Brugia pahangi: characterisation of a small heat shock protein cDNA clone

Infective larvae of Anisakis simplex (Nematoda) accumulate trehalose and glycogen in response to starvation and temperature stress

Anisakis simplex L3 larvae infect fish and other seafood species such as squid or octopi; therefore, humans consuming raw or undercooked fish may become accidental hosts for this parasite. These larvae are induced to enter hypometabolism by cold temperatures. It is assumed that sugars (in particular trehalose and glycogen) are instrumental for survival under environmental stress conditions. To elucidate the mechanisms of environmental stress response in A. simplex, we observed the effects of starvation and temperature on trehalose and glycogen content, the activity of enzymes metabolizing those sugars, and the relative expression of genes of trehalose and glycogen metabolic pathways. The L3 of A. simplex synthesize trehalose both in low (0°C) and high temperatures (45°C). The highest content of glycogen was observed at 45°C at 36 h of incubation. On the second day of incubation, tissue content of trehalose depended on the activity of the enzymes: TPS was more active at 45°C, and TPP was more active at 0°C. The changes in TPP activity were consistent with the transcript level changes of the TPP gene, and the trehalose level, while glycogen synthesis correlates with the expression of glycogen synthase gene at 45°C; this suggests that the synthesis of trehalose is more essential. These results show that trehalose plays a key role in providing energy during the thermotolerance and starvation processes through the molecular and biochemical regulation of trehalose and glycogen metabolism.

The role of small heat shock proteins in parasites

The natural life cycle of many protozoan and helminth parasites involves exposure to several hostile environmental conditions. Under these circumstances, the parasites arouse a cellular stress response that involves the expression of heat shock proteins (HSPs). Small HSPs (sHSPs) constitute one of the main families of HSPs. The sHSPs are very divergent at the sequence level, but their secondary and tertiary structures are conserved and some of its members are related to α-crystallin from vertebrates. They are involved in a variety of cellular processes. As other HSPs, the sHSPs act as molecular chaperones; however, they have shown other activities apparently not related to chaperone action. In this review, the diverse activities of sHSPs in the major genera of protozoan and helminth parasites are described. These include stress response, development, and immune response, among others. In addition, an analysis comparing the sequences of sHSPs from some parasites using a distance analysis is presented. Because many parasites face hostile conditions through its life cycles the study of HSPs, including sHSPs, is fundamental.

Tetracycline treatment targeting Wolbachia affects expression of an array of proteins in Brugia malayi parasite

Wolbachia is an intracellular endosymbiont of Brugia malayi parasite whose presence is essential for the survival of the parasite. Treatment of B. malayi-infected jirds with tetracycline eliminates Wolbachia, which affects parasite survival and fitness. In the present study we have tried to identify parasite proteins that are affected when Wolbachia is targeted by tetracycline. For this Wolbachia depleted parasites (B. malayi) were obtained by tetracycline treatment of infected Mongolian jirds (Meriones unguiculatus) and their protein profile after 2-DE separation was compared with that of untreated parasites harboring Wolbachia. Approximately 100 protein spots could be visualized followed by CBB staining of 2-D gel and included for comparative analysis. Of these, 54 showed differential expressions, while two new protein spots emerged (of 90.3 and 64.4 kDa). These proteins were subjected to further analysis by MALDI-TOF for their identification using Brugia coding sequence database composed of both genomic and EST sequences. Our study unravels two crucial findings: (i) the parasite or Wolbachia proteins, which disappeared/down-regulated appear be essential for parasite survival and may be used as drug targets and (ii) tetracycline treatment interferes with the regulatory machinery vital for parasites cellular integrity and defense and thus could possibly be a molecular mechanism for the killing of filarial parasite. This is the first proteomic study substantiating the wolbachial genome integrity with its nematode host and providing functional genomic data of human lymphatic filarial parasite B. malayi.

A small heat shock protein of Ostertagia ostertagi: stage-specific expression, heat inducibility, and protection trial

In this study, we isolated and analyzed a small heat shock protein (HSP) of Ostertagia ostertagi (Oo-HSP18). Oo-hsp18 is encoded by a single-copy gene and the full-length cDNA represents an 18-kDa protein. The expression of Oo-hsp18 is highly stage specific and restricted to the adult stage. The protein is synthesized in a tissue-specific manner and localized in the body muscle layer. The levels of Oo-hsp18 mRNAs are sharply induced by heat shock but not by other stressors such as levamisole and H2O2. A vaccination trial with recombinant Oo-HSP18 failed to protect calves against a challenge infection.

