13C and 1H Nuclear Magnetic Resonance Study of Glycogen Futile Cycling in Strains of the Genus Fibrobacter

We investigated the carbon metabolism of three strains of Fibrobacter succinogenes and one strain of Fibrobacter intestinalis. The four strains produced the same amounts of the metabolites succinate, acetate, and formate in approximately the same ratio (3.7/1/0.3). The four strains similarly stored glycogen during all growth phases, and the glycogen-to-protein ratio was close to 0.6 during the exponential growth phase. ¹³C nuclear magnetic resonance (NMR) analysis of [1-¹³C]glucose utilization by resting cells of the four strains revealed a reversal of glycolysis at the triose phosphate level and the same metabolic pathways. Glycogen futile cycling was demonstrated by ¹³C NMR by following the simultaneous metabolism of labeled [¹³C]glycogen and exogenous unlabeled glucose. The isotopic dilutions of the CH₂ of succinate and the CH₃ of acetate when the resting cells were metabolizing [1-¹³C]glucose and unlabeled glycogen were precisely quantified by using ¹³C-filtered spin-echo difference ¹H NMR spectroscopy. The measured isotopic dilutions were not the same for succinate and acetate; in the case of succinate, the dilutions reflected only the contribution of glycogen futile cycling, while in the case of acetate, another mechanism was also involved. Results obtained in complementary experiments are consistent with reversal of the succinate synthesis pathway. Our results indicated that for all of the strains, from 12 to 16% of the glucose entering the metabolic pathway originated from prestored glycogen. Although genetically diverse, the four Fibrobacter strains studied had very similar carbon metabolism characteristics.     

Gene-Flow in a Mosaic Hybrid Zone: Is Local Introgression Adaptive?

Genome-wide scans of genetic differentiation between hybridizing taxa can identify genome regions with unusual rates of introgression. Regions of high differentiation might represent barriers to gene flow, while regions of low differentiation might indicate adaptive introgression—the spread of selectively beneficial alleles between reproductively isolated genetic backgrounds. Here we conduct a scan for unusual patterns of differentiation in a mosaic hybrid zone between two mussel species, Mytilus edulis and M. galloprovincialis. One outlying locus, mac-1, showed a characteristic footprint of local introgression, with abnormally high frequency of edulis-derived alleles in a patch of M. galloprovincialis enclosed within the mosaic zone, but low frequencies outside of the zone. Further analysis of DNA sequences showed that almost all of the edulis allelic diversity had introgressed into the M. galloprovincialis background in this patch. We then used a variety of approaches to test the hypothesis that there had been adaptive introgression at mac-1. Simulations and model fitting with maximum-likelihood and approximate Bayesian computation approaches suggested that adaptive introgression could generate a “soft sweep,” which was qualitatively consistent with our data. Although the migration rate required was high, it was compatible with the functioning of an effective barrier to gene flow as revealed by demographic inferences. As such, adaptive introgression could explain both the reduced intraspecific differentiation around mac-1 and the high diversity of introgressed alleles, although a localized change in barrier strength may also be invoked. Together, our results emphasize the need to account for the complex history of secondary contacts in interpreting outlier loci.     

Isolation and characterization of six peach cDNAs encoding key proteins in organic acid metabolism and solute accumulation: involvement in regulating peach fruit acidity

As in many other fleshy fruits, the predominant organic acids in ripe peach ( Prunus persica (L.) Batsch) fruit are malic and citric acids. The accumulation of these metabolites in fruit flesh is regulated during fruit development. Six peach fruit-related genes implicated in organic acid metabolism (mitochondrial citrate synthase; cytosolic NAD-dependent malate dehydrogenase, and cytosolic NADP-dependent isocitrate dehydrogenase) and storage (vacuolar proton translocating pumps: one vacuolar H⁺-ATPase, and two vacuolar H⁺-pyrophosphatases) were cloned. Five of these peach genes were homologous to genes isolated from fruit in other fleshy fruit species. Phylogenetic and expression analyses suggested the existence of a particular vacuolar pyrophosphatase highly expressed in fruit. The sixth gene was the first cytosolic NAD-dependent malate dehydrogenase gene isolated from fruit. Gene expression was studied during the fruit development of two peach cultivars, a normal-acid (Fantasia) and a low-acid (Jalousia) cultivar. The overall expression patterns of the organic acid-related genes appeared strikingly similar for the two cultivars. The genes involved in organic acid metabolism showed a stronger expression in ripening fruit than during the earlier phases of development, but their expression patterns were not necessarily correlated with the changes in organic acid contents. The tonoplast proton pumps showed a biphasic expression pattern more consistent with the patterns of organic acid accumulation, and the tonoplast pyrophosphatases were more highly expressed in the fruit of the low-acid cultivar during the second rapid growth phase of the fruit.     

Long‐term Spatial Changes in the Distribution of the Brazilian Atlantic Forest

The aim of this study is to represent simultaneously changes in the spatial distribution of the Atlantic forest during the last 17,000 years. To characterize such changes, here we focused on three different forest physiognomies, evergreen, semi‐deciduous, and Araucaria, and we provide a list of indicator taxa for each class retrieved from the original published datasets. A review of the published fossil pollen records allowed us to classify regional behaviors in three main areas of distribution, north of 15°S, between 15° and 23°S and south of 23°S latitude that correspond to three climatic geographical barriers. Statistical probability density function method was used to illustrate changes in forest physiognomies throughout the three distribution areas. We show that the three modern barriers also functioned through the past. Asynchronous patterns of forest physiognomies are linked to an antiphasing pattern of monsoon precipitation between the northern and central area, whereas in the southern area, it is linked to the frequency and intensity of the polar advection in the subtropics. Our results attest to strong climate forcing on forest distribution between the late glacial and the interglacial period. They call into question the common reference to the last glacial maximum as a major (and sometimes as the only) driver of forest‐related vicariance and genetic diversity patterns, but suggest that instead, orbital cycles were the main drivers of the successive expansion/contraction of the Atlantic forest throughout the Quaternary.     

