Asexual reproduction changes predator population dynamics in a life predator–prey system

Many organisms display oscillations in population size. Theory predicts that these fluctuations can be generated by predator–prey interactions, and empirical studies using life model systems, such as a rotifer-algae community consisting of Brachionus calyciflorus as predator and Chlorella vulgaris as prey, have been successfully used for studying such dynamics. B. calyciflorus is a cyclical parthenogen (CP) and clones often differ in their sexual propensity, that is, the degree to which they engage into sexual or asexual (clonal) reproduction. Since sexual propensities can affect growth rates and population sizes, we hypothesized that this might also affect population oscillations. Here, we studied the dynamical behaviour of B. calyciflorus clones representing either CPs (regularly inducing sex) or obligate parthenogens (OPs). We found that the amplitudes of population cycles to be increased in OPs at low nutrient levels. Several other population dynamic parameters seemed unaffected. This suggests that reproductive mode might be an important additional variable to be considered in future studies of population oscillations.     

Prevalence of Epstein-Barr virus (EBV) antibodies in primate stocks of zoological gardens

Abstract: Examination of 387 serum samples from 41 primate species with two different ELISAs for the presence of IgG-antibodies against Epstein-Barr virus. Antibodies were detected in 15 out of 32 species of Old World primates and none in six species of New World primates by screening ELISA (Enzygnost, Behringwerke AG, Marburg), a testkit for human diagnostics. To avoid species-dependent factors which could influence the sensitivity of the Enzygnost assay, a competition ELISA was established. The modified test assessed antibodies in all species of Old World primates and three species of the New World primates.     

Identification of three urease accessory proteins that are required for urease activation in Arabidopsis

Urease is a nickel-containing urea hydrolase involved in nitrogen recycling from ureide, purine, and arginine catabolism in plants. The process of urease activation by incorporation of nickel into the active site is a prime example of chaperone-mediated metal transfer to an enzyme. Four urease accessory proteins are required for activation in Klebsiella aerogenes. In plants urease accessory proteins have so far been only partially defined. Using reverse genetic tools we identified four genes that are necessary for urease activity in Arabidopsis (Arabidopsis thaliana; ecotypes Columbia and N?ssen). Plants bearing T-DNA or Ds element insertions in either the structural gene for urease or in any of the three putative urease accessory genes AtureD, AtureF, and AtureG lacked the corresponding mRNAs and were defective in urease activity. In contrast to wild-type plants, the mutant lines were not able to support growth with urea as the sole nitrogen source. To investigate whether the identified accessory proteins would be sufficient to support eukaryotic urease activation, the corresponding cDNAs were introduced into urease-negative Escherichia coli. In these bacteria, urease activity was observed only when all three plant accessory genes were coexpressed together with the plant urease gene. Remarkably, plant urease activation occurred as well in cell-free E. coli extracts, but only in extracts from cells that had expressed all three accessory proteins. The future molecular dissection of the plant urease activation process may therefore be performed in vitro, providing a powerful tool to further our understanding of the biochemistry of chaperone-mediated metal transfer processes in plants.     

Strong and ubiquitous expression of transgenes targeted into the beta-actin locus by Cre/lox cassette replacement

Conventional approaches to produce transgenic mice recurrently yield unpredictable patterns and levels of transgene expression, a situation calling for the development of new techniques to overcome these drawbacks in the context of overexpression studies. Here we present an efficient method for rapid and reproducible transgenesis using the recombinase mediated cassette exchange (RMCE) (Bouhassira et al.: Blood 90:3332-3344, 1997) procedure. A lox511-EGFP-TK/neo-loxP cassette was placed under the control of the endogenous mouse beta-actin promoter. Heterozygous mice revealed strong and ubiquitous EGFP expression throughout embryogenesis and adulthood. Reproducibly, the same expression pattern was obtained with RMCE when it was used to replace the EGFP-harboring cassette by ECFP or placental alkaline phosphatase (PLAP) reporter genes (DePrimo et al.: Transgenic Res 5:459-466, 1996). Furthermore, the RMCE procedure proved efficient as well in embryonic stem (ES) cells as directly in zygotes. Our results demonstrate ubiquitous expression of floxed transgenes in the endogenous beta-actin locus and they support the general use of the beta-actin locus for targeted transgenesis.     