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.

Successful transgenesis of the parasitic nematode Strongyloides stercoralis requires endogenous non-coding control elements

Critical investigations into the cellular and molecular biology of parasitic nematodes have been hindered by a lack of modern molecular genetic techniques for these organisms. One such technique is transgenesis. To our knowledge, the findings reported here demonstrate the first heritable DNA transformation and transgene expression in the intestinal parasite Strongyloides stercoralis. When microinjected into the syncitial gonads of free-living S. stercoralis females, a construct fusing the S. stercoralis era-1 promoter, the coding region for green fluorescent protein (gfp) and the S. stercoralis era-1 3' untranslated region was expressed in intestinal cells of normally developing F1 transgenic larvae. The frequency of transformation and GFP expression among F1 larvae was 5.3%. By contrast, expression of several promoter::gfp fusions incorporating only Caenorhabditis elegans regulatory elements was restricted to abortively developing F1 embryos of S. stercoralis. Despite its lack of regulated expression, PCR revealed that one of these C. elegans-based vector constructs, the sur-5::gfp fusion, is incorporated into F1 larval progeny of microinjected female worms and then transmitted to the F2 through F5 generations during two host passages conducted without selection and punctuated by free-living generations reared in culture. Heritable DNA transformation and regulated transgene expression, as demonstrated here for S. stercoralis, constitute the essential components of a practical system for transgenesis in this parasite. This system has the potential to significantly advance the molecular and cellular biological study of S. stercoralis and of parasitic nematodes generally.

Both heat-shock and cold-shock influence trehalose metabolism in an entomopathogenic nematode

Heat-shock response is highly conserved in animals and microorganisms, and it results in the synthesis of heat-shock proteins. In yeast, heat-shock response has also been reported to induce trehalose accumulation. We explored the relationship between heat- (35 C) or cold-shock (1 and 10 C) and trehalose metabolism in the entomopathogenic nematode, Heterorhabditis bacteriophora. Because both heat- and cold-shocks may precede desiccation stress in natural soil environments, we hypothesized that nematodes may accumulate a general desiccation protectant, trehalose, under both situations. Indeed, both heat- and cold-shocks influenced trehalose accumulation and activities of enzymes of trehalose metabolism in H. bacteriophora. Trehalose increased by 5- and 6-fold in heat- and cold-shocked infective juveniles, respectively, within 3 hr of exposure, compared with the nematodes maintained at 25 C (culture temperature). The activity of trehalose-6-phosphate synthase (T6PS), an enzyme involved in the synthesis of trehalose, also significantly increased in both heat- and cold-shocked nematodes during the first 3 hr of exposure. Generally, the trehalose levels and activities of T6PS declined to their original levels within 3 hr when nematodes were transferred back to 25 C. In both heat- and cold-shocked nematodes, trehalase activity decreased significantly within the first 3 hr and generally returned to the original levels within 3 hr when these nematodes were transferred back to 25 C. The results demonstrate that the trehalose concentrations in H. bacteriophora are influenced by both heat- and cold-shocks and are regulated by the action of 2 trehalose-metabolizing enzymes, T6PS and trehalase. The accumulated trehalose may enhance survival of nematodes under both cold and warm conditions, but it may also provide simultaneous protection against desiccation that may result from subsequent evaporation or freezing. This is the first report of the relationship between trehalose metabolism and heat-shock for the Nematoda.

Construction of gender-enriched cDNA archives for adult Oesophagostomum dentatum by suppressive-subtractive hybridization and a microarray analysis of expressed sequence tags

