Different responses of tobacco antioxidant enzymes to light and chilling stress

The effect of elevated light treatment (25 degrees C, PPFD 360 mumol m-2 sec-1) or chilling temperatures combined with elevated light (5 degrees C, PPFD 360 mumol m-2 sec-1) on the activity of six antioxidant enzymes, guaiacol peroxidases, and glutathione peroxidase (GPx, EC 1.11.1.9) protein accumulation were studied in tobacco Nicotiana tabacum cv. Petit Havana SR1. Both treatments caused no photooxidative damage, but chilling caused a transient wilting. The light treatment increased the activities of ascorbate peroxidase (APx, EC 1.11.1.11) and guaiacol peroxidases while catalase (EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (EC 1.6.4.2) were unchanged. In contrast, chilling treatment did not increase any of the antioxidant enzyme activities, but decreased catalase and to a lesser extent DHAR activities. Glutathione peroxidase protein levels increased sporadically under light treatment and constantly under chilling. Both chilling and light stress caused induction of glutathione synthesis and accumulation of oxidised glutathione, although the predominant part of the glutathione pool remained in the reduced form. Antioxidant enzymes from the chilling treated plants were measured at both 25 degrees C and 5 degrees C. Measurements at 5 degrees C revealed a 3-fold reduction in catalase activity, compared with that measured at 25 degrees C, indicating that the overall reduction in catalase after four days of chilling was approximately 10-fold. The overall reduction in activity for the other antioxidant enzymes after four days of chilling was 2-fold for GR and APx, 1.5-fold for MDHAR, 3.5-fold for DHAR. The activity of SOD was the same at 25 and 5 degrees C. These results indicate that catalase and DHAR are most strongly affected by the chilling treatment and may be the rate-limiting factor of the antioxidant system at low temperatures.     

Two pregnancies after preimplantation genetic diagnosis for osteogenesis imperfecta type I and type IV

Osteogenesis imperfecta (OI) is an autosomal dominant genetic disorder characterized by the presence of brittle bones and decreased bone mass (osteopenia), as a result of mutations in the genes that encode the chains of type I collagen, the major protein of bone. The clinical features of the disease range from death in the perinatal period to normal life span with minimal increase in fractures. The present report describes two polymerase chain reaction (PCR)-based assays allowing preimplantation genetic diagnosis (PGD) on the one hand for OI type I, the mildest form, and on the other hand for OI type IV, which is intermediate in severity between OI type I and OI type III. In the couple referred for PGD for OI type I, the female partner carried a 1-bp deletion in exon 43 of the COL1A1 gene, resulting in a premature stop codon in exon 46. The synthesis of too little type I procollagen results from such a non-functional or COL1A1 null allele. In the other couple, referred for PGD for OI type IV, the male partner carried a G to A substitution in exon 19 of the COL1A2 gene, which results in an abnormal gene product due to an alphaGly247 (GGT) to Ser (AGT) substitution (G247S). Both mutations result in the loss of a specific restriction enzyme recognition site and can therefore be detected by PCR amplification followed by restriction fragment analysis. PCR amplification of genomic DNA of the parents-to-be with one of the two primers fluorescently labelled, followed by automated laser fluorescence (ALF) gel electrophoresis of the amplified and restricted fragments, allowed a distinction between the healthy and affected genotypes. PCR on single Epstein-Barr-virus (EBV)-transformed lymphoblasts resulted in acceptable amplification efficiencies (87% and 85% for OI type I and OI type IV respectively) and the allele drop-out (ADO) rate was assessed at 11.5% and 11.1% for OI type I and OI type IV respectively. With research blastomeres, 100% amplification rates were obtained and no contamination was observed in the blank controls, which validated the tests for clinical application. Embryos obtained after intracytoplasmic sperm injection (ICSI) were evaluated for the presence of the normal genotype of the non-affected parent. For OI type I, two frozen-thawed ICSI-PGD cycles and two fresh ICSI-PGD cycles were carried out for the same couple. The transfer of two unaffected embryos in the last cycle resulted in a twin pregnancy. A twin pregnancy was also achieved in one clinical ICSI-PGD cycle for OI type IV.     