Quantitative X-ray tomography of the mouse cochlea

Imaging with hard X-rays allows visualizing cochlear structures while maintaining intrinsic qualities of the tissue, including structure and size. With coherent X-rays, soft tissues, including membranes, can be imaged as well as cells making use of the so-called in-line phase contrast. In the present experiments, partially coherent synchrotron radiation has been used for micro-tomography. Three-dimensional reconstructions of the mouse cochlea have been created using the EM3D software and the volume has been segmented in the Amira Software Suite. The structures that have been reconstructed include scala tympani, scala media, scala vestibuli, Reissner's membrane, basilar membrane, tectorial membrane, organ of Corti, spiral limbus, spiral ganglion and cochlear nerve. Cross-sectional areas of the scalae were measured. The results provide a realistic and quantitative reconstruction of the cochlea.     

In vivo determination of mouse olfactory mucus cation concentrations in normal and inflammatory States

Objective

Olfaction is impaired in chronic rhinosinusitis (CRS). The study has two aims: (1) to determine whether changes in cation concentration occur in the olfactory mucus of mice with CRS, which may affect chemo-electrical transduction, (2) and to examine whether these alterations are physiologically significant in humans.

Study Design

Animal study in mice and translational study in humans.

Methods

Inflammation was induced by sensitization and chronic exposure of 16 C57BL/6 mice to Aspergillus fumigatus. The control group included 16 untreated mice. Ion-selective microelectrodes were used to measure free cation concentrations in the olfactory mucus of 8 mice from each treatment group, while the remaining mice were sacrificed for histology. To validate the findings in the animal model, olfactory threshold was measured in 11 healthy human participants using Sniffin’ Sticks before and after nasal irrigation with solutions that were composed of either of the cation concentrations.

Results

In 8 mice, olfactory mucus of chronically inflamed mice had lower [Na⁺] (84.8±4.45 mM versus 93.73±3.06 mM, p = 0.02), and higher [K⁺] (7.2±0.65 mM versus 5.7±0.20 mM, p = 0.04) than controls. No difference existed in [Ca²⁺] (0.50±0.12 mM versus 0.54±0.06 mM, p = 0.39). In humans, rinsing with solutions replicating ion concentrations of the mouse mucosa with chronic inflammation caused a significant elevation in the median olfactory threshold (9.0 to 4.8, p = 0.003) but not with the control solution (8.3 to 7.8, p = 0.75).

Conclusion

Chronic inflammation elevates potassium and lowers sodium ion concentration in mice olfactory mucus. Nasal irrigation with a corresponding solution induced olfactory threshold shift in humans.     

Uric Acid Accumulation in an Arabidopsis Urate Oxidase Mutant Impairs Seedling Establishment by Blocking Peroxisome Maintenance

Purine nucleotides can be fully catabolized by plants to recycle nutrients. We have isolated a urate oxidase (uox) mutant of Arabidopsis thaliana that accumulates uric acid in all tissues, especially in the developing embryo. The mutant displays a reduced germination rate and is unable to establish autotrophic growth due to severe inhibition of cotyledon development and nutrient mobilization from the lipid reserves in the cotyledons. The uox mutant phenotype is suppressed in a xanthine dehydrogenase (xdh) uox double mutant, demonstrating that the underlying cause is not the defective purine base catabolism, or the lack of UOX per se, but the elevated uric acid concentration in the embryo. Remarkably, xanthine accumulates to similar levels in the xdh mutant without toxicity. This is paralleled in humans, where hyperuricemia is associated with many diseases whereas xanthinuria is asymptomatic. Searching for the molecular cause of uric acid toxicity, we discovered a local defect of peroxisomes (glyoxysomes) mostly confined to the cotyledons of the mature embryos, which resulted in the accumulation of free fatty acids in dry seeds. The peroxisomal defect explains the developmental phenotypes of the uox mutant, drawing a novel link between uric acid and peroxisome function, which may be relevant beyond plants.     

Response of a zooplankton community to the addition of unsaturated fatty acids: an enclosure study

1. The effect of the addition of emulsions with different fatty acid composition to a semi-natural zooplankton community was studied in enclosures.
2. The reactions of different taxa in the zooplankton community to the addition of the emulsions were different. The copepods showed almost no reaction, nor did the selective cladocerans ( Bosmina ) or rotifers ( Synchaeta or Polyarthra ). The non-selective filterfeeding cladocerans Daphnia and Ceriodaphnia , and the rotifer Keratella , showed responses to the addition of the emulsions.
3.  Keratella showed the highest density in the enclosures with high amounts of highly unsaturated fatty acids added, whereas both Daphnia and Ceriodaphnia reached the highest numbers in the enclosures where we added emulsions of saturated fatty acids only.
4. Our results suggest that different taxa may be limited by different factors, even though they use similar food sources. Hence, we conclude that it is very difficult to generalize on the limiting factors in aquatic systems.     