In the present study, we constructed gender-enriched cDNA libraries for the adult stage of the parasitic nematode Oesophagostomum dentatum (order Strongylida) using suppressive-subtractive hybridization (SSH), sequenced clones from the female-library and male-library (480 from each) and conducted bioinformatic and microarray analyses of the expressed sequence tags (ESTs). In total, 873 ESTs (440 male and 433 female) were obtained, achieving a sequencing success of 91%The nucleotide sequences reported in this article (Tables 1-5) have been deposited in the EMBL, GenBank and DDJB databases under the Accession nos. AM157797-AM158083. Microarray analyses of 516 unique ESTs representing both gender-enriched libraries revealed differential hybridization for 391 of them (75.8%). Of these, 220 (56.3%) had significantly greater signal intensities in the female than in the male, and 154 (70%) of these were predicted to have homologues in C. elegans. These homologues were predicted to be involved in key biological processes, including embryonic nutrition, gametogenesis, molecular binding/transport or metabolism, nucleic acid synthesis and function, and signal transduction. Of the 171 ESTs with statistically higher signal intensities in male O. dentatum, 43.8% had homologues in C. elegans. These homologues included major sperm proteins (MSPs) or MSP-like molecules, keratin-like molecules, molecules involved in metabolism, PDZ domain-containing proteins, sugar binding proteins, protein kinases, serine proteases or protease inhibitors, molecules involved in proteolysis and other proteins, such as enzymes and various putative proteins. Of the 287 ESTs (from both gender-enriched cDNA libraries) with no known homologues in C. elegans, 50 (17.4%) had homologues in other nematodes, 8 had homologues in various other organisms and 104 (36.2%) had no homology to any sequence in current gene databases. The present study lays a foundation for the isolation and molecular, biochemical and functional characterization of selected genes from the gender-enriched cDNA archives established for O. dentatum.

Taenia solium: characterization of a small heat shock protein (Tsol-sHSP35.6) and its possible relevance to the diagnosis and pathogenesis of neurocysticercosis

A cDNA encoding for a predicted small heat shock protein (sHSP), Tsol-sfISP35.6, has been isolated by antibody screening of a Taenia solium c-DNA library. The clone was a full-length sequence (1172 bp) with an open reading frame of 945 bp and encoded for a 314 amino acid protein with deduced molecular mass of 35.6 kDa, isoelectric point of 5.6 arid the characteristic HSP20/alpha-crystallin domain duplicated. It was highly conserved, with a high sequence similarity with other platyhelminth sHSPs. Western blot analysis, using serum from neurocysticercosis patients (NCC), indicated that the purified Tsol-sHSP35.6 expression product was immunogenic, while in indirect ELISA, using the purified Tsol-sHSP35.6 expression product as antigen and serum samples from pigs and humans, 80% of T. solium infected pigs and 84% of patients with active, or 71% of patients with inactive NCC were sero-positive. The possible relevance of Tsol-sHSP35.6 in the diagnosis and pathogenesis of NCC is discussed.

An expressed sequence tag analysis of the life-cycle of the parasitic nematode Strongyloides ratti

14,761 expressed sequence tags (ESTs) were generated, representing five stages during the parasitic and free-living phases of the life-cycle of the parasitic nematode Strongyloides ratti. These ESTs formed 4152 clusters, of which 97% contained 10 or fewer ESTs and 66% were singletons. These 4152 clusters are likely to represent approximately 20% of S. ratti's genes. The clusters' consensus sequences were used to assign each cluster to one of three databases: (i) Caenorhabditis elegans and C. briggsae sequences; (ii) other nematode sequences; (iii) non-nematode sequences. This approach has identified putative nematode-specific genes, that may be targets for developing approaches for parasitic nematode control. Approximately 25% of the clusters have no significant alignments and may therefore represent novel genes. The EST representation between the libraries was used to analyse stage-specific or -biased expression in silico. This showed that 81% of clusters are present in only one library and 12% are present in any two libraries, indicating substantial stage-specificity of gene expression. The 30-most abundantly expressed clusters were analysed in further detail. Many of these have significantly different parasitic- or free-living-specific or -biased expression. Many of the parasitic-specific genes are, as yet, uncharacterised: one of these represents 25% of all ESTs obtained from the parasitic stage.

Heat shock and developmental expression of hsp83 in the filarial nematode Brugia pahangi

hsp83 was cloned from the filarial nematode Brugia pahangi. The mRNA was constitutively expressed at 37 degrees C in life cycle stages that live in the mammalian host (microfilariae and adult worms). Heat shock resulted in only a minimal increase in levels of transcription. A genomic copy of hsp83 was isolated and was shown to contain 11 introns while sequencing of the 5' upstream region revealed several heat shock elements. Using a chloramphenicol acetyltransferase (CAT) reporter gene construct the expression of hsp83 from B. pahangi (Bp-hsp83) was studied by transfection of COS-7 cells. Similar to the expression pattern in the parasite, CAT activity was detected at 37 degrees C and was not influenced by heat shock. When the free-living nematode Caenorhabditis elegans was transfected with the same construct, CAT activity was not observed at normal growth temperatures (21 degrees C) or under moderate heat shock conditions (28 degrees C). However exposure to more severe heat shock (35 degrees C) resulted in an increase in CAT activity. These results suggest that Bp-hsp83 has a temperature threshold > or = 35 degrees C for expression.

