Increasing uncoupling protein-2 in pancreatic beta cells does not alter glucose-induced insulin secretion but decreases production of reactive oxygen species

Aims/hypothesis: Levels of uncoupling protein-2 (UCP2) are regulated in the pancreatic beta cells and an increase in the protein level has been associated with mitochondrial uncoupling and alteration in glucose-stimulated insulin secretion. However, it is not clear whether an increase in uncoupling protein-2 per se induces mitochondrial uncoupling and affects ATP generation and insulin secretion. Materials and methods: Transgenic mice with beta cell-specific overexpression of the human UCP2 gene and INS-1 cells with doxycycline-inducible overproduction of the protein were generated and the consequences of increased levels of UCP2 on glucose-induced insulin secretion and on parameters reflecting mitochondrial uncoupling were determined. Results: In transgenic mice, an increase in beta cell UCP2 protein concentration did not significantly modify plasma glucose and insulin levels. Glucose-induced insulin secretion and elevation in the ATP/ADP ratio were unaltered by an increase in UCP2 level. In INS-1 cells, a similar increase in UCP2 level did not modify glucose-induced insulin secretion, cytosolic ATP and ATP/ADP ratio, or glucose oxidation. Increased levels of UCP2 did not modify the mitochondrial membrane potential and oxygen consumption. Increased UCP2 levels decreased cytokine-induced production of reactive oxygen species. Conclusion/interpretation: The results obtained in transgenic mice and in the beta cell line do not support the hypothesis that an increase in UCP2 protein per se uncouples the mitochondria and decreases glucose-induced insulin secretion. In contrast, the observation that increased UCP2 levels decrease cytokine-induced production of reactive oxygen species indicates a potential protective effect of the protein on beta cells, as observed in other cell type

Correction: Spore development and nuclear inheritance in arbuscular mycorrhizal fungi

<p>Abstract</p> <p>Background</p> <p>A conventional tenet of classical genetics is that progeny inherit half their genome from each parent in sexual reproduction instead of the complete genome transferred to each daughter during asexual reproduction. The transmission of hereditary characteristics from parents to their offspring is therefore predictable, although several exceptions are known. Heredity in microorganisms, however, can be very complex, and even unknown as is the case for coenocytic organisms such as Arbuscular Mycorrhizal Fungi (AMF). This group of fungi are plant-root symbionts, ubiquitous in most ecosystems, which reproduce asexually via multinucleate spores for which sexuality has not yet been observed.</p> <p>Results</p> <p>We examined the number of nuclei per spore of four AMF taxa using high Z-resolution live confocal microscopy and found that the number of nuclei was correlated with spore diameter. We show that AMF have the ability, through the establishment of new symbioses, to pass hundreds of nuclei to subsequent generations of multinucleated spores. More importantly, we observed surprising heterogeneity in the number of nuclei among sister spores and show that massive nuclear migration and mitosis are the mechanisms by which AMF spores are formed. We followed spore development of <it>Glomus irregulare </it>from hyphal swelling to spore maturity and found that the spores reached mature size within 30 to 60 days, and that the number of nuclei per spores increased over time.</p> <p>Conclusions</p> <p>We conclude that the spores used for dispersal of AMF contain nuclei with two origins, those that migrate into the spore and those that arise by mitosis in the spore. Therefore, these spores do not represent a stage in the life cycle with a single nucleus, raising the possibility that AMF, unlike all other known eukaryotic organisms, lack the genetic bottleneck of a single-nucleus stage.</p

The role of community and population ecology in applying mycorrhizal fungi for improved food security.

The global human population is expected to reach ∼9 billion by 2050. Feeding this many people represents a major challenge requiring global crop yield increases of up to 100%. Microbial symbionts of plants such as arbuscular mycorrhizal fungi (AMF) represent a huge, but unrealized resource for improving yields of globally important crops, especially in the tropics. We argue that the application of AMF in agriculture is too simplistic and ignores basic ecological principals. To achieve this challenge, a community and population ecology approach can contribute greatly. First, ecologists could significantly improve our understanding of the determinants of the survival of introduced AMF, the role of adaptability and intraspecific diversity of AMF and whether inoculation has a direct or indirect effect on plant production. Second, we call for extensive metagenomics as well as population genomics studies that are crucial to assess the environmental impact that introduction of non-local AMF may have on native AMF communities and populations. Finally, we plead for an ecologically sound use of AMF in efforts to increase food security at a global scale in a sustainable manner

Development of a kinetic metabolic model: application to Catharanthus roseus hairy root

A kinetic metabolic model describing Catharanthus roseus hairy root growth and nutrition was developed. The metabolic network includes glycolysis, pentose-phosphate pathway, TCA cycle and the catabolic reactions leading to cell building blocks such as amino acids, organic acids, organic phosphates, lipids and structural hexoses. The central primary metabolic network was taken at pseudo-steady state and metabolic flux analysis technique allowed reducing from 31 metabolic fluxes to 20 independent pathways. Hairy root specific growth rate was described as a function of intracellular concentration in cell building blocks. Intracellular transport and accumulation kinetics for major nutrients were included. The model uses intracellular nutrients as well as energy shuttles to describe metabolic regulation. Model calibration was performed using experimental data obtained from batch and medium exchange liquid cultures of C. roseus hairy root using a minimal medium in Petri dish. The model is efficient in estimating the growth rate

Redox activities and ROS, NO and phenylpropanoids production by axenically cultured intact olive seedling roots after interaction with a mycorrhizal or a pathogenic fungus

