How normal is abnormal? Discrimination between deformations and natural variation in gonad morphology of European whitefish Coregonus lavaretus

The gonad morphology of whitefish Coregonus lavaretus collected in Lake Thun, Switzerland, and two neighbouring lakes was assessed in order to differentiate between 'normal' and 'abnormal' character states of gonad morphology, which had been previously described in C. lavaretus from Lake Thun (constrictions, asymmetries, aplasia, compartmentations, fusions and hermaphroditism). In total, 4668 fish were collected and analysed using two complementary sampling schemes: (1) monthly samples of catches by the commercial fishermen and (2) samples of ripe spawners of all known 33 spawning sites of the three lakes. Considerable variation in gonad morphology in C. lavaretus populations of all lakes was found. Notably, all deviation types were observed in fish of all three lakes. Asymmetries and constrictions were frequent in all three lakes and showed systematic differences in frequency between the two sampling strategies. This indicates that asymmetries and constrictions represent to a large extent natural variation in gonad morphology of C. lavaretus and are also prone to considerable measurement error. In contrast, aplasia, fusions, compartmentations and hermaphroditism occurred predominantly in one C. lavaretus form of Lake Thun and in particular in populations spawning at great depths. This suggests that these deviation types are probably reliable indicators for gonad deformations and supports the interpretation that Lake Thun harbours a unique case of deformed gonads in C. lavaretus of yet unknown origin.     

MgATP-independent and MgATP-dependent exocytosis. Evidence that MgATP primes adrenal chromaffin cells to undergo exocytosis

The MgATP dependency of secretion was investigated in digitonin-permeabilized adrenal chromaffin cells. Shortly after permeabilization there is a component of Ca2+-dependent secretion that occurs in the absence of MgATP in the medium. This secretion occurs from cells which are permeable to Ca2+/[ethylene-bis(oxyethylenenitrilo)]tetraacetic acid buffers, to nucleotides, and to proteins. It is prevented by treatment of cells with metabolic inhibitors to reduce cellular ATP prior to permeabilization. The rate of MgATP-independent secretion is rapid and terminates by approximately 2 min after introduction of Ca2+. MgATP-independent secretion is labile and is lost unless Ca2+ is introduced within 8 min of permeabilization. MgATP-dependent secretion occurs at a slower rate than MgATP-independent secretion and continues at a constant rate for 12 min. Preincubation of permeabilized cells with MgATP enhances Ca2+-dependent secretion during a subsequent incubation in the absence of MgATP. Similar MgATP sensitivities are observed when MgATP is present only prior to or only during stimulation with Ca2+ with half-maximal stimulation occurring at 0.4-0.5 and 0.6 mM MgATP, respectively. The data indicate that intact cells are primed by intracellular ATP so that immediately upon permeabilization, there is a component of secretion which is independent of medium MgATP. MgATP partially maintains the primed state after permeabilization by acting before Ca2+ in the secretory pathway.     

IL-17 silencing does not protect nonobese diabetic mice from autoimmune diabetes

The long-held view that many autoimmune disorders are primarily driven by a Th1 response has been challenged by the discovery of Th17 cells. Since the identification of this distinct T cell subset, Th17 cells have been implicated in the pathogenesis of several autoimmune diseases, including multiple sclerosis and rheumatoid arthritis. Type 1 diabetes has also long been considered a Th1-dependent disease. In light of the emerging role for Th17 cells in autoimmunity, several recent studies investigated the potential of this subset to initiate autoimmune diabetes. However, direct evidence supporting the involvement of Th17 cells in actual pathogenesis, particularly during spontaneous onset, is lacking. In this study, we sought to directly address the role of IL-17, the cytokine by which Th17 cells are primarily characterized, in the pathogenesis of autoimmune diabetes. We used lentiviral transgenesis to generate NOD mice in which IL-17 is silenced by RNA interference. The loss of IL-17 had no effect on the frequency of spontaneous or cyclophosphamide-induced diabetes. In contrast, IL-17 silencing in transgenic NOD mice was sufficient to reduce the severity of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis, consistent with reports that IL-17 deficiency is protective in this experimental model of multiple sclerosis. We concluded that IL-17 is dispensable, at least in large part, in the pathogenesis of autoimmune diabetes.     