Developmentally regulated expression of a unique small heat shock protein in Brugia malayi

A screen of an expression library from the fourth larval stage (L4) of the parasitic nematode Brugia malayi resulted in the identification of a 727 bp full-length cDNA with 29-40% identity to members of the small heat shock family of proteins (Bm-hsp-s1). The open reading frame encoded a protein of approximately 18 kDA (Bm-HSP-s1). An alignment of the Bm-HSP-s1 sequence with the sequences of small HSPs from vertebrate and invertebrate species demonstrated that a majority of the identity was concentrated in the central alpha-crystallin domain. Bm-HSP-s1 was constitutively produced by L4 and adult parasites and at low levels by third-stage larvae (L3), but not by first-stage larvae (microfilariae). In adult parasites, Bm-HSP-s1 was localized to the body wall muscle cells and to the cells of the hypodermis/lateral cord. Bm-HSP-s1 production was induced in adult and L3 incubated at 42 degrees C and in L3s during the developmental transition from vector-stage to vertebrate-stage parasites at 37 degrees C. Neither increased nor decreased temperatures induced Bm-HSP-s1 production in microfilariae. Nitric oxide induced low-level, transient Bm-HSP-s1 synthesis in adults, but not in microfilariae. Bm-HSP-s1 did not function as a molecular chaperone to prevent heat-induced aggregation of a test substrate. The developmentally regulated expression and inducable nature of Bm-HSP-s1 suggests that it may have a stage-restricted role in maintaining parasite homeostasis.

cut-1-like genes are present in the filarial nematodes, Brugia pahangi and Brugia malayi, and, as in other nematodes, code for components of the cuticle

A fragment of a cut-1 like gene from the filarial nematode Brugia pahangi (designated Bp-cut-1) was isolated by PCR from genomic DNA. The sequence was used to design primers for use in RT-PCR and resulted in the isolation of a cDNA fragment from larvae in the process of the L3-L4 moult. Screening of a B. malayi genomic library identified a single clone, Bm-cut-1. Using primers designed from the Brugia sequences, semi-quantitative RT-PCR was carried out on 11 different life cycle stages chosen to cover periods around the moult and inter-moult periods. This analysis demonstrated that the cut-1 mRNA was most abundant preceding the moult, consistent with its function as a cuticular protein. Immuno-gold electron microscopy using an affinity purified antiserum raised to the highly conserved region of Ascaris CUT-1 confirmed that the protein was restricted to a tight band in the median layer of the cuticle. Despite the fact that no transcripts could be detected in mature adult worms by RT-PCR, immuno-gold microscopy revealed staining of the microfilarial cuticle within the uterus of the adult female worm, suggesting that other cut-1-like genes are present in Brugia.

Molecular characterisation of a hsp70 gene from the filarial parasite Setaria digitata

The filarial parasite Setaria digitata is the causative agent of cerebrospinal nematodiasis in its abnormal hosts such as sheep, goats and horses, and therefore is of significant veterinary importance. Since very little is currently known about the biology of this parasite at molecular level, we have cloned and characterised a hsp70 gene, the first gene to be reported from this parasite. The genomic clone isolated contained sequences from two hsp70 genes. One gene, hsp70-2, was completely sequenced and found to contain nine introns ranging in size from 78 to 195 bp. The region upstream of the initiation codon contained a putative TATA box, two CAAT box elements and three heat-shock elements. A putative transcription initiation site was also identified. The 5' untranslated region contained a splice acceptor sequence. The gene was typically AT rich, having a GC content of 44.5%. The deduced aa sequence potentially encoded a cytosolic protein of 645 aa, which had three consecutive repeats of a tetrapeptide motif, GGMP, at the carboxyl end. The gene appeared to be constitutively transcribed and was not significantly enhanced in response to heat shock in adult worms. Another hsp70 gene (hsp70-1) was located further upstream, arranged in direct tandem with hsp70-2. Southern blot analysis revealed the presence of two or three additional hsp70-related genes in the S. digitata genome.

Stage-specific gene expression in lymphatic filarial nematodes

Lymphatic filarial nematodes remain a significant cause of morbidity throughout much of the tropics. One approach to the development of rational control methods is an improved understanding of the basic biology of these organisms in relation to the mechanisms used to complete their life cycles. In this article, Eileen Devaney, Sam Martin and Fiona Thompson review new approaches to defining stage-specific molecules in filarial nematodes, and discuss their recent work on the isolation and characterization of stage-regulated cDNAs from Brugia pahangi.