Identification and Characterization of Proteins Involved in Rice Urea and Arginine Catabolism

Rice (Oryza sativa) production relies strongly on nitrogen (N) fertilization with urea, but the proteins involved in rice urea metabolism have not yet been characterized. Coding sequences for rice arginase, urease, and the urease accessory proteins D (UreD), F (UreF), and G (UreG) involved in urease activation were identified and cloned. The functionality of urease and the urease accessory proteins was demonstrated by complementing corresponding Arabidopsis (Arabidopsis thaliana) mutants and by multiple transient coexpression of the rice proteins in Nicotiana benthamiana. Secondary structure models of rice (plant) UreD and UreF proteins revealed a possible functional conservation to bacterial orthologs, especially for UreF. Using amino-terminally StrepII-tagged urease accessory proteins, an interaction between rice UreD and urease could be shown. Prokaryotic and eukaryotic urease activation complexes seem conserved despite limited protein sequence conservation for UreF and UreD. In plant metabolism, urea is generated by the arginase reaction. Rice arginase was transiently expressed as a carboxyl-terminally StrepII-tagged fusion protein in N. benthamiana, purified, and biochemically characterized (K_m = 67 mm, k_cat = 490 s⁻¹). The activity depended on the presence of manganese (K_d = 1.3 μm). In physiological experiments, urease and arginase activities were not influenced by the external N source, but sole urea nutrition imbalanced the plant amino acid profile, leading to the accumulation of asparagine and glutamine in the roots. Our data indicate that reduced plant performance with urea as N source is not a direct result of insufficient urea metabolism but may in part be caused by an imbalance of N distribution.Nitrogen (N) availability often limits plant performance in natural ecosystems (Vitousek and Howarth, 1991), causing a selective pressure to optimize the use of N resources. This ecophysiological selection has even led to a reduction of the N content of plant proteins in comparison with animal orthologs (Elser et al., 2006). Because N is a limiting resource, plants do not only require efficient N uptake mechanisms but also possess enzymatic pathways for N remobilization.Arg is the most important single metabolite for N storage in plant seeds. In a survey of 379 plant species, Arg N accounted on average for 17.3% of total seed N (Vanetten et al., 1967). In several rice (Oryza sativa) varieties, values ranging from 16.1% to 17.1% were measured (Mosse et al., 1988). To access the N stored in the guanidinium group of Arg, it must first be hydrolyzed by mitochondrial arginase to Orn and urea. Urea leaves the mitochondria and is hydrolyzed by urease in the cytosol, releasing ammonia, which is reassimilated into amino acids by the combined action of Gln synthetase and Glu synthase.Urea not only originates from Arg breakdown but may also be taken up from the environment by urea transporters (Kojima et al., 2007; Wang et al., 2008). Therefore, urease is involved in N remobilization as well as in primary N assimilation. Plant ureases and arginases are housekeeping enzymes found in many if not all plant species (Witte and Medina-Escobar, 2001; Brownfield et al., 2008). Urease is a nickel metalloenzyme that in Arabidopsis (Arabidopsis thaliana) requires three urease accessory proteins (UAPs; AtUreD, AtUreF, and AtUreG) for activation (Witte et al., 2005a). Studies in bacteria demonstrated that UAPs form a complex with apo-urease and are required for posttranslational Lys carboxylation of apo-urease and the subsequent incorporation of two nickel ions into the active center. After activation, the UAPs dissociate from urease. The exact molecular function of each accessory protein in this process is not yet understood (Carter et al., 2009). Like urease, arginase is a metalloenzyme. It is best activated by manganese (Carvajal et al., 1996; Hwang et al., 2001), not requiring accessory proteins for activation.Urea plays an important role in agriculture because it is the most used N fertilizer worldwide (http://www.fertilizer.org/ifa), intensively employed in Asia for the cultivation of rice. Urea N partly reaches the plant as ammonium or nitrate because the fertilizer is already degraded in the environment by microbial ureases and may then be subject to nitrification. Alternatively, plants are capable of taking up urea from fertilization directly and assimilate its N (Kojima et al., 2007; Wang et al., 2008). Although rice is a major crop plant and rice production is heavily dependent on urea fertilization, the enzymes and the corresponding genes involved in rice urea metabolism have not yet been investigated. In this study, we identified the genes and cloned the corresponding cDNAs coding for rice arginase, urease, and the UAPs UreD, UreF, and UreG. The functionality of the corresponding proteins was demonstrated and biochemical parameters were determined. The general gene and protein structure of plant UreD and UreF were investigated and a direct interaction of rice UreD with apo-urease was discovered, leading to a refinement of the mechanistic view of plant urease activation. In physiological experiments, rice urease and arginase activities showed no significant response to different N-fertilizing regimes, while the amino acid composition in urea-grown plants was strongly imbalanced, indicating that urea N disturbs plant metabolism downstream of N assimilation.