Combined effects of parasites and contaminants on animal health: parasites do matter

The cumulative effects of multiple stressors are becoming a priority concern for ecotoxicologists, ecologists and conservation biologists working to understand threats to ecosystems and species. In that context, parasites and pathogens are increasingly a focus of attention. Parasites interact with natural and anthropogenic stressors to increase mortality and reduce animal health in myriad ways in a wide spectrum of host and parasite taxa. The combined effects of parasites and other stressors can reduce either resistance or tolerance to infection. Recommendations are provided to guide further research.     

Free-living endohelminth stages: at the mercy of environmental conditions

During their free-living phases, endohelminths are directly exposed to environmental conditions in their respective macrohabitats. Both natural environmental factors and pollutants released into the environment through anthropogenic activities can influence the success of the free-living stages. This overview examines the effects of natural variables and pollutants on two specific properties (survival and infectivity) of free-living stages of endohelminths, mainly trematodes, while fully recognizing that other parasitic life history stages in addition to the hosts can also be affected. As most parasite pollution studies have been carried out in aquatic habitats, this paper focuses on parasites of aquatic or amphibious hosts.     

BAG2 Gene-mediated Regulation of PINK1 Protein Is Critical for Mitochondrial Translocation of PARKIN and Neuronal Survival

Emerging evidence has demonstrated a growing genetic component in Parkinson disease (PD). For instance, loss-of-function mutations in PINK1 or PARKIN can cause autosomal recessive PD. Recently, PINK1 and PARKIN have been implicated in the same signaling pathway to regulate mitochondrial clearance through recruitment of PARKIN by stabilization of PINK1 on the outer membrane of depolarized mitochondria. The precise mechanisms that govern this process remain enigmatic. In this study, we identify Bcl2-associated athanogene 2 (BAG2) as a factor that promotes mitophagy. BAG2 inhibits PINK1 degradation by blocking the ubiquitination pathway. Stabilization of PINK1 by BAG2 triggers PARKIN-mediated mitophagy and protects neurons against 1-methyl-4-phenylpyridinium-induced oxidative stress in an in vitro cell model of PD. Collectively, our findings support the notion that BAG2 is an upstream regulator of the PINK1/PARKIN signaling pathway.     

Comparison of a manual and an automated method to estimate the number of uterine eggs in anisakid nematodes: to Coulter or not to Coulter. Is that the question?

Studies reporting numbers of eggs in vagina and utero in nematodes often give little information of the technique used for the estimations. This situation hampers comparison among studies, because, so far, differences in estimations provided by different techniques have not been assessed. This note examines whether a manual method based on visual counts in aliquots and an automated method using a Coulter counter yield equivalent estimations of egg numbers in vagina and utero of 3 anisakid nematode species (Anisakis simplex, Pseudoterranova decipiens, and Contracaecum osculatum). The number of eggs from 50 females per nematode species was estimated using both techniques. The automated and manual methods yielded similar egg counts (correlation coefficients >0.9 in the 3 species), but the methods were not always statistically equivalent. The automated method was more precise and seemed less dependent on egg density, whereas the manual method was less time-consuming (contrary to previous perceptions) and less expensive. Despite the higher precision of automated counts, the manual technique seemed to produce similar estimates; thus, it may be particularly useful in developing countries where nematode parasitism is prevalent in humans and domestic animals, but scientific resources are limited.     

Recent horizontal transfer of a mariner transposable element among and between Diptera and Neuroptera

Transposable elements of the mariner family are widespread among insects and other invertebrates, and initial analyses of their relationships indicated frequent occurrence of horizontal transfers between hosts. A specific PCR assay was used to screen for additional members of the irritans subfamily of mariners in more than 400 arthropod species. Phylogenetic analysis of cloned PCR fragments indicated that relatively recent horizontal transfers had occurred into the lineages of a fruit fly Drosophila ananassae, the horn fly Haematobia irritans, the African malaria vector mosquito Anopheles gambiae, and a green lacewing Chrysoperla plorabunda. Genomic dot-blot analysis revealed that the copy number in these species varies widely, from about 17,000 copies in the horn fly to three copies in D. ananassae. Multiple copies were sequenced from genomic clones from each of these species and four others with related elements. These sequences confirmed the PCR results, revealing extremely similar elements in each of these four species (greater than 88% DNA and 95% amino acid identity). In particular, the consensus sequence of the transposase gene of the horn fly elements differs by just two base pairs out of 1,044 from that of the lacewing elements. The mosquito lineage has diverged from the other Diptera for over 200 Myr, and the neuropteran last shared a common ancestor with them more than 265 Myr ago, so this high similarity implies that these transposons recently transferred horizontally into each lineage. Their presence in only the closest relatives in at least the lacewing lineage supports this hypothesis. Such horizontal transfers provide an explanation for the evolutionary persistence and widespread distribution of mariner transposons. We propose that the ability to transfer horizontally to new hosts before extinction by mutation in the current host constitutes the primary selective constraint maintaining the sequence conservation of mariners and perhaps other DNA-mediated elements.      

