Expression and characterisation of a Psoroptes ovis glutathione S-transferase

Application two-dimensional gel electrophoresis coupled with LC-MS/MS to identify candidate serodiagnostic antigens for early detection Psoroptes ovis var. cuniculi infection

Currently, the 'gold standard' for diagnosis of Psoroptes ovis infections is detecting Psoroptes mites or eggs in skin scrapings under microscopy, but it is prone to be mis-diagnosed for detecting early infection of P. ovis. Hence, seeking a reliable diagnostic technique for detecting early-stage mite infections is extremely desirable. Enzyme linked immunosorbent assay (ELISA) has proven to be useful for the diagnosis of early-stage P. ovis infection. Thus, the purpose of this study was to screen serodiagnostic candidate antigens that can detect early P. ovis infection. Psoroptes ovis var. cuniculi wash proteins (PsoWA), which contained an enriched source of secretory and excretory antigens, were separated by two-dimensional gel electrophoresis (2-DE) and screened by immunoblot using sera from rabbits with early-stage Psoroptes infection (1 week and 3 weeks). Immunogenic proteins were submitted for sequencing by liquid chromatography tandem-mass spectrometry (LC-MS/MS) analyses. Three potential diagnostic antigens were identified (PsoSP3, Pso14-3-3(1) and Pso14-3-3(2)) in this study. These were further expressed in E. coli expression system to evaluate the serodiagnostic potential of these recombinant proteins for detecting early-stage P. ovis infection using an indirect ELISA (iELISA). Western blotting showed that 34 protein spots were recognized by rabbit sera of 1 week post-infection (wpi) and 3 wpi. The 2-DE results showed that a total of 199 proteins were detected with molecular weights varying from 20 to 100 kDa and isoelectric point (pI) from 4.1 to 9.3. Among these, 90 proteins were detected both at 1 wpi sera and 3 wpi sera, and the numbers of the specific identified proteins were 27 for 1 wpi sera and 82 for 3wpi sera. Moreover, rPsoSP3 showed better diagnostic efficacy than rPso14-3-3(1) and rPso14-3-3(2) in detecting early-stage P. ovis infection for its higher values of sensitivity, specificity and area under the receiver operating characteristic curve. Our study describes the first immunoproteomic analysis to identify early diagnostic candidate antigens of P. ovis, and the identified antigens of Psoroptes in our study have significant implications for the development of early-stage diagnostic tests. PsoSP3 is a promising early diagnostic antigen for detecting P. ovis var. cuniculi infection.

A genomic analysis and transcriptomic atlas of gene expression in Psoroptes ovis reveals feeding- and stage-specific patterns of allergen expression

Background

Psoroptic mange, caused by infestation with the ectoparasitic mite, Psoroptes ovis, is highly contagious, resulting in intense pruritus and represents a major welfare and economic concern for the livestock industry Worldwide. Control relies on injectable endectocides and organophosphate dips, but concerns over residues, environmental contamination, and the development of resistance threaten the sustainability of this approach, highlighting interest in alternative control methods. However, development of vaccines and identification of chemotherapeutic targets is hampered by the lack of P. ovis transcriptomic and genomic resources.

Results

Building on the recent publication of the P. ovis draft genome, here we present a genomic analysis and transcriptomic atlas of gene expression in P. ovis revealing feeding- and stage-specific patterns of gene expression, including novel multigene families and allergens. Network-based clustering revealed 14 gene clusters demonstrating either single- or multi-stage specific gene expression patterns, with 3075 female-specific, 890 male-specific and 112, 217 and 526 transcripts showing larval, protonymph and tritonymph specific-expression, respectively. Detailed analysis of P. ovis allergens revealed stage-specific patterns of allergen gene expression, many of which were also enriched in “fed” mites and tritonymphs, highlighting an important feeding-related allergenicity in this developmental stage. Pair-wise analysis of differential expression between life-cycle stages identified patterns of sex-biased gene expression and also identified novel P. ovis multigene families including known allergens and novel genes with high levels of stage-specific expression.

Conclusions

The genomic and transcriptomic atlas described here represents a unique resource for the acarid-research community, whilst the OrcAE platform makes this freely available, facilitating further community-led curation of the draft P. ovis genome.

