Temperature is a cue for gene expression in the post-infective L3 of the parasitic nematode Brugia pahangi

Effect of freezing on the metabolic status of L3 larvae of Anisakis simplex s. s

The fish-borne parasite, Anisakis simplex s. s., triggers a disease called anisakiasis, that is associated with a gastrointestinal infection. The Anisakis is also associated with allergic response which may lead to anaphylactic shock. The A. simplex s. s. L3 larvae may be freeze tolerant despite when the nematodes will be cooled rapidly to -20 °C according to the sanitary authorities of the USA and the EU. The aim of this work was to study the metabolic status of A. simplex s. s. L3 larvae when frozen in terms of viability, expression of genes involved in the nematodes' survival of freezing, as well content of carbohydrates which play a cryoprotective role in thermal stress and are the main source of energy. The levels of trehalose were significantly higher after slow freezing treatment (p < .0001), than the fast freezing (p < .002). The lower temperatures induce changes, especially in trehalose synthesis gene expression, genes responsible for oxidative metabolism, and chaperone proteins, but we cannot state clearly whether these changes occur during freezing, or because they are already prevalent during cold acclimation. The induction of mentioned genes seems to be a common trait of both cold- and dehydration tolerance.

How Can We Understand the Genomic Basis of Nematode Parasitism?

Nematodes are very common animals and they have repeatedly evolved parasitic lifestyles during their evolutionary history. Recently, the genomes of many nematodes, especially parasitic species, have been determined, potentially giving an insight into the genetic and genomic basis of nematodes' parasitism. But, to achieve this, phylogenetically appropriate comparisons of genomes of free-living and parasitic species are needed. Achieving this has often been hampered by the relative lack of information about key free-living species. While such comparative approaches will eventually succeed, I suggest that a synthetic biology approach - moving free-living nematodes towards a parasitic lifestyle - will be our ultimate test of truly understanding the genetic and genomic basis of nematode parasitism.

A novel member of the let-7 microRNA family is associated with developmental transitions in filarial nematode parasites

Background

Filarial nematodes are important pathogens in the tropics transmitted to humans via the bite of blood sucking arthropod vectors. The molecular mechanisms underpinning survival and differentiation of these parasites following transmission are poorly understood. microRNAs are small non-coding RNA molecules that regulate target mRNAs and we set out to investigate whether they play a role in the infection event.

Results

microRNAs differentially expressed during the early post-infective stages of Brugia pahangi L3 were identified by microarray analysis. One of these, bpa-miR-5364, was selected for further study as it is upregulated ~12-fold at 24 hours post-infection, is specific to clade III nematodes, and is a novel member of the let-7 family, which are known to have key developmental functions in the free-living nematode Caenorhabditis elegans. Predicted mRNA targets of bpa-miR-5364 were identified using bioinformatics and comparative genomics approaches that relied on the conservation of miR-5364 binding sites in the orthologous mRNAs of other filarial nematodes. Finally, we confirmed the interaction between bpa-miR-5364 and three of its predicted targets using a dual luciferase assay.

Conclusions

These data provide new insight into the molecular mechanisms underpinning the transmission of third stage larvae of filarial nematodes from vector to mammal. This study is the first to identify parasitic nematode mRNAs that are verified targets of specific microRNAs and demonstrates that post-transcriptional control of gene expression via stage-specific expression of microRNAs may be important in the success of filarial infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1536-y) contains supplementary material, which is available to authorized users.