Cell biology of molybdenum

The transition element molybdenum (Mo) is of essential importance for (nearly) all biological systems as it is required by enzymes catalyzing diverse key reactions in the global carbon, sulfur and nitrogen metabolism. The metal itself is biologically inactive unless it is complexed by a special cofactor. With the exception of bacterial nitrogenase, where Mo is a constituent of the FeMo-cofactor, Mo is bound to a pterin, thus forming the molybdenum cofactor (Moco) which is the active compound at the catalytic site of all other Mo-enzymes. In eukaryotes, the most prominent Mo-enzymes are (1) sulfite oxidase, which catalyzes the final step in the degradation of sulfur-containing amino acids and is involved in detoxifying excess sulfite, (2) xanthine dehydrogenase, which is involved in purine catabolism and reactive oxygen production, (3) aldehyde oxidase, which oxidizes a variety of aldehydes and is essential for the biosynthesis of the phytohormone abscisic acid, and in autotrophic organisms also (4) nitrate reductase, which catalyzes the key step in inorganic nitrogen assimilation. All Mo-enzymes, except plant sulfite oxidase, need at least one more redox active center, many of them involving iron in electron transfer. The biosynthesis of Moco involves the complex interaction of six proteins and is a process of four steps, which also includes iron as well as copper in an indispensable way. Moco as released after synthesis is likely to be distributed to the apoproteins of Mo-enzymes by putative Moco-carrier proteins. Xanthine dehydrogenase and aldehyde oxidase, but not sulfite oxidase and nitrate reductase, require the post-translational sulfuration of their Mo-site for becoming active. This final maturation step is catalyzed by a Moco-sulfurase enzyme, which mobilizes sulfur from l-cysteine in a pyridoxal phosphate-dependent manner as typical for cysteine desulfurases.     

Antifungal and antibacterial activities of Araucaria araucana (Mol.) K. Koch heartwood lignans

Five lignans (secoisolariciresinol, pinoresinol, eudesmin, lariciresinol, and lariciresinol-4-methyl ether) were isolated from an MeOH extract from Araucaria araucana (Mol.) K. Koch wood for the first time in this species and their structures determined with spectroscopic methods. The antimicrobial activities of these compounds were determined for the bacteria Citrobacter sp., Bacillus subtilis, Escherichia coli, Micrococcus luteus, Staphylococcus aureus, and Pseudomonas aeruginosa, and for the white rooting and staining fungi Mucor miehei, Paecilomyces variotii, Ceratocystis pilifera, Trametes versicolor, and Penicillium notatum, and in addition, the MeOH extract was evaluated against Aspergillus niger, Candida albicans, Fusarium moniliforme, F. sporotrichum and Trichophyton mentagrophytes. The most sensitive bacteria against pinoresinol were the Gram-positive. However, secoisolariciresinol exhibited a significant antifungal activity on fungi of white rooting and wood staining and this compound completely inhibited the mycelial growth of T. versicolor and C. pilifera at 300 and 400 microg per disc, respectively, whereas pinoresinol showed a moderate inhibitory activity. On the other hand, the MeOH extract had the highest activity against rooting and staining and pathogenic fungi as well as T. versicolor, Fusarium spp. and Trichophyton mentagrophytes, inhibiting completely the growth at 400 microg per disc.     

The coexistence of hybrid and parental Daphnia: the role of parasites

Parasite driven time-lagged negative frequency-dependent selection of hosts has been studied in natural populations by following changes in host genotype frequencies over time. However, such dynamics have not been considered at higher taxonomic levels, for example, between parental species and their hybrids. In a field study on a Daphnia hybrid system, we observed that one Daphnia taxon first was relatively under-infected, but became over-infected after a strong increase in frequency. This finding is consistent with the idea of parasite evolution towards the most frequent host taxon. In two experiments, we investigated whether the assumptions made by a model of negative frequency-dependent selection apply to our host taxa system. First, we showed that the parasite can change the outcome of taxa competition and secondly, we confirmed that the over-infection of one host taxon observed in the field has a genetic basis. Our results indicate that the incorporation of host-parasite interactions at the species level may allow us to gain a more complete picture of forces driving dynamic taxa coexistence in Daphnia hybrid systems. More generally, we suggest that if hybrids coexist in sympatry with parental taxa, the infection patterns as observed under natural conditions may be rather temporal and unstable.