The J Domain of Simian Virus 40 Large T Antigen Is Required To Functionally Inactivate RB Family Proteins

Transformation by simian virus 40 large T antigen (TAg) is dependent on the inactivation of cellular tumor suppressors. Transformation minimally requires the following three domains: (i) a C-terminal domain that mediates binding to p53; (ii) the LXCXE domain (residues 103 to 107), necessary for binding to the retinoblastoma tumor suppressor protein, pRB, and the related p107 and p130; and (iii) an N-terminal domain that is homologous to the J domain of DnaJ molecular chaperone proteins. We have previously demonstrated that the N-terminal J domain of TAg affects the RB-related proteins by perturbing the phosphorylation status of p107 and p130 and promoting the degradation of p130 and that this domain is required for transformation of cells that express either p107 or p130. In this work, we demonstrate that the J domain of TAg is required to inactivate the ability of each member of the pRB family to induce a G₁ arrest in Saos-2 cells. Furthermore, the J domain is required to override the repression of E2F activity mediated by p130 and pRB and to disrupt p130-E2F DNA binding complexes. These results imply that while the LXCXE domain serves as a binding site for the RB-related proteins, the J domain plays an important role in inactivating their function.     

Fostering Formal Commutativity Knowledge with Approximate Arithmetic

How can we enhance the understanding of abstract mathematical principles in elementary school? Different studies found out that nonsymbolic estimation could foster subsequent exact number processing and simple arithmetic. Taking the commutativity principle as a test case, we investigated if the approximate calculation of symbolic commutative quantities can also alter the access to procedural and conceptual knowledge of a more abstract arithmetic principle. Experiment 1 tested first graders who had not been instructed about commutativity in school yet. Approximate calculation with symbolic quantities positively influenced the use of commutativity-based shortcuts in formal arithmetic. We replicated this finding with older first graders (Experiment 2) and third graders (Experiment 3). Despite the positive effect of approximation on the spontaneous application of commutativity-based shortcuts in arithmetic problems, we found no comparable impact on the application of conceptual knowledge of the commutativity principle. Overall, our results show that the usage of a specific arithmetic principle can benefit from approximation. However, the findings also suggest that the correct use of certain procedures does not always imply conceptual understanding. Rather, the conceptual understanding of commutativity seems to lag behind procedural proficiency during elementary school.     

IRS1 phosphorylation does not mediate mTORC1-induced insulin resistance

Increased mammalian target of rapamycin complex 1 (mTORC1) activity has been suggested to play important roles in development of insulin resistance in obesity. mTORC1 hyperactivity also increases endoplasmic reticulum (ER) stress, which in turn contributes to development of insulin resistance and glucose intolerance. Increased IRS1 phosphorylation at Ser307 in vitro is correlated with mTORC1- and ER stress-induced insulin resistance. This phosphorylation site correlates strongly with impaired insulin receptor signaling in diabetic mice and humans. In contrast, evidence from knock-in mice suggests that phosphorylation of IRS1 at Ser307 is actually required to maintain insulin sensitivity. To study the involvement of IRS1^Ser307 phosphorylation in mTORC1-mediated glucose intolerance and insulin sensitivity in vivo, we investigated the effects of liver specific TSC1 depletion in IRS1^Ser307Ala mice and controls. Our results demonstrate that blockade of IRS1^Ser307 phosphorylation in vivo does not prevent mTORC1-mediated glucose intolerance and insulin resistance.     