Efficiency,thermodynamic and kinetic stability of marketed gadolinium chelates and their possible clinical consequences: a critical review

Gadolinium-based contrast agents are widely used to enhance image contrast in magnetic resonance imaging (MRI) procedures. Over recent years, there has been a renewed interest in the physicochemical properties of gadolinium chelates used as contrast agents for MRI procedures, as it has been suggested that dechelation of these molecules could be involved in the mechanism of a recently described disease, namely nephrogenic systemic fibrosis (NSF). The aim of this paper is to discuss the structure-physicochemical properties relationships of marketed gadolinium chelates in regards to their biological consequences. Marketed gadolinium chelates can be classified according to key molecular design parameters: (a) nature of the chelating moiety: macrocyclic molecules in which Gd3+ is caged in the pre-organized cavity of the ligand, or linear open-chain molecules, (b) ionicity: the ionicity of the complex varies from neutral to tri-anionic agents, and (c) the presence or absence of an aromatic lipophilic residue responsible for protein binding. All these molecular characteristics have a profound impact on the physicochemical characteristics of the pharmaceutical solution such as osmolality, viscosity but also on their efficiency in relaxing water protons (relaxivity) and their biodistribution. These key molecular parameters can also explain why gadolinium chelates differ in terms of their thermodynamic stability constants and kinetic stability, as demonstrated by numerous in vitro and in vivo studies, resulting in various formulations of pharmaceutical solutions of marketed contrast agents. The concept of kinetic and thermodynamic stability is critically discussed as it remains a somewhat controversial topic, especially in predicting the amount of free gadolinium which may result from dechelation of chelates in physiological or pathological situations. A high kinetic stability provided by the macrocyclic structure combined with a high thermodynamic stability (reinforced by ionicity for macrocyclic chelates) will minimize the amount of free gadolinium released in tissue parenchymas.     

Stimulation of the Cyclic GMP Pathway by NO Induces Expression of the Immediate Early Genes c-fos and junB in PC12 Cells

Abstract: Stimulation of several second messenger pathways induces the expression of immediate early genes such as c- fos , c- jun , junB , and junD , but little is known about their induction via the stimulation of the cyclic GMP pathway. Here we looked at the expression of early genes in pheochromocytoma PC12 cells after activation of cytosolic guanylate cyclase by sodium nitroprusside. This compound spontaneously releases NO, a molecule known to be involved in cell communication. We found that expression of c- fos and junB but not of c- jun or junD is increased upon activation of cyclic GMP pathway. c- fos mRNA expression was the most activated (fourfold at 30 min), whereas junB response was more modest (2.2-fold activation at 60 min). Nuclear extracts of stimulated cells show increased binding capacity to the AP1 binding site consistent with the dose-response curve. The activating effect of nitroprusside could be reproduced by dipyridamole, a selective cyclic GMP phosphodiesterase inhibitor and by 8- p -chlorophenylthio-cyclic GMP, a permeant selective cyclic GMP-dependent protein kinase activator, and abolished by KT5823, an inhibitor of that kinase. The results show that NO promotes early gene activation and AP1 binding enhancement through the stimulation of the cyclic GMP pathway.     

The dual roles of geminin during trophoblast proliferation and differentiation

Geminin is a protein involved in both DNA replication and cell fate acquisition. Although it is essential for mammalian preimplantation development, its role remains unclear. In one study, ablation of the geminin gene (Gmnn) in mouse preimplantation embryos resulted in apoptosis, suggesting that geminin prevents DNA re-replication, whereas in another study it resulted in differentiation of blastomeres into trophoblast giant cells (TGCs), suggesting that geminin regulates trophoblast specification and differentiation. Other studies concluded that trophoblast differentiation into TGCs is regulated by fibroblast growth factor-4 (FGF4), and that geminin is required to maintain endocycles. Here we show that ablation of Gmnn in trophoblast stem cells (TSCs) proliferating in the presence of FGF4 closely mimics the events triggered by FGF4 deprivation: arrest of cell proliferation, formation of giant cells, excessive DNA replication in the absence of DNA damage and apoptosis, and changes in gene expression that include loss of Chk1 with up-regulation of p57 and p21. Moreover, FGF4 deprivation of TSCs reduces geminin to a basal level that is required for maintaining endocycles in TGCs. Thus, geminin acts both like a component of the FGF4 signal transduction pathway that governs trophoblast proliferation and differentiation, and geminin is required to maintain endocycles.     

Hair canopy of cricket sensory system tuned to predator signals

Filiform hairs located on the cerci of crickets are among the most sensitive sensors in the animal world and enable crickets to sense the faintest air movements generated by approaching predators. While the neurophysiological and biomechanical aspects of this sensory system have been studied independently for several decades, their integration into a coherent framework was wanting. In order to evaluate the hair canopy tuning to predator signals, we built a model of cercal population coding of oscillating air flows by the hundreds of hairs on the cerci of the sand cricket Gryllus bimaculatus (Insecta: Orthoptera). A complete survey of all hairs covering the cerci was done on intact cerci using scanning electronic microscopy. An additive population coding of sinusoid signals of varying frequencies and velocities taking into account hair directionality delivered the cercal canopy tuning curve. We show that the range of frequencies and velocities at which the cricket sensory system is best tuned corresponds to the values of signals produced by approaching predators. The relative frequencies of short (< 0.5 x 10(-3) m) and long hairs and their differing responses to oscillating air flows therefore enable crickets to detect predators in a time-frequency-intensity space both as far as possible and at close range.