Preliminary analysis of Psoroptes ovis transcriptome in different developmental stages

Background

Psoroptic mange is a chronic, refractory, contagious and infectious disease mainly caused by the mange mite Psoroptes ovis, which can infect horses, sheep, buffaloes, rabbits, other domestic animals, deer, wild camels, foxes, minks, lemurs, alpacas, elks and other wild animals. Features of the disease include intense pruritus and dermatitis, depilation and hyperkeratosis, which ultimately result in emaciation or death caused by secondary bacterial infections. The infestation is usually transmitted by close contact between animals. Psoroptic mange is widespread in the world. In this paper, the transcriptome of P. ovis is described following sequencing and analysis of transcripts from samples of larvae (i.e. the Pso_L group) and nymphs and adults (i.e. the Pso_N_A group). The study describes differentially expressed genes (DEGs) and genes encoding allergens, which help understanding the biology of P. ovis and lay foundations for the development of vaccine antigens and drug target screening.

Methods

The transcriptome of P. ovis was assembled and analyzed using bioinformatic tools. The unigenes of P. ovis from each developmental stage and the unigenes differentially between developmental stages were compared with allergen protein sequences contained in the allergen database website to predict potential allergens.

Results

We identified 38,836 unigenes, whose mean length was 825 bp. On the basis of sequence similarity with seven databases, a total of 17,366 unigenes were annotated. A total of 1,316 DEGs were identified, including 496 upregulated and 820 downregulated in the Pso_L group compared with the Pso_N_A group. We predicted 205 allergens genes in the two developmental stages similar to genes from other mites and ticks, of these, 14 were among the upregulated DEGs and 26 among the downregulated DEGs.

Conclusion

This study provides a reference transcriptome of P. ovis in absence of a reference genome. The analysis of DEGs and putative allergen genes may lay the foundation for studies of functional genomics, immunity and gene expression profiles of this parasitic mite species.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1856-z) contains supplementary material, which is available to authorized users.

Characterisation of Dermanyssus gallinae glutathione S-transferases and their potential as acaricide detoxification proteins

BACKGROUND

Glutathione S-transferases (GSTs) facilitate detoxification of drugs by catalysing the conjugation of the reduced glutathione (GSH) to electrophilic xenobiotic substrates and therefore have a function in multi-drug resistance. As a result, knowledge of GSTs can inform both drug resistance in, and novel interventions for, the control of endo- and ectoparasite species. Acaricide resistance and the need for novel control methods are both pressing needs for Dermanyssus gallinae, a highly economically important haematophagous ectoparasite of poultry.

METHODS

A transcriptomic database representing D. gallinae was examined and 11 contig sequences were identified with GST BlastX identities. The transcripts represented by 3 contigs, designated Deg-GST-1, -2 and -3, were fully sequenced and further characterized by phylogenetic analysis. Recombinant versions of Deg-GST-1, -2 and -3 (rDeg-GST) were enzymically active and acaricide-binding properties of the rDeg-GSTs were established by evaluating the ability of selected acaricides to inhibit the enzymatic activity of rDeg-GSTs.

RESULTS

6 of the identified GSTs belonged to the mu class, followed by 3 kappa, 1 omega and 1 delta class molecules. Deg-GST-1 and -3 clearly partitioned with orthologous mu class GSTs and Deg-GST-2 partitioned with delta class GSTs. Phoxim, permethrin and abamectin significantly inhibited rDeg-GST-1 activity by 56, 35 and 17% respectively. Phoxim also inhibited rDeg-2-GST (14.8%) and rDeg-GST-3 (20.6%) activities.

CONCLUSIONS

Deg-GSTs may have important roles in the detoxification of pesticides and, with the increased occurrence of acaricide resistance in this species worldwide, Deg-GSTs are attractive targets for novel interventions.

Cloning and characterization of a novel sigma-like glutathione S-transferase from the giant panda parasitic nematode, Baylisascaris schroederi

Background

Baylisascaris schroederi, an intestinal nematode of the giant panda, is the cause of the often fatal disease, baylisascariasis. Glutathione S-transferases (GSTs) are versatile enzymes that can affect parasite survival and parasite-host interactions and, are therefore, potential targets for the development of diagnostic tests and vaccines.

Methods

In this study, we identified a full-length cDNA that encoded a novel, secretory sigma-like GST (Bsc-GSTσ) from a B. schroederi-omic dataset. Following cloning and sequencing, sequence and structural analyses and comparative modeling were performed using online-bioinformatics and proteomics tools. The recombinant Bsc-GSTσ (rBsc-GSTσ) protein was prokaryotically expressed and then used to detect antigenicity and reactivity using immunoblotting assays. In addition, the native protein in female adult B. schroederi was located via immunofluorescence techniques, while the preliminary ELISA-based serodiagnostic potential of rBsc-GSTσ was assessed in native and infected mouse sera.

