal recovered cell respiration above its routine reference values. Respiration was observed even at high NO concentrations, and the dependence of IC₅₀ on [O₂] exhibits a characteristic but puzzling parabolic shape; both these features imply that CcO is protected from complete inactivation by NO and are likely to be physiologically relevant. We present a kinetic model of CcO inhibition by NO that efficiently predicts experimentally determined respiration at physiological O₂ and NO concentrations and under hypoxia, and accurately predicts the respiratory responses under hyperoxia. The model invokes competitive and uncompetitive inhibition by binding of NO to the reduced and oxidized forms of CcO, respectively, and suggests that dissociation of NO from reduced CcO may involve its O₂-dependent oxidation. It also explains the non-linear dependence of IC₅₀ on O₂ concentration, and the hyperbolic increase of c₅₀ as a function of NO concentration.