Actin filaments elongate from their membrane-associated ends

In limulus sperm an actin filament bundle 55 mum in length extends from the acrosomal vacuole membrane through a canal in the nucleus and then coils in a regular fashion around the base of the nucleus. The bundle expands systematically from 15 filaments near the acrosomal vacuole to 85 filaments at the basal end. Thin sections of sperm fixed during stages in spermatid maturation reveal that the filament bundle begins to assemble on dense material attached to the acrosomal vacuole membrane. In micrographs fo these early stages in maturation, short bundles are seen extending posteriorly from the dense material. The significance is that these short, developing bundles have about 85 filaments, suggesting that the 85-filament end of the bundle is assembled first. By using filament bundles isolated and incubated in vitro with G actin from muscle, we can determine the end “preferred” for addition of actin monomers during polymerization. The end that would be associated with the acrosomal vacuole membrane, a membrane destined to be continuous with the plasma membrane, is preferred about 10 times over the other, thicker end. Decoration of the newly polymerized portions of the filament bundle with subfragment 1 of myosin reveals that the arrowheads point away from the acrosomal vacuole membrane, as is true of other actin filament bundles attached to membranes. From these observations we conclude that the bundle is nucleated from the dense material associated with the acrosomal vacuole and that monomers are added to the membrane-associated end. As monomers are added at the dense material, the thick first-made end of the filament bundle is pushed down through the nucleus where, upon reaching the base of the nucleus, it coils up. Tapering is brought about by the capping of the peripheral filaments in the bundle.     

Large acceleration of alpha-chymotrypsin-catalyzed dipeptide formation by 18-crown-6 in organic solvents

The effects of 18-crown-6 on the synthesis of peptides catalyzed by alpha-chymotrypsin are reported. Lyophilization of the enzyme in the presence of 50 equivalents of 18-crown-6 results in a 425-fold enhanced activity when the reaction between the 2-chloroethylester of N-acetyl-L-phenylalanine and L-phenylalaninamide is carried out in acetonitrile. Addition of crown ether renders the dipeptide synthesis in nonaqueous solvents catalyzed by alpha-chymotrypsin possible on a preparative scale. The acceleration is observed in different solvents and for various peptide precursors. Copyright 1998 John Wiley & Sons, Inc.     

Partially glucose-capped oligosaccharides are found on the hemoglobins of the deep-sea tube worm Riftia pachyptila

We report here the structural determination of N-linked oligosaccharides found on extracellular hemoglobins of the hydrothermal vent tube worm Riftia pachyptila. Structures were elucidated by a combination of electrospray ionization tandem mass spectrometry, matrix- assisted laser desorption/ionization mass spectrometry, normal-phase high performance liquid chromatography, and exoglycosidase digestion. The sugar chains were found to consist mainly of high-mannose-type glycans with some structures partially capped by one or two terminal glucose residues. The present study represents the first report of the occurrence of glucose capping of N-linked carbohydrates in a secreted glycoprotein of a metazoan. Previously, glucose capping has only been described for a membrane-bound surface glycoprotein from the unicellular parasite Leishmania mexicana amazonensis.      

Comparative accuracy of methods for protein sequence similarity search

MOTIVATION: Searching a protein sequence database for homologs is a powerful tool for discovering the structure and function of a sequence. Two new methods for searching sequence databases have recently been described: Probabilistic Smith-Waterman (PSW), which is based on Hidden Markov models for a single sequence using a standard scoring matrix, and a new version of BLAST (WU-BLAST2), which uses Sum statistics for gapped alignments. RESULTS: This paper compares and contrasts the effectiveness of these methods with three older methods (Smith- Waterman: SSEARCH, FASTA and BLASTP). The analysis indicates that the new methods are useful, and often offer improved accuracy. These tools are compared using a curated (by Bill Pearson) version of the annotated portion of PIR 39. Three different statistical criteria are utilized: equivalence number, minimum errors and the receiver operating characteristic. For complete-length protein query sequences from large families, PSW's accuracy is superior to that of the other methods, but its accuracy is poor when used with partial-length query sequences. False negatives are twice as common as false positives irrespective of the search methods if a family-specific threshold score that minimizes the total number of errors (i.e. the most favorable threshold score possible) is used. Thus, sensitivity, not selectivity, is the major problem. Among the analyzed methods using default parameters, the best accuracy was obtained from SSEARCH and PSW for complete-length proteins, and the two BLAST programs, plus SSEARCH, for partial-length proteins.      

Joint effects of parasitism and pollution on oxidative stress biomarkers in yellow perch Perca flavescens

Yellow perch Perca flavescens were collected from a contaminated site and a reference site in the St. Lawrence River, Quebec, Canada. Fish were assessed for oxidative stress (lipid peroxidation and reduced glutathione levels) and parasitism by the nematode Raphidascaris acus and metacercariae of the digenean Apophallus brevis. Lipid peroxidation is not only considered a measure of oxidative stress, but of stress in general, and thus serves as an indicator of fish health. Fish from the contaminated site exhibited higher levels of lipid peroxidation than those from the reference site, independent of parasitic infections. However, fish infected with R. acus at the contaminated site tended to have higher levels of lipid peroxidation than uninfected fish at the same site, whereas no difference was observed between infected and uninfected fish at the reference site. Yellow perch infected with > 10 metacercariae of A. brevis expressed higher levels of lipid peroxidation than those infected with < 10 metacercariae at both the contaminated and the reference sites. No differences were found in levels of reduced glutathione in liver or muscle in relation to site or either parasite species. Results support the use of lipid peroxidation as a biomarker of water contamination. They further suggest that lipid peroxidation may be used as a biomarker of pathological effects caused by parasitism. Most importantly, results demonstrate that contaminants and parasites occurring together exacerbate oxidative stress in fish, suggesting that parasitized fish in polluted environments are in a poorer state of health than uninfected fish.