Las raíces de las plántulas de olivo, en cultivo axénico, fueron colocadas alternativamente en contacto con Rhizophagus irregulares (micorrícicos) o con hongos Verticillim dahliae (patógenos). También se incluyeron tratamientos MeJA. Las raíces intactas (generación de anión superóxido, superóxido dismutasa y actividades de peroxidasa) se midieron en las actividades in vivo del apoplasto. Todos nuestros resultados mostraron que las actividades redox apoplásticas de raíces de las plántulas intactas en contacto con el hongo micorriza compatible fueron claramente atenuados en comparación con el hongo patógeno o tratado con MeJA, incluso en las primeras etapas usadas en el tratamiento. Los fenoles totales, flavonoides y glucósidos fenilpropanoides, también fueron cuantificados. Las raíces en contacto con el hongo micorriza no mejoraron la biosíntesis de compuestos fenólicos con respecto a los controles, mientras que los de contacto con el patógeno mejoraron de forma significativa la biosíntesis de todas las fracciones fenólicas medidas. Las especies reactivas del oxígeno y la acumulación de óxido nítrico en las raíces fueron examinadas por microscopía de fluorescencia. Todos ellas presentaron una acumulación mucho mayor en las raíces en contacto con el patógeno que con el hongo micorriza. En total, estos resultados indican que las raíces de las plántulas intactas de olivo, claramente diferenciadas entre micorrizas y hongos patógenos, atenuan las reacciones de defensa contra la primera para facilitar su creación, mientras que induce una reacción de defensa fuerte y sostenida contra el segundo. Ambas especies reactivas de oxígeno y nitrógeno parecían estar involucrados en estas respuestas desde los primeros momentos de contacto. Sin embargo, se necesitan más investigaciones para aclarar la diafonía propuesta entre ellos y sus respectivas funciones en estas respuestas ya que las imágenes de fluorescencia de las raíces revelaron que las especies reactivas del oxígeno se acumulan principalmente en el apoplasto (congruente con las actividades redox medidas en este compartimento), mientras el óxido nítrico se almacena principalmente en el citosol.Roots of intact olive seedlings, axenically cultured, were alternatively placed in contact with Rhizophagus irregularis (mycorrhizal) or Verticillim dahliae (pathogenic) fungi. MeJA treatments were also included. In vivo redox activities in the apoplast of the intact roots (anion superoxide generation, superoxide dismutase and peroxidase activities) were measured. All our results showed that apoplastic redox activities of intact seedling roots in contact with the compatible mycorrhizal fungus were clearly attenuated in comparison with the pathogenic fungus or treated with MeJA, even at the early stages of treatment used. Total phenolics, flavonoids and phenylpropanoid glycosides were also quantified. Roots in contact with the mycorrhizal fungus did not enhance the biosynthesis of phenolic compounds with respect to controls, while those in contact with the pathogenic one significantly enhanced the biosynthesis of all phenolic fractions measured. Reactive oxygen species and nitric oxid accumulation in roots were examined by fluorescence microscopy. All of them presented much higher accumulation in roots in contact with the pathogenic than with the mycorrhizal fungus. Altogether these results indicate that intact olive seedling roots clearly differentiated between mycorrhizal and pathogenic fungi, attenuating defense reactions against the first to facilitate its establishment, while inducing a strong and sustained defense reaction against the second. Both reactive oxygen and nitrogen species seemed to be involved in these responses from the first moments of contact. However, further investigations are required to clarify the proposed crosstalk between them and their respective roles in these responses since fluorescence images of roots revealed that reactive oxygen species were mainly accumulated in the apoplast (congruently with the measured redox activities in this compartment) while nitric oxid was mainly stored in the cytosol.-- Ministerio de Ciencia e Innovación. Proyecto CGL2009-12406 -- Junta de Extremadura. Proyecto PRI09A023peerReviewe

A new species of Stenobiella Tillyard (Neuroptera, Berothidae) from Australia

Stenobiella variola sp. n., a new species of beaded lacewing (Neuroptera: Berothidae), is described and figured from south-eastern Australia. A preliminary key to Stenobiella species is presented

Sterol-regulatory-element-binding protein I c mediates insulin action on hepatic gene expression

Effects of insulin on the expression of liver-specific genes are part of the adaptive mechanisms aimed at maintaining energy homeostasis in mammals. When the diet is rich in carbohydrates, secreted insulin stimulates the expression of genes for enzymes involved in glucose utilization (glucokinase, L-type pyruvate kinase and lipogenic enzymes) and inhibits genes for enzymes involved in glucose production (phosphenolpyruvate carboxykinase). The mechanisms by which insulin controls the expression of these genes have been poorly understood. Recently, the transcription factor sterol-regulatory-element-binding protein 1c has been proposed as a key mediator of insulin transcriptional effects. Here we review the evidence that has led to this proposal and the consequences for our understanding of insulin effects in physiological or pathological conditions

Insulin effects on sterol regulatory-element-binding protein-1c (SREBP-1c) transcriptional activity in rat hepatocytes.

The transcription factor sterol regulatory-element-binding protein-1c (SREBP-1c) plays a major role in the effect of insulin on the transcription of hepatic genes such as glucokinase and fatty acid synthase. We show here in cultured rat hepatocytes that insulin, through activation of the phosphatidylinositol 3-kinase pathway increases the abundance of the precursor form of SREBP-1c in endoplasmic reticulum. This precursor form is then rapidly cleaved, possibly irrespective of the continuous presence of insulin, leading to an increased content of the nuclear mature form of SREBP-1c. Nevertheless, the increased amount of the mature form of SREBP-1c in the nucleus is not a prerequisite for the rapid effect of insulin on the transcription of genes such as glucokinase, suggesting that additional actions of the hormone are involved, such as the activation of the nuclear form of SREBP-1c or of an unidentified SREBP-1c partner