The association between parasite infection and growth rates in Arctic charr: do fast growing fish have more parasites?

Trophically transmitted parasites are known to impair fish growth in experimental studies, but this is not well documented in natural populations. For Arctic charr [Salvelinus alpinus (L.)], individual growth is positively correlated with food consumption. However, increased food consumption will increase the exposure to trophically transmitted parasites. Using a correlative approach, we explore the association between parasite abundance and the individual growth of Arctic charr from five lakes within the same watercourse. The studied parasite species differ in their life cycles and cost to the host. We predicted a positive association between parasite abundance and fish growth for parasites of low pathogenicity reflecting high consumption rates, and a negative association at higher parasite abundances for more costly parasites. We found no direct negative associations between parasite abundance and fish growth. The relationship between parasite abundance and growth was linearly positive for the low costly Crepidostomum sp. and concave for the more costly Eubothrium salvelini. In natural fish populations, the negative effects of parasites on fish growth might be outweighed by the energy assimilated from feeding on the intermediate host. However, experimental studies with varying food consumption regimes are needed to determine the mechanisms underlying our observations.

     

A retroviral vector for siRNA expression in mammalian cells

Utilization of RNA interference (RNAi) for knockdown of gene expression has become a standard tool for the study of gene function. Short hairpin RNAs (shRNAs) expressed from RNA polymerase III promoters are widely used to achieve stable knockdown of gene expression by RNAi. We have constructed a retroviral-based shRNA expression vector, pSiRPG, as a tool for shRNA-based functional genomic studies. This vector is based on a widely used shRNA expression system and was modified to harbor an enhanced green fluorescent protein (EGFP) and a puromycin selection marker. The functionality of the elements in the pSiRPG vector was validated. The H1(TetO₂) promoter in the vector facilitates doxycycline-inducible shRNA expression, which was demonstrated in cells expressing the Tet repressor (TetR). However, we also demonstrated limited efficiency of the inhibition of shRNA expression in an uninduced TetR-expressing cell line. This observation strongly indicates that the H1(TetO₂) promoter, which is used in a wide range of vectors, is not optimal for tightly regulated shRNA expression. Stable repression of the NDRG1 protein level was observed when introducing pSiRPG constructs expressing shRNAs targeting NDRG1 into two mammary epithelial cell lines by retroviral delivery. This vector should therefore facilitate functional studies in breast cell lines that are hard to transfect with conventional plasmid-based methods.     

DNA barcoding of Scandinavian birds reveals divergent lineages in trans-Atlantic species

Birds are a taxonomically well-described group of animals, yet DNA barcoding, i.e., the molecular characterization of species using a standardized genetic marker, has revealed unexpected patterns of genetic divergences among North American birds. We performed a comprehensive COI (cytochrome c oxidase subunit I) barcode survey of 296 species of Scandinavian birds, and compared genetic divergences among 78 trans-Atlantic species whose breeding ranges include both Scandinavia and North America. Ninety-four percent of the Scandinavian species showed unique barcode clusters; the remaining 6% had overlapping barcodes with one or more congeneric species, which may reflect incomplete lineage sorting or a single gene pool. Four species showed large intra-specific divergences within Scandinavia, despite no apparent morphological differentiation or indications of reproductive isolation. These cases may reflect admixture of previously isolated lineages, and may thus warrant more comprehensive phylogeographic analyses. Nineteen (24%) of 78 trans-Atlantic species exhibited divergent genetic clusters which correspond with regional subspecies. Three of these trans-Atlantic divergences were paraphyletic. Our study demonstrates the effectiveness of COI barcodes for identifying Scandinavian birds and highlights taxa for taxonomic review. The standardized DNA barcoding approach amplified the power of our regional studies by enabling independently obtained datasets to be merged with the established avian barcode library.     

Influence of penicillin instability on interpretation of feedback regulation experiments

Summary The stability of penicillin G during production is reviewed and compared to reports on end-product regulation of penicillin biosynthesis. From this analysis, it appears that penicillin control of its own synthesis when added exogenously at the beginning of the process has not been proven, since the apparent decrease of net accumulation can be explained by gradual hydrolysis of the added penicillin. It is also concluded that the maximum amount of penicillin accumulated normally is not controlled by penicillin, but rather by its stability and the ability of the cells to maintain a high synthetic rate over extended time periods.     