Comparative analysis of the secretome from a model filarial nematode (Litomosoides sigmodontis) reveals maximal diversity in gravid female parasites

Filarial nematodes (superfamily Filarioidea) are responsible for an annual global health burden of ∼6.3 million disability-adjusted life-years, which represents the greatest single component of morbidity attributable to helminths affecting humans. No vaccine exists for the major filarial diseases, lymphatic filariasis and onchocerciasis; in part because research on protective immunity against filariae has been constrained by the inability of the human-parasitic species to complete their lifecycles in laboratory mice. However, the rodent filaria Litomosoides sigmodontis has become a popular experimental model, as BALB/c mice are fully permissive for its development and reproduction. Here, we provide a comprehensive analysis of excretory-secretory products from L. sigmodontis across five lifecycle stages and identifications of host proteins associated with first-stage larvae (microfilariae) in the blood. Applying intensity-based quantification, we determined the abundance of 302 unique excretory-secretory proteins, of which 64.6% were present in quantifiable amounts only from gravid adult female nematodes. This lifecycle stage, together with immature microfilariae, released four proteins that have not previously been evaluated as vaccine candidates: a predicted 28.5 kDa filaria-specific protein, a zonadhesin and SCO-spondin-like protein, a vitellogenin, and a protein containing six metridin-like ShK toxin domains. Female nematodes also released two proteins derived from the obligate Wolbachia symbiont. Notably, excretory-secretory products from all parasite stages contained several uncharacterized members of the transthyretin-like protein family. Furthermore, biotin labeling revealed that redox proteins and enzymes involved in purinergic signaling were enriched on the adult nematode cuticle. Comparison of the L. sigmodontis adult secretome with that of the human-infective filarial nematode Brugia malayi (reported previously in three independent published studies) identified differences that suggest a considerable underlying diversity of potential immunomodulators. The molecules identified in L. sigmodontis excretory-secretory products show promise not only for vaccination against filarial infections, but for the amelioration of allergy and autoimmune diseases.

Characterisation of hookworm heat shock factor binding protein (HSB-1) during heat shock and larval activation

When hookworm infective L3s infect their mammalian host, they undergo a temperature shift from that of the ambient environment to that of their endothermic host. Additionally, L3s living in the environment can be exposed to temperature extremes associated with weather fluctuations. The heat shock response (HSR) is a conserved response to heat shock and other stress that involves the expression of protective heat shock proteins (HSPs). The HSR is controlled by heat shock factor-1 (HSF-1), a conserved transcription factor that binds to a heat shock element in the promoter of HSPs, causing their expression. HSF-1 is negatively regulated in part by a HSF binding protein (HSB-1) that binds to and removes HSF-1 trimers bound to HSP gene promoters, resulting in attenuation of the HSR. Herein we describe an HSB-1 orthologue, Ac-HSB-1, from the hookworm Ancylostoma caninum. The Ac-hsb-1 cDNA encodes a 79 amino acid protein that is 71% identical to the Caenorhabditis elegans HSB-1, and is predicted to share the characteristic coiled-coil structural motif comprised of two interacting alpha helices. Recombinant Ac-HSB-1 immunoprecipitated Ce-HSF-1 expressed in mammalian cells that had been heat shocked for 1h at 42°C, but not from cells incubated at 37°C, indicating that HSB-1 only bound to the active DNA binding form of HSF-1. Expression of Ac-hsb-1 transcripts decreased following 1h of heat shock, but increased when L3s were incubated at 37°C for 1h. Activation of hookworm L3s induces a five-sixfold increase in Ac-hsb-1 expression that peaks at 12h, coincident with L3 feeding, but that subsequently decreases to two-threefold above control at 24h. Recombinant Ac-HSB-1 immunoprecipitates greater amounts of 70 and 40kDa proteins from extracts of activated L3s than from non-activated L3s. We propose that an increase in Ac-hsb-1 levels early in activation allows feeding to resume, but that a subsequent decrease in expression permits a HSR that protects non-developing L3s at host-like temperatures. Further investigations of the HSR will clarify the role of HSB-1 and HSF-1 in hookworm infection.