Cross Talk between Phosphatidylinositol 3-Kinase and Cyclic AMP (cAMP)-Protein Kinase A Signaling Pathways at the Level of a Protein Kinase B/β-Arrestin/cAMP Phosphodiesterase 4 Complex

Engagement of the T-cell receptor (TCR) in human primary T cells activates a cyclic AMP (cAMP)-protein kinase A (PKA)-Csk inhibitory pathway that prevents full T-cell activation in the absence of a coreceptor stimulus. Here, we demonstrate that stimulation of CD28 leads to recruitment to lipid rafts of a β-arrestin/phosphodiesterase 4 (PDE4) complex that serves to degrade cAMP locally. Redistribution of the complex from the cytosol depends on Lck and phosphatidylinositol 3-kinase (PI3K) activity. Protein kinase B (PKB) interacts directly with β-arrestin to form part of the supramolecular complex together with sequestered PDE4. Translocation is mediated by the PKB plextrin homology (PH) domain, thus revealing a new role for PKB as an adaptor coupling PI3K and cAMP signaling. Functionally, PI3K activation and phosphatidylinositol-(3,4,5)-triphosphate (PIP3) production, leading to recruitment of the supramolecular PKB/β-arrestin/PDE4 complex to the membrane via the PKB PH domain, results in degradation of the TCR-induced cAMP pool located in lipid rafts, thereby allowing full T-cell activation to proceed.T-cell receptor (TCR) stimulation alone is insufficient for activation of T cells, and sustainable T-cell immune responses require a second signal in addition to the TCR-mediated signal. The second signal is typically elicited by ligands B7-1 or B7-2 on antigen-presenting cells engaging the coreceptor CD28 to prevent anergy and apoptosis and enhancing interleukin-2 (IL-2) production and clonal expansion (4). Although CD28 plays a central role in T-cell activation in vivo (5), relatively little is known about the molecular basis for the increased efficacy of T-cell activation upon TCR and CD28 costimulation. Involvement of Lck, Itk, phosphatidylinositol 3-kinase (PI3K), SLP-76, Vav-1, and phospholipase C-γ (PLC-γ) has, however, been reported (43). CD28-mediated signals are transmitted via a short intracellular stretch in the receptor containing a conserved YMNM motif (32). Phosphorylation of Tyr173 in this motif by Lck and Fyn following CD28 ligation is key to efficient signal transduction (41), generating a binding site for the SH2 domain of the p85 regulatory subunit of PI3K (37, 40). CD28 may also contribute to TCR-dependent PI3K activity without recruiting PI3K directly (18). Whether engagement of CD28 alone can also induce PI3K activity has been a matter of controversy. However, recent reports confirming phosphorylation of the protein kinase B (PKB) substrate glycogen synthase kinase 3 (GSK3) upon CD28 ligation has demonstrated that this is indeed the case (6, 15). In addition, CD28 can recruit growth factor receptor-bound protein 2 (Grb2), and such association of Grb2 occurs via the phosphorylated YMNM motif as well as via the C-terminal PXXP motif (22, 35). The PXXP motif also binds and regulates Src family kinases (SFKs) (21, 47), and knock-in mice mutated in this motif were recently reported to have impaired IL-2 secretion (16).Ligation of the TCR induces cyclic AMP (cAMP) production (27). However, the significance of this observation is still not fully understood, as it is well established that cAMP potently inhibits T-cell function and proliferation (2, 45, 46, 50). The spatiotemporal dynamics of the activation-induced cAMP gradient also are not completely appreciated. We have previously shown that cAMP is rapidly produced in lipid rafts following engagement of the TCR in primary T cells (3). This activates a pool of PKA type I targeted to rafts by association with the anchoring protein Ezrin, forming part of a supramolecular complex where Ezrin, EBP50, and PAG provide a scaffold that is able to coordinate PKA phosphorylation and activation of Csk, thereby inhibiting T-cell activation (44, 50). In addition, we have demonstrated that CD3/CD28 costimulation leads to recruitment of type 4 phosphodiesterase (PDE4) isoforms to rafts, resulting in degradation of the TCR-induced cAMP pool (3). Thus, we envisage that TCR-induced cAMP production constitutes a negative feedback loop capable of abrogating T-cell activation in the absence of a second signal. In order then to allow full T-cell activation to proceed, cAMP-mediated inhibition must be lifted. This appears to occur in the presence of a costimulus involving CD28 acting to trigger recruitment of PDE4 to lipid rafts, thereby degrading cAMP at this spatially critical location and resulting in an overriding positive feed-forward signal rather than the negative feedback loop activated from the TCR. In addition, a recent publication by Conche et al. has also found a possible stimulatory effect of cAMP, as the paper surprisingly showed that a transient cAMP increase shortly after TCR triggering may potentiate the calcium component of the TCR signaling. This could constitute a positive feed-forward in addition to the negative feedback signal by cAMP (12).Spatial organization and recruitment of mediators of specific pathways as outlined above are essential to ensure signaling specificity and amplification. Among the many protein scaffolds linking effector molecules into linear pathways, β-arrestins have been reported to confer cross talk with a growing list of molecules important in cellular trafficking and signal transduction, including Src family members and mitogen-activated protein (MAP) kinases (reviewed in reference 14). The arrestins were first identified as having a role in desensitization of G protein-coupled receptors (GPCRs) (9); later, they were discovered to be involved in receptor internalization by interacting with clathrin and AP-2, thereby bringing activated receptors to clathrin-coated pits for endocytosis (19, 26). A role for β-arrestin in the spatially localized degradation of cAMP by scaffolding PDE4 isoforms to the proximity of cAMP generation at the plasma membrane has also been suggested (3, 7, 30, 38).In the present study, we uncover a novel pathway that defines how T-cell costimulation elicits recruitment of PDE4 to lipid rafts to overcome cAMP-mediated inhibition of T-cell activation. This pathway is initiated by CD28 engagement leading to PI3K activation and phosphatidylinositol-(3,4,5)-triphosphate (PIP3) production and resulting in recruitment of a supramolecular complex of PKB/β-arrestin/PDE4 targeted to the plasma membrane due to sequestration via the PKB plextrin homology (PH) domain. Functionally, this pathway is essential for CD28 costimulation to strengthen and sustain T-cell immune responses.     