Results

Bsc-GSTσ contained a 621-bp open reading frame that encoded a polypeptide of 206 amino acids with two typical sigma GST domain profiles, including a GST_N_Sigma_like at the N-terminus and a GST_C_Sigma_like at the C-terminus. The presence of an N-terminal signal sequence indicated that Bsc-GSTσ was a secretory protein. Sequence alignment and phylogenetic analyses showed that Bsc-GSTσ was a nematode-specific member of the Sigma class GSTs and shared the closest genetic distance with its homologue in Ascaris suum. Further comparative structure analyses indicated that Bsc-GSTσ possessed the essential structural motifs (e.g., βαβαββα) and the consensus secondary or tertiary structure that is typical for other characterized GSTσs. Immunolocalization revealed strong distributions of native Bsc-GSTσ in the body hypodermis, lateral chords, gut epithelium, gut microvilli, oviduct epithelium, and ovaries of adult female worms, similar to its homologue in A. suum. Building on good immunogenic properties, rBsc-GSTσ-based ELISA exhibited a sensitivity of 79.1% and a specificity of 82.0% to detect anti-B. schroederi IgG antibodies in the sera of experimentally infected mice.

Conclusion

This study presents a comprehensive demonstration of sequence and structural-based analysis of a new, secretory sigma-like GST from a nematode, and its good serodiagnostic performance suggests that rBsc-GSTσ has the potential to detect B. schroederi and, therefore, could be used to develop an ELISA-based serological test to diagnose baylisascariasis in giant pandas.

Sheep psoroptic mange: an update

Psoroptic mange is one of the most severe skin conditions of sheep. This highly contagious disease is responsible for huge economical losses in many sheep-raising countries. It is also a significant welfare concern. Our understanding of the biology of Psoroptes ovis and of the host-parasite relationship during psoroptic mange made remarkable progress during the last decade. These data combined with the availability of powerful molecular tools have opened new avenues of research. Clearly, there is still a long way to go before a vaccine becomes a reality. Additionally, other diagnostic tools and control methods should be further investigated such as breeding for genetic resistance and the use of biocontrol agents.

Ovine IgE and its role in immunological protection and disease

The importance of internal and external parasites in limiting productivity and compromising the welfare of sheep has provided the impetus for extensive research on ovine IgE with the objectives of better understanding protective immunological responses and developing novel methods of control; particularly vaccination. The molecular structures of ovine IgE and its high affinity receptor have been determined and the former information has assisted the development of monoclonal antibodies (mAb) to ovine IgE by 2 of 3 groups who have produced these reagents. The availability of these mAbs has enabled the description of IgE responses following infections with a wide variety of parasites in sheep and in an ovine model of atopic asthma. While IgE responses are consistently associated with parasitic diseases of sheep, it has not been proven that this antibody isotype is involved in protection. The foundation of present knowledge and reagents, together with new emerging technologies, should allow the role of IgE in parasitic diseases of sheep to be determined.

Progress and opportunities in the development of vaccines against mites, fleas and myiasis-causing flies of veterinary importance

Despite the potential benefits offered by vaccination against ectoparasites, there have been few commercial successes with this strategy, in spite of sustained efforts using increasingly sophisticated techniques. This review outlines the progress and challenges offered by recent research into vaccination against some of the major ectoparasites of veterinary importance, and provides an insight into the opportunities arising from our increased understanding of the immunology of host-parasite relationships and the potential for exploitation of this knowledge and that arising from new genomic data provided by expressed sequence tag projects.

A physiological and biochemical model for digestion in the ectoparasitic mite, Psoroptes ovis (Acari: Psoroptidae)

Mites are an important group of arthropod pests affecting crops, animals and humans. Despite this, detailed physiological studies on these organisms remain sparse due largely to their small size. Unifying models are required to draw together the diverse information from studies on different groups and species. This paper describes a model for digestion in the parasitic mite, Psoroptes ovis, the causative agent of psoroptic mange or sheep scab disease. The limited information about this species is supplemented with data from other acarines, especially house dust mites and ticks. We review the range of enzymes and allergens found in mites and consider their possible roles in digestion in mites, generally and in particular, P. ovis. Histological studies, enzyme biochemistry and molecular biology and experimental evidence suggest that P. ovis utilises a digestive system reliant upon acid peptidases functioning in a largely intracellular environment. The actions of the digestive enzymes are supplemented by the involvement of bacteria as potential direct and indirect sources of nutrition. It is possible that some extra-corporeal digestion also takes place. The interaction of bacteria and digestive enzymes on the skin surface of the sheep may be responsible for the excessive pathological reactions evident in clinical sheep scab.