Characterisation and expression of an Hsp70 gene from Parastrongyloides trichosuri

Parastrongyloides trichosuri is a nematode parasite of Australian brushtail possums that has an alternative free-living life cycle which can be readily maintained indefinitely in a laboratory setting. The ability to maintain this parasite in a free-living cycle and induce it to parasitism at the free-living L1 stage makes this an excellent model for the study of genes associated with parasitism. A 70kD protein from infective larvae of P. trichosuri that appears to be immunogenic in infected possums has been identified as a heat shock protein (Hsp)70 homologue. The complete gene for Pt-Hsp70 was cloned and sequenced. The protein encoded by the Pt-Hsp70 gene is the likely orthologue of the Caenorhabditis elegans protein, Hsp70A, also known as hsp-1. Reverse transcriptase-PCR data indicate that Pt-Hsp70 (designated Pt-hsp-1) is expressed at readily detectable levels in all developmental stages of both the parasitic and free-living P. trichosuri life cycles and the promoter is mildly inducible by heat shock. Bioinformatic analysis of expressed sequence tag databases indicates that C. eleganshsp-1 homologues, together with C. eleganshsp-3 homologues, are the predominant members of the Hsp70 superfamily that are normally expressed in parasitic stages of the Strongyloididae family. Promoter fusions to a beta-galactosidase coding sequence were prepared and introduced into wild type C. elegans to produce transgenic nematodes. Reporter gene expression was clearly present within embryonic cells and within intestinal cells of larval and adult stages. Thus, the expression of the Pt-hsp-1 promoter within P. trichosuri and transgenic C. elegans appears similar to the known expression of C. elegans hsp-1. This promoter should be of value in efforts to develop genetic manipulation tools for P. trichosuri.

Thermoregulation in the life cycle of nematodes

An unanswered question in the biology of many parasites is the mechanism by which environmental (or external) and intrinsic signals are integrated to determine the switch from one developmental stage to the next. This is particularly pertinent for nematode parasites, many of which have a free-living stage in the environment prior to infection of the mammalian host, or for parasites such as filarial nematodes, which utilise an insect vector for transmission. The environmental changes experienced by a parasite upon infection of a mammalian host are extremely complex and poorly understood. However, the ability of a parasite to sense its new environment must be intrinsically linked to its developmental programme, as progression of the life cycle is dependent upon the infection event. In this review, the relationship between temperature and development in filarial nematodes and in the free-living species Caenorhabditis elegans is summarised, with a focus on the role of heat shock factor and heat shock protein 90 in the nematode life cycle.

daf-7 and the development of Strongyloides ratti and Parastrongyloides trichosuri

daf-7 is a key ligand in one of the three pathways that control dauer larva development in Caenorhabditis elegans. Given the similarities between dauer larvae of free-living nematodes and third stage infective larvae of animal parasitic nematodes, we hypothesised that daf-7 may be involved in the development of these infective larvae. To investigate this, we cloned daf-7 orthologues from Strongyloides ratti and Parastrongyloides trichosuri and analysed their RNA level by semi-quantitative RT-PCR during the S. ratti and P. trichosuri life cycles and in a range of in vitro and in vivo conditions. We found that, in both species, the RNA level of daf-7 was low in free-living stages but peaked in the infective L3 (iL3) stage with little or no expression in the parasitic stages. This contrasts with the daf-7 RNA level in C. elegans, which peaks in L1, decreases thereafter, and is absent in dauer larvae. The RNA level of daf-7 in infective larvae was reduced by larval penetration of host skin or development in the host, but not by a shift to the body temperature of the host.

Biochemical and molecular characterization of two cytidine deaminases in the nematode Caenorhabditis elegans

Two cytidine deaminases (CDDs) from the free-living nematode Caenorhabditis elegans have been cloned and characterized. Both Ce-CDD-1 and Ce-CDD-2 are authentic deaminases and both exhibit RNA-binding activity towards AU-rich templates. In order to study their temporal and spatial expression patterns in the worm, reporter gene constructs were made using approx. 2 kb of upstream sequence. Transfection of C. elegans revealed that both genes localized to the cells of the intestine, although their temporal expression patterns were different. Expression of Ce-cdd-1 peaked in the early larval stages, whereas Ce-cdd-2 was expressed in all life cycle stages examined. RNA-interference (RNAi) assays were performed for both genes, either alone or in combination, but only cdd-2 RNAi produced a consistent visible phenotype. A proportion of eggs laid from these worms were swollen and distorted in shape.