Scaffold hopping from pyridones to imidazo[1,2-a]pyridines. New positive allosteric modulators of metabotropic glutamate 2 receptor

Imidazo[1,2-a]pyridines were identified via their shape and electrostatic similarity as novel positive allosteric modulators of the metabotropic glutamate 2 receptor. The subsequent synthesis and SAR are described. Potent, selective and metabolically stable compounds were found representing a promising avenue for current further studies.     

Moose summer and winter diets along a large scale gradient of forage availability in southern Norway

Studies on dietary functional responses in large herbivores are traditionally conducted by following individual animals. The method is very time-consuming, and hence, typically provides only a narrow array of forage species compositions. Here we use a range level approach to look at moose (Alces alces) selectivity for and utilization of forage species in relation to availability in both summer and winter. We compare 12 Norwegian ranges representing a large scale gradient in plant communities. The most important forage species in the diet were birches (Betula spp., comprising 43% of all trees browsed in summer and 27% in winter), rowan (Sorbus aucuparia, 25% of trees browsed in summer, 37% in winter), and bilberry (Vaccinum myrtillus, 42% of herbaceous epidermal fragments in summer feces). Selectivity for birches was positively related to its availability and negatively related to availability of rowan, Salix spp., and aspen (Populus tremula) together (all more selected for than birches). Multiple regression models including availability of several forage species were thus superior to single-species models in explaining the diet content of main forage plants. Selectivity for birches was also stronger in summer than in winter, while the opposite pattern was found for rowan. The finding is relevant for our evaluation of the quality of summer and winter ranges, and hence, their relative influence on population productivity. Our study underlines the need to incorporate species composition of available forage when quantifying dietary functional responses in selective herbivores such as moose. Furthermore, care should be taken when extrapolating data on moose diet across ranges or seasons.