Improved two-stage protein expression and purification via autoinduction of both autolysis and auto DNA/RNA hydrolysis conferred by phage lysozyme and DNA/RNA endonuclease

We report improved release of recombinant proteins in Escherichia coli, which relies on combined cellular autolysis and DNA/RNA autohydrolysis, conferred by the tightly controlled autoinduction of both phage lysozyme and the nonspecific DNA/RNA endonuclease from Serratia marcescens. Autoinduction occurs in a two-stage process wherein heterologous protein expression and autolysis enzymes are induced upon entry into stationary phase by phosphate depletion. Cytoplasmic lysozyme and periplasmic endonuclease are kept from inducing lysis until membrane integrity is disrupted. After cell harvest, the addition of detergent (0.1% Triton X-100) and a single 30 min freeze-thaw cycle results in >90% release of protein, green fluorescent protein. This cellular lysis is accompanied by complete oligonucleotide hydrolysis. The approach has been validated for shake flask cultures, high-throughput cultivation in microtiter plates, and larger scale stirred-tank bioreactors. This tightly controlled system enables robust growth and resistance to lysis in routine media when cells are propagated and autolysis/hydrolysis genes are only induced upon phosphate depletion.     

Clever leukemic stem cells branch out

Individual tumors harbor heterogeneous populations of genetically distinct subclones. Two recent papers in Nature by Notta et al. (2011) and Anderson et al. (2011) reveal genetic heterogeneity in functional leukemic stem cells, which has important implications for how both cancer and normal stem cell populations may adapt to selective pressure.     

Seasonal dietary shifts enhance parasite transmission to lake salmonids during ice cover

Changes in abiotic and biotic factors between seasons in subarctic lake systems are often profound, potentially affecting the community structure and population dynamics of parasites over the annual cycle. However, few winter studies exist and interactions between fish hosts and their parasites are typically confined to snapshot studies restricted to the summer season whereas host‐parasite dynamics during the ice‐covered period rarely have been explored. The present study addresses seasonal patterns in the infections of intestinal parasites and their association with the diet of sympatric living Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) in Lake Takvatn, a subarctic lake in northern Norway. In total, 354 Arctic charr and 203 brown trout were sampled from the littoral habitat between June 2017 and May 2018. Six trophically transmitted intestinal parasite taxa were identified and quantified, and their seasonal variations were contrasted with dietary information from both stomachs and intestines of the fish. The winter period proved to be an important transmission window for parasites, with increased prevalence and intensity of amphipod‐transmitted parasites in Arctic charr and parasites transmitted through fish prey in brown trout. In Arctic charr, seasonal patterns in parasite infections resulted mainly from temporal changes in diet toward amphipods, whereas host body size and the utilization of fish prey were the main drivers in brown trout. The overall dynamics in the community structure of parasites chiefly mirrored the seasonal dietary shifts of their fish hosts.     

Ornithodoros moubata complement inhibitor is an equally effective C5 inhibitor in pigs and humans

Experimental evidence suggests that C inhibition and more particularly combined inhibition of C and the TLR coreceptor CD14 may be of therapeutic benefit in sepsis and other inflammatory conditions. A barrier to the testing and further development of many inhibitors is that their activity is species specific. Pig is a relevant species for experimental models of human disease, and this study undertakes a comprehensive comparison of the inhibitory efficacy of the C5 inhibitor Ornithodoros moubata C inhibitor (OmCI) in human and porcine whole blood ex vivo models of Escherichia coli-induced sepsis. The effect of OmCI on complement activity in pigs undergoing E. coli sepsis was also examined. Porcine and human serum, and whole blood anticoagulated with lepirudin, was incubated with E. coli and the effect of OmCI investigated. The ex vivo results were virtually identical in pig and human. OmCI completely ablated the activity of all three C pathways at 0.64 μM. E. coli-induced C activation and expression of CD11b (wCD11R3 in the pig), was abolished ex vivo at 0.32 μM OmCI. Combining anti-CD14 and OmCI reduced the formation of IL-8 and TNF-α more potently than the single inhibitors. OmCI also efficiently bound E. coli-induced leukotriene B(4) in pig and human plasma. In support of our ex vivo findings, in vivo the activity of all C pathways was inhibited at 0.6 mg OmCI/kg pig. In conclusion, OmCI efficiently inhibited pig and human C activation, has accompanying anti-inflammatory effects and is a promising candidate inhibitor for further in vivo studies of sepsis.